Nanocellulose in pigment coatings : Aspects of barrier properties and printability in offset

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Department of Physics, Chemistry and Biology

Master's Thesis

Nanocellulose in pigment coatings

- Aspects of barrier properties and printability in offset

Sofie Nygårds

2011-06-07

LITH-IFM-A-EX--11/2533--SE

Linköping University Department of Physics, Chemistry and Biology 581 83 Linköping

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Department of Physics, Chemistry and Biology

Nanocellulose in pigment coatings

- Aspects of barrier properties and printability in offset

Sofie Nygårds

Thesis work done at Innventia AB, Stockholm

2011-06-07

Supervisor

Christian Aulin and Göran Ström, Innventia

Examiner

Thomas Ederth

Linköping University Department of Physics, Chemistry and Biology 581 83 Linköping

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Avdelning, institution

Division, Department

Chemistry

Department of Physics, Chemistry and Biology Linköping University

URL för elektronisk version

ISBN

ISRN: LITH-IFM-A-EX--11/2533--SE _________________________________________________________________

Serietitel och serienummer ISSN

Title of series, numbering ______________________________

Språk Language Svenska/Swedish Engelska/English ________________ Rapporttyp Report category Licentiatavhandling Examensarbete C-uppsats D-uppsats Övrig rapport _____________ Titel Title

Nanocellulosa i mineralbestrykningar - Några aspekter på barriäregenskaper och tryckbarhet i offset.

Nanocellulose in pigment coatings - Aspects of barrier properties and printability in offset

Författare

Author

Sofie Nygårds

Nyckelord

Keyword Nanocellulose, Microfibrillated cellulose, Coatings, Barrier, Printability, Air permeability, Offset, Surface Energy

Sammanfattning

Abstract Papers are coated in order to improve the properties of the surface, to improve printability and to include new functionalities like barriers properties. Typical coating formulation contains a high number of components, some are made from minerals and others are manufactured from petroleum. The barrier properties of today's paper based packages are plastics and/or aluminum foil. Environmentally friendly substitutie of these nonrenewable materials are needed. Nanocellulose is a promising material and of a growing interest as an alternative to petroleum-based materials, since nanocellulose films/coatings have been shown to have excellent mechanical and barrier properties.

This project aimed to evaluate nanocellulose in combination with minerals in paper coatings. The project had two approaches. One was to evaluate the barrier properties of MFC coatings with mineral included. The second part was about coatings for printing matters, and evaluation of the possibility to replace petroleum-based binders in the coating color with MFC. Barrier properties were evaluated by measuring the air permeability of the coatings. The properties of the coating affecting the printability in offset printing examined was the surface energy, the gloss, the roughness of the coatings, the strength and the offset ink setting.

Carboxymethylated nanocellulose formed denser films and had superior barrier properties compared with enzymatically pretreated nanocellulose. Adding of minerals did not affect the barrier properties of the MFC coatings to a significant extent. Therefore, minerals cannot be added to enhance the barrier but it can be added to reduce the cost of the coating process without losing any barrier properties.

The print quality depends on how the ink interacts with the coating. These coatings did have a relatively high surface energy, which is preferable for printing with waterborne ink. It was also shown that the absorption abilities increased when the amount of MFC was increased. However, offset printing demands high surface strength and addition of MFC in the coating color drastically decreased the strength. This means that the coatings produced in this work are not strong enough and thereby not suitable for offset printing. However other printing technologies put lower demand on surface strength and are still possible.

Datum

Date

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Abstract

Papers are coated in order to improve the properties of the surface, to improve printability and to include new functionalities like barriers properties. Typical coating formulation contains a high number of components, some are made from minerals and others are manufactured from petroleum. The barrier properties of today's paper based packages are plastics and/or aluminum foil. Environmentally friendly substitute of these nonrenewable materials are needed. Nanocellulose is a promising material and of a growing interest as an alternative to petroleum-based materials, since nanocellulose films have been shown to have excellent mechanical and barrier properties.

