Sean Egan, Nelipak Healthcare Packaging, discusses best practices for healthcare packaging seal integrity.
Ensuring seal integrity is critical to the product efficacy of healthcare packaging, as the seal maintains necessary sterile barriers. Seals must always remain intact under the strains of shipping and handling, yet peel open quickly and easily for the end-user in a surgical environment.
Understanding and applying best practices during the heat sealing process and using custom built cleanroom sealing machines designed to the specifications of a medical device, pharmaceutical thermoformed blisters or trays can result in better quality products that consistently have the necessary seal strengths and properties.
In the heat sealing process, coated lidding material is activated under controlled pressure and temperature parameters creating a bond between the tray/blister and the lidding material. After cooling, this bond is tensionable and the pack is considered sealed; the quality of this seal can be evaluated either visually and/or mechanically.
Factors to consider in establishing a consistent heat sealing process are:
- The sealing machine
- Heat seal parameters, such as pressure, temperature and time
- The sealing dies
- The blister
- The lidding material
- Impurities on the blister and/or lidding material
It is important to establish the lower and upper limits of the sealing process during the validation stage. This makes it possible to take into account fluctuations during the sealing process. Using blisters and lidding material that are known to give a good seal when the machine is set in a certain way can help track down batch discrepancies. If these are introduced into the process when problems occur it can quickly be determined whether the blister or the lidding material is the cause.
When changes occur, they may result in serious complications with the bond between the tray/blister and the lidding material. Changes to the sealing machine, the heat seal parameters and the sealing dies are usually easily observable. If they are the reason for the problems, ‘the original state’ should be restored and the process can resume as normal. However, if the blister or the lidding material is the cause, the resulting changes are often not discernible with the naked eye.
Evaluating heat sealing
Conclusions drawn regarding the quality of bonds are not always found to be correct, particularly when the evaluation is based solely on visual inspection. Sometimes seals whose quality is actually satisfactory are rejected. Mechanical inspection techniques such as peel and burst testing provide more accurate conclusions on seal integrity than visual inspection alone.
The peel test is preferable to evaluate seal integrity and strength, but to enable a reliable comparison be made of the quality within a single production run it is critical to always break the seal at the same angle of the blister with respect to lidding material and at the same speed. Some characteristics observed from peel testing may be a subjective matter of opinion – such as whether the seal ‘looks nice’. What is more important is whether, after peeling the seal, you can establish a basis of properties that indicate what to expect from the applied coating in a certain combination of blister and lidding material.
Minimising the risk of impurities
Impurities that lodge between the blister and the lidding material give rise to poor visual and mechanical bond properties. Therefore, consider the following best practices for reducing impurities:
- Leave lidding material and blisters in the original packaging for as long as possible
- Avoid touching the coating, especially at the points where joints will be made later
- Avoid touching the blister’s sealing flange
- In the case of pre-treatment of blister and lidding material (such as sterilisation), keep a few originals in reserve so you can verify whether the pre-treatment has affected the quality of the bond
- Test the effect of disinfectants or detergents on the quality of the bond in advance (even if they are not meant to come into contact with the blister’s seal flanges)
- Test the effect on the seal of gloves that you do or do not use in combination with disinfectants or detergents
- Test the effect of the contents of the packaging on the quality of the bond, particularly if you work with liquids or sticky substances
Problems involving blisters and lidding material are usually due to material from different production batches being used during one sealing cycle –for example, blisters sealed in a single cycle with lidding material that has identical coating but is from two different batches. They show not only different results in the peel test, but also visual differences. This can usually be solved by modification of the heat seal parameters.
