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What is "MVTR"?
M.V.T.R.
stands for “Moisture Vapor Transmission Rate”, a measure
of the passage of gaseous H2O through a barrier. It's
also known as "W.V.T.R.", or Water Vapor Transmission Rate".
When
is an MVTR barrier important?
Products as diverse as frozen meat patties and fine papers are
extremely sensitive to moisture gain or loss. In the case of meat
patties, excessive loss of moisture while product is being held
in a freezer results in “freezer burn”. Freezer burn is
unsightly and adversely affects the taste of the cooked meat. For
fine papers, excessive moisture gain results in limp, hard-to-process
sheets.
Traditional
solutions generally involve plastic film, either as a laminant in
the paper or as a bag around the product. Both solutions are expensive
and/or incur added labor costs, and both greatly reduce or eliminate
the recyclability of the shipping container. Michelman MVTR coatings
can provide the high moisture resistance needed without compromising
the recyclability of the container.
How
is moisture resistance measured?
Moisture resistance is measured in a special chamber
[Photo],
divided vertically by the substrate/barrier material. A dry atmosphere
is in one chamber, and a moist atmosphere is in the other. A 24-hour
test is run to see how much moisture passes through the substrate/barrier
from the “wet” chamber to the “dry” chamber.
Standard test procedures (TAPPI T-464, ASTM E96) can specify any
one of five combinations of temperature and humidity in the “wet”
chamber. The toughest conditions are 100°F / 90%RH (Relative
Humidity), and these are the conditions under which we normally
test Michelman barrier coatings. MVTR results reported without reference
to the test conditions are largely meaningless.
Michelman
Moisture-Resistant Coatings
Listed below are those Michelman coatings which are recommended
for MVTR applications. These coatings have multiple properties,
and may appear on other cross references as well.
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