1 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Microinjection moulding (µIM) of thermoplastic polymers :

From theory to experiment

J. Giboz1,2, T. Copponnex1, P. Mélé2

2: LMOPS - UMR CNRS 5041University of SavoieLe Bourget du LacFrance

1:HE-ARCUniversity of applied scienceSaint-ImierSwitzerland

2 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Outline

I. Main goal� Influence of the moulding conditions in injection moulding processes:

“µpart vs Macroparts”

II. Processing techniques� Material chosen and processing conditions

III. Experimental Results / Discussion� “µpart vs Macroparts”: Difference in Structure and properties

IV.Conclusions

3 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Main Goal

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

Chemical degradation?

Mechanical properties?

Thermal properties?

Homogeneity?

Giboz J., Copponnex T. , Mélé P. , J Micromech. Microeng., 2007, 17 R96-R109

Do the processing conditions modify the properties and the structure of polymers?

4 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Processing techniques (1)

Babyplast 6/10®

5T Clamping force

0,15mm thick

Sesame nanomolder®

1,5T Clamping force

HDPE Borealis MG9641

x10

Moulding conditions

T = 220°C, V inj = 200 mm/sTmould = 80°C Tmould = 30°C

1,5mm thick

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

5 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

3-Plates mould(CNC Machining)

Mould insert (Made by UV-LIGA)

Injection gates geometry

Ø: 0,2mm

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

Processing techniques (2)

6 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Reference: 1,33

Process capability

3.72 3.73 3.74 3.75 3.76 3.770.1

1

10

40

70

95

99.5

SPC1 SPC2

R=0,988

Cum

ulat

ed fr

eque

ncy

(%)

Part length (mm)

R=0,997

3.72 3.73 3.74 3.75 3.76 3.770

5

10

15

20

Fre

quen

cy

Length (mm)

SPC 1

0.691.17Cpk

1.511.35Cp

0.0060.007σ

3.7593.747Mean

SPC 2SPC 1

The µIM process is capable to produce the part withthe specified tolerances

Two series of 300 parts

Length

Normal probability plot

Fre

quen

cyC

umul

ated

Fre

quen

cy(%

)

Length (mm)

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

7 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Experimental results

Influence of the processing conditions on

the Microstructure and properties of Polymer

8 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Theoretical analysis

Theoretical shear rates higher than allowable ones

Plate

Cal

cula

ted

wal

l she

ar r

ates

(s-

1 )

Speed (mm/s)

Micropart

0101

102

103

104

105

106

0 200 400 600 800 1000 1200

1

Speed (mm/s)

Maximum shear rates(≈ 40 000s-1)

0 200 400 600 800 1000 1200101

102

103

104

105

106

Speed (mm/s)

Micropart (Ø0,2mm)

Plate (0,5x6mm)

Brydson J.A., Flow properties of polymer melts, 1970, Van Nostrand Reinhold, New York

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

+=2

)12(2

WH

Q

n

nγ&

⋅+=

3

4

4

13

r

Q

n

n

πγ&

9 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Experimental analysis

Molecular weight distribution:

Gel Permeation Chromatography

Chemical functions:

Fourier Transformed – Infrared spectroscopy (ATR mode)

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

10 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria40

60

80

100

4000 3500 3000 2500 2000 1500 1000 500

Wave number (nm-1)

%R

efle

ctan

ce Micropart Plate Pellet

No degradation occurs with the

µIM process

Separation as a function of the molecular weight

Experimental Results

2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,50,0

Mw : 120000 g/mol

Mn : 13000 g/mol

Wei

ghtf

ract

ion

(Der

ivat

ive)

Molecular weight (log)

0,0

0,1

0,2

0,3

0,4

0,5

0,6

2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,50,0

0,1

0,2

0,3

0,4

0,5

0,6

Micropart Plate Pellet

Mn MwI. Goal

II. Processing techniques

III. Results

IV. Conclusion

Gel PermeationChromatography

FT-IR spectroscopy

11 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

OM(Optical microscopy)

Polymer morphology: Crystalline structure

WAXS(Wide angle X-Ray Scattering)

