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Sealing parameters for polyamide pouches

PMP News was asked the following question:

"I am currently trying to find sealing parameters for polyamide pouches. Do you have any experience with that? Would you be able to give me any ranges in terms of temperature and time and sealing strength?"

We went to Alison Tyler, Technical Director for Beacon Converters Inc., for an answer, and she provided the following detailed response:

"Polyamides are a large group of polymer structures that occur naturally such as silk, casein (from milk), and zein (from corn). Synthetic materials made from polyamides include ballistic materials (bulletproof vests), mountaineering climbing ropes, air bags in your car, the frames of your glasses, fireproof garments for firefighters, and the more familiar “Nylon,” which refers to several synthetic polyamides developed originally by DuPont in 1939. Nylon is used in many packaging applications as a highly durable and puncture-resistant layer. There are several types of nylon – the most common are nylon 6/6, nylon 6, and nylon 6/12. In addition, Nylon films can be produced in more than one way, which yield different products. The two most common are cast nylon and biax nylon. Biax nylon has superior tear strength and balanced properties in machine and cross direction of the film. Cast Nylon has better clarity and has great strength in the machine direction.

"For the purposes of this discussion, we will focus on Nylon used in packaging films. Nylon can be used as a monofilm – an example of this is Reynolds Oven Bags – these are monolayer nylon. Nylon is the ideal structure for oven bags because it is heat resistant, tough, and puncture resistant and also has a high resistance to oils. Nylon is more commonly utilized in a multilayer structure. In medical packaging, Nylon is almost always a layer in a multilayer structure. For example, a simple film could be outside 100-gauge Nylon, then an adhesive layer, then a polyethylene seal layer. Nylon doesn’t do all the jobs that need to be done. It is most often the tough layer or the backbone of a film. Hence, in a simple film example that can be found in the version of this blog in the Medical Packaging Community, a layer of peelable polyethylene is added.
"So getting to the specifics of your question, you are most likely sealing something other than the Nylon itself. The sealing layer will have a lower melting temperature than Nylon. Low-density polyethylene (the heat seal layer in our example) melts at about 108 degrees C (226 degrees F). A heat seal curve can be generated by sealing the materials at the same pressure and dwell time and varying the pressure in ~10 degree increments. A good place to start is the melt or freeze point of the layer you are sealing. For this example we would say 226 degrees F (rounded to 230 F; samples sealed at 230 degrees F, 240 degrees F, 250 degrees F, 260 degrees F, 270 degrees F, 280 degrees F, 290 degrees F, 300 degrees F. All the samples are tested for tensile peel and plotted to make a curve.

"Take an example of a heat seal curve (an example can be found in the version of this blog in the Medical Packaging Community). From this you could determine a good starting place for your validation work depending on the target minimum seal strength you have for your seal. Remember that there will be a distribution of your seal strengths around a mean, so don’t select the minimum spec as your target or you will likely create seals that are below specification. For a 0.75 seal strength minimum, a good place to start would be around 275 degrees F from this curve. A seal-strength specification is based on your product package system. Some products are fine with a 0.50 seal strength – other require weld seals. If your product and process put a lot of stress on your seals, you may want to select a slightly higher seal strength to test. 0.75-1.0 is very typical. There is no “standard” seal strength requirement. Many people believe that 1 lb/in. is required, but it isn’t required by FDA or in any ASTM test method. You need to have a seal strength that stays sealed until the point of use, but you also need a seal strength that peels easily at that point of use – so finding the correct balance can be a complicated task that your packaging supplier can help you navigate."


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