The document discusses various double and triple bubble processes used to produce plastic films. It begins by explaining the single, double, and triple bubble processes at a high level. It then provides more details on specific double and triple bubble processes for making PVC shrink sleeves, polyolefin shrink films, PVdC films, nylon casings, and high barrier shrink films. Each process section outlines the critical machine components required and potential applications for the resulting films.

1. What is Double/Triple Bubble
process, how it works, what kind
of machine is required
Well Curious to know!
Follow me…….

2. ABOUT US
 EXTRU-TECH SOLUTIONS INC. is a consulting and service
providing company with head office in Toronto, Canada.
 We provide consultancy services to the plastic packaging industry,
research companies, as well as Extrusion machine manufacturers
around the world.
 We provide project management, extrusion troubleshooting, process
improvement, Die (both Blown and Cast-any number of layers) and
extruder maintenance services.
 We also troubleshoot any downstream process problems specially the
film quality (wrinkles, gels, instability etc.) and winding problems.
 We also help in newer developments weather it is related to new
equipment, new process or new film recipes (new products) etc.
Disclaimer:
Most of the information shared in this presentation is gained through years of hands ON working experience on
various Double and Triple-Bubble processes.
The sole purpose of this presentation is to share the knowledge among interested professionals.

3. Single Bubble Process
Most of us are familiar with the
Blown film process where we melt
the plastic granules, extrude the
homogenous melt through an
annular die, blow the air through the
die to make a bubble, cool it from
outside using an air ring and also
from inside using the internal bubble
cooling (IBC) technology and the
bubble is collapsed, treated
(sometimes) and winded either in
sheet or tubular form. This is a
straight forward single bubble
process called Blown film process.

4. Double-Bubble Process
 As the name indicates, there supposed
to be two bubbles… but how?
 In this process the first bubble is formed
in a similar manner as in the blown film
using an annular die but the
downstream cooling and forming
process is different for different type of
double-bubble process depending upon
the polymer/recipe as well as the size
requirements.
 After pre-heating the primary
Bubble/tube is re-blown to make a
secondary bubble and this process is
called as double-bubble.
 The secondary bubble is collapsed and
the film is winded either as tube or
sheet depending upon the application.

5. Triple-bubble process
 Triple-bubble process is basically the
continuation of the double-bubble
process. After collapsing the secondary
bubble, this flat tube is re-blown third
time between a set of circular IR heaters
or hot air for
annealing/thermoregulation and this
process is called the Triple-bubble
process.
 Annealing/Thermoregulation is a very
critical step in any shrink film process
because with annealing we can control
the percentage of shrinkage required in
the final product as per application.
 Typical shrinkage requirements:
Sausage casings – 15%,
High barrier shrink bags - 40-60% ,
Lidding film – 0-<5%.

6. Why Double and Triple bubble
The main purpose of making the film using the
Double or Triple-Bubble technology is to get a
good controlled shrinkage (5-90%), improved
mechanical properties out of thin film (down
gauging).

7. Process Types: Double and
Triple-Bubble
1. PVC Double-Bubble process: Shrink sleeves, Labels, safety seals etc.
2. Polyolefin (POF Shrink film) Double-Bubble process: common materials
are Mettallocenes, Plastomers, Polypropylene. This process was initially
started to produce the BOPP film but now many other POF films are
made using this method.
3. PVdC Double-Bubble process: Usually Monolayer process using PVdC
(Polyvinyledene Chloride) for sausage casings and Cling film.
4. Nylon casing Triple-Bubble process: Mono and Multilayer using PA
(Nylon), PE and Tie resins.
5. Barrier Shrink film Double and Triple-Bubble process: Is typically a co-
extrusion process using PE, PVdC, EVA, Tie resins, EVOH, PA, and PET etc.

8. 1. PVC casing (Shrink Sleeve)
This is one of the oldest product made using the
Double-Bubble technology.
Also this is the only Double-Bubble process
where the first bubble is formed using the
traditional blown film technique i.e. the bubble is
formed using an air ring.
Typical Material: PVC
Applications: Shrink sleeves for bottles, Cap
closure as safety seal, labels, bundling film etc.

