In the today's packaging world, professionals are looking for accurate and repeatable water vapor transmission rate (WVTR) test results that prevent both over-packaging expenses and under-packaging by understanding the water vapor barrier performance of their packaging films. Under-packaging products can result in costly product shelf life failures as well as a potentially negative brand image among retailers and consumers. Similarly, over-packaging results in wasteful and unnecessary spending for packaging materials. This article will discuss how to choose the right WVTR permeation instrument for your applications.
We will explain why “Not All Sensors Are Created Equal.”
To help explain this statement, let’s begin with a couple of case studies:
CASE STUDY #1
The customer manufactures various barrier films with WVTR range between 0.5 to 150 g/(m2 · day). In the permeation instrument market, there are a couple of WVTR test instrument options available:
Instrument Option 1: Test range spec is 0.005 to 1000 g/(m2 · day). This instrument uses a Modulated IR sensor (ASTM F1249)
Instrument Option 2: Test range spec is 0.002 to 1000 g/(m2 · day). This instrument uses an absolute P2O5 sensor (ASTM F3299)
Since the two instruments look like they have similar test ranges, the customer wanted to just go with the cheaper one (the option 2). This may be your initial reaction as well however, there is one thing you have not yet considered that will make a huge impact on your decision. Is there a difference between the two instrument sensor types? This is an important question and the answer is a big “YES.”
It is a fact that P2O5 sensors wear out with exposure to moisture and are therefore considered a consumable sensor. The generic P2O5 sensor would only last 2-4 months in this application, and you must replace sensor when it’s dead. Furthermore, if the WVTR level of your samples are not in the ultra-low range, they transmit more moisture, therefore, the P2O5 sensor would be depleted faster.
In this case, it would be more sensible to choose the modulated IR sensor method (ASTM F1249) that is (used in MOCON PERMATRAN-W® 3/34). The best features of this sensor are its accuracy, repeatability, long sensor life (4-5 years), and its smart operation features. Since the IR sensor is a concentration sensor, periodic calibration is needed for obtaining accurate test results.
CASE STUDY #2
An OLED barrier supplier produces Roll-to-Roll (R2R) coated high barrier materials. The WVTR range of his products range from 10-5 to 10-2 g/(m2 · day). They heard that the test method with the new ASTM P2O5 sensor would be more accurate. There are a few WVTR instruments with P2O5 sensor available in the market place:
Instrument option 1: Test range spec is 0.00005 to 50g/(m2 · day). Absolute P2O5 sensor method (ASTM F3299)
Instrument option 2: Test range spec is 0.002 to 1000 g/(m2 · day). Absolute P2O5 sensor method (ASTM F3299)
In this case, they paid attention to the instrument test range and were surprised that an instrument which conforms to the same ASTM Method could have different test ranges. This was due to the quality of the sensors used and accuracy of the instrument. They decided to choose Option 1 which can meet the test range for their specific application. In this case, the instrument which met the required sensitivity for their application was the MOCON AQUATRAN® Model 3.
After learning about the above case studies, one can conclude that Not All Sensors (or Instruments) Are Created Equal... and therefore, will not always give you the correct test data.
Instruments that claim to conform to the same ASTM Test Method may use different sensor types and therefore have a different test range. Instruments may also be labeled with a similar technical range, however due to the different sensors used they may have different lengths of sensor life.
For these reasons, it is imperative that you look carefully at the instrument specifications before choosing to invest in an instrument.
Which Method is Best for your Application?
It is imperative to match the WVTR range of your samples, to the WVTR range of the instrument, and then look carefully at the useful life time of the sensor.
Modulated IR sensor and P2O5 sensor would serve different applications. For example, if the application is for generic packaging applications where WVTR is with the range of 10-3 to 103 g/(m2 · day), then the instrument with modulated IR sensor suites the purpose. An example is the recently developed MOCON PERMATRAN-W 3/34.
When working with ultra-high barrier materials to protect OLED and other electronics, the low WVTR measurement requires a more accurate sensor. Best practice is to select an instrument that conforms to the Coulometric P2O5 sensor method. An example is the MOCON AQUATRAN Model 3.
When business decisions are made based on results generated from a permeation measuring instrument they must be accurate, repeatable, reliable and dependable. Be sure that you are asking the right questions when looking to purchase an instrument or choose an outside lab to perform permeation testing for you.
For more information, please read the article “A Comparison of ASTM Test Standard F1249 vs F3299”
Georgia Gu is part of the PackageIntegrity.com Editorial Team and is also the Sr. Global Applications Specialist at AMETEK MOCON. To learn more about Georgia, visit her Bio Page or email her directly at Georgia.Gu@Ametek.com.