Microfibrillated Cellulose in Barrier Coating Applications

Microfibrillated Cellulose in Barrier Coating Applications

The Use of Microfibrillated Cellulose in Barrier Coating Applications

Jonathan Phipps
Principal Scientist
FiberLean Technologies Ltd.

Specialty Papers US

Introduction

  • Microfibrillated cellulose (MFC) is well established as an additive in graphic papers
    • Increased wet web, tensile and Z direction strength
    • Increased filler content
    • Improved smoothness, formation and filler retention
    • Reduced porosity
  • Packaging grades present new challenges
    • Bending stiffness and delamination resistance
    • Water-intensive printing methods (flexography and ink-jet)
    • Replacement of plastics / laminates
    • Waterbased barrier coatings

FiberLean process for Microfibrillated Cellulose manufacture

Barrier Coating Applications: FiberLean process for microfibrillated cellulose manufacture

Impact of Microfibrillated Cellulose on Graphical paper physical properties

Impact of microfibrillated cellulose on Graphical paper physical properties - tensile

Tensile

Impact of microfibrillated cellulose on Graphical paper physical properties - burst

Burst

Impact of microfibrillated cellulose on Graphical paper physical properties - roughness

Roughness

Impact of microfibrillated cellulose on Graphical paper physical properties - permeability

Permeability

Lab study : Messmer recirculating hand sheets (12 sheets) 70% Eucalyptus, 30% NBSK, 550 CSF, Intracarb 60 filler

  • In current applications, microfibrillated cellulose (MFC) is added as a filler.
  • It is possible to increase filler content by 10% or more and suffer no strength loss.
  • Wet web strength is also increased – typically by more than dry strength.
  • MFC increases fibre bonding and fills voids in sheet – rapid decrease in permeability.

Impact of Microfibrillated Cellulose on coating holdout

  • Reduction in permeability and pore size improves holdout of coating components on surface
  • Benefits in graphical papers
    • Reduced Coatweight
    • Improved Gloss
    • Improved printing properties
  • Benefits for barrier coatings
    • Reduced Coatweight
    • Reduced permeability (improved barrier)
    • Elimination of precoat
Barrier Coating Applications: Impact of Microfibrillated Cellulose on coating holdout - no MFC 1

No MFC

Barrier Coating Applications: Impact of Microfibrillated Cellulose on coating holdout - 2% MFC 1

2% MFC

Barrier Coating Applications: Impact of Microfibrillated Cellulose on coating holdout - no MFC 2

No MFC

Barrier Coating Applications: Impact of Microfibrillated Cellulose on coating holdout - 2% MFC 2

2% MFC

Pilotmachine basepaper, Helicoater (short dwell) 500 m min-1: 80 gsm base 70% Eucalyptus, 30% NBSK, 450 CSF, 20% GCC filler. 10gsm coating of Kaolin/GCC 10pph latex

Coating MFC at the wet end

Coating Microfibrillated Cellulose at the wet end 1

  • Microfibrillated cellulose holds too much water for conventional coating…
  • …but it can be applied at the wet end near the wet line
  • Dewatering is achievable with existing elements – vacuum boxes, presses and dryers
  • MFC immobilises rapidly and keeps coating on surface

 

Coating Microfibrillated Cellulose at the wet end 2

Properties of wet-end coated sheets

Properties of wet-end coated sheets - porosity & smoothness Properties of wet-end coated sheets - brightness
Porosity and smoothness – 50% MFC/50% GCC* coatings Brightness – all coatings

Pilot coated papers: 100 gsm base (100% Unbleached long fibre Kraft) . Coatings of 50/50 MFC/GCC and 20/80 MFC/GCC Speed ~25 m min-1

Microfibrillated Cellulose as a precoat for barrier applications – lab studies

Barrier Coating Applications: Microfibrillated Cellulose as a precoat for barrier applications – lab studies

