. . . .? ybsong@lgchem.com

01 Introduction

.

,

.

() ,

.

, (Die Drool

Phenomenon) . ,

(Drool) .

116 .

Pipe profile, film casting, fiber spinning,

film/melt blowing, wire/cable sheathing

.

,

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1 | Examples of die drool Phenomenon16

(a) LLDPE, string extrusion1

(b) LLDPE, string extrusion2

(c) EVA/LLDPE compound, cable sheath extrusion3

(d) mLLDPE, string extrusion4

(e) metallocene based polyolefin elastomer resin, string extrusion5

(f) partially foamed polymer melt, string extrusion6

(g) regranulated LDPE, film blowing7

(h) unfilled HDPE, string extrusion8

.

, 1946

.

,

, ,

.

,

16.

,

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02 Die Drool Formation Mechanism

,

,

.

9,

10,

.

1981 Klein 12

. Klein

,

,

,

.

,

,

13,14. Chaloupkova Zatloukal

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. . . .?

.

Suction.

Suction

4,15( 2).

.5

18,19 HDPE

. , HDPE

-

- slip-stick

(

)

, HDPE

,

. ,

20.(3)

,

.

,

.

. ,

, /

,

.

(solid metal die wall, liquid

polymer melt, and air)

.

driving force.

, /

,

. ,

2.

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2 | The predicted pressure field at the die exitfor the extrusion of mLLDPE.15

0.

,

(

0 -negative pressure)

.

.

,

driving force

suction.

,

. -

16.

,

driving force

.

wall slip.

wall slip

. 10-12,14

Wall slip

, -

.

, .

,

,

.

.

slip

.

no-slip condition

. 15,16

.

.

, wall slip

16.

- Flow-Induced Molecular Weight

Fractionation Theory

- Stress-Induced Cohesive Chains

Disentanglement Theory

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3 | Separation of slip layer and polymer bulk dueto cohesive failure inside flowing polymermelt inside circular die with no adhesive slip

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03 Die Drool Causes and EliminationMethod

, 1

/

. 1

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04 Effect of Die Design on Die DroolPhenomenon

60,

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.

, ,

16. ,

/

.

.

.

.

.

[ Low Surface Energy Die Materials ]

2,17,21-23. ,

polytetrafluoroethylene

(PTFE)21PTFE22

. PTFE

.

.

0.8

,

23.

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. , , , PTFE,

10,

2.

[ Die Design Changes ]

, Foster

4 anti-drool

24.

frusto-conical

.

.

15 5(c)

champering .

45 champering ,

6

. 6 (Die drool

amount, DDA).

AD

, ADie

. tD ,

tDie.

( - -

) .

5(b) Flared

25-27.

flared

flared .

HDPE

flared champering

19.

,

(champering and flared shape)

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4 | Original (left) and modified (right) die exitsurface according24

5 | Detail description of the removable capillary15

drool

conductor

plasticcovering

harmlessdrips

Cooling medium channel

DDA = AD

ADie

tD

tDie

. . . .?

.

flared champering

(same

conclusion was found in reference27 for

mLLDPE material), HDPE

15 flared

capillary 2/15

.(7) , ,

56%,

97%15.

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6 | Dependence of the die drool amountproduced by mLLDPE extrusion on the dieexit angle (processing conditions: 400 g.hr-1, 85C, Die No. 1 - straight die, Die No. 5 -15chamfered die, Die No. 4 - 45chamfereddie)15

7 | Dimensionless build-up ratio as the functionof dimensionless flared length (processingconditions : 750 g.hr-1, 160C). LC1 is flaredlength and L is capillary length. Error barsrepresent three independent measurements19

0

1

2

3

4

5

10 20 30 40 50

Die

Droo

l Am

ount

DDA

(-)

Die No.1

Die No.5 Die No.40

1x10-4

3x10-4

2x10-4

4x10-4

6x10-4

5x10-4

7x10-4

1/15 2/15 3/15 4/15 5/15 6/15 7/15 8/15

Dim

ensi

onle

ss b

uild

up ra

tio, B

R (-)

Dimensionless flared length, LC1/L (-)Die exit angle ()

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05 Conclusion

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1 | Summary of factors inducing formation of die drool16

Method Factors inducing die drool

Die design abrupt corners at die lips

dead corners inside extrusion die (thermal degradation)

high surface energy die wall materials

high surface roughness

short die land length

Polymer material low molecular weight fractions

multimodal polymers (low molecular weight tail)

high elasticity of polymer

linear architecture of macromolecules

high content of fillers

high concentration/incompatible additives or pigments

high concentration of volatiles

dissimilar material properties in blends

high content of stearates, ester lubricants, extending oils or waxes

chemical reactions between polymer and metal barrel/screw/die (PVC or PVDC materials)

Processing high processing temperature (thermaldegradation)

draw down

intensive cooling of die exit

Other factors die swell

shark skin

wall slip

vortices (thermal degradation)

slip-stick

pressure fluctuations in screw

excessive screw/barrel wear

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