DDT_WS1213_11_Funktionales Drucken_V2_S - IDD

Transcription

Digitale Drucktechnologie
11 Digitale Drucktechnologien
im Funktionalen Drucken
Bilder: University of Cambridge, imaging.org, Comsol, Kodak
Agenda
1. Introduction
 What is „Functional Printing“?
 Visual vs. Functional Printing
2. InkJet & Functional Printing



Printing Process – Process Steps of InkJet
Fluids & Properties
InkJet & Printed Electronics
1. Electrophotography & Functional Printing
2. Wrap up
Digitale Drucktechnologie | 11 Digitaldruck im Funktionalen Drucken | 2
Introduction
 Visual Printing
„Printing“ means the production of printed media, which are appraised or
consumed by human beings through their visual sense. Printed media are:
Books, journals, newspapers, posters, packaging.
from: Brockhaus Encyclopedia
 Printing as a production technique
The reproduction of patterns by means of transfer of matter (printing ink,
printing fluid) to the surface of targets by applying mechanical (printing form),
hydrodynamical (inkjet, coatings), or electromagnetic forces.
An IDD working hypothesis
Introduction – Visual Printing
A closer examination of an offset printed reproduction of Michelangelo‘s famous „Adam‘s
Creation“, Sistine chapel, Rome, reveals:
 Visual printing: Gray shades and colors are created from 4 colors (Cyan, Magenta, Yellow
and Black, CMYK) by ink dots of adequate screening, density and size, or by toner particles.
Bilder: Fineart China, IDD
Visual vs. Functional Printing
Visual printing
 Printing denotes the production of a product, which
a person appraises and uses visually.
 This are e.g. books, newspapers, magazines,
posters and packaging.
Visual printing products
Functional printing
 The printing processes are used additive for the
structuring of surfaces and for dosing of material.
 The results are not visually evaluated, but rather
have a measurable function.
 For example medical control strips, antenna,
conducting paths, RFID´s, OLED´s and solar cells.
Source: Brockhaus Enzyklopädie
Electroluminescence Panel
Bilder: IDD
Visual printing (gravure):
 Colored areas are composed of
isolated ink pixels
 Diameter ~ 100 µm, thickness ~ 1
µm
idd 2010
idd 2010
Functional printing:
 Printing of diluted solutions of
organic semiconductors, e.g. 1 %
P3HT in toluene
 OLED emitter layer on PET
 Homogeneity of layer thickness (30
+/- 5 nm)
 Smooth surfaces (nm range)
Bilder: IDD
Introduction – Tasks of a Printing Press
 Substrate transport
 Substrate deposition
 Metering of the printing fluid
 Repeated ink deposition processes
according to the number of
required layers
 Transfer of the printing fluid to the
substrate using
a specific printing technique
 Positioning of the printing ink
according to the desired
device layout
 Drying of solvent based inks and
removal of the solute
Comparison: Visual printing and printed electronics by flexography
Requirement
visual printing
printed electronics
functional material
pigment, dye
e.g. polymers, small molecules
resolution of structures
> 40 µm
0,5 … 5 … < 10 µm
thickness of layer
~ 1 µm
<100 – 300 nm
register between layers
± 5 µm
1 - 5 µm
dyn. viscosity
50 – 500 mPas
~ 1 mPas
homogeneous layer
not important
very important
formulation of liquid
optimized for price
influences morphology
adhesion of layers
one main problem
main problem
Agenda
1. Introduction



