ABSTRACT - tappi.org
Transcript of ABSTRACT - tappi.org
PO Innovations in Extrusion Coating –High Value Solutions in a Critical Processing Technology M. Kirchberger, Borealis GmbH, St.-Peter-Str. 25, A-4021 Linz, Austria ABSTRACT Linear structured materials such as polypropylene (PP) or metallocene-catalysed polyethylene (mLLD) are well known for providing enhanced physical performance compared to conventional polyethylene. Based on their advantageous physical performance these materials rapidly became established as a preferred material in many plastic conversion technologies (e.g. injection moulding, film and fibre). However critical conversion technologies, such as extrusion coating, have until now been incapable of economically utilizing linear structured material as described above. New developments, especially the introduction of long chain branched PP grades and optimised bimodal mLLD materials, enable the problems in this area to be overcome. The presentation will provide an overview of the use of high value PO innovations, resulting in the ideal combination of material and processing technology. INTRODUCTION The unique attributes of linear structured materials such as polypropylenes and low density polyethylenes produced with metallocene catalyst (mLLD) are well known on the market. Compared to conventional LDPE´s these materials provide superior physical properties including improved stiffness and heat resistance, excellent puncture and tear resistance and better sealing behaviour. Based on this advantageous property profile the interest in linear structured materials has been continuously growing. In extrusion coating, however, this rapid utilisation has not been seen. The main factor contributing to this limited growth is related to the linear structure of mLLD´s and PP´s. These polymers are characterised by a narrow molecular weight distribution resulting in limited melt strength and extensibility in the melt phase. Conversion technologies utilising high elongational flow, such as extrusion coating, are not readily able to utilise linear structured materials because of this fact. Developments by the PO producers, especially the introduction of new enhanced technology concepts, enable the problems in this area to be overcome.
PO MARKET SITUATION Polyolefins have become the largest plastic materials over the last decade. The average annual growth rate of polyolefins in Western Europe over the last 5 years was approx. 2.8%. The prediction for the future is that the growth of polyolefins will remain at the same level. As shown in figure 1 the linear structured material such as PP and LLD showed continuous growth whilst LDPE stagnated or slightly declined. Whilst the linear structured materials will also continue to grow in the future at approx. 3.5% for LDPE, a further slight decline is expected.
Figure 1: PO Market Situation WE
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Source: CMAI World PO Analysis 2005 – Figures Domestic Demand WE
Volume [kto]
PO MARKET SITUATION IN EXTRUSION COATING When the first commercial extrusion coating process was introduced around 55 years ago, the plastic for coating was low-density polyethylene (LDPE). Still today the extrusion coating market is dominated by highly branched autoclave LDPE grades. Especially LDPE´s with broad MWD (molecular weight distribution) and a high degree of LCB (long chain branching) show the required visco-elastic properties for extrusion coating. This can be seen from the West European figures for 2003 given in figure 2, where LDPE with 550kt has a share of almost 85% of the total polymer consumption for extrusion coating. PP and LLD´s play only a small part in terms of volume. Their advantageous property profile combined with their great innovation potential gives expectations of significant growth in the future. Figure 2: Extrusion coating resin consumption Western Europe 2003
Market overview extrusion coating industryConsumption of resin WE 2003
LDPE 88.1 %
HDPE 3.8 %
PP 3.1 %
ADHESIVES 3.0 %
EVA/EBA 1.4 %
LLDPE C4 0.4 %
>> Total extrusion coating market: 515 kt>> Total extrusion coating market: 515 kt
Source: CMAI
Extrusion coating Applications Products made by extrusion coating are always multilayer products. The basic principle is still to combine the properties of plastics and other materials, especially paper and cardboard, aluminium foil or white tin into new material combinations. Modern lines can utilise multiple laminator and co-extrusion possibilities; thus the final constructions may easily consist of 7-9 layers. Extrusion coating and extrusion laminating are the most recommended and economical process technologies for bulk production. A very successful example of the economic efficiency of this converting technology is the production of liquid resistant packaging materials. Figure 3 shows the different extrusion coating application areas in Western Europe. Figure 3: Extrusion coating resin markets by application in Western Europe
Extrusion coating market segmentationExtrusion coating markets by application WE 2003
Liquid packaging 45 %AAGR 3 %
Flexible packaging 20 %AAGR 5 %
Industrial applications 18 %AAGR 0.5 %
Other rigid packaging 11 %AAGR 2 %
Photographic paper 6 %AAGR 2 %
>> Total usage: 515 kt>> Total usage: 515 kt
Source: CMAI
Position of Polyolefins in packaging applications The growth rate of Polyolefins in the packaging area has been extraordinarily high. The particularly good applicability of PO materials for packaging can be made transparent if the technical suitability and the general market profile are taken into account. With their technical performance and high cost-efficiency, PO materials gain the best comparative position.
