This property is
significant to the performance of opaque films
like OPPalyte. Customers expect these products
to obstruct light transmission in a
predictable way, which is important for the
appearance of printed graphics and protecting
light-sensitive packaged products. OPPalyte
film light transmission values range from 15%
to 50%, depending on the product design and
film thickness.
NOTE:
Metallized
films are very effective at blocking
light transmission, but the preferred
test for these films is optical
density.
In OPPalyte films,
light transmission is determined mostly by
pigment and cavitation characteristics, which
are controlled by proprietary resin
formulations and film-making process
conditions. Since light transmission is
usually a critical property for white opaque
films, it is measured regularly. Product will
be rejected if values are outside the
specified tolerance limits.
A
unidirectional perpendicular light beam is
directed onto the film specimen, and a photo
detector measures the total light transmitted
by the specimen after it enters an integrating
sphere. Commercial hazemeters are typically
used for this testing, but ASTM D 1003 also
allows for the use of a spectrophotometer,
provided that it meets the procedure
requirements. ExxonMobil uses the BYK-Gardner
XL-211 haze-gard and haze-gard plus hazemeters
consistent with ASTM guidelines.
The
hazemeter when set up to measure light
transmission will display the final result as
a percentage to the nearest tenth.
Light
Transmission
(%)
=
Total
light
transmitted by specimen
x
100
Incident
light
The
same test equipment with a different setup is
also used to measure and display haze.