Fluids & Properties
2. Wrap up
InkJet Printing – Process Steps
1. Ink acquisition
 pump
 capillary force
2. Pre-dosing
 motion of the piezo
3. Dosing of the ink
 meniscus motion
4. Ink transfer to the substrate
5. Fluid dynamics on the substrate &
6. Solidification
Bild: NovaPackTech
Printing process – Pre-dosing
 The pre-dosing is feasible due to the pressure difference in the fluid chamber.
 The pressure difference is produced by:
 Motion of the piezo
 The piezo materials change shape or volume in the electric field and thus the
pressure waves are produced.
 By piezo, the imaging signals form and the pressure waves can be adjusted to
the fluid properties.
H. Kipphan, Handbook of Print Media, Springer, 2000
www.wikipedia.org: „Piezoelectricity “
Printing Process – Pre-dosing (Wave Forms)
 The imaging signal for the piezo is adjustable, so the pressure waves can be
controlled.
 The pressure waves and thus the imaging signal in the fluid channel affect:
 The maximum possible firing frequency
 The repeatability of droplet formation
 The possibility of long printing run
H Y Gan; J. Micromech. Microeng. 19 (2009) 055010
Printing process – Pre‐dosing (Wave Forms)
Start (or Standby)
 The voltage decreases to zero so the
piezo goes back to a relaxed position.
 In this phase the fluid is pulled into
the chamber through the inlet.
Phase 1
 The negative section draws fluid into
the pumping chamber.
DMP2831 User Manual
Printing process – Pre‐dosing (Wave Forms)
Phase 2
 The steepness of the slope provides
the energy for the initial ejection.
 It is followed by a hold period.
Phase 3
 The dampening segment prevents
the printed head from sucking air
back in.
 This section brings the PZT back to a
position “zero”.
 Adjustment is needed for different
materials.
Printing Process – Pre-dosing (Pulse Width)
Study by Leu and Lin
 Optimal droplet ejection for a
trapeze-like signal form was studied
 The optimal pulse width is found to
be:
t dwell 
L
c
 The rise time trise of the pulse affects
the velocity of the jetted drop.
L – fluid channel length
c – sound velocity in fluid
T. Leu, J Lin; Materials Science Forum Vol. 594 (2008), 155-162
Printing Process - Dosing
The dosing process of the fluid depends on:
Without satellite droplets
 The nozzle geometry:
 drop velocity and mass
 Fluid properties and channel geometry
 drop velocity
 formation of the satellite droplets
With satellite droplets
(viscosity decrease)
 Pre-dosing and thus on the wave propagation
on the nozzle:
 formation of the satellite droplets
Bild:H. Dong; Rev. Sci. Instrum. 77, 085101, 2006
Printing Process – Dosing (Models)
Model by Taylor
 The ligament is assumed to be infinitely long and stationary, with no
internal velocity distribution. The velocity v of the droplet is then given
1
by:
  2

v  2

D


Model by Keller
 The basis of the Keller model for shortening is a conical ligament, where
D′ = 2bx.
 The shortening speed is given by:
1
3
 8 

v(t )  
5

bt


and thus varies with time.
σ – surface tension
ρ – density of fluid
t – time
v – droplet velocity
D – surface area
b – shortening factor
S. D. Hoath, G. D. Martin; NIP25 and Digital Fabrication 2009
Model by Hoath and Martin
 The basis of the model for shortening is a truncated conical ligament with initial
length L.
 The total mass is M and there is an initial axial velocity profile due to ligament
extension between the break-off position and the drop.
 If the mass acceleration of the drop tail m allows, the velocity of the jetted drop
is given as a function of:
dv
 f (vT , p, L, D, t )
dt
with 𝜈𝑇 the droplet velocity given by Taylor model.
L – filament length
t – time
m – filament mass
vT – Taylor-velocity
ρ – density of fluid
D – surface area
M – total droplet mass
v – droplet velocity
p – shortening factor
S. D. Hoath, G. D. Martin; NIP25 and Digital Fabrication 2009
Study by Xu and Basaran
 The fluid inflow in the nozzle can be described as:
Q 
We
2
sin t
with a initial velocity of the formed drop given by:
v  1  R 2  We sin t
 The maximal droplet volume is than given by:
VMAX  
We

