1. Micro-Moulding of Polymers: Process and Product Assessments
Dr Ben Whiteside, Dr Mike Martyn, Prof Phil Coates,
IRC in Polymer Engineering, University of Bradford, Bradford UK.
P S Allan, G. Greenway and P Hornsby,
Wolfson Centre for Materials Processing, Brunel University, Uxbridge, UK

2. Contents Micromoulding Results of studies at Bradford
Process technology
Results of studies at Bradford
Process dynamics
Process interaction
Product properties

3. Battenfeld Microsystem 50
Purpose built micro injection process
Servo-electric injection
Automatic parts handling
Clean room filtration
Modular
A purpose designed machine – started with a blank piece of paper in terms of specking the machine – has several features

4. Battenfeld Microsystem 50
Hopper
Metering Piston
Extrusion screw
Heated Regions
Shut off valve
Injection piston

5. Operation Cycle

6. The Data Acquisition Setup
Dynisco PCI 4011 Piezo load transducer
J-type thermocouples
Temposonics R series displacement transducer
Dynisco PCI 4006 piezo load transducer

7. 1 Process Measurement – Data Capture
Injection Pressure
Cavity Pressure
Ram Displacement
Ram Velocity
3 Temperature Channels
Max sampling rate ~ Hz

8. Mould temperature investigation

9. Hypothesis
The high surface area to volume ratio of micro-moulded products allows rapid removal of heat from the product through the cavity wall
Mould temperatures should be higher than those used in conventional IM to prevent premature solidification and part-filled products

10. Step plaque moulding
Material: HAPEX (40% sintered hydroxyapatite HDPE matrix)
Produced by IRC in Biomaterial Science
Queen Mary and Westfield College, London

11. Cavity Pressure – Hapex, step plaque

12. Product Mass – Hapex, step plaque
0.12% variation

13. Mould temperature - conclusions
For products ~25mg recommended mould temperatures for standard injection moulding can be used with confidence for the Hapex material
Further investigations to be performed at smaller length scales

14. High shear rate experiments

15. Calculated wall shear rates
0.1 x 0.1mm
0.2 x 0.2mm
0.5 x 0.5mm
1.0 x 1.0mm

16. Dynisco Pressure Transducer
In-process rheometry
Dynisco Pressure Transducer
435-30M
Capillary die
inserts
0.5 x 8.0 mm
0.5 x 0.25 mm
1.0 x 16 mm
1.0 x 0.25 mm
Thermocouple
Measurements performed on a 30 tonne Cincinnatti Milacron servo-electric injection moulding machine with a custom rheometric nozzle

17. High-shear capillary rheometry test results

18. Shear heating effects
Source: Anthony Bur, Steven Roth, NIST

19. ‘Top Hat’ Cavity Large diameter = 1.0mm Small diameter = 0.5mm
Gate dimension 0.1 x 0.2mm
Material BP Rigidex 5050 HDPE

20. Molecular weight measurement
Sample material taken from runner system and cavity
Gel Permeation Chromatography (GPC) analysis performed by Rapra Technology Ltd on each sample to determine molecular weight distribution

21. Molecular weight distributions
Source: RAPRA UK

22. High shear investigation - conclusions
The process contains shear rates orders of magnitude higher than those encountered in conventional IM
Viscosity curves behave predictably in this region
Shear heating will be a factor
Stable materials show no sign of degradation
Temperature sensitive materials?

23. Surface feature replication

24. Surface feature replication
Plaque cavity 25 x 2.5 x 0.25 mm
Fabricated using micro-milling technique
Kern machine
0.2mm cutter at rpm.
Left in an unpolished state.

25. Surface feature replication - gate
Cavity
Product
AFM scan size 75 µm x 75 µm
Pitch of scroll marks ~ 6µm

26. Surface feature replication - gate
Cavity
Product
AFM scan size 75 µm x 75 µm

27. Surface feature replication -downstream
Cavity
Product
AFM scan size 75 µm x 75 µm
Pitch of scroll marks ~ 6µm

28. Surface feature replication - comments
Mould features of the order of a few µm are accurately replicated on the product assuming pressure is sufficient
Further work to be performed to investigate the limit to which a feature is adequately moulded on a product

29. Morphology Measurement
Surface following microtomy
Surface following etching
Component sectioned using glass-knife microtomy
Surface is etched using potassium permanganate solution to produce representative surface
Surface imaged using microscopic technique (TEM, AFM etc)

30. Morphology Measurements - Structure
Nano-indent
Crystal
Structure

31. Morphology Measurements – Spherulite size

32. Morphology Variation
800 µm
Line of indents 25µm separation

35. Morphology Measurements – Amorphous layer

36. The Rondol Micro-Injection Compounder

37. The Rondol Micro-Injection Compounder

38. The Rondol Micro-Injection Compounder
Prism twin-screw extruder

39. The Rondol Micro-Injection Compounder
Advantages:
Minimise residence time of polymer in plasticising screw
Exposure to single heating/cooling cycle
Positive displacement allows use of low viscosity materials

40. Operation

41. The Rondol Micro-Injection Compounder

42. Initial testing It works!
Able to process low molecular weight materials
Dosing control can fluctuate
Toggle clamp can result in flashing

43. Experimental Battenfeld Microsystem50 Stepped plaque cavity
60mg total shot mass
HDPE 5050
Injection speed – 200, 400, 600 mm/s
Screw speed 40revs/m
Melt temp 200C
Mould temp 50C