Shape Engineered Pigments Based Barrier Coatings for SBS Paperboard

1. 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

2. Discussion Points • Introduction • Objectives • Experimental Design • Results & Discussion • Conclusions

3. 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.

4. Introduction Cont’d • 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.

5. Introduction Cont’d • 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.

6. 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 • 1:1- phyllosilicates such as kaolin (china clay) • 2:1- phyllosilicates such as MMT and laponite.

7. The Structure of Clay Minerals Cont’d

8. Clay Minerals Natural Synthetic Micron <Micron & Nano> Nano Nano Kaolin Clay Shape Engineered (Kaolin) Montmorillonite Hectroites etc. Laponite Clay Clay Minerals Properties

9. Microcomposites No intercalation or exfoliation Conventional filled polymer Nanocomposites Complete exfoliation Layered Materials in Polymers Microcomposite vs. Nanocomposite Pigments particles size: length (m) width (m) thickness (m) Pigments particles size: length (m) width (m) thickness (nm)

10. 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).

11. 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.

12. 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)

13. Materials Table 1. The Characteristic of the Mineral Pigments Table 2: The Characteristic of the Binders (Resins)

14. Kaolin Clay 1 Kaolin Clay 2 Kaolin Clay 3 SEM- Shape Engineered Pigments

15. Materials Cont’d Table 3: The Characteristic of the Base Substrate

16. 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.

17. Sample ID for Different Formulations

18. 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 100°F as well as at 81% RH and 100°F (reported). • Water vapor molecules that permeated the samples were measured and MVTR were calculated.

19. Testing Cont’d • 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)=0.048838*Q (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.

20. Results and Discussion

21. Comparison of Barrier and Mechanical Properties of Selected Size Press Coated Samples

22. Comparison of Barrier and Mechanical Properties of Selected Rod & Size Press + Rod Coated Samples

23. Influence of Application Method [Size Press vs. Rod Coating and Double Coat (SP +Rod)] on Barrier Properties

24. Influence of Binders on Permeability Coefficient of Selected Coatings(With Kaolin Clay#2, SF- 50-60)

25. Influence of Application Methods on Permeability Coefficient of Selected Coatings(Equal Coat Wt.)(With Kaolin Clay#2, SF- 50-60)

26. Influence of Binders & Application Methods on MVTR of Selected Coatings(With Kaolin Clay#2, SF- 50-60)

27. Influence of Pigments on Permeability Coefficient of Selected Coatings[With Binder “A” Acrylic]

28. Influence of Pigments on MVTR of Selected Coatings[With Binder “A” Acrylic]

29. Influence of Shape Factor (Coat Wt. ~32 gsm) on Barrier Properties for Pigments Only (No Binder)

30. A B Comparison of Elastic Modulus at 50 and 75% RH and 730F of Selected Rod Coated Samples

31. 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).

32. Conclusions Cont’d • 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.

33. 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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