We – Weber number
Ω – firing frequency
t – time
ρ – Fluid density
μ – fluid viscosity
Q. Xu, O. A. Basaran; PHYSICS OF FLUIDS 19, 102111 2007
Printing Process – Ink Transfer
 The velocity of the drop is non-linear, so three
parameters are important:
 Acceleration
 Medium resistance
 Terminal velocity
FACCELERATI ON
 Medium resistance refers to forces that oppose
the relative motion of an object through a
medium
 An object is moving at its terminal velocity if
its speed is constant due to the restraining
force exerted by the medium through which it
is moving
FRESISTANCE
E. R. Lee; Microdrop generation; CRC Press; 2003
Printing Process – Ink Transfer (Acceleration)
 The acceleration depends on
 gravity force
 the acceleration of drop due to the
motion of the piezo
 And thus the acceleration force is:
Satellite drop with higher acceleration
FACCELERATI ON  Fg  Fa  m( g  a)
Satellite droplet
 The initial acceleration a of drop and of its
satellite drop can be different
Satellite drop with lower acceleration
 The gravity force leads to the further
difference in the acceleration because of
difference in the mass
g – gravitational acceleration
a – initial acceleration due to the piezo motion
Bild:H. Dong; Rev. Sci. Instrum. 77, 085101, 2006
Printing Process – Ink Transfer (Medium Resistance)
 Depending on Reynolds Number, the fluid
flow is turbulent or laminar
 By laminar flow the Stokes Law dominates
drag: the origin of this force is the
resistance of a medium to change in its
shape
FACCELERATI ON
FStokes  6rv
 By turbulent flow the dynamic pressure
dominates drag: the origin of this force is
the energy needed to accelerate the
molecules of the media with object moving
through it
FDrag 
1
 Cd A v 2
2
 For the Reynolds Number less than 1, the
laminar flow dominates
ρ – air density
η – viscosity of air
ν – droplet velocity
FRESISTANCE
Cd – drag coefficient
A – frontal area
r – droplet radius
 The atmosphere is not a perfect continuum,
so the resistance of the medium is less than
predicted by Stokes Law
 Cunningham’s correction factor is used to
account for non-continuum effects when
calculating the drag on small particles:
2 
 A1  A2 e
CC  1 
d 
 A3d

