12009 TAPPI Flexible Packaging –Trends and Technology

Developments Symposium

Effect Of Time, Temperature, And Draw Down On Interlayer Peel Strength During Coextrusion Coating, Film Casting and Film Blowing

Presented by:Hariharan.KTechnical Specialist, Packaging & Industrial Polymers, E I DuPont India Pvt. Ltd.

2

OutlineBackground

Experimental

Results

Discussion

Time

Temperature

Area Creation

Practical Implications

Conclusions

3

Coextrusion• Combination of resins in the melt

• Cost effect technique to make functional articles

Nip Roll Chill Roll

Die

Line Speed

Air gap

Substrate

Not drawn to scale

4

Many factors influence adhesion• Compatibility of polymers and their ability to interdiffuse

• Presence of functional groups to promote chemical bonding at the interface

• Contact time and temperature

• Thickness and physical properties of the layers

• Stress imparted by drawing and other means

• The environment the article is subjected in its end use (RH, temperature, chemicals, etc.)

5

Effect of Time in the Air Gap on Foil Adhesion

25 μm Coatings onto Al Foil

0

200

400

600

800

1000

1200

0 50 100 150 200TIAG, ms

Peel

Str

engt

h,

g/25

mm

Time in Air Gap Known to Effect Adhesion to Solid Substrates

Antonov and Soutar (1991)

Little attention given to affect on interlayer adhesion in coextrusion.

EMAA

LDPE

6

Blown FilmMorris (1996)

Blown Film Results(HDPE-Adh-EVOH)

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

EVOH Process time (sec)

Peel

Str

engt

h (g

/25m

m)

ADH1

ADH2

ADH3

ADH3

ADH1

ADH2

7

Coextrusion tie resin technology

PE Tie EVOH

Tie resin is polyethylene or ethylene copolymer based to promote diffusion at PE/Tie interface

Tie has anhydride groups for chemical interaction at Tie/EVOHinterface

Tie may contain modifiers such as rubber that enhance peel strength

8

Blown Film

• Tie resins• ADH1: LLDPE,

low anhydride• ADH2: LLDPE,

high anhydride• ADH3: rubber

modified LLDPE, medium anhydride

• Stress believed to be involved

Blown Film Results(HDPE-Adh-EVOH)

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

EVOH Process time (sec)

Peel

Str

engt

h (g

/25m

m)

ADH1

ADH2

ADH3

ADH3

ADH1

ADH2

Morris, 1996 SPE ANTEC

9

Current StudyPurpose: Look at the effect of process time on interlayer adhesion in coextrusion coating/cast film

What is the appropriate process time?

Constant velocitytf = TIAG = L/vf

Linear model

( )DDRDDR

DDRvLt

ff ln1

⎟⎠⎞

⎜⎝⎛

−=

Newtonian Model

.)ln(1⎟⎟⎠

⎞⎜⎜⎝

⎛ −=

DDRDDR

vLt

ff

Velocity Profile in Air Gap

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

z/L

(V-V

o)/(V

f-Vo)

Constant Velocity

Linear ModelCanning and Co, 1999, DDR=7.27

Newtonian Model

10

ExperimentalStructure: Kraft Paper/LDPE//(tie-EVOH-tie-LDPE)

19 5 6.3 5 25 micronsResins:

Variables:• Die gap: 0.5 mm, DDR 18

• Air gap: 13 - 25 cm (5 – 10 in)

• Line speed: 61 – 183 m/min (200 – 600 fpm)

• Process time: 0.22 – 1.3 s

Resin Description LDPE Standard coating grade EVOH 44 mol % ethylene Tie 1 LLDPE with low anhydride Tie 2 LLDPE with high anhydride Tie 3 Rubber modified LDPE with intermediate anhydride

11

ExperimentalStructure: Al/(EAA-LDPE)

50 5 25 micronsResins:

• EAA: 9% AA, 10 MI

• LDPE: 0.923 g/cc, 4.5 MI

Variables:• Die gap: 0.5 mm, DDR: 20

• Air gap: 11.4 – 22.9 cm (4.5 – 9 in)

• Line speed: 61 – 183 m/min (200 – 600 fpm)

• Process time: 0.21 – 0.42 s

12

ResultsCoextrusion Coating Results

Paper/LDPE//(tie/EVOH/tie/LDPE)

0

200

400

600

800

1000

1200

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Process Time, s

Peel

Str

engt

h to

EVO

H, g

/25m

m

Tie3

Tie2

Tie1

13

ResultsCoextrusion Coating

50-μm Al//(5-μm EAA - 25μm LDPE)

