Ingress Through Seals Theoretical Calculation

When designing a package for a barrier application, the focus is on the transmission rate of the material used to construct the package. They are usually composite materials with a distinct barrier layer and a sealant layer. However, if the package is intended for a high barrier application, ingress through the seals should also be considered.

Calculating Ingress through the Seal

WVTR or O2TR: The Water Vapor Transmission Rate or the Oxygen Transmission Rate through the seal can be determined using formula 1(a) and 1(b) respectively.

Ingress-through-seals-formula-01

Ingress-through-seals-formula-02WVT or O2T: The Water Vapor Transmission or Oxygen Transmission through the seal on a package can be determined using formula 2(a) and 2(b) respectively. This assumes that the same material has been used on both sides of the package.

Ingress-through-seals-formula-03

Ingress-through-seals-formula-04

where

WVTRs =
The water vapor transmission rate through the sealant layer of a seal of a given width (g/100in2/day)
WVTRm =
The water vapor transmission rate of the sealant material (g/100in2/day/mil)
WVTs =
The water vapor transmission through the seal of a package (g/day)
O2TRs =
The oxygen transmission rate through the sealant layer of a seal of a given width (cc/100in2/day)
O2TRm =
The water vapor transmission rate of the sealant material (g/100in2/day/mil)
O2Ts =
The oxygen transmission through the seal of a package (cc/day)
Ws =
The width of the seal (inches)
ts =
The thickness of the sealant of a laminate or composite material (inches)
Ps =
The inside seal perimeter of a package (inches)

Example Calculations

Assumptions:

  • Package Size: 4″ x 7″ I.D. rectangular pouch
  • Material used to construct the pouch: Foil laminate of 48 ga PET/0.001″ Foil / 0.002″ LDPE with no pinholes. Same material used on both sides of the pouch.
  • WVTRm of LDPE = 0.9 g/100in2/day/mil O2TR of LDPE = 400 cc/100in2/day/mil
  • Seal Width (Ws) = 0.375″

Calculations:

Ingress of Water Vapor through the Seal:

Ingress-through-seals-formula-05

Ingress of Oxygen through the Seal:

Ingress-through-seals-formula-06