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 biodegradablerenewable, recyclable and/or biodegradable materials.

The need to reduce the amount of non-non-recyclablerecyclable materials is ever increasing.

5

Introduction Cont’d This study is an attempt to limit or replacelimit 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

Tetrahedral Structure

Octahedral Structure

Tetrahedral Structure

Octahedral Structure

Tetrahedral Structure

Tetrahedral Structure

Octahedral Structure

Tetrahedral Structure

Octahedral Structure

Tetrahedral Structure

Tetrahedral Structure

Octahedral Structure

Tetrahedral Structure

8

Clay Minerals Properties

Clay Minerals

Natural Synthetic

Micron<Micron &

Nano>Nano Nano

Kaolin Clay

Shape Engineered

(Kaolin)

MontmorilloniteHectroites etc.

Laponite Clay

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).

Effective Flow Length (Le) Actual Flow Length (L)

Substrate

Clay Platelets Water Molecule

Effective Flow Length (Le) Actual Flow Length (L)

Substrate

Clay Platelets Water Molecule

Substrate

Clay Platelets Water Molecule

Substrate

Clay Platelets Water Molecule

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:

1. Formulation of barrier coatings using shape engineered pigments

2. Application of barrier coatings onto SBS baseboard

3. Characterization of the barrier and mechanical properties

4. Optimization (future papers)

13

Materials

Binder TypeSolids,

%pH

Viscosity, cps

Avg. Particle Size, nm

A Acrylic54.5- 55.5

7.5 400 250-325

B SBR48.5-50.0

8.0 250 150-200

Mineral PigmentAspect 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 1. The Characteristic of the Mineral Pigments

Table 2: The Characteristic of the Binders (Resins)

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SEM- Shape Engineered Pigments

Kaolin Clay 1

Kaolin Clay 2

Kaolin Clay 3

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Materials Cont’dTable 3: The Characteristic of the Base Substrate

SubstrateProperties

Solid Bleached Sulfate (SBS), 270 g/m2

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)

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

Pigm

ents

Bin

ders

Pigm

ent

Load

ing

S1 2 A 6%

S4 2 A 100%

S5 1 A 6%

S8 1 A 100%

S9 3 A 6%

S12 3 A 100%

S13 2 B 6%

S16 2 B 100%

S17 1 B 6%

S20 1 B 100%

S21 3 B 6%

S24 3 B 100%

ID

Lab

Padd

er (S

ize

Pres

s)

Pigm

ents

Bin

ders

Form

ula

P1 1

P2 2

P3 3

C1 2 A

C2 1 A

C3 3 A

C4 2 B

C5 1 B

C6 3 B

ID

Dra

wdo

wns

(Rod

Coa

ting

) Pigment Only

100

Parts Pi

gmen

t + 1

0 Pa

rts Bin

der

Pigm

ents

Bin

ders

C1S4 2 A

C2S8 1 A

C3S12 3 A

C4S16 2 B

C5S20 1 B

C6S24 3 B

Size

Pre

ss

+ R

od

ID

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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 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.

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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.

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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)

PermeabilityCoeff. (µm2)

MVTR (g/m2·d)

Elastic Modulus (GPa)

50% RH & 730F81%RH &1000F

50%RH & 730F

75%RH & 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/m2*d)

Elastic Modulus (GPa)

50% RH & 730F81%RH &

1000F50%RH &

730F75%RH &

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

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.0 6.0 12.0 18.0 24.0 30.0 36.0 42.0 48.0

PPS Porosity (ml/ min)

Perm

eabi

lity

Coe

fficient

, K x

104 (µ

m2 )

S4 S8 S12 S16 S20 S24 C1 C2 C3

C4 C5 C6 C1S4 C2S8 C3S12 C4S16 C5S20 C6S24

Size PressRodSP+ Rod

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.0 6.0 12.0 18.0 24.0 30.0 36.0 42.0 48.0

PPS Porosity (ml/ min)

Perm

eabi

lity

Coe

fficient

, K x

104 (µ

m2 )

S4 S8 S12 S16 S20 S24 C1 C2 C3

C4 C5 C6 C1S4 C2S8 C3S12 C4S16 C5S20 C6S24

Size PressRodSP+ Rod

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Influence of Binders on Permeability Coefficient of Selected Coatings

(With Kaolin Clay#2, SF- 50-60)

S 16

S 4

C1 C 4 C

4S16

C1S

4

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

A B

Binders

Perm

eabi

lity

Coe

fficient

, K x

104 (µ

m2 )

25

Influence of Application Methods on Permeability Coefficient of Selected Coatings

(Equal Coat Wt.)(With Kaolin Clay#2, SF- 50-60)

C 4

C1

C1S

4

C4S

16

0.00

0.25

0.50

0.75

1.00

1.25

A B

Binders

Perm

eabi

lity

Coe

ffic

ient

,

K x

104 (µ

m2 )

26

Influence of Binders & Application Methods on MVTR of Selected Coatings

(With Kaolin Clay#2, SF- 50-60)S

4 S 16

C 4C

1

C1S

4

C4S

16

0

200

400

600

800

1000

1200

A BBinders

MV

TR (g

/m2 x

d)

C1

C 4

C4S

16

C1S

4

0

200

400

600

800

1000

1200

A BBinders

MV

TR (g

/m2 x

d)

27

Influence of Pigments on Permeability Coefficient of Selected Coatings

[With Binder “A” Acrylic]

S 12

S 8

S 4

C 3

C1 C 2 C

3S12

C2S

8

C1S

4

0.0

1.3

2.6

3.9

5.2

50-60 10-20 80-90

Pigments Shape Factors

Perm

eabi

lity

Coe

ffic

ient

,

K x

104 (µ

m2 )

28

Influence of Pigments on MVTR of Selected Coatings

[With Binder “A” Acrylic]

S 12S 8

S 4 C 3

C1

C 2

C3S

12C2S

8

C1S

4

0

200

400

600

800

1000

1200

50-60 10-20 80-90

Pigments Shape Factors

MV

TR (g

/m2 x

d)

C 2C1

C 3

C1S

4 C2S

8

C3S

12

0

200

400

600

800

1000

1200

50-60 10-20 80-90

Pigments Shape Factors

MV

TR (g

/m2 x

d)

29

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

Binder)

Clay

3

Clay

2

Clay

10.00

1.00

2.00

3.00

50-60 10-20 80-90

Pigments Shape Factors

Perm

eabi

lity

Coe

ffic

ient

,

K x

104 (µ

m2 )

30

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

C6-

50%

RH

C5-

50%

RH

C4-

50%

RH

C3-

50%

RH

C2-

50%

RH

C1-

50%

RH

C 6

-75%

RH

C 5

-75%

RH

C 4

-75%

RH

C 3

-75%

RH

C1-

75%

RH

C 2

-75%

RH

0.0

1.0

2.0

3.0

4.0

5.0

6.0

50-60 10-20 80-90 50-60 10-20 80-90

Pigments Shape Factors

Ela

stic

Mod

ulus

(GPa

)

A B

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.

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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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