Slot Die Coating Principle and Application

Slot Die Coating Principle and Application Dr. Klaus Peter Crone, R&D 19.05.2016 2011 2016 COATEMA Coating Machinery GmbH www.coatema.de 1

contents Basics of slot die coating Homogeneous slot die coating Structured slot die coating Slot die mathematics Coatema Slot die types, concepts and innovations Scaling up Summary new technologies 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 2

Basics of slot die coating Why at all slot die? Key features : homogeneous layers (mostly thin) dosing system (premetering) touchfree (except in impregnation mode) closed system (no evaporation of solvents) full area non stop coating (meanwhile even stripe and start-stop coatings) The slot die is the only system, that combines all these features. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 4

Basics of slot die coating Range of coating parameters Printing Speed (m/min) 0.1 - >1000 Ink viscosity (mpa s) 1-40.000 Layer Thickness (µm) 0,05 - >1000 Coating accuracy (%) <1 (standard 2-5) Coating width (m) up to approx. 4 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 5

Basics of slot die coating How does it work : from reservoir Dosing pump Slot die Manifold (Distribution chamber) Meniscus Slot coated layer substrate Coating roller 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 6

Basics of slot die coating Slot Die examples 100 mm 11 o clock 300 mm 9 o clock 300 mm double sided 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 7

Basics of slot die coating standard design lips slot area manifold 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 8

Basics of slot die coating standard design The shim as spacer determines coating width and slot width shim coating width 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 9

Basics of slot die coating standard design with WC-lips Basic material: corrosion free hard steel Option: WC-lips for abrasive liquids 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 10

Basics of slot die coating Operating modes of a slot die Bead mode Slot die Manifold (Distribution chamber) Meniscus meniscus is formed between die lips and substrate adhesive stabilization of meniscus by die lips very low minimum flow rate possible range of rheological parameters limited for stability preferrably for low coating speed Coating roller stabilization of meniscus by adhesion to die lips 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 11

Basics of slot die coating Operating modes of a slot die Curtain mode Freely falling liquid curtain No adhesive stabilization of wetting line by die lips Curtain width shrinks while falling Minimum flow rate necessary for stable curtain Preferrable for high coating speed Slot die Manifold (Distribution chamber) Freely falling liquid curtain Coating roller Coating roller 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 12

Basics of slot die coating Operating modes of a slot die Curtain mode free falling curtain with edge holders 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 13

Basics of slot die coating Operating modes of a slot die Curtain mode A YouTube-video shows the curtain coating of wooden plates. Courtesy Italdecor srl 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 14

Basics of slot die coating Operating modes of a slot die Impregnation mode slot die acts as an impregnator with defined liquid release sucking strength of web must be smaller than release strength of the slot die slot die with high retention ability has to be used preferrably for low porosity nonwovens 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 15

Basics of slot die coating Operating modes of a slot die Impregnation mode A heated slot die impregnates a glass fiber textile in contact 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 16

Basics of slot die coating Pros and cons of slot die coating Advantages: - completely closed system - no change of solid concentration by evaporation - no hazardous vapors - premetering system coating thickness depends on width, speed and pump flow only V p = v B x - very low layer thicknesses <1µm possible by dilution Disadvantages: - relatively complex and sensitive - works only with adequate rheology - has to be treated with care (cleaning, no scratches) - expensive (depending on complexity) - inherent limited profile homogeneity (countermeasures see below) 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 17

Technologies Homogeneous coating with slot dies PET edge Coating edge 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 19

Homogeneous Coating Target of homogeneity The target in thickness profile depends on application. E.g. window foils: target is determined by sensitivity of human eye - standard optical density for window foils in dark state: D = 0.6 0.7 (absorption 75-80%) - in this range the human eye detects density variations of: ΔD = 0.01 0.003 (depending on the regularity of the variations) - density is proportional to layer thickness: I = I 0 10 -ax D = - log I/I 0 = ax ΔD / D = Δx / x target of layer homogeneity: 1.7 0.4 % 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 20

Homogeneous Coating Why should a slot die coat homogeneously? Δp 3 Δp 1 theoretical thickness profile Δp 2 Condition for good profile: Δp3 «Δp1 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 21

Homogeneous Coating Practical thickness profile measured thickness profile 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 22

Homogeneous Coating Principles to improve the coating profile large manifold, long slot area, highly parallel lips (standard) coat hanger design - profile is compensated by a tilted manifold - conical manifold cross section to keep flow speed constant (optional to prevent precipitation) - works perfect for adequate rheology only slot width adjustment - slot width is locally narrowed or widened to adjust the local flow resistence - slot width can be modified by microns only. So despite adjustability the die has nevertheless to be highly precise and a sufficient manifold volume is necessary. (the adjustment is a fine tuning only.) 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 23

