Tappi PaperCon 2018
Charlotte, North Caroline
April 15-18, 2018
Per Svending, VP Marketing
RISI global paper and board 15-year forecast, Aug -17
Containerboard growth by 84 million ton to 2031
Demand for high quality print on boxes is growing even more rapidly.
Growth drivers
Quality ladder for printed corrugated boxes
High growth print methods are challenging the substrates ability to manage large amounts of water
Wet-in-wet coating on top of the wire section
- MFC-mineral composite applied as a low solids slurry on top of the still consolidating base layer.
- The composite has the ability to stay on the surface without penetrating into the base.
- The top layer can be drained using existing foils and vacuum boxes.
- Pressing and drying works as normal but with press solids increased.
- The top layer is strong and has good adhesion while offering good coverage, low porosity, good smoothness and excellent printability.
MFC-mineral composite coating has inkjet and flexo printability making it well suited for printed white boxes
Images scanned from pilot made WT linerboard
Coated WTL quality but with uncoated WTL drying rate
White Top application uses strength and opacity benefits of MFC-mineral composite technology
Less than 15% of the bleached fiber needed to make printable surface
Less than 15% of the bleached fiber needed to make printable surface
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| First pilot result | The goal |
Key challenges involved in making MFC-mineral wet-end coating work on high speed paper machines
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For evaluation and control of new application. |
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MFC is very viscous even at low levels of solid content. |
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There is no off-the-shelf equipment. |
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MFC is known to really hold on to water. |
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MFC will close the surface. |
New lab methods had to be developed
Multi-layer handsheets and Helicoater wet-in-wet
How to make a composite gel structure like this work in a coating application?
Very high viscosity at low shear rate for a 10% solids composite.
Dilution is obviously a possibility but will naturally result in more water to drain, through the base sheet.
Optimizing solids, viscosity and drainage is a key consideration for successful high speed operation of this coating method.
The MFC-mineral composites are shear-thinning
Alternative application principles evaluated
Pilot trial application of 30 g/m2 dry MFC-mineral composite at 500 m/min on top of 70 g/m2 base
Several alternatives have been evaluated on high speed pilot machines with varying results. Under the right conditions high-speed application works!
The coating still stays on the surface
Despite much higher shear rate and drainage intensity, the MFC-mineral coating is held out on the surface.
Drainage is reasonably good and can be further improved through use of suitable chemistry
- Common retention/drainage aids have been found to work.
- Absence of fibers impacts on flocculation.
- Our test method is less dynamic than the real application.
Increased press solids so far only proven on slow pilot machines
Similar couch solids also proven at high speed while pressing is current target for high speed optimisation
Reduced permeability is primarily good news
Positive impact on printability
- MFC on the surface closes up the sheet more than MFC in the sheet.
- Allows the use of coarse, low cost minerals.
- Possible to tailor the absorption properties and print density through selection of mineral components.
- Improved ink hold-out compared to regular white top liner and with better ink drying.
- Almost at glossy double coated WTL level in terms of ink density.
Mercury porisometry measurements on conventionally and MFC-mineral wet-end coated white top liner
MFC-mineral coating yields larger pores and more pore volume
Print properties as a function of pore structure
Coated WTTL and MFC-mineral composite coated linerboard
Print properties as a function of pore structure
Coated WTTL and MFC-mineral composite coated linerboard
Adding a soft nip for smooth and matte finish
Surprise, surprise. No smearing!
The MFC-mineral composite coating is good at accepting moisture from inkjet printing.
Our inkjet printing development partner is Screen GP IJC, in Cambridge, UK.
New technology is always challenging but ultimately the reward will be big!