Figure 4: Performance assessment of packaging materials PERFORMANCE POSITIONING OF PO MATERIALS IN EXTRUSION COATING The challenging and contradictory demands on packaging materials are forcing the market to re-think the use of traditional packaging systems. The beneficial properties of linear polyolefins are of high interest to extrusion coaters. Up to now, processability limitations related to low melt strength and low melt extensibility have restricted the use of such materials. The prerequisite for better economics in high speed extrusion coating is a process combining high draw-down and small neck-in with improved end product properties. Figure 5 shows the present situation of PO materials in extrusion coating.
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10 20 30Market profile
Technologicalprofile
Chemical resistanceWater toleranceSealabilityBarrier performanceTemperature ToleranceForming versatilityMass (density)FragilityProtection
Paper
CartonsCorrugated
Pulp
LL&LDPE
HDPE
PVC
PSEPS
PET
Lamin.
Tinplate
Alu
Glass
PP
Diversity of formCostDistribution efficiencyPan-European suitabilityDecorative optionsEnvironmental perceptions
30
20
40
10 20 30Market profile
Technologicalprofile
Chemical resistanceWater toleranceSealabilityBarrier performanceTemperature ToleranceForming versatilityMass (density)FragilityProtection
Paper
CartonsCorrugated
Pulp
LL&LDPE
HDPE
PVC
PSEPS
PET
Lamin.
Tinplate
Alu
Glass
PP
Diversity of formCostDistribution efficiencyPan-European suitabilityDecorative optionsEnvironmental perceptions
30
Source Pira, 1999
Figure 5: Performance positioning of PO Coating materials A: High Value PE Materials for Extrusion Coating Borstar® PE a versatile technology platform for enhanced PE materials Borealis has advanced its position in the polyolefins industry with the introduction of its proprietary materials technology for polyethylene and polypropylene. This process consists of a loop and gas phase reactor as shown in Figure 5. The process is designed to produce bimodal polyethylenes with optimal final product application properties by controlling the polymer molecular structure. The fundamental feature of the technology is its dual reactor operation which allows materials to be produced in a wider range of densities and MFR with broad (bimodal) molecular weight distribution and tailored comonomer distribution.
Figure 6: The PE process flow diagram
Convent. PP mLLD
LDPE
Unmet needsChemical
resistance
Heat resistance
Stiffness
Barrier
Sealing
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LowBad Good Excellent
Processability
Convent. PP mLLD
LDPE
Unmet needsChemical
resistance
Heat resistance
Stiffness
Barrier
Sealing
High
Medium
LowBad Good Excellent
Processability
CatalystPrepoly-merizationreactor
Loop reactor
Diluentrecycle
Gas
65 bars, 95ºC
Gas phasereactor
20 bars,80-100ºC
PolymerDegassingPelletizing
PE
Flash
PolymerEhyleneComonomerHydrogen
CatalystPrepoly-merizationreactor
Loop reactor
Diluentrecycle
Gas
65 bars, 95ºC
Gas phasereactor
20 bars,80-100ºC
PolymerDegassingPelletizing
PE
Flash
PolymerEhyleneComonomerHydrogen
Bimodal mLLD from bimodal PE process With the introduction of metallocene catalyst systems the beneficial advantages of the bimodal PE technology can be expanded even further. The controlled reactivity of a single-site catalyst gives better control over the polymer design which will lead to improved product characteristics. The tailoring of comonomer insertion can be further optimized depending on the targeted end application. In combination with the broad (bimodal) molecular weight distribution, new and different materials with enhanced processability can be created.