9. Critical Components
 Extruder: That can provide the homogenous good
quality melt.
 Die: Short residence time, no restrictions and/or
Dead spots.
 Air ring: Single lip is commonly used to make the
First/primary bubble.
 Hot water tank: Hot water is used for pre-heating
the primary bubble.
 Re-blowing: Re-blowing is done after pre-heating
(Pre-heat temperature around 80 deg.C i.e. the Tg
for PVC) using compressed air or air blower. The
water cooled sizer is used to stabilize the second
bubble.
 The sizing ring is similar to the one used in PPTQ
lines or in modern days so called Aqua frost / Aqua
quenched lines.
 Winder: The finished film is collapsed and winded
on a spindle/surface winder.
Tg : Glass Transition Temperature
PPTQ: Polypropylene Tubular Quenched

10. Applications

11. 2. Polyolefin (POF Shrink film)
Double-Bubble Process
 In this process the size of the primary tube is dictated by the size of the water
cooled mandrel being used. The primary bubble can be formed using a internal
water cooled mandrel or an external mandrel similar to the one used in
PPTQ/Aqua frost/Aqua quench process. With internal cooling mandrel, outside
cooling is done using a water ring.
 The diameter of the secondary bubble is dependent on the diameter of the
primary tube and film recipe with minor variations due to film thickness. Usually
these lines are dedicated to a fixed lay flat. Typical B/R is 5:1.
 Primary tube thickness range: 350-750 micron, Final film thickness range: 12-30
micron (Approx.)
 The size of the water cooled mandrel is relative to the die size. (Approx. B/R :1/1).
 Typical Structures: 3 and 5-layers
 PP/PE/PP
 PP/PP/PE/PP/PP
 PP/PE/PE/PE/PP

12. Critical components
 Water quenching:
 1. The primary bubble is formed either like PPTQ
process means the melt is slightly cool down
using an air ring and then passed through a
water quenched mandrel.
 2. The second method is by using a combination
of water cooled mandrel and a water ring for
outside cooling. The bubble is supported by a
continuous supply of compressed air. Sometimes
this compressed air can also be used to maintain
the size of secondary bubble.
 Scrap winder: If for any reason the second
bubble is lost, this scrap winder comes in handy
and takes care of the primary tube.
 Primary nip: Usually one of the rubber roll has
two ‘V’ grooves at the location of both the
edges of primary tube to prevent the edge
deformation (cracks) in the thick primary tube.

13. Critical Components
 Pre-heating IR chamber: This IR heater chamber is just slightly
larger than the primary bubble diameter for better heat transfer.
The length is usually in the range of 1-1.5 mtrs.
 Film guides: The bubble guide rings play a crucial role in keeping
the tube in center of the IR chamber for uniform heat transfer and
also to prevent the tube from coming in contact with the IR
heaters that can lead to fire.
 Second IR Heater tunnel: This heater tunnel provide the desired
temperature to re-blow the second bubble. The tunnel is slightly
bigger than the possible diameter of the secondary bubble.
 Third IR Heater chamber: Sometimes this is used to control the
thickness variation of the secondary bubble. The segmented
heaters work in the similar fashion as the die lip heaters in a
regular blown film line.
 Cooling air rings: There are two or three air rings for cooling and
stabilizing the second bubble. As the amorphous primary tube
inflates it starts crystallising and relieves lots of heat in this
process. The secondary bubble will blow up to a certain diameter
after that the increase in tensile strength will not allow it to blow
further. The air helps in removing this excess heat.
 Annealing: Annealing is done using a combination of hot and cold
rolls just before the winder.
 Applications: Scratch resistant film, bundling film, Safety seal etc.

14. Applications

15. 3. PVdC Double-Bubble Process
 PVdC processing is very complicated and require special equipment as well
as special skills.
 PVdC comes in powder form and is very corrosive when melted. Usually the
Screw, barrel and die are made out of Dura nickel alloy or good quality
Stainless steel.
 The screw design is crucial because there is a very narrow process window
means we need to melt and mix the material within this temperature range,
also the residence time should be kept to a minimum otherwise PVdC will
degrade.
 Using the special design screw and die the molten PVdC is extruded through
an annular die in to a cold water tank.
 After cooling, this tube passes through a hot water bath .
 After re-heating the water is wiped out and the secondary bubble is blown
using either a powerful air blower or compressed air.
 This secondary bubble (5-6 times larger diameter) is collapsed.
 The film can be separated as sheet or can be winded as double layered film.

16. Critical Components
Oil Sizing: the primary bubble is formed by
filling the oil inside through the center of the
die and by trapping this oil with the help of nip
rolls, this bubble is formed in a water tank. The
oil level is maintained using level sensor and
automatic refill arrangement.
Hot water Tank: The cold flattened tube is
passed through warm water (about 35 deg. C)
to re-heat the tube for re-blowing.
Randomization: During the re-blowing a neck is
formed which is tightly hold using a set of
frictional rollers assembled in a ring formation.
The ring and so as the bubble is rotated in order
to randomize the gauge.
Collapsing frame and Winding: The secondary
bubble is collapsed using a special sturdy
collapsing frame with aluminum/steel rollers
and can be winded in single (sheet) or double
(tube).

