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)

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

Property CPP 1 BOPP 1

Haze (%) 2 – 3.5 1 – 2

Gloss (%) 86 - 89 88 – 92

Elongation (%) 600 200

Modulus/Stiffness (kpsi) 75 - 130 350+

Impact (Glass Transition Temp. 0C) 3 4

Area Factor (yield - in2/lb) 31,000 30,500

Heat Resistance (0C) 145 - 160  150 – 160* 

Tensile Strength (psi) 7,000 15,000

Tear Strength (g/mil)TDMD

50030

105

Surface Treatment (dyne) 36 - 38 36 – 38

Barrier: O2 (cc/100in2/day)H2O (gm/100in2/day)

2200.8

1200.4

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.

•

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.

• 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.

• 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.

• 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).

• 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

• 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

• 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.

• 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.

• 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

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

• 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.

• 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