Nanocellulose, also referred to as microfibrillated cellulose (MFC), is cellulosic fibrils mechanically disintegrated from plant cell walls. The fibrils have a width less than 20 nm and a length of up to several µm. MFC is manufactured by pressing cellulose fibers through a high-pressure homogenizer that disintegrates the fibers into their sub-structural elementary fibrils. By using different types of pre-treatments of the pulp to partly open up the fiber cell wall in combination with the homogenization, different types of MFC are obtained. MFC generation 1 is manufactured from enzymatically pretreated pulp whereas MFC generation 2 is pre-treated by carboxymethylation.

This project aimed to evaluate MFC in combination with minerals in paper coatings. The project has two approaches. One is to evaluate the barrier properties of MFC coatings with mineral included. The second part is about coatings for printing matters, and evaluation of the possibility to replace petroleum-based binders in the coating color with MFC. Barrier properties were evaluated by measuring the air permeability of the coatings. The properties of the coating affecting the printability in offset printing examined was the surface energy, the gloss, the roughness of the coatings, the strength and the offset ink setting.

MFC generation 2 formed denser films and had superior barrier properties compared with MFC generation 1. Adding of minerals did not affect the barrier properties of the MFC coatings to a significant extent. Therefore, minerals cannot be added to enhance the barrier performance but can be added to reduce the viscosity of the dispersion in order to reduce the cost of the coating process without losing any barrier properties.

The print quality depends on how the ink interacts with the coating. These coatings did have a relatively high surface energy, which is preferable for printing with waterborne ink. It was also shown that the absorption abilities increased when the amount of MFC was increased. However, offset printing demands high surface strength and adding of MFC in the coating color drastically decreased the strength. This means that the coatings produced in this work are not strong enough and thereby not suitable for offset printing. However other printing technologies that put less demand on surface strength are still possible. Examples of such technologies are flexography and inkjet.

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Sammanfattning

Papper bestryks för att förbättra ytans egenskaper, för att förbättra tryckbarheten och för att införa nya funktioner som till exempel barriäregenskaper. Typiska bestrykningssmetar består av flera olika komponenter, några är gjorda av mineraler och andra tillverkas från olja. Barriäregenskaperna i dagens pappersbaserade förpackningar består av plast eller aluminiumfolie. Dessa icke förnyelsebara material behöver ersättas av mer miljövänliga alternativ. Nanocellulosa är ett lovande material och är av växande intresse som alternativ till petroleumbaserade material då filmer av nanocellulosa har visats ha utmärkta mekaniska egenskaper och barriäregenskaper.

Nanocellulosa kallas också "microfibrillated cellulose" (MFC) och är cellulosafibriller som är mekaniskt framställda från cellväggar i växter. Fibrillerna har en diameter på mindre än 20 nm och en längd på upp till flera mikrometer. MFC framställs genom att pressa cellulosafibrer genom en homogenisator med högt tryck, som fördelar fibrerna till deras beståndsdelar, de elementära fibrillerna. Förbehandling av fibrerna behövs, och beroende på vilken förbehandling som använd så fås olika typer av MFC. MFC generation 1 görs med en enzymatisk förbehandling och MFC generation 2 förbehandlas med karboxymetyl.

Projektet syftade till att utvärdera MFC i kombination med mineraler i pappersbestrykningar. Detta projekt kan delas upp i två delar. Första delen var att utvärdera barriäregenskaper hos MFC-bestrykningar med mineral tillsatta. Den andra delen handlade om tryckytor och utvärdering av möjligheten att ersätta oljebaserade bindemedel i bestrykningarna med MFC. Barriäregenskaper utvärderades genom att mäta luftgenomsläpplighet av bestrykningarna. Egenskaperna hos tryckytorna som påverkar tryckbarhet för offsettryck som undersöktes var ytenergi, glans, ytråheten, styrka och färgklibb.

