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O N T H E Q U A L I T Y L I N E

Enhanced Water Vapour Permeability Tester for High Barrier Materials

Alyce Hartvigsen, PBI Dansensor A/S, Ringsted, Denmark

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Agenda of Presentation

• Introduction– Review of permeation & traditional WVTR test method

– Review of Dynamic Humidity Method for WVTR

– Challenges for high barrier materials (very low WVTR)

• Improved Measurement Sensitivity for High Barrier Materials– Potential areas of improvement

– Implementation of modifications for improvement

• Effects on Performance: Comparison Test Data from Conventional and New Systems

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Model of Permeability Phenomenon

Phase 2Phase 1 Package Wall

F F

p2

p1

c2

c1

Sorption Desorption

Diffusion (Fick’s Law)

Gas or vapour transfer through a package wall

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Typical Permeation & Time Lag Curve

LTime, t

Q (

ml at

ST

P)

Steady State

Unsteady State

A

B

Q: amount of penetrant permeated as a function of time t

L: time lag

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Gravimetric Permeability Measurement Methods

Cup method Desorption („Wet Cup“)

High RH (climate chamber)

Cup method Absorption („Dry Cup“)

Absorbent material

Water or salt solution

Low RH (climate chamber)

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Challenges to Test High Barrier Materials

• Instrument resolution and detection limits:• What does a WVTR value 0,001 g/m2/24 hr

mean in practical terms?

• Typical sample size = 50 cm2 (0,005 m2):

• For this sample, a WVTR of 0,001 g/m2/24 hr translates to 0,000005 g/sample/24 hr

• Practical lower limit of typical analytical balance: 0,0002 g

• A gravimetric test would require minimum 40 days of measurement to get one data point

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• High significance of ambient leak rate:• Ambient leak of just 1 ppm water vapour will

give a significant contribution to measured WVTR

• Leak rate is dependent on ambient conditions (temperature, relative humidity), and therefore can vary considerably in non-climatised room

• The ambient leak rate must be deducted from the overall measurement to obtain the WVTR result for the sample

Challenges to Test High Barrier Materials (2)

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Challenges to Test High Barrier Materials (3)

• Very long stabilisation & testing times:• Thicker samples: stabilisation time proportional to

the square of sample thickness

• Individual measurements more time-consuming

• Multiple measurements required to confirm the attainment of steady state permeation

• Thus: testing of high barrier materials can be far more time-consuming than for other materials

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Dynamic Relative Humidity Measurement Method

Measuring Principle : Compare time required for incremental RH increase in Upper Chamber (i.e. 9.5 --> 10.5 % RH)

Lower Chamber: saturated atmosphere

Upper Chamber

dry

Sensor and Electronics

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High Barrier Tester: Potential Improvements

• Higher measurement sensitivity

• Reduction in ”dead volume”

• Faster measurement time for high barriers

• Minimization of intrinsic leak rate

• Minimization of adsorption/desorption effect

• Minimization of signal/measurement noise

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Higher Measurement Sensitivity

• Reduction in air space surrounding sensor increases concentration of water vapour molecules èhigher sensor response for same water vapour concentration

• Optimised sensor humidity range èhigher resolution in measurement range

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Reduction in ”Dead Volume”

• Optimised, compact sensor design

• Optimised location of sensor in measuring chamber

• Minimum distance from sample to sensor

• Specially designed inlet and outlet valves for drying air

• New chamber geometry to provide most effective air flushing during dry-down stage

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Faster Measurement Time for High Barriers

• Reduced chamber volume yields higher concentration of water vapour & therefore relative humidity è faster detection of change in relative humidity

• Reduction of ”dead volume” provides more immediate sensor response to changing humidity

• Optimised chamber geometry provides faster dry-down time between cycles

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Minimization of Intrinsic Leak Rate

• Optimised chamber design eliminates potential leak sources within chamber

• New air inlet and outlet valves designed to minimize potential leakage

• Drying air routing system optimised to eliminate sources of leakage

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Minimization of Adsorption/Desorption

• Reduction of interior chamber surface area decreases adsorption/desorption effect

• Special coating of chamber interior surfaces inhibits adsorption/desorption effects

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Minimization of Signal/Measurement Noise

• Improved Start/Stop algorithm for measurement cycle minimizes noise caused by ”false start/stop”

• Better averaging of measurement results reduces noise variations

• Optimisation of electronics design (sensor, PCB board) minimizes sources of electronic noise

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Comparison of Traditional & Improved Testers

1.3%4.6%Standard deviation of equilibrium cycles

255 seconds 4700 secondsAvg time for actual RH measurement

13 minutes135 minutesAvg time for complete measuring cycle (1)

0.31 g/m2/24 hr0.37 g/m2/24 hrMeasured WVTR (g/m2/24 hr)

Aclar Rx20eAclar Rx20eTest Film

Aclar Rx160 (0,42 g/m2/24 hr)

Aclar Rx160 (0,42 g/m2/24 hr)

Calibration Film

Improved TesterTraditional TesterProperty

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Comparison of Traditional & Improved Testers (2)

1.1%9.7%Standard deviation of last 10 cycles

2170 seconds 12400 secondsAvg time for actual RH measurement

80 minutes350 minutesAvg time for complete measuring cycle (1)

0.037 g/m2/24 hr0.030 g/m2/24 hrMeasured WVTR (g/m2/24 hr)

Barrier SampleBarrier SampleTest Film

Aclar Rx160 (0,42 g/m2/24 hr)

PET with reduced S.A. (1 g/m2/24 hr)

Calibration Film

Improved TesterTraditional TesterProperty

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Summary

• Improved barrier materials are reaching the sensitivity limit of available WVTR testers

• Measurement of very high barriers requires improvements in sensor detection limits, reduction of ambient leak rate and minimization of system & electronic noise

• Modifications to the Dynamic Relative Humidity Method have produced a system with higher measurement sensitivity, reduction in testing cycle and overall testing times, and less influence of system noise

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O N T H E Q U A L I T Y L I N E

Thank you for your Attention!

For more information, please visit our website:

www.pbi-dansensor.com

O N T H E Q U A L I T Y L I N E

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