Technoform- A test tool to determine Thermoformability

May 8, 2006 Transmit Technology Group, LLC

Applications of Thermoformability Analyzer

Amit Dharia

Transmit Technology Group, LLC

Irving, Texas


Objectives• To demonstrate the need for an industry wide

standard Quantitative test method for “Measuring” and “Reporting” Thermoformability of plastic materials (2005)

• To illustrate applications of test equipment and test method in understanding and resolving issues related to Thermoformability.


Outline

• Structure-Property- Process relationship • Current test methods • Description of Technoform • Application and data interpretation• Products – Basic, Standard, Advanced• Conclusion


Thermoforming Process

• Extruding sheet stock

• Heating sheet above Tg

• Stretching heated sheet in rubbery state

• Cooling

• Trimming

• Finishing

• Regrinding and recycling scrape


Structure - Properties -Thermoformability

• Rate of change of strength with the change in strain rate at forming temperature

• % Crystallinity – Breadth of rubbery Plateau • Molecular weight, Molecular weight

distribution, molecular architecture (branching, crosslinking) – MFR, Melt Elasticity, Rheology


Other parameters

• Density - % filler, type of fillers, degassing• Geometry – Thickness, area, multi-layered

structures, adhesion between layers• Residual stresses between and within in

extruded layer sheet stock• Thermal diffusivity (Cp, K. Rho)• Extrusion quality ( gels, unmelts, thickness

variation, grain patterns)• Color (IR absorption)


Test Methods Test Method Major Short coming

MFR Easy, measure of only MW

Melt Tension > Tm, cooling effect, uni-directional, not applicable to all materials

Sag test No external force, geometry dependent, measure of only melt strength

Stress Relaxation

Repeatable, correlates with Sag test, expensive equipment

DMTA Repeatable, effect of temperature

Hot tensile test Inconsistent results, grip extrusion, annealing


Major disadvantages of current methods

• Most tests are conducted in melt or near melt phase • Test Specimens do not reflect actual test geometry

(shape, size, clamping mode)• Tests do not account for orientation, thermal stresses,

thickness variations• Isothermal environment, does not account for transient

nature of heating/ cooling • Effects of secondary process parameters can not be

evaluated• Results cannot be directly used.


What processors want to know?

• Will this material thermoform? • Will this new material process the same? • Will this lot process the same as the last one?• Why this lot does not process the same?• How fast material will heat?• What is the right forming temperature range?• Will melt adhesion between layers survive heating and

stretching step?• Will material discolor, fed or degrade during heating?


What processors want to know? -II

• What is the maximum draw down?• How fast part can be made? • What is the MD and TD shrinkage?• Will material tear at the corners and ribs?• How much regrind can I use?• Will grains retain shape and depth?• Does extruded sheet have gels or unmelts?


What Industry Needs?

• A standard test method which reflects all unit steps – heating, 3D stretching, forming, and cooling

• A test equipment which can be precisely controlled, is rapid, easy to use, provides repeatable and quantitative information, using the least amount of material.

• Easy to use “Thermoformability Index” standard for comparing, contrasting effects of selected process/ material variables


VariablesMaterial Feed Stock Process

Molecular Structure Thickness Forming Method

Tg, Tm, % Xc Residual stresses Part geometry

% LCB, % Xl Layers Plug geometry

ηo, ηel Color Plug material

Rho, k, Cp Volatiles Plug temperature

Type of fillers % regrind Forming speed

% of fillers impurity

Additive package Extrusion, storage

Shrinkage


Desired Test Method

• MEANINGFUL

• Rapid

• Easy to use

• Quantitative

• Repeatable

• A good problem solving tool


Test Input – Output

Input Range Output

Method Plug assist, Vacuum Temp. vs. Time

Resin Type Any type Force vs. Time

Sheet Thickness 10 mil to 375 mil Force vs. Draw Depth

Forming Temperature 60 C to 280 C Draw vs. time

Heat Soak time Variable Force at Max Draw Depth

Plug Material Epoxy, Polished Aluminum Force vs. Depth

Plug temperature 23 C to 120 C

Forming Speed 10- 180 mm/second

Plug Dwell time Variable

Maximum Force 100 lb

Cooling Time Variable


Typical GUI Screen

Sag

Elastic

Plastic

Strainhardening

Thinning


ResultsV,T


Technoform


Schematics of Technoform


Melt Strength = Resistance to Deformation @ TMelt Elasticity =Capability to deform @ T

Stress(Force)

% Draw or A/Ao

Strain Hardening


Heating rates for various plastic materials(Heater at 600 C, 3” from upper, 2” from lower)

30

80

130

180

230

0 20 40 60 80

t (seconds)

T (c

)

PP

HDPE

HIPS

PVC

ABS

Acetal

PMMA

Nylon


Effect of Crystallinity

0

5

10

15

20

25

30

50 70 90 110 130

Forming distance, mm

Forc

e (N

)HDPE PP HIPS PETG ABS PMMA PVC


Comparison of various PELDPE, LLDPE, MDPE @ 60 mm/s

0

5

10

15

20

25

30

35

0 20 40 60 80

Depth, mm

Fo

rce

, lb

f

LDPE120

LLDPE120

MDPE120


Effect of Forming Temperature

0

2

4

6

8

10

12

14

125 145 165 185

Temperature (C)