Homogeneous Coating High precision coat hanger slot die manifold small to minimize dead volume (optional conical to prevent precipitation) tilted manifold to correct the pressure profile long slot area 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 24

Homogeneous Coating Slot die with slot width adjustment slot (shim edge) differential adjustment screws space for bending the die lip 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 25

Homogeneous Coating automatic slot width and gap width adjustment can be done pneumatically or motorized computerized adjustment of slot width or gap width Slot width: for uniformity Gap width: for very small coating windows 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 26

Homogeneous Coating Typical menisci for homogeneous coating meniscus on full width meniscus on reduced width (limited by shim) 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 27

Homogeneous Coating Typical coating profiles perfect thickness profile bowlike thickness profile 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 28

Structured coating Levels of complexity Web direction current status 1 full area, homogeneous requirements are met, thickness profile variation of 0.5 % 2 stripes downweb requirements are met, good edge definition 3 stripes crossweb (intermittent coating) requirements are partially met, edge definition of 0.5-1 mm depending on liquid requirements are not met, 4 abc arbitrary patterns concepts for realization exist, research project is going on 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 30

Structured coating Level 2: downweb stripes downweb stripes of different width are made by appropriate shims 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 31

Structured coating Level 2: downweb stripes, stripe widening manifold shim manifold slot area slot area 100µ typ. moving substrate or Problem: Stripe widening by capillary forces at the edges of the shim teeth. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 32

Structured coating Level 2: downweb stripes suppression of stripe widening by meniscus guide manifold shim meniscus guide + + = well defined stripes 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 33

Structured coating Level 2: downweb stripes practical shim and meniscus guide meniscus guide shim meniscus guide + shim 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 34

Structured coating Level 3: crossweb stripes (intermittent coating) Slot die Manifold (Distribution chamber) Meniscus Intermittent coating requires sudden start / stop of the fluid flow. Coating roller Different methods are available. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 35

Structured coating Level 3: intermittent coating techniques technique effectiveness 1 stop the pump very low: gives badly defined edges 2 reverse the pump (suck back) low: only slightly better than 1 3 reverse the pump (suck back) + lift the die 4 reverse the pump (suck back) + lift the die + suck or blow away the meniscus 5 die internal control mechanism (yet confidential) fair quite well: best achievable edge definition about 0.5 1 mm goal: 0.1 mm 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 36

Structured coating Level 3: intermittent coating Two different stripe patterns, one on top of the other Leading edge Battery paste Leading edge Silicone Trailing edge Silicone Trailing edge Battery paste 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 37

Structured coating Level 4: arbitrary patterns Pattern coating requires active control devices within the slot die to control the flow locally. Up to now there are no technical solutions available. Slot die Manifold (Distribution chamber) Meniscus But there is a unique concept to realize arbitrary patterns using an SMSD (scanning micro slot die) Research is going on! Coating roller 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 38

Technologies Slot die mathematics dv p /dt = B v x Δp = 12 η l V p D 3 B D = 3 12 η l V p Δp B v max = C(d) [ σ h / (d-h) + Δp d / (η b) ] h/(ηb) 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 40

Slot die mathematics ρ v da = 0 Continuity equation (conservation of mass) Any flow of liquids is described by a set of differential equations: To describe the meniscus flow of a slot die means, to solve these differential equations for given boundary conditions. Can be done by appropriate computer programs. v t + (v )v = {- p + η Δv + f } / ρ Navier-Stokes-equations (equations of motion for incompressible fluids, ρ=const), Δ = differential operators 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 41

Slot die mathematics Simulation of slot die flow Single layer, 120µm thick Single layer, 2cm width, 250µm gap YouTube Videos Flow Science Inc. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 42

Slot die mathematics Estimation of practical parameters: For practical applications, some important parameters can be estimated by analytical calculations. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 43

Slot die mathematics Calculation of coating thickness Shim thickness dv p /dt = B v x Distance to substrate Coating thickness wet Coating speed Coating width Flow rate of the pump Coating roller Contrary to a widespread misunderstanding the wet coating thickness does not depend on the shim thickness. Shim thickness and distance to substrate only help to stabilize the meniscus. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 44

Slot die mathematics Calculation of internal pressure Slot Die Mathematics: Manifold Pressure dependent on Shim Thickness and Viscosity 8000000 7000000 6000000 Δp = 12 η l V p D 3 B manifold pressure (Pa) 5000000 4000000 3000000 2000000 1000000 640 0 30 40 50 60 70 shim thickness (µ) 80 90 100 110 400 160 viscosity (mpas) 40 10 Vp = 22 ml/min B = 400 mm l = 28 mm 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 45