Figure 7: Key advantages of PE process in combination with single-site catalyst
Bimodal mLLD Polymer properties
Processing of bimodal mLLD Extrusion coating involves very high shear stress and draw-down speeds. The molecular structure of metallocene catalysed polyethylenes, predominantly their narrow MWD, has a negative impact on processability. It is known that the implementation of bimodal MWD changes the shear thinning behaviour. The bimodality, especially the low MW part, enables extrudability without extraordinary shear and back pressure in the extruder. By performing extruder output tests and comparing the output potential of bimodal mLLD vs. unimodal mLLD the benefit of the bimodal MWD can be seen. The increased shear thinning effect for bimodal mLLD leads to lower melt pressure and higher output capability.
bimodal mLLD
Processing Stiffness
Toughness
Bimodal MWD Tailored Comonomer Distribution
output sealing tºhot tack strength
ESCRelongation
COFsecant modulus
bimodal mLLD
Processing Stiffness
Toughness
Bimodal MWD Tailored Comonomer Distribution
output sealing tºhot tack strength
ESCRelongation
COFsecant modulus
Figure 8: Bimodal mLLD lower melt pressure and motor load in extrusion coating
Adopting processability of bimodal mLLD – The BorPlusTM Concept The attainable changes in rheological properties for bimodal mLLD´s would not be sufficient to allow stable processing on modern high speed extrusion coating equipment. A common way on overcoming limitation in processability is to combine the mLLD with some amount of a LDPE component. For this purpose a dedicated LDPE quality was developed which gives the ability to combine the mechanical performance of the bimodal LLD component with the high processing capability of LDPE in an ideal way. Figure 9 shows the basic principle of the technology concept in which the linear structured mLLD is combined with the LDPE component
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Figure9: The BP technology concept Processing performance Based on the visco-elastic properties of bimodal mLLD in combination with an optimised LDPE blending partner a clear shift in output/neck-in balance can be achieved as shown in figure 10. The higher output capability means higher coating capacity and higher draw-down. In parallel, the neck-in level is kept under control by the tailored composition.
Fig 10: Processability benefits of bimodal LLD
L in e a r Branched
mLLD + LDPE
Pilot EC-line: Neck-in vs. Line speedNip distance 200 mm coating weight 10 g/m²
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Pilot EC-line: Neck-in vs. Line speedNip distance 200 mm coating weight 10 g/m²
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max. linepressurereached
End product properties Heat sealability Heat sealing is one of the primary functions of extrusion coating, since this is the main method to create close and tight packaging. Proper sealing/ high seal strength is an important factor in achieving good packaging integrity. Hot tack is the seal strength of the polymer in a semi-molten state. High hot tack strength at low temperatures allows packaging manufacturers to increase production line speeds. Figure 11 presents the hot tack curves of PE coating materials. This comparison shows the clear advantages of linear structure mLLD grades due to lower S.I.T. and distinctively higher hot tack strength
Figure 11: Hot Tack of different PE coating materials. ESCR In liquid packaging the ability of the material to withstand chemical stress in direct contact with aggressive surface active contents is of high importance for packaging integrity. Linear polymers show a clear benefit in this property compared with traditional LDPE. The tailoring of the co-monomer composition via the bimodal process technology allows a further improved balance of stiffness and environmental stress crack resistance as shown in figure 12.