MFC generaion 2 bildade mer kompakta filmer och hade betydligt bättre barriäregenskaper än MFC genetraion 1. Tillsättning av mineraler påverkade inte barriäregenskaper för MFC-bestrykningarna. Därmed kan mineraler inte tillsättas för att förbättra dessa barriäregenskaper, dock kan mineralerna tillsättas för att minska viskositeten på smeten och därmed minska kostnaderna för bestrykningsprocessen utan att förlora några barriäregenskaper.

Tryckkvaliteten beror på hur färgen interagerar med pappret. Bestrykningarna i detta projekt hade en relativt hög ytenergi, vilket är att föredra vid tryck med vattenburen färg. Det visade sig också att absorptionsförmågan ökade när mängden MFC ökade. Dock kräver offsettryck hög ytstyrka och tillsättningen av MFC i bestrykningssmeten minskade drastiskt styrkan i bestrykningen. Detta innebär att bestrykningarna framställda i det här projektet inte är tillräckligt starka för att lämpa sig för offsettryckning. Däremot skulle det kunna lämpa sig för andra tryckmetoder som inte ställer lika höga krav på ytstyrkan. Exempel på sådana tryckmetoder är flexografiskt tryck och inkjettryck.

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3 Experimental details ... 8 3.1 Barrier coatings ... 8 3.1.1 Coating process ... 9 3.1.2 Air permeance ... 10 3.1.3 SEM ... 10 3.2 Graphical Coatings ... 10 3.2.1 Coating process ... 11 3.2.2 Surface energy ... 11 3.2.3 Gloss measurements ... 12 3.2.4 Surface roughness ... 12 3.2.5 Strength ... 12 3.2.6 Ink setting ... 13

4 Results and discussion ... 14

4.1 Barrier coatings ... 14 4.1.1 Air permeance ... 14 4.1.2 SEM ... 17 4.2 Graphical Coatings ... 20 4.2.1 Surface energy ... 20 4.2.2 Gloss measurements ... 23 4.2.3 Surface roughness ... 24 4.2.4 Strength ... 24 4.2.5 Ink setting ... 26 5 Conclusions ... 29 6 Future work ... 30 7 Acknowledgment ... 31 References ... 32 Appendix I ... 33 Appendix II ... 38

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1 Introduction

Innventia AB is a world leader in research and development relating to pulp, paper, graphic media, packaging and biorefining. This work was carried out within the Paper Chemistry and Nanomaterials research group connected to Material Processes, one of three business areas of the company.

1.1 Background

Papers are coated in order to improve the properties of the surface, to improve printability and to include new functionalities like barriers for e.g. oxygen, water vapor and oil/grease. A coating formulation contains a high number of components, some of which are minerals and others are manufactured from petroleum. Sustainability is one of the most important issues today and research aimed for new materials based on renewable sources to replace traditional oil based products is important.

Today’s paper based packages have a barrier consisting of plastic and/or aluminum foil. The majority of engineered plastic materials used today are based on fossil raw materials. The use of conventional petroleum-based polymer products creates many potential problems due to their non-renewable nature and ultimate disposal. Wood-based polymers offer advantages with respect to sustainability and limited environmental impact. Nano-scale cellulose fibers are a promising material and of growing interest as an alternative to petro-based materials such as polyethylene (PE) and polyethylene terephthalate (PET), since nanocellulose films/coatings have been shown to have excellent mechanical and barrier properties. New energy-efficient methods for the manufacture of nanocellulose have recently been developed at Innventia AB.

1.2 Aim

This project aimed to evaluate nanocellulose (microfibrillated cellulose (MFC)) in paper coatings. Films made from this material have shown good oxygen barrier properties and high strength. Thus it is interesting to study the properties of coating layers containing this material in combination with minerals.

The first part of the project aimed to study if the barrier properties can be improved by increasing the diffusion pathway when minerals are added.

The second part was devoted to porous pigment coatings for print applications. The aim was to exclude or reduce petroleum based latex binder in the coating formulation, and evaluate the possibilities of MFC in the coatings. The coatings for print applications were evaluated with respect to properties that are important for printability in offset printing.