FACCELERATI ON




 And so the resistance force:
FRESISTANCE 
FStokes
CC
 The Cunningham’s correction factor becomes
significant when particles become smaller
than 15 µm
FRESISTANCE
λ – mean free path
d – droplet diameter
An – experimentally determined coefficients, For air: A1=1,257; A2=0,4; A3=0,55
www.wikipedia.org: „Cunningham correction factor “
Drops can be deformed from perfect spheres due aerodynamic forces or electric
fields.
 The correction factor for low Reynolds Number for non-spherical drops is given
by:
1 2d
C NS   S
3 3d n
Real
S1 = S2
 And so the resistance force of medium:
FRESISTANCE 
FStokesC NS
CC
Spherical
dn
ds
 This factor is negligible for drops below 100 µm in
diameter.
dn – diameter of a circle with the same projected frontal area in the direction of motion
ds – diameter of a sphere with a surface area equal to that of the deformed drop
The further correction is an upward acting force exerted by a medium, that
opposes an object's weight: Buoyancy Correction
 The Buoyancy correction is given by:
4
CB   r 3 g 
3
FACCELERATI ON
 And so the resistance force:
FRESISTANCE 
FStokesC NS
 CB
CC
 This effect is negligible for air because air has approximately
1/1000 density of fluid
FRESISTANCE
ρ – air density
r – droplet radius
www.wikipedia.org: „Apparent weight “
 As a fluid drop falls through the air, the fluid in the drop can circulate internally.
 This reduces the surface resistance to air flow.
 Since the viscosity of fluids is much higher than the viscosity of air this
correction is generally on the order of 0,5 % or less.
Y. ABE; Ann. N.Y. Acad. Sci. 1077: 49–62 (2006)
Printing Process – Ink Transfer (Terminal Velocity)
 The terminal velocity is reached, if the acceleration
force is equal to resistance force of the medium:
FACCELERATION  FRESISTANCE
 And so by:
FStokesC NS
 CB  m( g  a)
CC
a – initial acceleration due to the piezo motion
www.rechtsaudit.com
Printing Process – Fluid Dynamics
 The result of a drop impact phase can be:
 Bouncing
 Splashing
 Spreading
 The impact of the drop by spreading can be divided into two steps:
 Initial phase: contact line is formed
 Impact phase: a thin film is formed
Bouncing
Splashing
Spreading
M. Rein; Fluid Dynamics Research 12 (1993) 61 93
 At lower impact velocities the process of spreading
occurs
Spreading
 When the kinetic energy of the drop is extremely
small, the process of spreading is dominated by
intermolecular forces
 If the drop strikes the surface with a finite velocity,
spreading is greatly influenced by the kinetic
energy of the drop
 At higher impact velocities the jetting motion leads to
a disintegration of the fluid and splashing occurs. The
critical velocity is:
 d
vcritical 
a
d – droplet diameter
Splashing
a – acceleration of the droplet
ρ – density of the fluid
D. B. van Dam, C. Le Clerc; Phys. Fluids, 16, 9, 2004
 At the initial phase the shock wave with velocity cS is significant for forming the
contact line
 In the ideal case, the first contact between the base of the
drop and the wall is point like and a contact zone of radius
re then develops
 The contact edge velocity ve depends on the impact velocity
vi, and the angle θ:
ve 
vi
tan 
Initial phase and contact line propagation
 Inside the drop the shock propagates with a velocity cs that is of the same order
of magnitude as the sound speed
 As long as the impact velocity vi is greater than cs sinθ the shock remains
attached to the contact edge and the fluid ahead is not yet disturbed by the
impact
v 
 When the contact angle becomes larger than the critical angle  C  sin 1  i 
 cs 
the shock separates from the contact edge and moves up the undisturbed
surface of the drop
Not disturbed fluid ahead
With shock waves disturbed fluid ahead
 Before a droplet impacts the surface, a pressure wave have to put the air below
the droplet
 If the pressure wave velocity is lower than contact edge velocity ue and the
contact is not point like, an air bubble can be included into the droplet
3
 The air bubble volume is than given by:
Vb – bubble volume
vi – initial velocity of the drop
ρair – density of the air
4   
Vb ~   air 
9  vi   air
ηair – kinematic viscosity of the air
ρ – density of the fluid
 For the low surface energy the droplet impact onto a solid substrate can be
divided into two steps:
 The radius of the droplet–substrate interface expands
 The fluid comes to rest
Contact with substrate
Expantion of drop radius
Fluid oscillation
Drop at rest
Soft Matter, 2008, 4, 703–713
 First, the fluid expands very quickly and reaches a
maximum radius
 The kinetic and surface energy of the drop are
dissipated by viscous processes in the thin sheet of
fluid, and are transformed to additional surface
energy:
EK  EP  ES  EK'  EP'  ES'  ED'
 The spread factor fMAX is the radius of the maximal
spread fluid scaled with the initial drop radius and
can be calculated from energy balance equation:
1
2
For large Re: f MAX
 13 WE  4 1  cos  
Ek – kinetic energy
Ep – potencial energy
Es – surface energy
ED – dissipation energy
RE – Reynolds number
WE – Weber number
Θ – contact angle
M. Rein; Fluid Dynamics Research 12 (1993) 61 93; www.fhnw.ch
Printing Process – Solidification
 The drying phenomena described here are:
 Coffee stain effect: edge effects
 Periodic bulging: non-uniform film formation
 Fast evaporation: non-uniform film formation
Coffee stain effect
Periodic bulging
Fast evaporation
S. K. Cho; J. MICROELECTROMECH. SYS., VOL. 12, NO. 1, 2003
H. Hu, R. G. Larson; J. Phys. Chem. B, Vol. 110, No. 14, 2006 7091
Coffee stain effect: Drift of material in a thin liquid film of a solvent/solute
system (or mixture) towards the edges of the liquid film, and the deposition of
material at the edges forming a rim.
Pre-condition for coffee stain effect:
Pinning of the contact line.
Picture: IDD
Driving forces for the coffee stain effect:
1. Evaporation rate gradients induce a fluid flow to the edge.
2. Marangoni effect. Gradients in surface tension result in a fluid flow to the
edge.
Coffee stain
Colloid microspere
Salt deposit
Droplets deposited by
inkjet and gravure printing:
material accumulation at
the border lines.
E. Tekin, P. J. Smith; Soft Matter, 2008, 4, 703–713
www.wikipedia.org: „Stain “
Theory by Deegan
 The capillary flow is induced by the
differential evaporation rates (J)
across the drop: fluid evaporating
from the edge is replenished by fluid
from the interior.
 If the contact line is pinned material
at the edge accumulates forming the
characteristic rim.
bare substrate
surface
Printed layer (dried)
Wall-shaped rim
Interferometric height profile of a
printed OLED polymer layer (av.
thickness 30 nm) is bounded by a
„rim“ of deposited polymer (width
30 µm, height 100 nm).
www.wikipedia.org: „Stain“
R. D. Deegan; PHYSICAL REVIEW E VOLUME 62, NUMBER 1
Marangoni effect: Gradients in surface tension
induce a flow from regions of smaller surface
tension to regions of larger surface tension.
Surface tension gradients have their origin in
1. Temperature gradients. Usually linear
dependence:   0  αT. Enhanced
evaporation rate at the border induces larger
cooling at the edge.
2. Concentration gradients, usually higher
concentration -> higher surface tension, see
fig. (for surfactants it is the opposite).
Enhanced evaporation rate at the border
induces accumulation of solute at the edge
-> higher concentration (C).
 Fluid flow to the edge results in accumulation
of material and forming of the characteristic
rim.
P3HT in toluene
Evaporation
 large
2-component fluid
substrate
 small
Fluid drag
Printed lines with high contact angle or low
surface energy substrates frequently exhibit
periodic bulging.
Theory by Cho and Moon
 It is well understood how a long fluid column
breaks into droplets in air due to minimal
surface energy.
 Analogically, the fluid drops on the substrate
can build a periodic structure due to
hydrodynamic instabilities.
Fluorescent
micrograph
of
bulging
fingers evolving from the coffee-ring of a
drying droplet of an OLED light emitter
material dissolved in toluene
pcap small
pcap large
PEDOT:PSS printed on a polymer foil
S. K. Cho; J. MICROELECTROMECHANICAL SYSTEMS, VOL. 12, NO. 1, 2003
 The instability can be determined by considering the pressure variations in the
fluid column when it is perturbed by a small periodic disturbance of wavelength
λ
 The pressure difference between the regions A and B is given by:
PA  PB 
2  LG
b02
 2 b0 