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Sealing test: Hot-tack pilot scale results
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Sealing test: Hot-tack pilot scale results
Figure 12: ESCR/Secant Modulus performance of bimodal mLLD B: High value Polypropylene Materials for Extrusion Coating Based on its advantageous material properties including superior heat resistance, stiffness and sealability, polypropylene is an ideal candidate for retortable packaging applications. However critical conversion technologies, such as extrusion coating, have thus far not been readily able to economically utilise PP. New developments, especially the introduction of long chain branched PP grades, enable the problems in this area to be overcome. THE DAPLOY® HMS PROCESS
As described in previous presentations, Borealis has developed a new post-reactor process following polymer synthesis for introducing long-chain branches into the linear polypropylene structure. The resulting structure of this new polypropylene-based polymer can be illustrated as follows:
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Secant Modulus MD ESCR (4w)
LDPE Competitor bimodal mLLD
ESCR/Secant Modulus Performance of Bimodal mLLDRelative cast film property comparison (40 micron film)
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LDPE Competitor bimodal mLLD
ESCR/Secant Modulus Performance of Bimodal mLLDRelative cast film property comparison (40 micron film)
ESCR: 10% Igepal, 50 C, weeks – Special strain at break %
Figure 13: Introduction of long-chain branches in a newly developed post-reactor process leads to the unique structure
Changes in rheological behaviour Due to this new, unique branched polymer structure, HMS-PP grades stand out, unlike conventional (linear, non-branched) polypropylenes, by combining significantly increased melt strength with much improved drawability of the polymer melt. For characterisation of the extensional flow properties the Rheotens test was introduced. This measurement simulates industrial spinning and extrusion process. In principle a melt is pressed or extruded through a round die and the resulting strand is hauled off. The stress on the extrudate is recorded, as a function of melt properties and measuring parameters. Figure 14 shows the experimental setup schematically and gives an example how the melt strength and melt extensibility is determined from the curves obtained from the Rheotens experiment. Branched PP shows the feature of high melt strength and high melt extensibility. This means a melt strand of branched PP can be drawn down to high elongations.
Figure 14: Elongational behaviour of polyolefin melts at 200 °C (Rheotens apparatus)
HMS-C MFR = 16
HMS-H MFR = 22
(measured at 200°C)
Rheotens F
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Drawability
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Rheograph (extruder)
Processing performance and application benefits of HMS-PP The attainable improvements with respect to processability were internally evaluated on a semi-commercial coating pilot line. Achievable coating speed and neck-in at 10g/m² were evaluated for describing the processing window. Coating weight variation (draw resonance) and level of edge weaving were used to determine the processing stability. The modification is applicable for nearly all types of PP material. This provides the opportunity to benefit from the wide property range of PP and to create dedicated system solutions. The following table summarises the attainable improvements in processing and gives an overview of achievable product variations based on material properties evaluated on an injection moulded specimen.
4-51n.a.n.a.[mm]InternalEdge weaving
0.20.05n.a.n.a.[g/m2]InternalDraw resonance
150131n.a.n.a.[mm]InternalNeck-in
300 m/min500 m/min.100 m/min.<50[m/min.]InternalMax. coating speed
Coating weight 10 g/m2
130153128150°CISOVicat A
780150010501400[MPa]ISO178Flexural modulus
16222520[g/10 min.]ISO1133MFR (230/2.16)
UnitNormPhysical properties
HMS-CHMS-HPP/PE modifiedConvent. PP
4-51n.a.n.a.[mm]InternalEdge weaving
0.20.05n.a.n.a.[g/m2]InternalDraw resonance
150131n.a.n.a.[mm]InternalNeck-in
300 m/min500 m/min.100 m/min.<50[m/min.]InternalMax. coating speed
Coating weight 10 g/m2
130153128150°CISOVicat A
780150010501400[MPa]ISO178Flexural modulus
16222520[g/10 min.]ISO1133MFR (230/2.16)
UnitNormPhysical properties
HMS-CHMS-HPP/PE modifiedConvent. PP
End product properties The three PP coating materials were tested with respect to different coating/film layer properties. The main target was to determine the differences in properties especially related to packaging applications. In these analysis the influence of heat treatment on coating layer toughness and barrier properties were studied.
