Different type of screening equipment and their application in chemical industry
Cpp
1. CPP
CPP stands for cast polypropylene. It is a
non-oriented film. The main characteristics
of CPP which define it’s usage in packaging
are:
•Load carrying capacity (per unit area)
•Better resistance against tear propagation
(High tear strength & elongation)
2. Property CPP BOPP
Tear Strength Better Good
Modulus (stiffness) Better Best
Low Temp Impact Resistance Better* Good
Dimensional Stability Best Good
Haze Better Best
Heat Sealing Better Good**
Barrier Better Best
Area Factor (Yield) Best Better
4. PROCESS DESCRIPTION:
• RAW MATERIAL FEEDING
• For each extrusion system there is one
Continuous Gravimetric Loss-in weight
Feeding System and there are three
feeding components. Each of these
feeding components are collected in the
plastic buckets on the ground. These
components are picked-up from the
buckets through vacuum loading systems
which in turn discharge them into
individual feed hoppers.
•
5. PROCESS DESCRIPTION:
RAW MATERIAL FEEDING
• From feed hoppers, the feeding
components are simultaneously dosed
into an Integral Weighed Hopper through a
cascade mixer. The weight of blended
material in the weighed hopper is
continuously monitored to sense changes
in extruder throughput rates. The
throughput rates of each of the feeders
are automatically adjusted to maintain the
preset blending percentage proportion &
to keep constant level of Integral Weighed
Hopper.
6.
7.
8. • EXTRUSION SYSTEM
• According to the formulations for a film to
be produced, the appropriate raw
materials are automatically fed into each
of the extruders as mentioned above.
Inside the extruders, the solid pellets are
heated &, melted into homogenous melt.
This melt stream is filtered through a
polymer filter.
• After filtration the melt stream from each
of the extruders is conveyed through melt
pipes to a feedblock . The desired layer
sequences ( BAAAC, ABCBA, AAABC )
are created in the feedblock section
through selector plug cartridges housed
inside the feedblock.
9.
10. • From feedblock section, the layered melt
stream enters the coextrusion flat die.
Inside the die, the melt takes the form of a
web. To maintain the individual layer
thicknesses of the melt web as required,
the individual extruder screw RPMs are
maintained accordingly.
11.
12. • MELT CASTING
• The melt web from the die comes on to
the moving Chill Roll. Here quenching of
the melt takes place & it gets solidified
This process is called casting. The
temperature of chill roll is maintained at 12
- 25 deg. C.
• To avoid any air entrapment between the
melt web and the chill roll surface ( and
hence the physical impressions on the
final cast film ), Cooling Air Blade System,
Depression Air Blade System & Edge
Fastening Systems are used at a point
where the melt web from die touches the
moving chill roll ( the Touch Down Point).
13. • The Cooling Air Blade System forces the
melt web onto the chill roll by blowing a
turbulence free air stream on to the melt
web uniformly all accross the width. The
Depression Air Blade System is positioned
behind the die on the tangency of the cast
cylinder. It creates a depression effect by
sucking the air available between melt
web & chill roll. This depression effect
favours the complete adhesion of melt
web on to the
14. • chill roll. The Edge Fastening System is
composed of 2 point charging electrodes.
These electrodes block the film on to the
chill roll from edge of melt web & limit the
neck-in process
15. • THICKNESS MEASUREMENT &
CONTROL
• The thickness of cast film is measured by
a Thickness Gauge moving across the
running cast film. The thickness profiles
are displayed on to a computer. The
deviation in thickness at any given point is
detected by the microprocessor system,
which in turn gives feedback to the
thermal blocks of the die. These thermal
blocks act on the point of gauge deviation
by thermal expansion or contraction as
required.
16.
17. • WEB OSCILLATION
• After thickness gauge, the cast film
passes through Side Slip Unit. Here it
goes through a sidewise oscillation
process. This type of web oscillation
causes physical distribution of film
thickness variation points across the web
width so as to achieve a good winding
performance of the film onto roll at winder.
18. • After web oscillation, the edges of the final
film are trimmed out with the Trimming
Unit. These trims are fed to a grinder
which cuts them into small pieces called
Fluff. This fluff material is transported
through a transport blower & piping to the
refeed hopper of main extruder (extruder
with highest throughput)..
Edge Trim system
19.
20. Edge trim system
• In the refeed hopper, fluff gets mixed up
with the virgin material & gets conveyed to
the extruder. This type of in-line recovery
of the film is possible with non - barrier
films only. When producing barrier films, it
is only possible to cut and stock the
trimmed edges and not automatically
recover them in-line because EVOH &
PA6 materials used in these films are not
compatible with other polyolefins
21. • FILM SURFACE TREATMENT
• After edge trimming unit, the cast film
passes through a Corona Treatment Unit
consisting of two electronic generators,
four electrodes & two silicone rubber
coated rollers. Here the film surface can
be treated on one side or the other side or
both sides contemporaneously. Such a
treatment improves the adhesion level of
the film by increasing the Surface Energy
(polarity) on the treated surface.
22. • WINDER
• After corona treatment, winding of
the film takes place on the winder. A
winder with good tension control
unit is required for a satisfactory
winding quality