Fo

rce

(N

)

ABS

PP

HDPE

HIPS

PETG

PMMA

ACETAL


Force100 = f (T, V, material)

• F(ABS) =9.2348 -0.0547 T (R2 =99%)

• F(PMMA)=7.1587 -0.0341 T(R2=98%)

• F(PETG)=10.096 -0.0601 T (R2=92%)

• F(HIPS)=9.6782 - 0.0503T(R2=93%)

• F(HDPE)=5.2771 -0.0266 T (R2=86%)


Effect of Melt Strength (% HMSCOPP in COPP)

0

0.5

1

1.5

2

2.5

0 50 100 150

0

20

40

60

80

100


HMSCOPP

0

10

20

30

40

0 50 100 150

Draw Depth (mm)

Foc

e lb

f (1

70

C)

0

1

2

3

4

Forc

e lb

f

170 C

180 C

190 C

210C


COPP vs. HMSCOPP

40

60

80

100

120

170 180 190 200 210

T, C

Dra

w d

ep

th a

t Y

ield

COPP

HMSPP


Isothermal vs. Non-Isothermal20 mm/s, 130 C, HIPS

02468

1012

1 2 3 4 5

Draw Depth (Inches)

Fo

rce

(lb

)

130 C-20I 130 C-20NI


Effect of Plug TemperatureHIPS 35 mil, 130 C, 40 mm/s, No control

0

2

4

6

8

10

12

0 20 40 60 80 100 120 140

Draw Depth, mm

Forc

e, L

bf Series1

Series2

Series3


Effect of Plug Temperature-II35 mil HIPS, 130 C, 40 mm/s, Plug at 23 C

0

2

4

6

8

10

12

0 20 40 60 80 100 120

Depth, mm

Fo

rce

, Lb

f #1

#2

#3

#4


Effect of Plug induced cooling -IIIHIPS (with and without hole)

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120

Draw Depth, mm

Fo

rce

, lb

f

wo with


Effect of Plug Material35 mm HIPS, 40 mm/s, 130 C

0

1

2

3

4

5

6

0 20 40 60 80 100 120

Depth (mm)

Fo

rce

(lb

)

WF WFT Bix


Effect of Sheet Thicknesson heating rates

0

100

200

300

0 500 1000time (sec)

Surfa

ce

Tem

pera

ture

(C)

100 mil 150 mil 250 mil


Effect of Sheet Thickness

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100

Depth (mm)

Froc

e (lb

f)

95 150 250


Effect of Color on heating Rate

32

82

132

0 50 100

time (sec)

Su

rfa

ce

Te

mp

era

ture

(C

)Red Blue Metalic


Effect of Color CoPP, 35 mil, 40 mm/s, 160 C

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 20 40 60 80 100 120

Depth (mm)

Fo

rce

(lb

)

0

2

4

6

8

10

12

blue red Metallic


Effect of Lot to Lot Variation

170 C, 40 mm/s, 190 mil TPO

0123456789

10

0 10 20 30 40 50 60 70

Depth (mm)

Fro

ce (

lbf)

1-1 1-2 1-3


Effect of Regrind (FR-ABS)

125 mil, 160 C, 40 mm/sec

0

2

4

6

8

10

12

14

0 20 40 60 80 100

Depth (mm)

Fro

ce (

lbf)

50% RG 100% RG


Effect of Regrind (GPPS)125 mil, 190 C, 40 mm/sec

0

2

4

6

8

10

12

14

0 50 100

Draw Depth (mm)

Fo

rmin

g F

orc

e (

lbf)

PS Virgin

PS Regrind


Processing Window of Commercial TPOs

0

10

20

30

0 20 40 60 80 100

Depth (mm)

Forc

e (lb

f)170 180 190 170TPO


COPP- Nano clay Composites

Force @ yield

0.9

0.95

1

1.05

1.1

1.15

1.2

COPP(0.8) COPP2.6NC COPP2.6C

Fy,190


CoPP-Nano Clay Composites

50

75C

OP

P(0

.8)

CO

PP

2.6N

C

CO

PP

2.6CDra

w D

epth

@ y

ield

Dy,190/100


How to Standardize?

• Thermoforming Index (TFI)– Force required to draw a sheet of thickness X at

speed Y mm/second using a Plug of specified geometry G at Temperature Tf to area ratio A (or volume ratio V), with plug temperature Tp.

• TFI = [Force (M, Tm)/ Force (GPPS, Ts)]


Thermoforming Index (example)

• 125 mil, GPPS, 40 mm/s force to draw to 45 mm depth @ 160 C is 7 lbs.

• 125 mil, PP, 40 mm/s Force required to draw to 45 mm depth @ 170 C is 3.5 lbs.

• TFI of PP = F 45,PP * thickness (GPPS)

F 45, GPPS * thickness (PP)

= 3.5*0.125/ 7* 0.325

= 0.5


Conclusions

• Easy and rapid test method with overall operation similar to actual Thermoforming process

• Economical vs. Field trials• Test equipment and method can be applied to wide

range of Industrial applications• TFI offers one simple number (like MFI)

representing material’s Thermoformability • Test equipment and method can be applied to wide

range of Industrial applications

Technoform- A test tool to determine Thermoformability

Technology

Transcript of Technoform- A test tool to determine Thermoformability