co-extrusion blow molding

CO-EXTRUSION BLOW MOLDING With A Continuously or Sequentially Foamed Layer Wolfgang Meyer W. Müller USA, Inc.

Annual Blow Molding Conference October 6-7, 2014 Chicago, IL

W. Müller GmbH, Troisdorf, Germany W. Müller USA, Agawam, MA

Manufacturing

Engineering R&D

Customer Service

W. Müller USA, Agawam, MA

Field Service

Sampling up to 7 Layers

Parts Service

• More than 1,200 extrusion heads installed in North, Central and South America

S18/35-80 P-PE, ReCo 3 S5/35-85 P-PE, CoEx 6 S1/160 RV-PE, CoEx 3 Accumulator

W. Müller USA, Agawam, MA

Foam Blow Molding • Existing Technologies • Our Objective

Pilot Project: Foaming of Preform Trilayer Co-Extrusion with Foam Trilayer Sequential Co-Extrusion with Foam

• Topics

Presentation

• Foam Blow Molding is not a new technology

• Commercial application are not widespread

• Reasons for Foam Blow Molding Light-weighting Lower part weight while maintaining rigidity Increased rigidity without adding weight Thermal insulation Noise reduction (from airflow)

• Why ?

Foam Blow Molding

• … is based on continuous extrusion blow molding with chemical or physical blowing agents or a combination thereof. Chemical blowing agents are often unacceptable

for food/beverage packaging and automotive applications. Physical blowing agents are preferred.

• … uses nucleating agents to achieve a uniform microcellular structure. Adds cost

• Existing Technolgy ...

Foam Blow Molding

• … allows gas to escape to the surface causing open pores Not ideal for food and beverage packaging Not suitable for exhaust and fluid carrying ducts Can be solved with trilayer co-extrusion

• … introduces blowing agents in the extruder barrel … does not adequately control gas volume

injected in each parison of a multi-parison extrusion head

• … tries to make do with existing extrusion heads, seldom designed with flow channels to avoid pressure drop.

• … not suitable for sequential foaming of a parison or a layer

• Existing Technology ...

Foam Blow Molding

Foam Blow Molding

• Our Overall Objective

• Develop a multi-parison trilayer extrusion head • for discontinuous/sequential extrusion of a center foam layer • with a controllable and consistently repeatable cellular structure

in each parison • without the use of nucleating agents.

• Explore potential applications in the industrial/automotive sector

• Apply expertise gained for applications in the packaging sector

• Inject gas in the extrusion head instead of in extruder

• Produce a monolayer foamed preform with a consistently fine cellular structure

• Push out preform via an accumulator in preparation for sequential foam extrusion.

• Evaluate Impact of blowing agent on viscosity and melt temperature Length of mixing section Effect of gas pressure and compressor

• First Steps:

Pilot Project: Foaming of Preform


S1/25 T-PE Extrusion Head

• Equipment:

• Effect of Mixer Length and Gas Pressure (w/ PA)

Picture 1 Picture 2 Picture 3

# of Mixing Elements 2 4 4 Melt Pressure – Elbow 53 bar 103 bar 192 bar Gas Pressure 45 bar 105 bar 390 bar Melt Pressure – Mixer Entry 37 bar 80 bar 171 bar


• Nitrogen blowing agent is least costly, environmentally friendlier than CO2 and suitable for many resins.

• Blowing agent reduces melt viscosity, material dependant; run with up to 50⁰F lower than normal melt temperatures.

• Suitable mixers are not commercially available, determined required minimum length of a static mixer

• Compressor must generate up to 600 bar / 8,700 PSI. The higher the pressure, the finer the cell structure.

• Flow channel must remain unchanged in size from point of gas injection to extrusion die. Avoid 90⁰ turns.

