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Suppress Static Sparks when Unwinding 1/14

Suppress Static Sparks when Unwinding Release Liners and Laminated Webs

Kelly Robinson, PE, PhD


1. Introduction – Static sparks:a) ignite flammable solvents,b) shock people and machine control systems,c) cause sheets to stick and jam, andd) damage products.

2. Tribocharging causes charging at the unwinding nip3. Measure static with 2 instruments

1. Electrostatic Fieldmeter2. Non-contacting Electrostatic Voltmeter

4. Unwinding Roll charge control5. Suppress Sparks6. Summary

Suppress Static Sparks when Unwinding Release Liners and Laminated Webs


I. Introduction

2. Prevent shocks to operators.1. Eliminate ignitions.

3. Prevent static problemsin customer applications(sheet sticking, process jams).


Release liner

PSA Label

Product Application

Static sparks can damage the silicone release liner causing release failure

(PSA label sticks to support).

I. Introduction

Image courtesy of


2. Tribocharging

Charge is separated at the unwinding nip where the exiting web peels from the outside surface of the unwinding roll.

Unwinding nip

Unwinding roll

+

+

– – Exiting

web

Support on outside

surface

Liner on inside surface

–

+


ElectricField

+ + + + + + ++ + + + + + + +

2TOP mCoulombsσ

2BOTTOM mCoulombsσ

Control Volume

EFloor

3. Measure Static - Fieldmeter

The electrostatic fieldmeter responds to the total amount of charge in the control volume.

E α ( σTOP + σBOTTOM )A5


VSURFACE

non-contacting electrostaticvoltmeter probe

3. Measure Static - Voltmeter

What is the charge density σTOPon the top surface?

Plastic or insulating paper sheet+ + + + + + + + + + +

–– –– –– –– –– –

2TOP mCoulombsσ

2BOTTOM mCoulombsσ

Measuring the surface potential VSURFACE with the sheet on a grounded surface removes the contribution from σBOTTOM.

Here, the voltmeter responds only to the charge density σTOP on the top surface.

VSURFACE α σTOPA3


4. Unwinding Roll

EROLL responds to the static charges on the outside surface of the unwinding roll. ESPAN is nearly zero!

Unwinding nip

Unwinding roll

+

+

– –

Exiting web +

+

+

+

+

+ + + + EROLL ≅

+10 KV/cm

ESPAN ≅ 0 KV/cm

Control volume for fieldmeter

Support on outside

surface


–

–

+ +

+

–

+ – + –

VTOP ≅ +200 V

VBOTTON ≅ –200 V

– +


4. Winding Roll w/ balanced charge

EROLL responds to the static charges on the outside surface of the unwinding roll. ESPAN is nearly zero!

– EROLL ≅ +10 KV/cm

ESPAN ≅ 0 KV/cm


+

Winding nip

Winding roll

+

+

–

+ +

+

+

+

+ +

– –

– – Incoming web with balanced charge

– +

+ Support

on outside surface


– –

+

+

–

VTOP ≅ +200 V


–

+


4. Unwinding Roll Charge Control

SBROLL dissipates static on the outside surface of the unwinding roll. SBSPAN dissipates static on the inside surface of the exiting web.

However, sparking may still occur at the unwinding nip!

Unwinding nip

Unwinding roll

+

+

– –

Exiting web is nearly

charge-free

EROLL ≅ 0 KV/cm

ESPAN ≅ –10 KV/cm


SBROLL

SBSPAN Support

on outside surface


VTOP ≅ 0 V

VBOTTON ≅ 0 V

–


4. Suppress Sparks

SBROLL dissipates static on the outside surface of the unwinding roll. The static curtain deposits + charges that suppress sparks.

SBSPAN is inactive.

EROLL ≅ 0 KV/cm

Static curtain or static brush

Unwinding roll

+

+

– –

Exiting web has balanced charge

–

ESPAN ≅ 0 KV/cm


SBROLL

SBSPAN

+ + + +

+

+ Support

on outside surface


–

+ –

VTOP ≅ +200 V


– –

+ – +


4. Suppress Sparks

SBROLL dissipates static on the outside surface of the unwinding roll. SBSPAN dissipates static on the inside surface of the exiting web.

The grounded lay-on roller suppresses sparking at the unwinding nip!