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1.3 Methods

The barrier properties of the MFC-based coated sheets were evaluated through air permeability measurements. These measurements are quick and easy. Since the barrier properties for oxygen is most important, it is desirable to measure oxygen transmission rate through the coated sheets. These measurements take much longer time and thereby it is not possible to do these measurements on all samples. But my expectation was to be able to measure oxygen transmission rate on some samples to assure that the oxygen transmission rate was proportional to the air permeability. Unfortunately, there were many problems with this equipment and I was not able to get any results. Thereby the barrier properties are only evaluated through air permeability measurements.

There are many properties of the coating affecting the printability, some of the most important properties will be evaluated in this work. These are the surface energy, the gloss, the roughness of the coatings, the strength and the offset ink setting.

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2 Theory

This work involved nanocellulose combined with minerals in coatings for improved barrier and printing properties. This section contains the theoretical background.

2.1 Microfibrillated Cellulose (MFC)

Cellulose is the most abundant polymer on Earth1, and the major reinforcing constituent of plant fiber cell wall. The Young’s modulus of the cellulose I crystal (the form found in nature) can be as high as 220 GPa.2 Cellulose is a linear homopolymer, composed of β-1,4-linked D-glucose rings, see Figure 1. Cellulose has several hydroxyl side groups that contribute to its hydrophilic behavior.

Figure 1. The repetitive unit of cellulose.3

The cellulosic chains are arranged in elementary fibrils that are partially crystalline, where the crystalline parts are held together by van der Waals forces and hydrogen bonding4. These fibrils are considered to be the most basic structure in a cellulosic fiber. The fibers are built-up of fibril aggregates, which are themselves composed of these elementary fibrils, see Figure 2. The aggregates are held together by an amorphous matrix consisting primarily of lignin and hemicelluloses.5

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The term “nanocellulose” or “microfibrillated cellulose” (MFC) refers to cellulosic fibrils mechanically disintegrated from plant cell walls. The first method for producing MFC was explored by Turbak et al.7 and Herrick et al.8 more than two decades ago. The MFC fibrils have a width between 5 to 20 nm and a length of up to several thousand nm, and therefore MFC is also referred to as nanocellulose3. The diameter depends on the plant source, pre-treatments of the pulp prior to distintegration9 and disintegration procedure.

Most important characteristics of MFC are rheology as well as fibril length. MFC have high aspect ratio and exhibit gel-like characteristics in water (see Figure 3) with pseudo plastic and tixotropic properties10. The viscosity is very high even at low MFC concentrations. Nanocellulose gels are also shear thinning, meaning that the viscosity is decreased with increased shear rate9.

Figure 3. Photo of a MFC gel at 2 wt.% (Innventia AB).

The MFC gel consists of strongly entangled and disordered networks of cellulose nanofiber1. When the MFC is dried into films, the fibrils forms a dense network held together by strong inter/intra-fibrillar bonds. That combined with the fact that the fibrils are partly non-permeable crystalline suggest that these films should have good barrier properties.3

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2.1.1 MFC Manufacture

MFC is generally manufactured by pressing cellulose fiber suspensions through a high pressure homogenizer that disintegrates the fibers into their sub-structural elementary fibrils. The first generation MFC was produced by the aid of a mechanical high-pressure homogenizer. The pulp fibers are pumped with high pressure in to the homogenizer valve, which is spring-loaded. As this valve opens and closes in rapid succession a large pressure drop with shearing and impact forces are created which delaminates the fibers and liberates the microfibrils, see Figure 4.11

Figure 4. The fibers are pressed through a slit formed between the valve seat and the preassurized homogenizer valve.10

Over the years many different delamination techniques have been developed, such as microfluidizers. With this method the fiber suspension is pumped through a Z-shaped chamber, where the fibers are forced through narrow slits under high pressure, see Figure 5.10

Figure 5. The fiber suspension is pumped through a Z-shaped chamber under high preasure conditions.10

This intensive mechanical treatment often involves several passes through the homogenizer equipment, and requires very high energy consumption; as high as 30 000 kWh/tonne12. Pre-treatment of the pulp to partly open up the fiber cell wall in combination with the homogenization process has decreased the energy consumption significantly.

