Enhanced Water Vapour Permeability Tester for High Barrier Materials. Alyce Hartvigsen, PBI Dansensor A/S, Ringsted, Denmark

Transcription

1 ON THE QUALITY LINE Enhanced Water Vapour Permeability Tester for High Barrier Materials Alyce Hartvigsen, PBI Dansensor A/S, Ringsted, Denmark 1

2 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 2

3 Model of Permeability Phenomenon Gas or vapour transfer through a package wall Phase 1 Package Wall Phase 2 F p2 F c2 c1 Sorption p1 Desorption Diffusion (Fick s Law) 3

4 Q (ml at STP) Typical Permeation & Time Lag Curve B Steady State A Unsteady State Q: amount of penetrant permeated as a function of time t L: time lag L Time, t 4

5 Gravimetric Permeability Measurement Methods Cup method Absorption ( Dry Cup ) High RH (climate chamber) Absorbent material Low RH (climate chamber) Water or salt solution Cup method Desorption ( Wet Cup ) 5

6 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, 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 6

7 Challenges to Test High Barrier Materials (2) 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 7

8 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 8

9 Dynamic Relative Humidity Measurement Method Sensor and Electronics dry Upper Chamber Lower Chamber: saturated atmosphere Measuring Principle : Compare time required for incremental RH increase in Upper Chamber (i.e > 10.5 % RH) 9

10 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 10

11 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 11

12 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 12

13 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 13

14 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 14

15 Minimization of Adsorption/Desorption Reduction of interior chamber surface area decreases adsorption/desorption effect Special coating of chamber interior surfaces inhibits adsorption/desorption effects 15

16 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 16

17 Comparison of Traditional & Improved Testers Property Traditional Tester Improved Tester Calibration Film Aclar Rx160 (0,42 g/m2/24 hr) Aclar Rx160 (0,42 g/m2/24 hr) Test Film Aclar Rx20e Aclar Rx20e Measured WVTR (g/m2/24 hr) 0.37 g/m2/24 hr 0.31 g/m2/24 hr Avg time for complete measuring cycle (1) 135 minutes 13 minutes Avg time for actual RH measurement 4700 seconds 255 seconds Standard deviation of equilibrium cycles 4.6% 1.3% 17

18 Comparison of Traditional & Improved Testers (2) Property Traditional Tester Improved Tester Calibration Film PET with reduced S.A. (1 g/m2/24 hr) Aclar Rx160 (0,42 g/m2/24 hr) Test Film Barrier Sample Barrier Sample Measured WVTR (g/m2/24 hr) g/m2/24 hr g/m2/24 hr Avg time for complete measuring cycle (1) 350 minutes 80 minutes Avg time for actual RH measurement seconds 2170 seconds Standard deviation of last 10 cycles 9.7% 1.1% 18

19 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 19

20 ON THE QUALITY LINE Thank you for your Attention! For more information, please visit our website: 20

21 BACK TO LIST