| Film and tape
stored at reduced temperatures must be allowed to
warm up until its temperature is above the dew point
of the ambient air before the package or can is
unsealed; otherwise moisture will condense and spotting
may occur. Moisture
condenses on an object if its temperature is below
the dew point of the surrounding air. In summer,
the dew point may reach 75° F in temperate
climates and 90° F in tropical climates so
that materials stored at 40° to 50° F
dry bulb may have moisture condense on them when
removed to the outside air. Under these conditions,
condensation occurs readily on glass, metal, film
base, or other non-porous material, but is generally
not visible on cardboard boxes, corrugated cartons,
etc. This is because the paper absorbs the moisture
as rapidly as it condenses and water droplets
do not have time to form. Any moisture condensation
that may occur inside a sealed container is harmless
because the amount of water vapor the air contains
is infinitesimal.
The possibility of damage from
condensation occurs after the container is removed
from refrigeration and opened exposing the film
to large volumes of moisture-laden air.
Moisture condensation on film
taken from refrigerated areas can easily be prevented
by allowing the container to warm up above the
dew point of the ambient air before it is opened.
The amount of time required depends on the thickness
of the package, how well it is insulated, the
temperature difference, and the dew point of the
outside air. Usually the shipping preparation
time plus the time in transit and receiving at
the laboratory is sufficient. The approximate
warm up time necessary for film packages to avoid
moisture condensation after removal from cold
storage is twelve hours for a carton of ten 1000
ft. x 35mm rolls for a temperature rise of 25°
F or thirty hours for a temperature rise of 100°
F. A safe procedure would be to instruct the laboratory
to hold the film for twenty-four hours before
opening the cartons. topˆ |