Enzymatic pre-treatment is one method that can be used. The enzymes degrade the amorphous regions of cellulose, and this effect is enhanced by first mechanically refining the pulp so damaged zones are introduced in the cellulose. The nanofibers produced have a diameter of circa 10-20 nm and are usually over 1 µm in length.9 The MFC manufactured this

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way is called MFC generation 1. This enzymatic pre-treatment reduces the energy consumption with 93 % to 2000 kWh/tonne.

MFC generation 2 is manufactured from pulp pre-treated with carboxymethylation, which introduces charges to the surface of the fibers. The resulting electrostatic repulsive effect between surfaces of different fibrils facilitates the delamination process and also limits the aggregation of individual microfibrils. These microfibrils are somewhat smaller than generation 1, with a diameter between 5 to 15 nm13. The pre-treatment step can reduce the energy consumption with 93-98 % to 500-2000 kWh/tonne.

2.2 Barrier coatings

A package should provide protection and work as a barrier. Paperboard offers both mechanical strength and flexibility for the production of packages but lacks barrier properties and need to be surface treated to improve the functionality. This treatment of paperboards has been dominated by lamination with plastic materials, but in recent years, environmental aspects have become more important and fossil-based materials need to be replaced with environmentally friendly materials.

Exposure to oxygen can cause permanent changes in food quality and decrease the shelf-life of the product. Therefore, to prevent content from oxidation it is important to have very low oxygen permeability.

A barrier dispersion consisting of MFC can be applied using a coating technique. Filler can be added to the barrier polymer to reduce the price of the coating, to enhance the opacity, for mechanical reinforcement and to improve the barrier performance at high relative humidities (RH.s). The addition of fillers can increase or decrease the permeability, depending on the compatibility and adhesive properties between the polymer and the filler and also on their relative concentration. The barrier properties are, in general, improved by increasing the diffusion path length of the permeating species, see Figure 6.14

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Fillers with a high shape factor (ratio between width and height) are believed to have a significant impact on reducing the permeability of the matrix, compared to more blocky systems. This is due to at a constant coat weight, the tortuous path increase for minerals exhibiting high aspect ratio, see Figure 7.

Figure 7. The diffusion path increases using fillers with a high shape factor.

2.3 Pigment coatings for printing matters

The coatings for printing papers and board consist of pigments, binders and additives dispersed or dissolved in water. The main part of the coating color is pigment. In this work ground calcium carbonate (GCC) were used for the printing coatings, which is the most commonly used pigment in Europe. The coating color also normally contains latex, which works as a binder and binds the pigment particles to each other and to the substrate. The glass transition temperature, Tg, is an important parameter of the latex and affects the porosity and

stiffness of the coating layer. In order for the latex to work as a binder it must form a film, which is possible if the coated papers or boards are dried in a temperature higher than approximately Tg.

To get a high print quality the coating of the paper or board must cover the substrate and be homogenous. The print quality is determined by the surface structure and the way the ink interacts with the pore system of the coating layer. The strength of the coating can also be a critical parameter in some printing methods. Lithographic offset demands strong coatings, because the used inks are tacky, and expose the coating surface to a high delamination force. The final print result is also affected by variables like surface roughness, surface energies and the absorptions ability.15 16

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3 Experimental details

The experimental work was divided in two parts, the first was devoted to MFC in barrier coatings with mineral fillers. The second part considered MFC in pigment coatings for printing applications.