Microfibrillated Cellulose coatings as barrier substrates

Microfibrillated Cellulose coatings as barrier substrates: Base Paper
MFC coatings as barrier substrates: Base Paper + MFC Layer MFC coatings as barrier substrates: Base Paper + barrier coating
MFC coatings as barrier substrates: Base layer + MFC + barrier coating

Surfaces of lab coated papers

  • Optical images taken at boundaries between base, MFC layer and coating
  • Relative height of surface measured with LaserScape profiler
Barrier Coating Applications: Surfaces of lab coated papers 2
Barrier Coating Applications: Surfaces of lab coated papers 1

Barrier properties of lab coated papers

Barrier Coating Applications: Barrier properties of lab coated papers

Pilot 50:50 Microfibrillated Cellulose-mineral coated papers

Barrier Coating Applications: Pilot 50:50 Microfibrillated Cellulose-mineral coated papers Barrier Coating Applications: Pilot 50:50 Microfibrillated Cellulose-mineral coated papers Barrier Coating Applications: Pilot 50:50 Microfibrillated Cellulose-mineral coated papers

Barrier Coating Applications: Pilot 50:50 MFC-mineral coated papers

Pilot coated papers: 72 gsm base (Bleached Kraft 80/20 hardwood/softwood) . Coating of 50% MFC/50% CaCO3 Speed ~25 m min-1

Pilot coated papers – calculated barrier coating permeability vs. MFC layer Coat Weight

 

Barrier Coating Applications: Pilot coated papers – calculated barrier coating permeability vs MFC layer Coat Weight

Coating Microfibrillated Cellulose at high speed

Many Challenges!

  • Barrier Coating Applications: Coating Microfibrillated Cellulose at high speed

    8.5% solids, 20% MFC/80% GCC coating – 500 m/min

    Viscosity vs. Shear Rate

  • Permeability & Drainage
  • Coating strength vs. solids
  • Coating Elongation

Rheology of Microfibrillated Cellulose suspensions

Viscosity and consolidation

Barrier Coating Applications: Rheology of Microfibrillated Cellulose suspensions

20% MFC/80% GCC suspensions – viscosity vs. shear rate
Cup and Bob geometry

Barrier Coating Applications: Rheology of Microfibrillated Cellulose suspensions

Typical Elastic modulus vs. strain – oscillation 1Hz
Parallel Plate geometry

Barrier Coating Applications: Rheology of Microfibrillated Cellulose suspensions

Elastic modulus (LVE region) vs. solids content

Permeability and drainage of Microfibrillated Cellulose suspensions

  • Permeability of vacuum-dewatered suspensions determined by simple filtration experiments
  • Permeability is independent of layer thickness and starting solids content
  • Drainage time required on machine can be estimated
  • Dwell time over vacuum boxes –
    • 20cm wide box @20 m/min – 0.6s
    • 50cm wide box @500 m/min – 0.06s

Permeability of 20% MFC/80% GCC filtercake as function of initial solids

Barrier Coating Applications: Permeability & drainage of microfibrillated cellulose suspensions

Calculated time to drain 30gsm of 20% MFC/80% GCC coating as a function of initial solids

Barrier Coating Applications: Permeability & drainage of microfibrillated cellulose suspensions

Visualisation of high speed coating

  • Short exposure photography at point of application
  • Microfibrillated cellulose/mineral suspension forms contour coating onto extremely rough wet base
  • Coating remains on surface despite lack of base consolidation
Barrier Coating Applications: Visualisation of high speed coating

 

Barrier Coating Applications: Visualisation of high speed coating

Conclusions

  • Microfribrillated Cellulose (MFC) is well established as a wet end additive
    • Increased strength and/or filler content
    • Reduced porosity
    • Improved coating holdout
  • Wet end coating of MFC for barrier applications is very promising
    • Smooth, non-porous surface for further coating
    • Excellent oil and grease resistance
  • High speed applications are developing quickly