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Application of NFC by foam coating technique
Karita Kinnunen, Tuomo Hjelt, Eija Kenttä
VTT Technical Research Centre of Finland
Foam
Outline
Benefits of foam coating
Foam coating principles
Role of foam, foam formation, foam killing
Requirements of the foam for foam coating
Foam coating facilities
Results
Conclusions
Foam coating in paper industry
A well-known technique in the textile, non-woven industry and in plastic film production
In paper applications the first patents of the technology date back to the beginning of the 20th century, but still
foam coating technology has not gained ground in paper industry
However, some applications are found
in paper making industry…
Foam coating benefits
Non-contact application
No side streams
Allows very thin coatings, e.g. 0.5 gm-2
• Even application of small quantities on large areas
• Less tendency to migrate into the substrate
For nanomaterials no binders required
Versatile process
• Compatible with a wide range of materials
• Higher concentrations possible, e.g. compared to spraying
• Simple
• Occupationally safe method
Foam coating principles
Foam used as a carrier phase to transfer the coating material onto the substrate
Liquid containing foaming agents is mixed with air using a foam generator
o Air content greater than 80%, preferably 90-95%
Application onto the moving web using a narrow slot type applicator
On the web the bubbles collapse due to absorption, leaving the coating material on the web surface
vertexvertex
Requirements of the foam for foam coating
• Average bubble size < 100 µm
• Bubble size remains constant during the coating process
• Foaming agents compatible with the coating material
Air content 66% Air content 94%
2000 µm 2000 µm
Foam coating facilities at VTT(KCL co-operation) IR-dryers
KCL pilot coater
The foam generator The foam applicator
Magnojet – foam applicator J. Zimmer Maschinenbau GmbH Klagenfurt, Austria
RESULTS
Application of
nanoparticles and unmodified nanofibrillar cellulose
Foam stability in the process Influence of ambient temperature and hose length on foam stability
• VTT Masuko ground NFC
• Analyzed by:
• magnifying high-speed camera monitoring of foam coming from the applicator
• Turbiscan Online measurement device (light scattering method) installed between the foam generator and the foam applicator
• cold (16.5 oC), hot (55 oC) water.
79.0
Testing of foam stability
Foam stability in the process Influence of ambient temperature and hose length on foam stability
• VTT Masuko ground NFC
• Analyzed by:
• magnifying high-speed camera monitoring of foam coming from the applicator
• Turbiscan Online measurement device (light scattering method) installed between the foam generator and the foam applicator
• cold (16.5 oC), hot (55 oC) water.
79.0
Foam stability in the process Influence of ambient temperature and hose length on foam stability
• VTT Masuko ground NFC
• Analyzed by:
• magnifying high-speed camera monitoring of foam coming from the applicator
• Turbiscan Online measurement device (light scattering method) installed between the foam generator and the foam applicator
• cold (16.5 oC), hot (55 oC) water.
What our results show?
1) The stability of the foam can be measured using devices based on light
scattering.
2) that a good foam – right chemistry - is rather insensitive to changes in
process conditions.
Foam generator Hansa Industrie-Mixer GmbH & Co. KG, Germany
Application of nanofibrillar cellulose NFC foaming
NFC, solids content 2.98% Foamed NFC, 90% air
Nanoparticle coated paper Coating layer thickness below 1 µm
Coated paper Uncoated paper
a) b)
Element maps
SEM images
Coated paper Uncoated paper
SEM cross section image
1 µm
SEM x50 SE images from uncalendered paper surfaces
Base paper NFC coated paper
Application of nanofibrillar cellulose
Application of nanofibrillar cellulose Contact angle
0
5
10
15
20
25
30
35
40
0 1 2 3 4 5
con
tact
an
gle
[°]
time [s]
Water
0
10
20
30
40
50
60
0 2 4 6 8 10 12 14
con
tact
an
gle
[°]
time [s]
Diiodomethane
• Water and DIM (~offset ink):
• More hydrophilic and oleophobic surface with NFC1 and NFC2
Base paper Pure foam NFC1 NFC2 NFC3
Application of nanofibrillar cellulose Air permeance, opacity
• NFC3 sealed the surface
• No influence on optical properties
85,0
85,5
86,0
86,5
87,0
87,5
88,0
88,5
89,0
89,5
90,0
90,5
91,0
Ref Base Pure foam NFC1 NFC2 NFC3
Op
acit
y, %
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
Ref Base Pure foam NFC1 NFC2 NFC3
Air
per
mea
nce
, PP
S20
, μm
/Pa*
s
Application of nanofibrillar cellulose Inkjet printing, KCL Versamark2000
Print Density Cyan 50%
GretagMacbeth D196
NFC3 sealed the surface -> Decrease in print density
0,00
0,10
0,20
0,30
0,40
0,50
0,60
0,70
0,80
0,90
Ref. NFC1 NFC2 NFC3 Ref. NFC1 NFC2 NFC3
Pri
nt
Den
sity
Cya
n 5
0%
, Gre
tagM
acb
eth
D1
96
Droplet size : 11 pl 3 pl
Summary of results
Thin, uniform coating layer
Foam coating enables application of undiluted NFC
Different NFC grades have different influences on
contact angle values
Nanofibrillar cellulose applied to the paper surface
decreases air permeance
For nano-scale materials no binders are needed
Conclusions
Foam coating enables very thin coatings of nanomaterials
Foam coating method has been proven at pilot scale
A large variety of materials possible
Higher concentrations possible e.g. compared to spraying
Cooperation partners
KCL, Oy Keskuslaboratorio -
Centrallaboratorium Ab, Finland • All pilot services for paper industry under one roof • www.kcl.fi
Hansa Industrie-Mixer GmbH & Co. KG,
Germany • Heiligenrode (near Bremen) • A centre for foam technology: Research,
development and manufacturing • www.hansamixer.de
J. Zimmer Maschinenbau GmbH Klagenfurt, Austria • Digital textile printing and coating machine sector • www.zimmer-austria.com
Funding
“Scale-up Nanoparticles in Modern Papermaking”, SUNPAP
The research leading to these results has received funding
from the European Community's 7th Frame work
Programme under grant agreement no 228802
