Shape Engineered Pigments Based Barrier Coatings for SBS Paperboard

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Shape Engineered Pigments Based Barrier Coatings
for SBS Paperboard
Dr. Lokendra Pal (WMU) Dr. Margaret Joyce
(WMU) Dr. Paul Fleming (WMU) Dr. David Knox
(MeadWestvaco) Now with Hewlett-Packard
Company
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Discussion Points

• Introduction
• Objectives
• Experimental Design
• Results Discussion
• Conclusions

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Introduction

• Paper and board have very high permeability i.e.
  virtually no ability to block diffusion or
  movement of water and water vapors.
• Plastic materials have completely different
  chemical structures, and can easily be made
  resistant to water and water vapor transmission.
• Hence paperboard packages are commonly extrusion
  coated off-line with polyethylene (PE),
  polypropylene (PP) PET, etc.

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Introduction Contd

• Consumer pressure to use environmentally
  sensitive packaging assemblies has created a
  large and expanding market for renewable,
  recyclable and/or biodegradable materials.
• The need to reduce the amount of non-recyclable
  materials is ever increasing.

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Introduction Contd

• This study is an attempt to limit or replace the
  above mentioned technologies with an online
  alternative shape-engineered environmental
  friendly clays.
• This will improve the productivity and hence the
  economics of production, providing the barrier
  performance of the grade can be achieved.

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The Structure of Clay Minerals

• Most clay minerals are part of a large family of
  silicate minerals called phyllosilicates.
• Two dimensional sheets of
• tetrahedrally co-ordinated silica linked to
• octahedrally co-ordinated alumina or magnesium
• 11- phyllosilicates such as kaolin (china clay)
• 21- phyllosilicates such as MMT and laponite.

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The Structure of Clay Minerals Contd
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Clay Minerals Properties
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Microcomposite vs. Nanocomposite

• Microcomposites
• No intercalation or exfoliation
• Conventional filled polymer

Pigments particles size length (?m) width (?m)
thickness (?m)

• Nanocomposites
• Complete exfoliation
• Layered Materials in Polymers

Pigments particles size length (?m) width (?m)
thickness (nm)
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Tortuous Path for a Particle to Migrate Through a
Layer of Platey Pigments

• Clay platelets provides high tortuosity, hence
  the effective flow path, (Le ) of the air, water
  vapor or gas molecules (or atom) is significantly
  greater than the porous medium length (L).

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Objectives

• To study the influence of shape-engineered
  pigments on structural and functional properties
  of barrier coatings.
• To determine if the barrier characteristics of
  SBS paperboard can be improved by incorporating
  shape-engineered pigments.
• To determine the dependence of barrier properties
  on pore structure.

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Experimental Design

• This work is divided into four phases
• Formulation of barrier coatings using shape
  engineered pigments
• Application of barrier coatings onto SBS
  baseboard
• Characterization of the barrier and mechanical
  properties
• Optimization (future papers)

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Materials
Table 1. The Characteristic of the Mineral
Pigments
Mineral Pigment Aspect Ratio Avg. Particle Size, nm BET Surface Area, m2/g
Kaolin clay 1 10-20 150-200 20-22
Kaolin clay 2 50-60 450-550 18-20
Kaolin clay 3 80-90 950-1050 12-14
Table 2 The Characteristic of the Binders
(Resins)
Binder Type Solids, pH Viscosity, cps Avg. Particle Size, nm
A Acrylic 54.5- 55.5 7.5 400 250-325
B SBR 48.5-50.0 8.0 250 150-200
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SEM- Shape Engineered Pigments
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Materials Contd
Table 3 The Characteristic of the Base Substrate
Substrate Properties Solid Bleached Sulfate (SBS), 270 g/m2 Solid Bleached Sulfate (SBS), 270 g/m2
Substrate Properties Uncalendered (0 PLI) Calendered (1600 PLI)
Thickness, mils 14.20 (0.45) 12.2 (0.39)
PPS Porosity, ml/min 249.05 (8.52) 84.4 (5.01)
Permeability, µm2 4.33 x10-3 1.28 x 10-3
Roughness, µm 5.90 (0.28) 4.323 (0.19)
Brightness, 85.33 (0.30) 84.96 (0.21)
MVTR (g/m2day) 1149 (89.01) 1115.46 (81.24)
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Coating Preparations Application

• Coatings were prepared using three shape
  engineered clays, each at two levels with two
  different binders.
• The coating solids and Brookfield viscosities
  were measured.
• Coatings were applied on SBS baseboard using a
  lab padder (size press) and various Mayer Rod.
• The coated samples were then calendered at 1600
  PLI, 2-nip smooth side.
• All the coated paperboard samples were
  conditioned for 24 hrs at 50 RH and 230C before
  any measurements were made.

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Sample ID for Different Formulations
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Testing

• The samples were tested for moisture vapor
  transmission rate (MVTR), PPS porosity, caliper
  and stiffness (elastic modulus).
• MVTR of each test sample was determined by the
  gravimetric cup method with the coated side
  towards the humid air
• Measurements were carried out at 75 RH and 100F
  as well as at 81 RH and 100F (reported).
• Water vapor molecules that permeated the samples
  were measured and MVTR were calculated.