  1  cos  

  

for a contact angle θ and surface tension of gas-liquid phase  LG
 A stable film is formed for PA > PB
S. K. Cho; J. MICROELECTROMECHANICAL SYSTEMS, VOL. 12, NO. 1, 2003
 The fast evaporation can disturb the uniformity of the film formation:
 The periodic bulging can be supported due the hydrodynamic instabilities
can not be compensate
 The mixing between dried and liquid fluid drops is broken
 All this effects lead to a non-uniform film formation
Print direction
Picture left: www.wikipedia.org
Agenda
1. Introduction



Fluids & Properties
2. Wrap up
Fluids – Properties
Fluids for inkjet printing:
 Solid content:
 Density:
1-50 mPas
40-80 mN/m
0,2-1 µm
depends on the viscosity and dissolved mass
fraction
0,5-20% (50%)
about 1000 kg/m3
 Solvent:
 Flash point:
 Volatility:
 Evaporation rate:
high
low
low




Viscosity:
Surface tension:
Particle size:
Polymer mass:
Common solutions
Polymer solutions
Colloidal dispersions
Curable/cross-linkable inks
Fluids – Shear ratio estimation
Max. estimated, typical shear ratio in each process step
1. Ink acquisition
15  1/s
4. Ink transfer
-
2. Pre-dosing
90  1/s
5. Dynamics on the
substrate
800,000  1/s
100,000  1/s
6. Solidification
-
1
2
3
Possible to measure
5
Not possible to measure
Fluids – Shear Ratio Estimation
 Shear ratio in a channel:

vMAX
rCHANNEL
vMAX
2rCHANNEL
 Shear ratio on the substrate:
z with t the time between
vMAX 
impact of the drop and
2t
maximal weight z reached
2rDROP
Volume A
is a height of a rectangle
with the same volume as
the drop and weight z
 Shear ratio:
maximal drop weight z
2rDROP