Figure 15: Influence of heat treatment on coating layer toughness (Dynatest)
Figure 16: Impact of heat treatment on barrier properties
121ºC – 30 min
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PP/PE modified HMS-H HMS-C
Measured on 50 µm film at 100% RH
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Application Benefits of High Value PO Coating grades The introduction of linear structured PO coating grades enables an approach towards the ideal combination of high extrusion capability with superior end properties. This facilitates increased production efficiency with value generating potentials in the extrusion coating operation as well as in converting and packaging. The improved mechanical performance, temperature resistance and sealing behaviour is furthermore realised by improved package integrity. The new combination of product performance parameters offers genuine downgauging potentials for extrusion coated structures and opens up new markets and applications.
Figure 17: Performance positioning of high value PO coating materials
Convent. PP mLLD
LDPE
Chemical resistance
Heat resistance
Stiffness
Barrier
Sealing
High
Medium
LowBad Good Excellent
Processability
Convent. PP mLLD
LDPE
Chemical resistance
Heat resistance
Stiffness
Barrier
Sealing
High
Medium
LowBad Good Excellent
Processability
Convent. PP mLLD
Convent. PP mLLD
bimodal mLLD
HMS PP bimodal mLLD
HMS PP
Summary: High value PO coating materials contribute to the needs for value added packaging solutions in the extrusion coating market. With the ideal combination of high processability and enhanced coating layer performance many advantages with respect to process/converting economics can be derived. The parallel interaction between improved material properties and market requirements form the basis for creating new, revolutionary products. In order to supply high performance solutions for any application, it is important to understand the demands of this market. A number of beneficial features have been emphasised within this presentation. The combination of these beneficial properties ultimately leads to a range of benefits for all parts of the value chain involved in extrusion coating applications.
Figure 18: Impact of high value PO coating grades in the value chain
Converter Packer Retailer Consumer
High Draw-Down
Low Neck-In
Production regularity
Cost efficiency
Product diversification
Downgauging
Packaging efficiency
Packaging integrity
Cost efficiency
Product diversification
Packaging integrity
No off taste or flavour
Innovative design solutions
Environmental/legal aspects
Attractiveness
No off taste or flavour
Convenience
Packaging integrity
High Draw-Down
Low Neck-In
Production regularity
Cost efficiency
Product diversification
Downgauging
Packaging efficiency
Packaging integrity
Cost efficiency
Product diversification
Packaging integrity
No off taste or flavour
Innovative design solutions
Environmental/legal aspects
Attractiveness
No off taste or flavour
Convenience
Packaging integrity
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M.Kirchberger – Borealis GmbH10th Tappi European PLACE Conference, Vienna, May 2005
PO innovations in extrusion coatingHigh value solutions in a critical
processing technology
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PO market situation WE
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Volume[kto]
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Market overview extrusion coating industry
Total extrusion coating market: 515 ktSource: CMAI
Consumption of resin WE 2003
• LDPE 88.1%
• HDPE 3.8%
• PP 3.1%
• ADHESIVES 3.0%
• EVA / EBA 1.4%
• LLDPE C4 0.4%
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Extrusion coating market segmentation
Total usage: 515 ktSource: CMAI
Extrusion coating markets by application WE 2003
• Liquid packaging 45%AAGR 3%
• Flexible packaging 20%AAGR 5%
• Industrial applications 18%AAGR 0.5%
• Other rigid packaging 11%AAGR 2%
• Photographic paper 6%AAGR 2%
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Performance assessment of packaging materials
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Technologicalprofile
Chemical resistanceWater toleranceSealabilityBarrier performanceTemperature ToleranceForming versatilityMass (density)FragilityProtection
Paper
CartonsCorrugated
Pulp
LL&LDPE
HDPE
PVC
PSEPS
PET
Lamin.
