Factors Influencing the Surface St th fC t dP Strength of Coated Papers Dan Varney – Omya Inc. Peter Dahlvik, Guillermo Bluvol, Karl-Heinz Kagerer, and Manfred Arnold Applied Technology Service; Business Unit Paper; Omya International AG Applied Technology Service; Business Unit Paper; Omya International AG CH-4665 Oftringen PaperCon 2011 Page 393
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Factors Influencing the SurfaceSt th f C t d PStrength of Coated Papers
Dan Varney – Omya Inc.
Peter Dahlvik, Guillermo Bluvol, Karl-Heinz Kagerer, and Manfred Arnold Applied Technology Service; Business Unit Paper; Omya International AGApplied Technology Service; Business Unit Paper; Omya International AGCH-4665 Oftringen
PaperCon 2011 Page 393
Objectives
To evaluate the effect of different coating color parameters on the surface strength of double coated papers insheet-fed offset (SFO) printingsheet-fed offset (SFO) printing
To correlate lab test data with observed edge picking during commercial SFO printing trials
PaperCon 2011 Page 394
Background
Latex binder is considered one of the most expensivecoating componentscoating components
Continuous fine tuning of the binder level is important to cost reduction efforts – requires total systems approachq y pp
One opportunity is to take advantage of the lower binder demand and higher solids potential of GCC
However, the high tack inks used in SFO printing demandadequate surface strength
Thus, a balancing act exists between optimizing coating costs and maintaining adequate coating surface strength
PaperCon 2011 Page 395
What is Edge Picking?
Occurs in SFO where high-tack inks are used
Coating is pulled out at the edge between printedand non-printed areas
Adversely impacts printquality and leads to morefrequent washing
printing area
Excessive edge picking can damage the rubber blankets edge picking
Thus, adequate surfacestrength is very important
g p g
PaperCon 2011 Page 396
Theoretical Considerations
Tack development of inks through press influenced by ink setting characteristics of coated surfaceink setting characteristics of coated surface
Ink setting impacted by pigments and latex
Fine pigments create many small pores leading to- Fine pigments create many small pores, leading to- Higher capillary pressure and faster ink setting
- Latex impact via - Chemistry of polymer- Effect on pore structure of coating layer
Choice of pigments and binders (type and amount) willgreatly affect ink/coating interaction and, thus, surfacestrength
PaperCon 2011 Page 397
Specially Designed Printing Method
Used redesigned printing plate and higher tack inksto exacerbate (enhance) edge picking.
This method also involved evaluating edge picking by This method also involved evaluating edge picking by
- Visual examination of prints
- Assessment of rubber blankets- Assessment of rubber blankets
- Ranking edge picking between 0 (worst) and 100 (best)
PaperCon 2011 Page 398
Redesigned Print Test Formh dlishort
bars in 6 colors
headlines
6th unit: blue
different screensin black
shortshort bars in 5
colors
1st unit: open areaon rubber blanket
PaperCon 2011 Page 399
Evaluated Parameters
Pilot coater Sheetfed offset press
Solids content of coating color
Pigment type
Man Roland R706 Press
Color sequence – KCMYCBlueg ypGCC vs. high glossing clay
Lab print gloss and paper glossresults followed the same trend
60
5050
40
71 6568 71 6568 686565 68682 3 4 5 6 7 8 9 10 11
7.5 %Latex
50/50ClayGCC
30 17.5 %Latex
7.5 %Latex
5 %Latex
5 %Latex
5 %Latex
100 t GCC 95 100 t GCC 95
100Clayhigh
100GCCNSPD
100GCC60
100GCC90
71 6568 71 6568 686565 6868
GCC95100 parts GCC 95 100 parts GCC 95
gglossing
NSPD 60 90
7.5 % Latex7.5 % Latex
PaperCon 2011 Page 408
RI Test Ink Setting vs. Edge Picking
6Ink setting (6 = fastest / 0 = slowest)
5
44
3
2
1R² = 0.8091
0 10 20 30 40 50 60 70 80 90 1000
Edge pick print press (100 = best / 0 = worst)
PaperCon 2011 Page 409
IGT Ink Setting vs. Edge Picking
50Optical density
40
R² = 0.806830
2020
10
0 10 20 30 40 50 60 70 80 90 1000
Edge pick print press (100 = best / 0 = worst)
PaperCon 2011 Page 410
P&I Ink Tack Slope vs. Edge Picking
50The lower the better
40Passes to fail had a similarly good correlation (R2 = 0.7733)
30
20
R² = 0.7414
20
10
0 10 20 30 40 50 60 70 80 90 1000
Edge pick print press (100 = best / 0 = worst)
PaperCon 2011 Page 411
Wet Pick vs. Edge Picking
m/s (the higher the better)
4
3Dry pick results had poor correlation as well (R2 = 0 4748)3
2
R² = 0.4574correlation as well (R2 = 0.4748)
1
0 10 20 30 40 50 60 70 80 90 1000
Edge pick print press (100 = best / 0 = worst)
PaperCon 2011 Page 412
Pore Size Distribution - Mercury Porosimetry
0.25log differential intruded volume/cm³ g-1
0.25log differential intruded volume/cm³ g-1
Uncalendered results showed
0.20NPSD GCC (TP9)
GCC 90 (TP11)
(TP1-6) GCC 950.20
NPSD GCC (TP9)
GCC 90 (TP11)
(TP1-6) GCC 95
slightly larger pore size
0.15
0 10
GCC 90 (TP11)
GCC 60 (TP10)(TP7) GCC 95/Clay
0.15
0 10
GCC 90 (TP11)
GCC 60 (TP10)(TP7) GCC 95/Clay
0.10
0.05
(TP8) Clay0.10
0.05
(TP8) Clay
0.010.00
0.1 10.010.00
0.1 1µm diameterµm diameter
PaperCon 2011 Page 413
Conclusions (I)
Specially designed commercial SFO printing methodprovided differentiation regarding edge picking
Good correlation found between degree of edge picking g g p gand lab ink setting/tack measurements. Thus, quantifying ink/coating interaction as a function of time best “lab scale simulation” of surface strength
Hg intrusion porosimetry data indicated that coating pore structure mainly depends on pigment finenessy p p g
Calendering offered an improvement in surface strength
PaperCon 2011 Page 414
Conclusions (II)
Ink setting and ink tack results indicate that pore structure of coating layer is crucial to degree of pick strength
Slower ink setting favors higher surface strength viaPigments GCC vs clay and coarse vs fine- Pigments – GCC vs. clay and coarse vs. fine
- Higher solids - Higher latex amountg
Lower surface strength of clay coatings due to- Faster ink setting (from finer pore size)- Higher specific surface area (higher binder demand)- Hydrophobic nature of clay- Hydrophobic nature of clay
PaperCon 2011 Page 415
Conclusions (III)
NPSD GCC had better surface strength than expected NPSD GCC had better surface strength than expected
Choice of pigments along with maximizing coating solids p g g g g- Allowed for reduction in binder level w/o compromising
surface strengthImproved sheet and print gloss- Improved sheet and print gloss
Future work to assess further the impact of coarser claysand coating PCC