MFC gels used in this work:

 MFC generation 2, batch 104, Modo dissolving plus, 544 µekv/g  MFC generation 1, batch 105, Modo dissolving plus, low charge

The MFC was diluted to suitable concentration for coating operations with Milli-Q water. Some experiments were made without minerals, and in some experiments the mineral clays with high shape factor were added to the dispersion. In this part of the work, three different minerals from Imerys were used:

 Barrisurf HX, shape factor: 100 (Figure 8)  Barrisurf LX, shape factor: 60

 Mica WG 333, shape factor: unknown but probably >100

Figure 8. Barrisurf (Imerys)

During the experiments different amount of minerals was added, but the total concentration of MFC and minerals in the dispersion kept constant. The ratio of MFC to minerals are: 100:0, 95:5, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 10:90. The dispersion was stirred with a propeller stirrer at roughly 800 rpm for 45 minutes, (Figure 9).

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The base papers used were Korsnäs SF VIT N 120 g/m2, Hp home & office 80 g/m2, Hp everyday inkjet 80 g/m2, 4CC 130 130 g/m2 (Stora Enso), Avery Inkjet + laser paper 80 g/m2, Yes color copy 100 g/m2 and Tumba svenskt arkiv 80 g/m2.

3.1.1 Coating process

A laboratory rod coater (K Control Coater model K202) was used to apply the dispersion to the base paper with a constant speed, see Figure 10. Depending on which rod was used, different wet coating thickness was obtained, see Table 1. The papers were then dried restrained at room temperature.

The paper was weighed before and after the coating process and the coat weight was calculated from the weight difference.

Figure 10. The laboratory rod coater.

Table 1. Standard bars for K Control Coater. Close wound bars will produce a wet coating thickness from 6 to 120 µm. Higher coating weights up to 500 µm can be obtained using spirally wound bars.

Type

Number Wire diameter (mm) Wet film deposit (µm)

Close wound

1 0,08

6

2 0,15

12

3 0,31

24

4 0,51

40

6 0,76

60

8 1,27

100

9 1,50

120 Spirally wound

300 0,51

300

500

1

500

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3.1.2 Air permeance

The air permeance of the coated sheets was measured using a L&W Air Permeance Tester, with a measuring range covering 0.003 – 100 µm/Pa s, or L&W Air Permeance Tester, low range, with a measuring range covering 200 – 10 000 pm/Pa s, (Figure 11).

Figure 11. The air permeance tester. (Lorentzer & Wettre)

3.1.3 SEM

The surface characteristics were characterized by a scanning electron microscope.

3.2 Graphical Coatings

All coating colors were based on 100 parts per hundred (pph) pigment. The pre-dispersed pigment, grounded calcium carbonate (HYDROCARB HC 90) was stirred with a dissolver disk while 1 or 4 pph MFC generation 1 or generation 2 was added slowly in small portions and stirred at approximately 5000 rpm for 30 minutes. Then 0, 3, 5, 7 or 9 pph latex (DL 920) was added to the coating color and stirred with a propeller stirrer. One series coating color without MFC but with 0, 3, 5, 7 or 9 parts latex was also prepared. In these coating colors 0.5 pph carboxymethyl cellulose (CMC) was added as a thickener. Milli-Q water was added to reach a viscosity suitable for the coating process.

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3.2.1 Coating process

A laboratory rod coater (K Control Coater model K202) was used to apply the coating color to a base paperboard with a constant speed. The rod used gave a grammage (g/m2) of the dry coatings around 30 g/m2. The paperboards were dried in a hot oven at 105° C for 15 minutes.

3.2.2 Surface energy

The surface energy was calculated from the contact angle various liquid drops form with the surfaces. The contact angles were measured with FIBRO DAT 1100, an automatic device that gently places a drop of liquid on the substrate. Three different liquids were used; diiodomethane, water and ethylene glycol. For each substrate eight drops were measured, and a mean value was calculated. The contact angle of the droplet was recorded over time. The volume, height and base diameter was also reported as a function of time.