Tinplate
Alu
Glass
PP
Diversity of formCostDistribution efficiencyPan-European suitabilityDecorative optionsEnvironmental perceptions
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Source Pira, 1999
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Performance positioning of PO materialsin EC
Convent. PP mLLD
LDPE
Unmet needsChemical
resistance
Heat resistance
Stiffness
Barrier
Sealing
High
Medium
LowBad Good Excellent
Processability
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A - High value PE materialsfor Extrusion Coating
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The Borstar® PE process... a versatile technology platform for enhanced PE materials
Independently controlled cascaded reactors enable tailoring of:• Molecular weight distribution > step change improvement in mPE processing
• Comonomer distribution > sealing properties beyond product density
CatalystPrepoly-merizationreactor
Loop reactor
Diluentrecycle
Gas
65 bars, 95ºC
Gas phasereactor
20 bars,80-100ºC
PolymerDegassingPelletizing
PE
Flash
PolymerEhyleneComonomerHydrogen
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Bimodal mLLD – key advantages of bimodalPE process in combination with single-site
bimodal mLLD
Processing Stiffness
Toughness
Bimodal MWD Tailored Comonomer Distribution
output sealing tºhot tack strength
ESCRelongation
COFsecant modulus
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Bimodal mLLD PropertiesProcessing of bimodal mLLD
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Improving processability of bimodal LLD The BorPlus™ - concept
Linear
Bimodal mLLD
Branched
LD+
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Improving processability of bimodal LLD
Pilot EC-line: Neck-in vs. Line speedNip distance 200 mm coating weight 10 g/m²
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max. linepressurereached
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Bimodal mLLD - end product properties
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Sealing test: Hot-tack pilot scale results
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Bimodal mLLD - end product properties
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LDPE Competitor bimodal mLLD
ESCR/Secant Modulus Performance of Bimodal mLLDRelative cast film property comparison (40 micron film)
ESCR: 10% Igepal, 50 C, weeks – Special strain at break %
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B - High value PP materialsfor Extrusion Coating
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The Daploy® HMS process
The introduction of long-chain branches in a post-reactor process
Linear
Standard PP
Branched
HMS modified PP
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HMS-PP: changes in rheological behaviour
Elongational behaviour of polyolefin melts at 200°C (Rheotens apparatus)
Measured at 200ºC
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Daploy™ HMS-CMFR = 16
Conventional PPMFR = 20
Rheograph(extruder)
Rheotens
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HMS-PP: processing and application benefits
4-51n.a.n.a.[mm]InternalEdge weaving
0.20.05n.a.n.a.[g/m2]InternalDraw resonance
150131n.a.n.a.[mm]InternalNeck-in
300 m/min500 m/min.100 m/min.<50[m/min.]InternalMax. coating speed
Coating weight 10 g/m2
130153128150°CISOVicat A
780150010501400[MPa]ISO178Flexural modulus
16222520[g/10 min.]ISO1133MFR (230/2.16)
UnitNormPhysical properties
HMS-CHMS-HPP/PE modifiedConvent. PP
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HMS-PP: end product properties
Influence of heat treatment on coating layer toughness (Dynatest)121ºC – 30 min
14
12
10
8
6
4
2
0
14
12
10
8
6
4
2
0
Penetration energy at 23°C [N/mm] Penetration energy at 0°C [N/mm]
before heat treatment after heat treatment before heat treatment after heat treatment
PP/PE modified HMS-H HMS-C
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Page 20
02.04.2005
Presented by M. Kirchberger
HMS-PP: end product propertiesWVTR as a function of temperature
Influence of heat treatment on barrier properties (WVTR)
Measured on 50 µm film at 100% RH
1000
1
100
10
40 60 80 100 120 Temperature [ºC]
WVTR as a function of temperature
HMS-C
PP/PE modified
HMS-H
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02.04.2005
Presented by M. Kirchberger
Summary: performance positioning of high value PO coating grades
Convent. PP mLLD
LDPE
Chemical resistance
Heat resistance
Stiffness
Barrier
Sealing
High
Medium
LowBad Good Excellent
Processability
Convent. PP mLLD
bimodal mLLD
HMS PP
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Presented by M. Kirchberger
Converter Packer Retailer Consumer
High Draw-Down
Low Neck-In
Production regularity
Cost efficiency
Product diversification
Downgauging
Packaging efficiency
Packaging integrity
Cost efficiency
Product diversification
Packaging integrity
No off taste or flavour
Innovative design solutions
Environmental/legal aspects
Attractiveness
No off taste or flavour
Convenience
Packaging integrity
Summary: impact of high value PO coating grades in the value chain