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Non-destructive testing of foil pouches. Determining a reliable method for checking for punctures

来源: | 作者:pmo90dc87 | 发布时间 :2018-08-15 | 2569 次浏览: | 分享到:
ABSTRACT
Several technologies used for checking for punctures in foil pouches were reviewed.
There were two that would be applicable, these were the Vacuum decay and Force decay
methods. Vacuum decay is a method where the pouch is placed into a sealed chamber and
a vacuum is applied. This vacuum will create a pressure differential from the inside of the
pouch to the outside. After the vacuum is switched off the vacuum level is monitored and
a change is measured. If a puncture exists there will be a change that is larger than one
expected due to imperfections in the test chamber. This method will work unless the
pouch has a very large puncture or it is not sealed. In this case there will not be a change
in the vacuum decay measurement.
The force decay starts like the vacuum decay except that a transducer is used to measure
the force exerted on a plate resting on the pouch. The inflation of the pouch due to
pressure differential is the source of the force. The vacuum is applied until a
predetermined force measurement is achieved then it is monitored for the rate of decay in
the force reading. The accept/reject set point determines if the pouch is good or bad.
We tried to locate off the shelf test units capable of predicting a 50µm hole 100% of the
time. Pouches were provided to various manufactures and they were asked to create
specific holes and do the required testing. It was determined that the Force Decay method
is the most appropriate test.
1. INTRODUCTION
In most packaging processes that involve foil as the final barrier to moisture,
oxygen, and light there is a concern about the incidence of punctures in the foil.
These punctures can be created as the foil is being rolled in thin sheets when
particles are rolled into the foil, these are called micro voids. The most common
defect is caused from the handling of the packages during the assembly of the foil
with product. These defects are sometimes hard to see as the Human eye can only
reliably see punctures that are larger than 100 µm. Punctures smaller that this can
still pose significant concern about the efficacy of the product. There are several
technologies available to check for this type of defect, some are destructive while
others are not. Most were developed for the food industry and involve sampling a
small portion of the total quantity produced. The cost of designing a system that
can reliably inspect 100% of product from an automated line would be significant.
The reliability of such a system and its capability would be in question if this is
required for a medical product as this could add sterility to the other requirements
for a barrier package. Because it is a medical product and could be considered a
release test this test would need to meet the stringent requirements of the FDA.
During the manufacture of a medical device there were several occurrences of foil
pouches with punctures. These punctures were random in location and position in
the batch. There was only one discovered in each batch and not all batches had
occurrences. These punctures were found at different stages of the process. They
appeared to have the same shape and size, see Figure 1. The packages, in general,
ranged from pristine looking (Figure 1) to poorly handled (Figure 2). Most of the
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punctures had the same appearance where it is evident something impacted the
package and scraped it from the outside (see figure 1). The average puncture size
was ≈ 711 µm. After several investigations the source of the punctures was not
evident. It was then decided that an inspection other than 100% human eye
needed to be developed as punctures were found after 200% inspection.
According to the University of Utah, a naked eye (an eye without any mechanical
assistance that has 20/20 vision) can see objects about 0.1 mm or 100 µm