|
Natural
Kraft : |
| |
A
strong paper made from long fibers of unbleached wood pulp. |
|
Wet
Strength Kraft : |
| |
The
same as natural Kraft but with additives, which enable it to
retain about one-third of its dry tensile strength when saturated
with water. Ideal as an outer ply for moisture resistance. |
|
Bleached
Kraft : |
| |
Any Kraft sheet can be fully or semi-bleached to attain a white
or off-white color. However, bleaching lowers the strength of
Kraft paper to some degree and must be considered in sack performance. |
|
Extensible
Kraft : |
| |
In
making this sheet, the paper fibers are mechanically compacted,
mainly in the MD direction, yielding a paper with a greater
ability to absorb more impact than natural Kraft. Extensible
paper will do more "work" because of its higher stretch than
natural Kraft. Less total basis weight and/or fewer paper plies
can be used in such sacks with little or no loss of strength.
There is also a modified extensible Kraft, which makes the bunching
or compacting of fibers more balanced in both directions. |
|
Free
dried Kraft : |
| |
A
unique process that allows unrestricted natural shrinkage during
the drying process. This provides high cross-direction stretch
for improved sack performance |
|
Clay-Coated
Bleached Kraft : |
| |
|
A bleached sheet
coated with three to six pounds of clay coating to improve opacity
and increase smoothness, porosity and printability. |
| |
|
|
Silicone
Coated Kraft : |
| |
|
A coating that is
used to provide release properties. |
|
Polythylene
Coated Kraft : |
| |
|
An extrusion coating
of plastic resin to provide moisture protection. |
|
Wax
Kraft : |
| |
|
A sheet with its
surface either saturated or coated to provide moisture protection.
|
|
Polyvinyl
den chloride coated Kraft (PVDC) : |
| |
|
An extrusion or
emulsion coating of plastic resin for grease and odor protection.
|
|
Greaseproof,
glassine or parchment sheet : |
| |
|
A specially treated
and very dense sheet, which provides a barrier to grease or
oily ingredients.
|
| Barrier
Films and Coatings used in paper sack |
| |
Although
there is no universal, economical barrier possessing all the
properties required for all products, there are many material
options available which, when combined with Kraft paper, offer
a balanced, cost/performance ratio package. Paper can be treated,
coated, laminated or combined with other materials to meet
the unique requirements of a specific end use. The barrier
properties of coatings or films tend to be straight-line relationships
to density and gauge and will improve as density and gauge
increase. The material properties as well as physical location
or position of the barrier ply help determine the overall
effectiveness of a paper sack construction. Barrier plies
do not usually contribute significantly to the overall strength
of a paper sack. However, there are a few strength plies that
can be used in a sack, which may or may not also offer barrier
properties. Such plies permit the reduction of paper plies
or provide a super strong, reinforced sack with maximum protection
for special products or requirements. |
|
Common
Barrier Material Used in Paper Shipping Sacks : |
| |
|
| |
|