Unwinding roll + – –


charge-free

SBROLL SBSPAN

Grounded lay-on roller

Support on outside

surface


VTOP ≅ 0 V

VBOTTON ≅ 0 V

EROLL ≅ 0 KV/cm

ESPAN-1 ≅ -200 KV/cm

ESPAN-1 ≅ 0 KV/cm

–


5. Summary

1. Release liners / laminates are prone to charge separation at the unwinding nip.

2. Balanced charge causes high static on the winding roll.

3. Use two static bars to neutralize on both surfaces of webs exiting unwinding rolls.

4. Suppressing sparks with brushes / blankets form balanced charge.

5. Use a conductive or static dissipative lay-on roller to suppress nip sparks

Unwinding roll + – –


charge-free

SBROLL SBSPAN

Grounded lay-on roller

Support on outside

surface


VTOP ≅ 0 V

VBOTTON ≅ 0 V

EROLL ≅ 0 KV/cm

ESPAN-1 ≅ -200 KV/cm

ESPAN-1 ≅ 0 KV/cm

–


Questions?Kelly Robinson, PE, PhD, IEEE Fellow

Owner, Electrostatic AnswersTel: 585-425-8158

[email protected]

THANK-YOU!Comments?


Kelly Robinson, PE, PhDOwner, Electrostatic Answers, Rochester NY

• Accomplished Engineer: Institute of Electrical and Electronics Engineers (IEEE) FellowUS National Fire Protection Assoc. (NFPA) Static Electricity CommitteeElectrostatics Society of America (ESA) Distinguished Service Award Ph.D. in Electrical Engineering from Colorado State UniversityProfessional Engineer registered in New York.

• Business Owner: founded Electrostatic Answers, an engineering consulting company dedicated to eliminating injury and waste from static electricity.

• Inventor: 14 patents and 2 pending applications.

• Active Technical Writer & Speaker:Journal of Electrostatics (peer reviewed journal) Associate EditorPaper Film & Foil Converter Contributing Editor, writes

“Static Beat” a regular column on static controlConverting Quarterly, AIMCAL publication, contributes articles. AIMCAL John Matteucci Award

Speaker Introduction


Triboelectric Series

http://www.thebakken.org/electricity/science-of-static.html

Around 585 BC, Thales of Greece rubbed amber with a piece of fur. The amber could then pick up light objects like straw or feathers.

http://www.thebakken.org/electricity/science-of-static.html


Tribocharging

By Sei This vector image was created with Inkscape. - Own work, CC BY-SA 3.0,https://commons.wikimedia.org/w/index.php?curid=5505464

Chemical structure of poly dimthyl siloxane (PDMS),the repeat unit of silicone rubber


Tribocharging

Release liners and laminated web are prone to tribocharging because the inside surface of the incoming web touches

the outside surface of the winding roll.

Winding nip

Incoming web

Release liner on inside surface

Support on outside

surface

Winding roll

Support exposed

on outside surface


ElectricField

+ + + + + + ++ + + + + + + +

2TOP mCoulombsσ

2BOTTOM mCoulombsσ

Control Volume

SurfaceArea A

EFloor

qsdEε Enclosed

SurfaceCV

0 =⋅∫∫

( )AσσA Eε BottomTop0 +=

( ) Eεσσ 0BottomTop =+

( ) cmKVE

mμCσσ 22BottomTop

≈

+

Measure Static - Fieldmeter


3. Measure Static - Fieldmeter

Common industry

standard for acceptably low static:

KV/cm KV/in KV/10 cm

E < ±2 (KV/cm) = ± 5 (KV/in) = ± 20 KV/(10 cm)


Plastic or insulating paper sheet+ + + + + + + + + + +

How much chargeis on the surfaceof this sheet?

VSURFACE

non-contacting electrostaticvoltmeter probe

SURFACES VACσ

AQ

==

SURFACES Vdεσ

=

SURFACECVQ =

d

permittivity εmaterial property

Measure Static - Voltmeter


3. Measure Static - Voltmeter

Surface voltage are typically in the range ±200 V = ±0.2 KV.

V (Volts) Range: ± 3,000 V

Response time: 3 mS

V (Volts) Range: ± 3,000 V

Response time: 50 µS


– – – ––

+

+ + + +

A6

Machine frame

Web

Neutralsurface

Chargedsurface

– – – – –

Staticcharge

Electricfield

Staticdissipater

– ––

–+–

+++ +

Ions generated by static dissipater

A static dissipater is located to neutralize a charged web.

Static Dissipators


Neutralization is complete after the motion of the ions stops.

Machine frame

Web

Neutralsurface

Previously chargedsurface

Staticdissipater

– ––

–+–

+++ +

Ions generated by static dissipater

– –– – +–+ ++ +

Static Dissipators

Suppress Static Sparks when Unwinding 27/14A6

Machine frame

Web

Chargedsurface

Neutralsurface

– – – – –Static

charges

Static dissipater

– ––

–+–

+++ +

Ions generated by staticdissipater

– – – ––

+

+ + + +

Electricfield

A static dissipater is located to neutralize a charged web.

Static Dissipators


Neutralization is incomplete because the web is electrically insulating.

Machine frame

Web

Chargedsurface

Neutralsurface

– – – – –

Staticcharges

Staticdissipater

– ––

–+–

+++ +

Ions generated by staticdissipater

++ + + +

Electricfield

Static Dissipators

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