Slot Die Coating Principle and Application

Transcription

1 Slot Die Coating Principle and Application Dr. Klaus Peter Crone, R&D COATEMA Coating Machinery GmbH 1

2 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 COATEMA Coating Machinery GmbH 2

3 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 COATEMA Coating Machinery GmbH 3

4 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 COATEMA Coating Machinery GmbH 4

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

6 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 COATEMA Coating Machinery GmbH 6

7 Basics of slot die coating Slot Die examples 100 mm 11 o clock 300 mm 9 o clock 300 mm double sided COATEMA Coating Machinery GmbH 7

8 Basics of slot die coating standard design lips slot area manifold COATEMA Coating Machinery GmbH 8

9 Basics of slot die coating standard design The shim as spacer determines coating width and slot width shim coating width COATEMA Coating Machinery GmbH 9

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

11 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 COATEMA Coating Machinery GmbH 11

12 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 COATEMA Coating Machinery GmbH 12

13 Basics of slot die coating Operating modes of a slot die Curtain mode free falling curtain with edge holders COATEMA Coating Machinery GmbH 13

14 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 COATEMA Coating Machinery GmbH 14

15 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 COATEMA Coating Machinery GmbH 15

16 Basics of slot die coating Operating modes of a slot die Impregnation mode A heated slot die impregnates a glass fiber textile in contact COATEMA Coating Machinery GmbH 16

17 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) COATEMA Coating Machinery GmbH 17

18 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 COATEMA Coating Machinery GmbH 18

19 Technologies Homogeneous coating with slot dies PET edge Coating edge COATEMA Coating Machinery GmbH 19

20 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 = (absorption 75-80%) - in this range the human eye detects density variations of: ΔD = (depending on the regularity of the variations) - density is proportional to layer thickness: I = I ax D = - log I/I 0 = ax ΔD / D = Δx / x target of layer homogeneity: % COATEMA Coating Machinery GmbH 20

21 Homogeneous Coating Why should a slot die coat homogeneously? Δp 3 Δp 1 theoretical thickness profile Δp 2 Condition for good profile: Δp3 «Δp COATEMA Coating Machinery GmbH 21

22 Homogeneous Coating Practical thickness profile measured thickness profile COATEMA Coating Machinery GmbH 22

23 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.) COATEMA Coating Machinery GmbH 23

24 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 COATEMA Coating Machinery GmbH 24

25 Homogeneous Coating Slot die with slot width adjustment slot (shim edge) differential adjustment screws space for bending the die lip COATEMA Coating Machinery GmbH 25

26 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 COATEMA Coating Machinery GmbH 26

27 Homogeneous Coating Typical menisci for homogeneous coating meniscus on full width meniscus on reduced width (limited by shim) COATEMA Coating Machinery GmbH 27

28 Homogeneous Coating Typical coating profiles perfect thickness profile bowlike thickness profile COATEMA Coating Machinery GmbH 28

29 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 COATEMA Coating Machinery GmbH 29

30 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 mm depending on liquid requirements are not met, 4 abc arbitrary patterns concepts for realization exist, research project is going on COATEMA Coating Machinery GmbH 30

31 Structured coating Level 2: downweb stripes downweb stripes of different width are made by appropriate shims COATEMA Coating Machinery GmbH 31

32 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 COATEMA Coating Machinery GmbH 32

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

34 Structured coating Level 2: downweb stripes practical shim and meniscus guide meniscus guide shim meniscus guide + shim COATEMA Coating Machinery GmbH 34

35 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 COATEMA Coating Machinery GmbH 35

36 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 mm goal: 0.1 mm COATEMA Coating Machinery GmbH 36

37 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 COATEMA Coating Machinery GmbH 37

38 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 COATEMA Coating Machinery GmbH 38

39 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 COATEMA Coating Machinery GmbH 39

40 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) COATEMA Coating Machinery GmbH 40

41 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 COATEMA Coating Machinery GmbH 41

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

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

44 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 COATEMA Coating Machinery GmbH 44

45 Slot die mathematics Calculation of internal pressure Slot Die Mathematics: Manifold Pressure dependent on Shim Thickness and Viscosity Δp = 12 η l V p D 3 B manifold pressure (Pa) shim thickness (µ) viscosity (mpas) Vp = 22 ml/min B = 400 mm l = 28 mm COATEMA Coating Machinery GmbH 45

46 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) volume flow (ml/min) viscosity (mpas) Δp = Pa B = 400 mm l = 28 mm COATEMA Coating Machinery GmbH 46

47 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 COATEMA Coating Machinery GmbH 47

48 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) COATEMA Coating Machinery GmbH 48

49 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 COATEMA Coating Machinery GmbH 49

50 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 COATEMA Coating Machinery GmbH 50

51 Slot die mathematics Comparison of theory and praxis COATEMA Coating Machinery GmbH 51

52 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 COATEMA Coating Machinery GmbH 52

53 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 COATEMA Coating Machinery GmbH 531

54 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 COATEMA Coating Machinery GmbH 54

55 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 COATEMA Coating Machinery GmbH 55

56 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 COATEMA Coating Machinery GmbH 56

57 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 COATEMA Coating Machinery GmbH 57

58 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 COATEMA Coating Machinery GmbH 58

59 Types, concepts and innovations gap width adjustment Possible misalignments between slot die and roller ok ok ok COATEMA Coating Machinery GmbH 59

60 Types, concepts and innovations gap width adjustment COATEMA Coating Machinery GmbH 60

61 Types, concepts and innovations gap width adjustment computerized adjustment of gap width for very narrow coating windows COATEMA Coating Machinery GmbH 61

62 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 COATEMA Coating Machinery GmbH 62

63 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 COATEMA Coating Machinery GmbH 63

64 THANK YOU COATEMA Coating Machinery GmbH Dr. Klaus Peter Crone Roseller Str. 4 D Dormagen / KCrone@coatema.de COATEMA Coating Machinery GmbH 64

65 COATEMA Coating Machinery GmbH 65