Paper and Paperboard
companies generally pack their material in air
tight moisture proof packaging at a certain moisture
that meets most of the customers’ needs. It is
better to Studies have shown that problems can
be expected as when there is difference between
the press room RH and temperature and paper storage
room. But to get better performance the material
should be sufficiently preserved in the press
room to attain the temperature of the pressroom
and unpack the material just before printing or
converting. The time required for the skid to
attain temperature balance is too long and it
depends on the size of the skid and temperature
difference etc.. Even if the paper is used for
one stage of operation it is better to wrap it
again with moisture proof packing. Also care should
be taken to prevent paper from storing the skid
close to heaters.
Temperature 23 ± 1șC
and RH of 55 ± 5%
- Too low moisture
- Too High ply bond
between layers of board
- Too hard a coating
on the top or bottom
- Too narrow male
tool in the die
- Too narrow a gap
in the female groove
- Deeper crease
than what a paperboard can take
- Dust and impurities
in the female groove or in the male tool
As a guideline use
the following formula to fix the groove width
and select male die
Groove width > 2*caliper of of the board +
Male tool width
Male tool thickness = 0.7mm (2 Pt) for calipers
upto 500 um
= 1.05 mm (3Pt) for caliper more than 500 um
As a rule give extra 0.1 mm thickness in CD direction
for groove widths
Avoid any dust and impurities in the male tool
and female groove. The moisture of the paperboard
should be sufficiently high. The room RH should
be high
Choose the proper glue
to match the surface of the board. It is difficult
to glue in UV or aquaes varnished cartons and
laminated cartons. To increase the anchorage of
glues in the cartons the glue flap should be knurled
in the gluing operations or given half cuts in
the creasing operations.
The folding properties of paperboard
are a function of ply bond strength & stiffness
and depend on two physical states -
- Rigid
state: plies are well bonded
- Flexible
state: plies are delaminated
These two states can exist
simultaneously in adjacent areas, acting as a
hinge in 'scoring' operation. Folding properties
depend on:
- Board
properties - strength of top liner, correct
ply bond, moisture content
- Scoring
condition - good scoring requires optimum
elasticity
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During
storage, shipping, displays, & final use, cartons
are exposed to forces of compression. A carton
that can resist a certain compressive force when
it is evenly distributed over its entire surface
may collapse under a much smaller load exerted
by the hand on a limited area or on the edges.
Rigidity relates to the elastic properties of
the raw materials like stiffness. Geometric mean
of MD & CD stiffness values are a good indicator
to predict carton compression resistance.
Bulge is the result of pressure exerted by the
contents of a carton on its sidewall, causing
them to bow or due to improper lay out of the
key line. The dimension of cartons play an important
role For eg. most of the cornflakes cartons are
very big for weight of the contents inside. The
material to be packed should have to be taken
into consideration while choosing the dimensions
of the cartons. This can cause problems in high-speed
automatic filling machines as well as packing
in transit containers.
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