| Gas Barriers |
| An introduction Basic Reference 1 |
Wrapping refers to a means of separating
something that lies "inside" from an "outside".
This is done to protect the contents from outside factors
such as humidity, light, pressure, and air. The wrapping
(packaging material) must seal the contents from outside
factors and protect them to prevent degradation in quality.
"Barrier properties" is the term used
for the function of sealing contents from outside
factors that will invite quality degradation. Oxygen,
nitrogen, carbon dioxide, water vapour, and other
gases in the air have a major impact on the freshness
and quality of food products and medicines, and
barrier properties for these gases are thus extremely
important. For this reason, the packaging materials
must have barrier properties with respect to these
gases. |
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| Figure 1-1 "Packaging Materials" seal
the contents from the outside air and prevent degradation
of the quality of the package contents. |
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| For many years, bottling and canning
have been used as methods to seal contents from
the outside air, enabling these contents to be preserved
for many years. When plastics were invented in the
20th century, they came to be used as packaging
materials. Plastics with excellent gas barrier properties
were developed, and supported our lifestyles as
packaging materials not only for food products but
cosmetics and pharmaceuticals as well. |
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| Figure 1-2 polyethylene(left)and ethylene-vinyl
alcohol copolymer(right) |
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| Figure 1-2 shows polyethylene
(PE), an ordinary plastic, and ethylene-vinyl alcohol
copolymer (EVOH), a plastic with excellent gas barrier
properties. A comparison of these plastics shows
that they are both transparent and are almost identical
in appearance. However, EVOH has more than 10,000
times the oxygen gas barrier properties of PE. Why
is there such as tremendous difference in the oxygen
gas barrier properties of these plastics? To answer
this question, we will present a brief explanation
of the mechanisms and so forth that give rise to
barrier properties. Next time, we will discuss the
required form of expressing gas transmission quantity
when a comparison is made of the quantity of gas
transmitted. |
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