vMAX
rDROP
Volume A
maximal drop weight z
Fluids - Viscosity
Fluids for inkjet:
 Viscosity in the range of 1-50 mPas
Viscosity defines:
 Form of the droplet
 Volume of the droplet
Possible problems:
 Low viscosity in range of 2-4 mPas: satellite
droplets can be formed
 Viscosity higher than 30 mPas: the filament of
the droplet can not be broken
Low viscosity
Middle viscosity
High viscosity
Umur Caglar: Studies of inkjet-printing; Tempere 2009
H. Dong; Rev. Sci. Instrum. 77, 085101, 2006
Fluids – Surface Tension
Fluids for Inkjet:
 Surface tension in range of 40-80 mN/m
Surface tension affects:
 Velocity of the droplet tails
 Breaking of the droplet
 Formation of the satellite droplet
Possible problems:
 High surface tension requires the strong pressure pulse
 Too low or too high surface tension can lead to:
 Wetting of the nozzle plate
 Clogging the nozzle because of entrained air bubbles
Fluids – Possible Problems with Surface Tension
Wetting of the nozzle plate: Study by Beulen and Jong
 The wetting characteristics of the ink on the nozzle
plate surface are functions of surface energies of:
 the nozzle plate–air interface,
 the ink–air interface and
 the nozzle plate–ink interface
 The contact angle less than 20° indicates that thin
ink layers can be formed
 For the low Reynolds number the flow is viscosity
dominated:
Fgravity  gRH 2  O(109 ) N
Fcapillary  2 sin  2RH  O(107 ) N
ρ – fluid density
σ – surface tension of fluid
de Jong; J. Acoust. Soc. Am., 120, No. 3, 2006
Fluids – Possible Problems with Surface Tension
Entrained air bubbles: Study by de Jong, Briun and
Jeurissen
 An ink layer on the nozzle plate can also induce air entrapment
 After an air bubble is entrapped, the oscillations leads to growth
of the bubble
 If a resonance volume of the air bubble given by:

3A P
R0res  
2
2 2
 4ln  A  64 

3
n 0
2
n




1
3
is reached, the jetting is stopped
ρ – fluid density
γ – is a factor of 5/7
ω – jetting frequence
ν – surface tension of fluid
An – cross section of the nozzle
ln – nozzle lenght
Po – ambient pressure
de Jong; J. Acoust. Soc. Am., 120, No. 3, 2006
R. Jeurissen; BUBBLES IN INKJET PRINTHEADS
Fluids – Particle Size
Fluids for inkjet:
 Particle size: 0,2-1 µm
Particle size affects:
 The repeatability of the droplet formation
 Quality of the printed layer
 Electrical properties of the printed layer
Possible problems:
 Clogging the nozzle by sedimentation
 Experimental studies shows, that the particle has to be 50-100 times less
than nozzle size to suspend the clogging
Fluids – Possible Problems with Particle Size
 The sedimentation of the dispersed particles is
proportional to the acceleration of the jetted fluid
 So the sedimentation velocity of the dispersed
particles is given by:
2
vPartikel

4 P   f a  d
3
f
cw
 For the high shear ratios in the inkjet nozzle the
particle size is critical
ρp – particle density
ρf – fluid density
a – acceleration of the fluid
d – particle diameter
sw – Drag coefficient
Siver particles in water
Magdassi; Chem. Mater., Vol. 15, No. 11, 2003
www.wikipedia.org: „Sedimentation“
Fluids – Polymer Mass
Fluids for inkjet:
 Depend on the reached viscosity and dissolved mass fraction
Polymer mass affects:
 The filament building and droplet break up
Possible problems:
 The droplet can not be formed
 The fluid flows out of the nozzle
E. Tekin; Soft Matter, 2008, 4, 703–713
B.J. de Gans; Adv. Mater., 2004, 16, No.3
Fluids – Possible Problems with Polymer Mass
Filament building: Experiments by Schubert
 For this study the polystyrene in acetophenone was
used
 The maximum printable polymer mass fraction by
the same viscosity is given by:

MAX
m
~M
2,14
W
 Above a certain concentration, the capillary force is
not able to break the filament and the ejected
droplet retracts back into the nozzle.
 Experiments with dilute solutions of linear and 6-arm
star PMMAs with the same molecular weight and
concentration confirm this study
PEO is solved in water/glycerol;
shear viscosity is constant,
surface tension is constant;
polymer mass grows
Pure glycerol and water
0.3 wt% poly(ethylen oxide), Mw=100.000
0.1 wt% poly(ethylen oxide), Mw=300.000
0.05 wt% poly(ethylen oxide), Mw=1.000.000
0.043 wt% poly(ethylen oxide), Mw=5.000.000
E. Tekin; Soft Matter, 2008, 4, 703–713
B.J. de Gans; Adv. Mater., 2004, 16, No.3
Fluids – Solid Content and Density
Fluids for inkjet:
 Solid content:
 Density:
0,5-20% (50%)
about 1000 kg/m3
They affect:
 The density of the fluid affects the duration of the jetting pulse: the high
density requires a long pulse
 The solid content can increase the risk of:
 Particle agglomeration
 Clogging the nozzle
Possible problems:
 Particle agglomeration
 Clogging the nozzle
The high solid content is desired because of the layer thickness and better
dielectric properties
Fluids – Solvents
Fluids for inkjet:
 Low volatility
 Low evaporation rate
 High flash point
Solvent properties affect:
 Repeatability of the long runs
 Spreading of the fluid on the substrate
Possible problems:
 Agglomeration risk and clogging of the nozzles
 Low repeatability by long runs
 Flash point defines the nozzle temperature settings to prevent deflagration of
the solvent
 The low volatility of the solvent can compensate the risk of clogging
Agenda
1. Introduction



Fluids & Properties
2. Wrap up
Flashback – Visual vs. Functional Printing
Visual Printing
 Gray shades and colors commonly
based on CMYK
 Aim: depicting information
Functional Printing
 Solid areas and small structures
 Aim: homogeous layers with certain
function (chemical sensitivity, semiconducting, etc.)
Flashback – Process Steps of InkJet Printing
1. Ink acquisition
 pump
 capillary force
2. Pre-dosing
 motion of the piezo
 meniscus motion
4. Ink transfer to the substrate
5. Fluid dynamics on the substrate &
6. Solidification
Bild: NovaPackTech
InkJet and Printed Electronics – Suitability
Layer thickness by inkjet:
 0,05 – 1 µm (depends on solid content)
Drop volume:
 1-30 pl
Resolution:
 300 – 1200 dpi or more
Minimal line weight:
 50 – 100 µm (depend on drop-surface interactions)
Layer thickness
Resolution
Printing time
Print speed:
 Maximal 1,75 m/s (depend on the resolution)
Printing accuracy:
 1-100 µm
Large areas
Small structures
Thin films
Suitability – Large Areas
Line Arrays
Angle Arrays
 This systems are fixed and printing
width is the width of the line array
 The nozzle row has an angle to
printing direction
 The arrays consist of multiple print
heads to increase the resolution of
the array relative to the individual
printheads
 The resolution grows geometrically
with rotation angle
 The line array is fixed and so the
high printing accuracy can be
reached
 Large printing width can be reached
 Very high resolutions can be
reached
 The printing width is reduced
 For large printing width the print
head have to be moved and so the
printing accuracy is reduced
Line array: XAAR 1001 print heads
www.go-intercon.com
H. Kipphan, Handbook of Print Media, Springer, 2000
Suitability – Large Areas
For large areas:




High printing resolution is favorable
Good spreading is favorable
Low evaporation rate is better for film building
Layer thickness depends on the resolution
Dewetting
Dewetting; coffee stain
Polymer insulator on metal sheet
Line dewetting; edge effects
PEDOT:PSS on foil
Images: IDD
Suitability – Small Structures
For small structures:
low accuracy; fast evaporation