17. Re-blowing Process & Applications
 The re-blowing process is quite simple. The primary tube is re-heated using
warm water, 35 deg.C (Tg for amorphous PVdC) at that the amorphous polymer
is soft enough to be re-blown using a low pressure high volume blower. The
primary bubble start re-blowing and at the same time started crystallizing. The
bubble can not blow after a certain diameter because of the increase in tensile
strength due to crystallization.
 The bubble is collapsed and passed over a set of hot and cold rolls (annealing
process) to control the shrinkage in the final film.
 The MD shrinkage is achieved by controlling the stretching in MD.
 The TD shrinkage has many factors, like resin type, additives used, quenching
temperature, hot water temperature, distance between die and quench water,
etc.
 Film thickness: 10-25 micron for single sheets, 20-50 micron for double
wounded.
Applications: Sausage casings, Cling film, cheese, poultry etc.

18. Applications

19. 4. Nylon Casing (Triple-Bubble
Process)
Nylon casings are made on dedicated lines for
various sizes (Tube diameter/Calibre).
These lines can be in horizontal or vertical
configuration.
Typical Structures: 3,5,7, and 9 layers
PA/Tie/PA
PA/Tie/PA/Tie/PA
PA/Tie/PE/Tie/PA
PA/EVOH/PA/Tie/PA
PA/EVOH/PA/Tie/PE/Tie/PA
Note: The size (diameter) consistency is very
crucial for the sausage filling process.

20. Critical Components
 Vacuum Sizer: This is one of the critical
components in the Nylon casing process. As
we all know the melt strength for Nylon is
very poor and in order to form a tube we
need to apply the vacuum. In order for the
vacuum to work we must have an opening
through the center of the die.
 Elevating Mechanism: The vacuum sizer
must be assembled on an elevating
mechanism with at least 8-12” traveling
distance from the die lip.
 Additional Cooling chamber: For high
output lines it is important to have an
additional cooling chamber to properly cool
the primary bubble/tube in order to keep it
in amorphous state.

21. Critical Components
 Moisture removal: It is important to wipe
out all the moisture from the surface of
primary tube before it enters in to the pre-
heating IR heaters otherwise this moisture
will leave water marks on the surface of
final product. The moisture can be removed
using air knives and squeeze rolls.
 Pre-heating : Preheating can be done using
Hot water or IR heaters.
 Cooling: An air ring is used to stabilise the
secondary bubble. As the amorphous
primary tube inflates it starts crystallising
and during this process eliminates lots of
heat that needs to be removed to stabilize
the size of secondary bubble.
 Size control: For automation we need to
measure the secondary bubble diameter as
well as third bubble diameter. On basis of
the feedback from this device we can
increase or reduce the length of these two
bubbles that will eventually change the
diameter of these bubbles.

22. Critical Components
 Annealing: Annealing is a heat stabilization process
where the polymer stresses (developed during bi-ax
orientation) are relieved and also the shrinkage can
be controlled for the final product . In PA casing
process this can be done either using IR heaters, Hot
air or Steam.
 Randomisation: It is one of the crucial step and is a
must for this product. Because Nylon film is very stiff
it is important to have a uniform roll geometry
otherwise the gauge bands will remain as memory
and the film can not be used on automatic filling
machines.
 Winding: Winding is done on spindle winder.
 Applications: Sausage casings

23. Applications

24. 5. High Barrier Double/Triple
Bubble process
 This is typically a co-extrusion process and the film is produced as 3,5,7,9 and 11 layers with
various barrier resins like PA, EVOH and PVdC along with PE, EVA and tie resins. The secondary
bubble can be made using IR heaters similar to the POF process but the best shrinkage properties
are achieved using a combination of hot water and hot air/IR heaters. Here we will discuss about
this second method because the first one is already covered in POF process.
 The PVdC based barrier film needs to be cross linked (By Irradiation) in order to improve the
mechanical properties.
 Common Structures:
PE/Tie/PVdC/Tie/PE
PE/Tie/EVOH/Tie/PE
PA/Tie/EVOH/Tie/PE
PE/PE/Tie/PVdC/Tie/PE/PE
PA/Tie/PA/EVOH/PA/Tie/PE
PET/Tie/PE/Tie/PA/EVOH/PA/Tie/PE
 Specifications: Primary tube thickness: 300-1000 micron, Final film thickness: 40-60 Micron,
Typical B/R: 2.5-5.0, MD Stretching: 3-5 times.
 Applications: Fresh meat packaging, Cheese Packaging, other high barrier packaging like coffee,
Lidding film, Balloon film etc.

