# Finite Element Solution to 1D Polymer Film Problem

• posted
Greetings!
I am having a hard time finding heat transfer coefficients (k) for
various polymers (nylon, polyester, polyethylene). Would anybody know
an online source?
I am trying to perform finite element methods to determine the
required seal times at various temperatures on packaging lines. Has
anybody perfomed this type of calculation before or know of an
available calculator/program?
Generally, packaging machines have dwell times of approximately 0.4+
seconds with sealer bar temperatures of 170-175 deg C. The sealing
material, generally polyethylene in this case, requires to be raised
to approximately 140-145 deg C in order to achieve an even seal. The
back side sealer bar is normally kept at room temperature, or slightly
above. The pressure applied to the sealer bar can vary, but it is
assumed that full contact is made between the sealer bar and the
polymer film and that the surface of the film reaches the sealer bar
temperature immediately.
Thank you for your suggestions and opinions.
• posted
Adhesion takes place at such a small scale that you cannot model it with your approach, you need a molecular approach, and even that won't be easy (trust me, I worked at 3M for 11 years). In addition, you have a phase change that is dominated by kinetics (i.e., Tx is not equal to Tm).
How did you manage to get a supercomputer account? ;)
John
• posted
John, I see how you are looking at this. But to simplify things, lets assume that when the seal layer reaches a specified temperature, we obtain a good seal. Obviously this is an oversimplified analysis, but it should be able to calculate the minimum time required for the sealant to reach a sealable temperature. My objective for this analysis is to set guidelines (generally minimums as most companies are trying to use too little dwell times-and speed up production) for customer packaging machines. There are also constraints on the maximum allowable temperature on the seal bars due to film deformation/burning.
• posted
snipped-for-privacy@shaw.ca (Drago) wrote in message
This is definitely more approachable.
I'm not sure that the Polymer Handbook would have the heat transfer constants that you are after or not. I don't have access to that book anymore (unless I can arrange with my boss to make a special trip to the University) :( Maybe someone else in the newgroup can help.
To get a good seal you will also need to allow time for the interdiffusion of the molten sealing polymer, not just for the time to get it up to the molten state. This will certainly vary from polymer to polymer, since it's basically proportional to the melt viscosity.
Good luck, John
• posted
I actually measure peel force over a combination of time and temperature to obtain a 2D contour map of the heat activation of laminates to prints, which is a similar problem to yours. I use Excel to plot peel vs time and peel vs temperature, then adjust the points in both dimensions until smooth curves are produced. It is then easy to draw contour lines by hand on a 2D graph. These show up the effects of film thickness (coat weight of thermoplastic polymer) and additions of plasticizer, tackifier etc. Time and pressure are assumed to be co-dependent, i.e. the higher the nip or bar pressure, the less time is required to get the same bond strength. I use 18 psi and contact times up to 4 minutes, but I'm interested im maximum adhesion, and peels start to level off around there. For such short contact times of 0.4 seconds, you need a fairly high pressure to get measureable peel forces, I would say.
• posted
Did you mean thermal conductivities here? Heat transfer coefficients are not material specific, rather they are dependent on local air/cooling fluid flow conditions.
• posted
Pardon the mix up of terms, yes I do want the thermal conductivities of those same materials. I visited the local university, unfortunately they do not have any polymer departments, so the information I have found is a bit old. A book I was able to find was "Engineering Properties of Thermoplastics" circa 1970 written by Ogorkiewicz. It does have some useful information on some of the resins in use today (LDPE, various Nylons, polypropylene) but it is not a complete list. Of the materials it does cover though, there is a wealth of information, much more than I need.
I still require a better source of information than which I currently have. I wonder if the packaging machine manufacturers have studied sealing in more detail. The manual that came with our Multivac does not have very much information on this topic however.
In the end, the only way to test this theorhetical dwell times will be to put it on a machine, but I would still like to be able to show why the machines cannot be made to seal faster without burning the outside layer/or getting no seal.
• posted
You could, for example, search for a given polymer for the property you = are looking for, e.g. thermal conductivity, at: =
or, if you know the supplier of your polymer, you could ask him for such an information for a specific grade of polymer ...
"Drago" schrieb im Newsbeitrag = news: snipped-for-privacy@posting.google.com...
• posted
Drago schrieb: