PA6 Film Resin Improves Performance in Multilayer Barrier Films

1

Improved performance with PA6 in multilayer
barrier films
PA6 with modified rheology

Ted Brink
Application Development Extrusion

DSM Engineering Plastics
PAGEV Turkish Plastics Industry Congress - 2006

Overview 2

• Introduction
• Why PA6 in food packaging
• Trends in barrier films
• Akulon XP – high productivity PA6
• Conclusion


DSM: over a century of successful
3
transformations

Evolution Bioterials / Biologics

Life Science Products

Performance Materials

Petrochemicals

Fertilizers

Coal

Technological competences
1902 1930 1950 1970 1990 2000
Mechanical engineering
Chemical engineering
Polymer technology
Material science
Fine chemicals
Biotechnology


DSM today 4

• Globally active “multi-specialty” chemical company
• active on 5 continents, more than 200 locations
• approximately ~ 21.000 employees
• Leadership positions in ~75 % of the portfolio
• R&D spending ~ 5 % of sales
Life
• Solid balance sheet Science
• € 8 billion sales in 2005 Products
Performance
Materials
DSM Nutritional
DEP Other Products
Industrial
Chemicals
€705 million sales in 2005
1300 employees


DEP: partner for innovative film concepts 5

• Today one of the leading PA6 film resin suppliers H O
N
• New plant started with 18.000 t/y capacity in 2001
• Additional capacity of 35.000 t/y in 2005
• Introduction of Akulon XP
• Portfolio of resins for the film industry


DSM product portfolio for film applications 6

• Akulon PA6 portfolio of standard grades
• Akulon PA66 for cast and blown film
• Akulon XP high productivity PA6
• Yparex PE-g-MAH tie resin
• Stanyl PA46 high heat resistant for specialty films
• Arnitel COPE breathable film


PA6 in barrier film 7

• food packaging (> 80 %)
• meat
• cheese
• fish
• sausage casings
• non-food applications
• release films for SMC
• medical film
• protective bubble film
• agricultural film


Food packaging 8


Why PA6 for film in food packaging? 9

• Oxygen barrier
• Aroma and flavour barrier
• Mechanical protection
• Puncture resistance
• Printability
• Transparency
• Heat resistance


Oxygen versus water permeation 10

film thickness 100μm
10000
oxygen permeability

LDPE EVA
HDPE PS
[ml/m2*day*bar]

1000
PP PVC-P PC
BOPP
100

10 PET
PA6

1
PVDC
EVOH 44 % cellophane
0.1
0.1 1 10 100 1000
water permeation at 23 °C, 85 % RH [g/m2*day]


Trends in PA barrier film 11

• Use of BOPA
• Improvement of barrier properties
• nanocomposites
• oxygen scavengers
• blends
• Active & intelligent packaging
• More complex film structures (Akulon XP)
• Down gauging – improved productivity (Akulon XP)
• Shift from PA6.66 to PA6


Examples of coextruded multilayer structures 12

cheese/meat
PA
tie layer
PE

fresh meat
PP
tie layer
PA
EVOH
PA
tie layer
PE

Multilayer film with viscosity match 13

desired situation

However, in practice ideal situations are rare


Multilayer film with viscosity mismatch 14

Viscosity mismatch:
• limits flexibility
• more grades
required
• different film
polymer with higher viscosity structures on one
machine not
always feasible
• quality risk
• more material use


Viscosity curves of LDPE and PA6 15

10000
viscosity [Pa.s]

1000
LDPE
Akulon F132
100

10
0.01 0.1 1 10 100 1000
shear rate [1/s]


Polymer flow in a coat hanger die 16

Coat hanger die:
• different flow rates in the die
• multilayer structures require viscosity match
to prevent interface disturbances


Standard materials result in interfacial
17
instability
Rheology mismatch PA6 and LDPE
processing window
10000
viscosity [Pa.s]

1000
PA6
LDPE
100

10
0.01 0.1 1 10 100 1000
shear rate [1/s] leads easily to problems

poor elasticity and viscosity
match creates wave effect

one component
missing at edges


Viscosity curves of unmodified materials 18

10000
viscosity [Pa.s]

LDPE
1000
Akulon F126
Akulon F130
Akulon F132
100
Akulon F136

10
0.01 0.1 1 10 100 1000
shear rate [1/s]


What determines interfacial stability? 19

Rheology of different components:
• shear viscosity
• normal stress
• elongational viscosity


The Akulon XP solution 20

Minimizes the difference in melt viscosity and melt elasticity
of coextruded materials.
Result: widening of processing window

10000 Akulon XP
Akulon XP exhibits:
enhanced
viscosity [Pa.s]

1000
shear-thinning
behaviour:
100 LDPE • less motor power at
MFI 1.9 high rpm
10
• higher zero shear
0.01 0.1 1 10 100 1000 viscosity
shear rate [1/s]

wide processing window


The “trick”: branching of the PA6 chain 21

Random long chain branching of PA6
• increase of zero-viscosity
• flow behaviour becomes more shear thinning
• enhanced melt strength in elongational flow

Furthermore:
• branching allows very high molecular weights, not possible
with linear PA6


Effects of branched polymers 22

Linear polymers show Newtonian flow behaviour

Short chain branching: Long chain branching:
• reduction of density • strong influence on rheology
• minor influence on rheology • enhanced shear thinning
• strain hardening

Effects of branching 23

Control of viscosity
• melt stability (uncontrolled polymerization)
• gels !!

Controlled branching is realized by:
• branching agent: addition of a trifunctional compound
• to prevent formation of gels: addition of a monofunctional
compound


Neck-in on cast film and extrusion coating 24

maximum die width

standard PA6 Akulon XP
extruded film width
chill
roll


Web stability in cast film and extrusion
25
coating

die

standard PA6 Akulon XP

chill
roll

web instability

Improved layer thickness distribution 26

classical PA6

thin sections are quality risk
edge trim and determine edge trim
barrier and mechanical properties

Akulon XP


The thermoforming process 27

IR heater

film
mould

vacuum


The thermoforming process 28

IR heater

film
mould

vacuum


Thermoforming issues 29

thin corners

Issues:
• thin corners
• limited elongation


Thermoforming behaviour 30

• drawing is influenced by:
• temperature
• stretch ratio
• drawing rate
• polymer viscosity
• molecular structure
• crystallization rate


Thermoforming of COPA and PA6 31

• advantage COPA is lower crystallization rate
• drawing of PA6 can be improved by:
• keep the sheet as amorphous as possible
• addition of amorphous polyamide
• addition of COPA

• improved thermoformability of Akulon XP compared to
regular PA6
• more even thickness in the corners
• higher elongation possible


Effects of Akulon XP in multilayer cast film 32

• less neck-in waste reduction (side trims)
improved machine efficiency
• better web stability higher production speed
• improved layer thickness less material use
distribution better quality
• wider processing window less down-time
higher output
• shear thinning less motor power at high rpm
higher output possible


Akulon XP properties 33

• improved processing efficiency
• cast film
• blown film
• extrusion coating
• thermoforming
• stretching
• barrier properties same as classical PA6
• mechanical properties comparable to classical PA6
• crystallization behaviour unchanged


Advantages of Akulon XP in non-film applications 34

• extrusion blow moulding
• improved melt strength
• monofilaments
• improved roundness at large diameters
• stock shapes
• improved symmetry in tubes with large diameters due to high melt stabilty
• convoluted tubes
• improved dimensional stability at low diameters tube


Conclusion 35

Akulon XP is a new polyamide 6
with improved processing
behaviour, which can lead to lower
conversion costs and improved
film properties


More information 36

Contacts and more information:

www.dsmep.com
www.akulon.com


37

İLGİNİZ İÇİN TEŞEKKÜR EDERİM


PA6 Film Resin Improves Performance in Multilayer Barrier Films

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