25. Critical Components- PVdC
based shrink film
 Water Quenching /Vacuum Sizer:
 Both of these methods are used to make the first
bubble called Primary tube in the range of 0.3-
1mm thickness and the lay flat from 40mm-
120mm.
 In the water free fall quenching method the primary
tube diameter is maintained using compressed air
inside the tube.
 In case of vacuum sizing the primary tube diameter
is dictated by the inner diameter of the sizer.
 Water quenching is important to keep the polymer
in amorphous state that helps in re-blowing the
second bubble.
 Starch Powder: There is an arrangement to spray
the starch inside the primary tube that helps to
prevent the blocking of tube during pre-heat
process. This starch also helps in easy opening of
the finished bags during packaging process.

26. Critical Components
 Hot Water: For some recipes it is possible to re-blow
the second bubble just by pre-heating the primary
tube in hot water. The best benefit of using Hot water
is the uniform heat for the entire circumference of the
primary tube.
 Hot air /IR Heater chamber: Stiff polymers need to
be re-heated close to their melting temperature and
require a secondary source of heating that can be
either Hot air or IR heaters. Sometimes, a
combination of both hot water and either hot air or IR
heaters are used for pre-heating. It is important to
maintain the uniform heat around the entire primary
tube circumference (for gauge uniformity) and the
heat sources must be carefully selected.
 Cooling Air ring: This is probably the most crucial
component of this entire process. After the pre-
heating section the primary tube immediately enters
in to the cold air ring. The design of the air ring also
dictates the size of the secondary bubble in co-
relation with the size of the Primary bubble/tube.

27. Critical components
 Re-blowing process: Once the desired pre-heating temperature
(depends upon the recipe) is achieved the secondary bubble can be
easily blown using compressed air .
 Typical orientation ratios are in the range of 2.5-5 X both in MD
and TD depends upon the polymers/recipe being used.
 Collapsing frame: This process is forced re-blowing and as the
amorphous primary tube starts inflating it crystallises and the tensile
strength increases. In order to collapse this bubble very strong
collapsing frame is required (usually stainless steel rollers are used).
 Annealing Section /Triple Bubble:
 -One option is to use hot and cold rolls before the winder.
 -Second option and probably the best is to make a third bubble that
will pass through IR tunnel but is more complicated and expensive
option.
 Both methods do their job of thermally set the bi-ax orientation.
 Annealing helps in controlling the final lay flat as well as the
shrinkage percentage during application.
 Irradiation: The finished rolls are transferred to the Unwind-rewind
station with Irradiation equipment. This is done to cross link the skin
layer of the film that improves the mechanical properties and
provides the much desired increment in puncture resistance
necessary for packaging meat having sharp bones.

28. Film properties
Excellent barrier against O2 and moisture,
High or controlled shrinkage depending upon
the recipe (raw materials) being used,
Excellent optical properties (high gloss and
transparency),
Excellent puncture resistance (keep in mind
PVdC based films need to be cross linked),
Low temperature, high strength sealability,
thanks to the requirement of low melting
temperature skin resins in case of PVdC as a
barrier layer.

29. Applications

30. Common Elements of
Double/Triple-Bubble
There are following critical steps that are common in all the double/Triple-bubble processes
discussed above:
Typical resins: PVC, PVdC, Nylon are the resins soft enough at their amorphous Tg so that they can
be easily re-blown in to secondary bubble. Some other resins like EVOH, PE, Ionomers etc. required
to be heated almost up to the melting temperature.
Sizing: in all the above processes we need to have some way of sizing the primary bubble either
vacuum sizing, water ring, cooling mandrel, compressed air with free water fall ring, oil sizing in
case of PVdC etc.
Pre-heating requirement: all the Double/Triple- Bubble formation require some kind of pre-heating
for the primary bubble/tube. Some resins can be re-blown at low temperatures (below 100 deg.C
that means hot water can be used), the others will need higher temperatures (close to their melting
temperature) means other heat sources will be required , that can be hot air, hot oil, IR heaters etc.
Annealing: All double/Triple-Bubble processes require some form of annealing in order to relieve
the stresses developed during the bi-axial orientation process. This procedure is also called as
thermoregulation by which the final shrinkage levels can be achieved.

31. More Questions???
Call us:
+1-647-687-0859
Email:
beniwal@extru-techsolutions.com
Contact: Ajay Beniwal
Extru-tech Solutions Inc.
11 Seascape Crescent, Brampton,
ON, Canada, L6P3C4
www.extru-techsolutions.com