Replacement of synthetic binders with nanofibrillated cellulose in board coating pilot scale studies

Transcription

1 Replacement of synthetic binders with nanofibrillated cellulose in board coating pilot scale studies Final Conference Heikki Pajari, Hille Rautkoski, Pertti Moilanen, VTT Technical Research Centre of Finland Anders Wigsten, StoraEnso AB

2 Outline Goals and background Pilot coatings Coating conditions, NFCs, coating colors and properties Coated board properties Standard properties (gloss, roughness,.) Surface strength (dry and wet) Printing trial Conditions, observations and printed properties Summary and conclusions

3 Goals and background The goal was to evaluate runnability and properties of coating colors and coated boards when part of latex was replaced by NFC Pilot scale coating and sheet fed offset printing trials Background Viscosity and coating layer strength critical factors High aspect ratio => increased viscosity Why should NFC increase the coating layer strength? Addition of NFCs to coatings decreased substantially dry surface strength in preliminary laboratory tests

4 Pilot coating

5 Coating trial Blade coating with jet application Running speed 500 m/min Coat weight 10 g/m 2 for pre and top coatings End moisture 5% Constant calendering conditions for top coating Uncoated and coated base boards

6 Three NFCs from dissolved spruce Nanofibrillated celluloses Abbreviation Pretreatment Fibrillation NFC-CTP Enzymatic Microfluidizer NFC-TE/CTP TEMPO oxidation Microfluidizer NFC-TE/PTS TEMPO oxidation Rotor-stator 2% 2% 9% NFC-CTP opaque viscous 10 µm NFC-TE/CTP transparent gel NFC-TE/PTS white liquid

7 Coating color recipes Precoating HC-60 XZ CTP TE/CTP TE/PTS FF-10 Sterocoll FS Solids, % *Ref/pre CTP/pre TE/CTP/pre TE/PTS/pre The amount of latex and NFC 13 pph *Latex 12.8 and CTP 0.2 pph in the machine circulation CC-75 Capim DG Topcoating XZ TE/CTP TE/PTS Sterocoll FS Blankophor P Solids, % Ref/top TE/CTP/top TE/PTS/top The amount of latex and NFC 15 pph

8 Coating colors: viscosity Solids content close to maximum for all coating colors Low shear rate High shear rate NFCs increased viscosity especially at low shear rates NFCs increased shear thinning Low/high ratio

9 Coating colors: immobilization solids and water retention Addition of NFCs decreased immobilization solids, poorer packing TEMPO pretreated NFCs increased water retention especially with calcium carbonate colors

10 Standard coated board properties

11 Single coated board: air permeance and opacity Addition of NFCs led to more open structures without affecting brightness

12 Double coated board: air permeance Addition NFCs to precoating increased air permeance, constant calendering conditions Topcoat Ref Ref Ref Precoat Ref TE/PTS TE/CTP Top coat Ref Ref Ref Pre-coat Ref TE/PTS CTP

13 Double coated board: gloss NFC in topcoating decreased gloss, constant calendering conditions Topcoat Ref Ref Ref Precoat Ref TE/PTS TE/CTP Top coat TE/CTP TE/CTP Pre-coat Ref TE/CTP

14 Double coated board: roughness and brightness Small changes in roughness and brightness when using coating colors with NFCs, constant calendering conditions Topcoat Ref Ref TE/PTS Precoat TE/PTS TE/PTS TE/PTS

15 Coated board properties: surface strength

16 IGT picking velocity Dry surface strength by measuring the picking velocity with IGT-device Determine the speed where the surface of the coated board is damaged Base boards No picking with uncoated base boards up to of 7 m/s and average picking velocity with precoated base boards around 3.1 m/s Picking mainly coating pick and in some cases surface pick Evanoff, P.C., Gerlach, W., Lyne, B.M. (ed.) Surface Strength Terminology. Tappi Press, 1983.

17 Single coated board: IGT picking velocity No clear differences between the reference and NFC-colors

18 Double coated board: IGT picking velocity Reference colors gave the best results although in most cases picking velocities were within experimental error

19 Double coated board: Prüfbau wet-pick Wet surface strength evaluated with Prüfbau printability tester No clear differences between the samples Wet-pick and wet repellence

20 Summary of coated board properties Gloss: NFCs decreased gloss of single and double coated boards Gloss 40% with latex, 30% with NFC-TE/PTS and 20% with NFC-TE/CTP topcoatings Air permeance: NFCs increased air permeance Roughness and brightness: influence of NFCs was not decisive Surface strength No clear influence of NFCs was observed with single coatings in IGT tests With double coated boards reference colors gave the best results

21 Sheet fed offset (SFO) printing trial

22 Sheet fed offset trial Printing machine: Roland Favorit RVF at KCL Ink: Hostmann-Steinberg Surprize Both double coated and pre-coated samples were printed, in addition two commercial reference boards were printed 500 printed sheets of each trial point Constant print density Ink sequence: black, cyan, magenta and yellow Test print layout

23 Observations and measurements Overall print quality quite good The quality with NFC-TE/PTS on pre-coated base was poor with excessive formation of hickeys/fisheyes Print density Print gloss

24 Double coated samples print density 100% Target density levels achieved with all samples Uncoated base board Coated base board Commercial boards

25 Double coated samples print gloss Print gloss lower with top coatings containing NFCs Uncoated base board Coated base board Commercial boards

26 Coating Summary No problems with coating colors containing NFC at the coater Addition of NFC decreases solids content of coating colors leading to increase in drying energy Replacement of latex with NFC does not improve cost efficiency in coating Printing trial Overall behavior good also with samples containing NFC Hickies in the printed image

27 Summary Coated and printed board properties with coating colors containing NFCs at the same level as with latex reference Decrease of gloss Decrease of surface strength due to addition of NFCs was in most cases close to experimental error In contrast, addition of NFCs led to clear decrease of surface strength in earlier low speed laboratory coatings

28 Acknowledgement The research leading to these results received funding from the European Community s Seventh Framework Programme under Grant Agreement No