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Testing Contd

• The porosity was measured using a PPS tester at
  1000 kPa.
• Thickness of the samples were measured using a
  Micrometer.
• The permeability coefficient, K was calculated
  from the PPS porosity and caliper data using the
  following relationship
• K (µm2)0.048838Q (ml/min) L (m)
• Stiffness was tested using a Taber stiffness
  tester at 50 and 75 RH and room temperature
  conditions.
• Composite elastic modulus was calculated from the
  Taber stiffness and caliper data.

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Results and Discussion
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Comparison of Barrier and Mechanical Properties
of Selected Size Press Coated Samples
ID PPS Porosity (ml/min) Permeability Coeff. (µm2) MVTR (g/m2d) Elastic Modulus (GPa) Elastic Modulus (GPa)
ID 50 RH 730F 50 RH 730F 81RH 1000F 50RH 730F 75RH 730F
S1 20.6 3.1x10-4 840 6.0 5.6
S4 29.0 4.4x10-4 884 6.3 5.8
S5 28.6 4.2x10-4 913 5.9 5.7
S8 30.2 4.7x10-4 950 5.9 5.8
S9 37.4 6.2x10-4 928 4.9 5.1
S12 32.6 5.1x10-4 958 5.9 5.6
S13 36.3 5.7x10-4 984 5.7 5.5
S16 43.9 7.1x10-4 1052 5.8 4.9
S17 50.7 7.6x10-4 958 7.0 6.7
S20 39.9 6.2x10-4 1038 5.9 6.3
S21 43.3 6.7x10-4 988 6.0 6.2
S24 45.2 7.1x10-4 989 5.7 5.2
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Comparison of Barrier and Mechanical Properties
of Selected Rod Size Press Rod Coated Samples
ID PPS Porosity (ml/min) Permeability Coeff. (µm2) MVTR (g/m2d) Elastic Modulus (GPa) Elastic Modulus (GPa)
ID 50 RH 730F 50 RH 730F 81RH 1000F 50RH 730F 75RH 730F
C1 5.63 1.0x10-4 1142 4.5 4.5
C2 6.89 1.2x10-4 1132 4.5 4.4
C3 17.75 3.0x10-4 984 5.0 4.9
C4 6.99 1.2x10-4 1020 5.4 5.3
C5 12.02 2.1x10-4 1079 5.0 4.8
C6 6.23 1.1x10-4 995 5.0 4.9
C1S4 2.32 3.9x10-5 754 4.0 4.0
C2S8 4.94 8.3x10-5 923 5.0 4.9
C3S12 3.44 5.9x10-5 788 5.3 5.3
C4S16 3.14 5.1x10-5 769 5.0 4.9
C5S20 6.66 1.1x10-4 986 6.3 6.0
C6S24 3.34 5.6x10-5 790 5.6 5.6
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Influence of Application Method Size Press vs.
Rod Coating and Double Coat (SP Rod) on Barrier
Properties
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Influence of Binders on Permeability Coefficient
of Selected Coatings(With Kaolin Clay2, SF-
50-60)
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Influence of Application Methods on Permeability
Coefficient of Selected Coatings (Equal Coat
Wt.)(With Kaolin Clay2, SF- 50-60)
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Influence of Binders Application Methods on
MVTR of Selected Coatings(With Kaolin Clay2,
SF- 50-60)
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Influence of Pigments on Permeability Coefficient
of Selected CoatingsWith Binder A Acrylic
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Influence of Pigments on MVTR of Selected
CoatingsWith Binder A Acrylic
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Influence of Shape Factor (Coat Wt. 32 gsm) on
Barrier Properties for Pigments Only (No Binder)
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Comparison of Elastic Modulus at 50 and 75 RH
and 730F of Selected Rod Coated Samples
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Conclusions

• The pigment shape factor appears to have a
  systematic effect on barrier properties although
  it is relatively low in some cases.
• The medium shape factor pigment (SF 55) provided
  the highest barrier properties for the SBS board
  tested, but the results might be different for
  boards of different roughness and porosity.
• The shape factor significantly impacted the
  saturation coat weight (where complete coverage
  occurs).

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Conclusions Contd

• The double-coated treatment method (size
  press/rod) produced the best results for same
  coat weight.
• The effect of application method on barrier
  properties was found to have a more significant
  impact on the barrier properties than the SF of
  the pigment.
• As expected, Taber stiffness and elastic modulus
  decreases with increase in relative humidity.
  However, there was only a slight impact of
  pigment shape factor and application method on
  stiffness.

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Further Optimization Work

• Clay
• Shape Factor
• Concentration
• Dispersion
• Orientation
• Resin
• Hydrophobic/hydrophilic character
• Permeability
• Coating Preparation Methods
• Coating Application Methods
• Size Press, Rod, Blade, Curtain etc.
• Multi layers
• Finishing Operations

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THANK YOU