DSC(Differential Scanning Calorymetry)

Multiscale relationshipsPictures from: Hobbs J., Chin J Polym Sci, 2003, 21, 135

1µµµµm

Spherolites Lamellas

The macroscopic properties of parts greatly depends on the morphology

Crystal

Scale (m)10-5 10-8 10-910-3

Plate

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

12 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Optical microscopy (Thickness)

Plate microscopy (Half thickness)

200µm

Skin Core

CoreSkin Shear zone Post-filled zone

Mendoza R., Material PhD Thesis,ENSAM Paris, 2005

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

HDPE structure

200µm

13 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Optical microscopy (Thickness)

A well defined “Skin-core” structureµpart morphology is more homogeneous / Macroparts

50µm

Micropart

50µm

Cryomicrotomed samples

5 µm thick

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

14 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Temperature cycle

DSC: Experimental results

Samples’ weight: 2.4mg ± 0.1mg10°C/min

5 min

10°C/min

3 min

5 min230°C

40°C

10°C/min 10°C/min

T°

time

Smaller lamellas thicknesses for µIMDistribution of lamellae thicknesses more homogeneous for µIM

110 115 120 125 130 1350

10

20

30

40

Hea

t flo

w (

J/g.

°C)

Temperature (°C)

Micropart Plate Pellet

Second heating

EndoEndo

1100

10

20

30

40

Hea

t flo

w (

J/g.

°C)

110 115 120 125 130 1350

Temperature (°C)

110 115 120 125 130 1350

10

20

30

40

Micropart Plate Reference (Pellet)

Hea

t flo

w (

J/g.

°C)

Temperature (°C)

EndoEndo

First heating

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

15 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

00,00

0,02

0,04

0,06

0,08

0,10

W

eigh

t dis

trib

utio

n (n

m-1)

C)(J/flow Heat :dTdE °

:T0mMelt temperature ofa perfect crystal (°K)

:M Crystal weight (g)

:eσ Surface energy (J.m-2)

*: Albérola et al., J Polym Sci B: Polym Phys 1990. 28, 569

Crystallite thickness in µIM are smaller / conventional processThickness distribution of crystallites is narrower

Gibbs-Thomson relation

Distribution of lamellas thicknesses

⋅−= ∞

m

e0m

∆Hl

2σ1TT

0 10 20 30 40

Lamellas thickness (nm)

Crystal thickness distribution*

( )MT2σ

ρTTdTdE

) l (f0me

c20

m

⋅⋅

⋅−⋅=

0 10 20 30 400,00

0,02

0,04

0,06

0,08

0,10

Lamellae thickness (nm)

Wei

ght d

istr

ibut

ion

(nm

-1)

Micropart Plate

0 10 20 30 400,00

0,02

0,04

0,06

0,08

0,10

Lamellae thickness (nm)

Wei

ght d

istr

ibut

ion

(nm

-1)

Micropart Plate

Second heatingFirst heating

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

Thermal and Shear effect?

16 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

*: Giboz, J., P. Mélé, T. Copponnex, “On the morphology of microinjection moulded thermoplastics polymer”

Submitted to Polymer

WAXS: Crystalline structure

40mm 1,5mm

Bragg’s law: Determination of the crystalline structured = n.λ / 2sin(θ)

110

200

No change in the crystalline structureLamellae thickness lower (as for DSC measurements)

002

12 16 20 24 360,0

0,1

0,2

0,8

0,9

1,0

Micropart Plate

Inte

nsity

(C

ount

s (A

.U)

2 Theta (deg)

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

Cristallinity(%)

Micropart 66 ± 3

Plate 58 ± 3

17 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Conclusions

I. Goal

II. Processing techniques

III. Results

IV. Conclusion

• Mould• Mould insert

Physical modification

• “Skin-core” structure• Crystallinity more important• Thinner crystalline entities• More homogeneous crystalline structure

• Small scale Productions• Capable process

Thermal VS Shear effects?

Polymerproperties

Development

Processing

Chemical modification

• No degradation

Part properties?

18 4M 2007 Conference, 3-5 October 2007, Borovets, Bulgaria

Conclusions

Thank you for your attention