Slot die mathematics Calculation of shim thickness Slot Die Mathematics: Shim Thickness dependent on Viscosity and Volume Flow 600 D = 3 12 η l V p Δp B shim thickness (µ) 500 400 300 200 90 100 70 50 volume flow (ml/min) 0 30 10 40 160 viscosity (mpas) 640 2560 10 Δp = 22800 Pa B = 400 mm l = 28 mm 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 46

Slot die mathematics Calculation of shear force on meniscus slot width w coating width B y coating gap d lip width b Shear force F s coating thickness h x web speed v Force caused by shear: Shear force in general: This force pulls the meniscus to the right. F s = η A v / d A d v The shear takes place mainly over the thickness h: F s = η B b v / h 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 47

Slot die mathematics Calculation of surface tension force on meniscus y x slot width w coating gap d lip width b coating width B surface tension force F t coating thickness h web speed v Force caused by surface tension: This force pulls the meniscus to the left. Surface tension σ causes pressure p inside of a fluid sphere: In the meniscus the pressure is approximately: p = 2 σ / r p = σ / (d-h) The corresponding pressure force is: F t = p A = p B h = σ B h / (d-h) 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 48

Slot die mathematics Calculation of vacuum force on meniscus reduced pressure Δp slot width w coating width B vacuum force F v coating gap d lip width b coating thickness h y web speed v x Force caused by reduced pressure on the rear of the meniscus: This force pulls the meniscus to the left. F v = p A = Δp B d 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 49

Slot die mathematics Estimation of coating speed slot width w coating width B y x coating gap d lip width b F s = F v + F t coating thickness h web speed v Stability of the meniscus: The meniscus is stable as long as the right bound shear force is smaller than the sum of left bound forces. At maximum speed the forces are equal: F s = F v + F t v max = C [ σ h / (d-h) + Δp d / (η b) ] h/(ηb) C(d) = scaling factor 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 50

Slot die mathematics Comparison of theory and praxis 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 51

Types, concepts and innovations Modification of die lips optimal static wetting lines Standard die lips are only weekly pinpointing the static wetting lines static wetting line dynamic wetting line static wetting line Undercut lips are strongly pinpointing the static wetting lines (similar to comma bar) stabilization of wetting lines by undercut lips 23.10.2014 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 531

Types, concepts and innovations Alternative designs standard delta design for more uniform pathlengths (p 2 - p 1 ) << (p 1 - p 0 ) (p 2 - p 1 ) << (p 1 - p 0 ) p 2 p 1 p 2 p 2 p 1 p 2 p 0 p 0 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 54

Types, concepts and innovations Alternative designs coat hanger design for tiny manifolds (p 1 - p 2 ) + (p 2 - p 0 ) = (p 1 - p 0 ) double manifold for 2-fold uniformization p 1 p 2 p 2 p 2 p 1 p 2 p 0 p 0 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 55

Types, concepts and innovations Alternative designs randomized predistribution stackable version - Predistribution by obstacles in the manifold - Reduced flow resistance by low σ coating - Slot area remains uncoated or hard coated Low σ coating Uncoated or hard coated 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 56

Types, concepts and innovations Alternative designs Cross Flow Slot Die - no precipitation of solids in dispersions by strong current perpendicular to coating flow - the liquid has to be pumped at sufficient pressure level - pressure difference inlet outlet has to be small to fulfill pressure condition This system is no longer dosing but pressure controlled. Insofar one of the main advantages of slot dies is lost. I 2 p 2 p 1 ~ p 2 >> p 0 p 1 I 1 To achieve constant flow I out the average pressure (p 1 + p 2 )/2 has to be controlled as a function of the flow I out = I 1 -I 2 I out p 0 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 57

Types, concepts and innovations Alternative designs 3-slot-die Problem: poorly soluble solids may precipitate at static wetting lines causing particles and streaks Solution: 3-slot-dies coat thin layers of pure solvent on top and beneath the main layer. Precipitation is prevented. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 58

Types, concepts and innovations gap width adjustment Possible misalignments between slot die and roller ok ok ok 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 59

Types, concepts and innovations gap width adjustment 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 60

Types, concepts and innovations gap width adjustment computerized adjustment of gap width for very narrow coating windows 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 61

slot die coating Summary Slot dies are versatile, precise instruments for many applications. Nevertheless it is true, what a wise man said: Whenever a coating method is said to be working, don t believe it unless you saw it. Coating is complex. If anybody claims to understand every detail for sure he is not an expert!!! So if you don t trust the theory, book trials in our technical center. 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 63

THANK YOU COATEMA Coating Machinery GmbH Dr. Klaus Peter Crone Roseller Str. 4 D-41539 Dormagen 021 33 / 97 84 0 KCrone@coatema.de 19.05.2016 2016 COATEMA Coating Machinery GmbH www.coatema.de 64

19.05.2016 2014 COATEMA Coating Machinery GmbH www.coatema.de 65