500

520

540

560

580

600

620

640

660

680

0.15 0.2 0.25 0.3 0.35 0.4 0.45

Process Time, s

Peel

Stre

ngth

to L

DPE

, g/2

5mm

14

Comparison of EC and BF Results

Coextrusion Coating ResultsPaper/LDPE//(tie/EVOH/tie/LDPE)

0

200

400

600

800

1000

1200

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Process Time, s

Peel

Str

engt

h to

EVO

H, g

/25m

m

Tie3

Tie2

Tie1

Blown Film Results(HDPE-Adh-EVOH)

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

EVOH Process time (sec)

Peel

Str

engt

h (g

/25m

m)

ADH1

ADH2

ADH3

ADH3

ADH1

ADH2

Extrusion Coating results suggest kinetic effect

15

Slope Differences

Ga = Wb(1 + Φ(R, T))where Ga = fracture energy

Wb = work of adhesion or bonding

Φ = local viscoelastic energy dissipation

R = rate

T = temperature.

Multiplying effect• Rubber modification increases Φ

• If Wb = constant, adding rubber shifts curve upward (blown film)

• If Wb increases with process time (kinetics), slope also increases

16

Differences between blown and cast film

Time scales• Process time

• Blown film: 5-10 s

• Cast film/EC: 0.2-1.0 s

• Crystallization time

• Blown film: 2-5 s

• Cast film/EC: 2-10 ms

Temperature during drawing

Interfacial area creation

17

Time Scales: Blown Film50 μm HDPE

80

90

100

110

120

130

140

150

160

0 10 20 30 40 50

z, cm

Tem

pera

ture

, ºC

CLH

FLH

FZH

Temperature measurements of outside of film using IR thermometer

CLHFLH

FZHz

18

Crystallization time: Blown Film

Plateau of Bubble Temperature

00.5

11.5

22.5

33.5

44.5

5

0 5 10 15

Process Time (sec)

Plat

eau

Wid

th (s

ec)

Morris, 1998

19

Time Scales: Cast Film/ECModel Prediction of Temperature at EVOH-

Tie InterfacePaper/LDPE//(tie-EVOH-tie-LDPE)

123 m/min, 13-cm air gap

20

70

120

170

220

270

320

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Time Since Die Exit, s

Tem

pera

ture

, C

WebChill Roll

Contact with Chill Roll

Die

Chill Roll

20

Time Scales: Cast Film/EC

Results using heat conduction model

Cooling in NipPaper/LDPE//(tie-EVOH-tie-LDPE)

123 m/min, 13-cm air gap

0

50

100

150

200

250

300

0 2 4 6 8 10 12

Time since contact with chill roll, ms

Tem

pera

ture

of E

VOH

-tie

Inte

rface

, C EVOH freezing

LDPE, tie freezing

21

Interfacial Area Creation

Blown film• A/Ao = (BUR)*(DDR)

Cast film and EC• A/Ao = DDR

A/Ao = go/g

22

Interaction of area creation and temperature in blown film

Data from Morris, 1998 SPE ANTEC

(45-mm HDPE - 23-mm EVOH) Blown FilmBUR = 2.2, DDR = 6, FLH (EVOH) = 20 cm

0

2

4

6

8

10

12

14

0 0.5 1 1.5 2

z/L

V/V

o, D

/Do,

A/A

o

100

110

120

130

140

150

160

170

180

Tem

pera

ture

of H

DP

E, C

D/Do

V/Vo

A/Ao

Temperature

23

Interaction of area creation and temperature in cast film/EC

0

2

4

6

8

10

12

14

16

0 0.2 0.4 0.6 0.8 1z/L

A/A

o

240

250

260

270

Tem

pera

ture

, C

A/Ao

Temperature

24

Summary

Blown film• Rapid increase in interfacial area near frostline

• Time available for bonding and relaxation after area creation has ceased is several orders of magnitude greater than for cast film

Cast film• High temperatures in air gap

• Exponential increase in interfacial area

• Very rapid freezing – little time for reaction and relaxation after interfacial area creation has ceased.

25

Practical Implications

Effect of Output on Peel Strength

0

200

400

600

800

1000

1200

Output (at constant air gap)

Peel

Str

engt

h, g

/25m

m

Tie3

Tie2

Tie1

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ConclusionsInterlayer adhesion generally increases with increasing process time

Character of curves differ between cast film/EC and blown film

• Cast film/EC appears to be kinetic effect; BF stress effect

• Related to differences in

• Time scales

• Temperature

• Area creation

27

Thank YouPRESENTED BYHariharan.KTechnical Specialist, Packaging & Industrial Polymers, E I DuPont India Pvt. Ltd.

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