Low printing resolution and thus less fluid is favorable
Good spreading leads to wider line
Low evaporation rate is better for line building
Good printing accuracy is needed for good line formation
Small droplets are favorable
Print ditection
resolution too low; coffee stain
resolution too high; coffee stain
sattelites; edge effects
Here: gold nano-particel dispertion on foil
Images: IDD
InkJet as a Laboratory Printing Technique
for Printed Electronics
 Small amounts of fluid needed to print layer to be
examined
 Small free surface area during printing
-> low amount of evaporated solvent
-> more hazardous solvents can be used
 Relatively small time
frame needed to
produce devices for
proof-of-concept or
measurements
Images: Dimatix, UC Berkeley
Examples of IJ-Systems in Printed Electronics – Dimatix
Dimatix DMP2831
 Printheads:
 DMC-11601 – 1pl drops
 DMC-11610 – 10pl drops
 16 nozzles are arranged in 1 row
 Frequency: 1 kHz - 20 kHz
 Wave form control
 Drop formation control
 Drop volume control
Images: Dimatix
Examples of IJ-Systems in Printed Electronics – PixDro
PixDro LP50
 Druckköpfe:
 S-Class
 Spectra SE3, SX3
 Xaar 1001
 Frequency: 1 Hz - 20 kHz in 1 Hz steps
 Wave form control
 Drop formation control
 Drop volume control
S-class
Spectra SE, Spectra SX3
Images: PixDro
Examples of Printed Devices – Proximity Sensor
Fabrication:




Cleaning of flexible aluminum sheet
Pre-treatment of aluminum sheet (atmospheric plasma for more hydrophilicy)
InkJet printing and annealing of ZnO dispersion
InkJet printing of conductive nano-silver layer
The senor structures
Finished sensor
Chin-Tsan Wang; Sensors 2010, 10, 5054-5062
Examples of Printed Devices – Polymer Microsieves
Fabrication:
 Pre-treatment of Al-foil with hydrophobic silane
 InkJet printing of deionized water and ethylene
gylcole
 Dispensing of PMMA in chloroform
 Etching / peeling of the PMMA layer
Equipment used:
 Dimatix DMP 2831
 10 pL printheads
(DMC-11610)
S. Jahn et al., Langmuir, Vol. 25, Nr. 1, S. 606–610, Jan. 2009.
Examples of Printed Devices – oFET
Fabrication:
 Pre-patterned PI-Substrate
 InkJet printing of PEDOT:PSS (source and drain)
 Spin-coating of F8T2 from xylene solution to produce a continuous film
(semiconductor)
 Spin-coating of PVP from isopropanol solution (isolation)
 InkJet printing of PEDOT:PSS (gate)
H Sirringhaus; Science 2000; 290:2123-2126
Examples of Printed Devices – Glucose Biosensor
Fabrication:




Pre-treatment of ITO coated glass
InkJet printing of PEDOT:PSS
InkJet printing of glucose oxidase (GOD)
Dip-coating of cellulose acetate membrane
Equipment used:
 Protoype of thermal inkjet
(Setti et al., Anal. Lett. 37 (8), 1559-1570)
Setti et al., Biosensors and Bioelectronics 20 (2005) 2019–2026
Electrophotography – Flashback
Korona
(Laser)
Electrophotography and Printed Electronics
Fabrication:
 Electrophotographic printing of silver toner on
ceramic substrate (aluminum oxide)
 Firing of printed layer (650 °C, 1 h)
Equipment used:
 Protoype of electrophotographic printer
(WO 2008/128648 A1)
Buettner et al., IMAPS/ACerS, 7th CICMT int. Conf. & Exh.
Impressum
Digitale Drucktechnologie
Vorlesung im Wintersemester 2012/13
Betreuung: Dipl.-Ing. Constanze Ranfeld
Prof. Dr.-Ing. E. Dörsam
Technische Universität Darmstadt
Fachgebiet Druckmaschinen und Druckverfahren
Magdalenenstraße 2
64289 Darmstadt
http://www.idd.tu-darmstadt.de

DDT_WS1213_11_Funktionales Drucken_V2_S - IDD

Transcription

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