• First Results


To avoid premature expansion, gas must be kept in solution in plastic melt from point of introduction to the bottom of the die

Soda bottle example: • Closed: -- Gas in

solution • Open: -- Cells are

formed that grow as pressure drops

• Pressure Drop


• Build a trilayer head with accumulators for the extrusion of each layer

• Employ a dynamic mixer for dispersion of the blowing agent shortening the mixing section to approx. 1.5 x D

• Produce trilayer structures with foam only in the middle layer

• Shorten and optimize dimensions of flow channels for foam

• Produce a repeatedly fine cellular structure, without the use nucleating agents

• Second Step Objectives:

Trilayer Co-Extrusion with Foam

1 2 3

1. Outer layer (more flexible) 2. Middle layer, continiuous or partially foamed 3. Inner layer (smooth)

• Layer Structure


S1/90 TT SeCo 3


Extruder 40/25D for Foam Layer

Extruder 35/25D for Inner Layer

Extrusion Tooling

Shutoff for Foam Layer

WTC Extrusion Die 1 WTC

Extrusion Die 2

Dynamic Mixer Drive

Accumulator for Inner Layer

Accumulator for Foam Layer

• Equipment:


Extruder 40/25D for Foam Layer

Ring Distributor

Dynamic Mixer Drive Accumulator for

Foam Layer

• Equipment:

S1/90 TT SeCo 3

Extruder 35/25D for Inner Layer

Extrusion Tooling

Shutoff for Foam Layer

Accumulator for Inner Layer

Secondary Extruder 35/25D for Outer Layer Accumulator for Outer Layer Primary Extruder for Outer Layer


• Equipment:

S1/90 TT SeCo 3 on test stand Dynamic mixer

Servo-electric WTC

• Evaluate Potential weight reduction Gas injectors Foam layer shutoff Ability to start and stop foam and to position repeatedly

• Second Step Objectives (Cont‘d):


• Duct produced in trilayer continuous co-extrusion




Extruded preform, uninflated (approx. 8mm wall thickness)

Blow molded, elongated cells (approx. 3mm wall thickness)



Repeatedly fine, uniform cellular structure

Net weight reduced from 260 to 180 grams = 30%

Solid outer and inner layer Smooth inner surface Noise from airflow reduced

• Gas Injector – Conical Valve


Pros: Opens under N2 pressure Reliable, safe operation No contamination

Cons: Injects large gas bubble Gas not homogenously

dispersed via dynamic mixer

• Gas Injector – Sintered Metal


Pros: Pre-disperses gas through

very small sintered insert (only 3.14 mm2)

Cons: Plastic melt penetrates pores

when gas pressure drops and no gas flows.

Clogs easily. OK for PE / PP.

Sintered Metal Insert

• Gas Injector – Combine advantages of both


• Compressor must meter a precise gas volume • Gas must be injected in small controlled doses

(x gram N2 / y gram plastic) For example via oscillating gas jet with up to 5 cycles/s,

pre-disperses gas

• Equipment:

Extrusion Die 2, (opens both layer 2 & 3 now, separately in future)

Extrusion Die 1

Gas Injector Dynamic Mixer

Mandrel


Layer 1: Outer (via Ring Distributor)

Layer 2: Foam

Layer 3: Inner

• Concept: Sequential Foam Blow Molding

Non-foam Connecting Areas

Inner Layer

Outer Layer

Layer

Foam

Trilayer Sequential Co-Extrusion

• Next steps

Trilayer Sequential Co-Extrusion

• Acquired a new blow molding machine for the lab to move ahead with further developments

• Test system components • Determine limitations • Start marketing a sequential trilayer co-extrusion system

by mid 2015 • Develop a simple continuous trilayer co-extrusion system

for consumer packaging applications.

Acknowledgments

• R&D by ... • Guido Knipp, Extrusion Head Design Engineer,

W. Müller GmbH, Troisdorf, Germany • Maik Hentschel, Owner,

pro.f.i.t (pro future innovative technology), Bobeck, Germany

• For providing test materials, thanks to ... • Borealis (PP) • Chevron Phillips (PPS) • DuPont (PA) • LyondellBassell (HDPE)

Acknowledgments

• Awards

• Dr. Reinold Hagen Award 2013, presented by the Dr. Reinhold Hagen Foundation at VDI Symposium Blasformen 2013, Baden Baden

• Innovation Award 2013, presented by Volksbank Bonn Rhein-Sieg eG

THANK YOU!

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