The contact angles generate a curve and the value of the contact angle used for calculating the surface energy was read from this curves. They are taken at different time depending on which liquid that was used. These times are determined from reference measurements on a plastic film. In present work, the contact angle used for calculating the surface energy was determined as the mean value out of 5 point on the curve when the drop had spread out to its static value. These times were for diiodomethane 0.06 – 0.1 s, for water 0.04 – 0.09 s, and for ethylene glycol 0.2 – 0.6 s. The volumes of the drops were 4 µl for water and ethylene glycol and 2 µl for diiodomethane.

The surface energy is composed of two additive components, one apolar and one polar. The surface energy was calculated from the contact angles obtained from all three liquids using the equations below.

θ symbolizes the contact angle. γl and γs are the surface tension of the liquid and the surface

energy of the solid, respectively. LW stands for Lifshitz-Van der Waals, and this part of the total surface energy is the apolar part, also referred as the dispersion part. γab is the Lewis acid-base part of the total surface energy (the polar part). Lewis acid character is symbolized by γ+

and Lewis basic character by γ-.

The surface energy was also calculated from only diiodomethane and water using the following equations.

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The superscripts d and p indicate dispersion part and polar part of the total surface energy respectively.

All substrates were conditioned in 23° C and 50 % relative humidity (RH) for at least 24 hours before the measurements.

3.2.3 Gloss measurements

The gloss of the coated substrates was measured with a Zehntner ZLR 1050 Instrument at three different angles, 20, 60 and 75 degrees. Three different measurements per sample were preformed and a mean value was calculated. The resulting value is in percentage, where 100 % is highest gloss and 0 % means no reflection at all.

All substrates were conditioned in 23° C and 50 % RH for at least 24 hours before the measurements.

3.2.4 Surface roughness

The roughness of the surface was analyzed with Parker-Print-Surf (PPS) technique. This technique measure the air flow that leaks out between the sample and the measurement area, which are translated into an average surface roughness in µm.

3.2.5 Strength

The surface strength was measured with IGT test (Figure 12). A disk coated with test oil was pressed against a strip of the sample attached to a drive wheel with a printing force of 350 N.

Figure 12. The IGT tester

The amount of oil on the disk was 13.7 ± 1.1 mg. The oil can have different viscosity; low, medium or high. The results of the test are expressed as a product of the oil viscosity and the velocity. During the test, the drive wheel was accelerated to a set final velocity. This means that the force applied to the surface is increases with distance along the sample strip. The location along the strip where the first picking occurs was determined. From that and the final velocity the picking resistance was calculated according to

Disk with oil Sample

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For each substrate ten different measurements were preformed and the mean value was calculated. All substrates were conditioned in 23° C and 50 % RH for at least 24 hours before the measurements.

3.2.6 Ink setting

The ink tack was studied with Ink Surface Interaction Tester (ISIT), a schematic picture is seen in Figure 13. The ink tack is the force of film splitting. These measurements were done on samples with 5, 7 or 9 pph latex, and 2 measurements were preformed for each sample.

Figure 13. The principal structure of ISIT.

A fixed amount of ink (cyan) was applied to the print disk using an IGT distributor. 100 ± 5 mg ink was applied to the roll on the IGT distributor and the ink application time from roll to print disk was 10 seconds. The test substrate was attached to the print cylinder with tape. The printing was performed at 0.5 m/s and with a printing force at 400 N.

A tack disk was then put in contact with the printed substrate with a controlled force of 8 N and the pulled away, see the stages of the experiment in Figure 14. The force at separation was recorded with time as a measure of the value of the ink tack.

Figure 14. The ink and paper in the stages in the ISIT experiment, the tack disk is pressed against the printed paper, and when pulled away a split occurs.17

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4 Results and discussion

In this section the results are presented and discussed. Again, the work was divided in two parts, barrier and print coatings.

The barrier properties of the coated papers were analyzed by measuring the air permeability. Some surfaces were also characterized with scanning electron microscope (SEM).

4.1.1 Air permeance

The air permeability of the MFC coated paper (4CC from Stora Enso) as a function of MFC dispersion concentration during coating is shown in Figure 15. MFC generation 1 (batch 105) and MFC generation (batch 104) was used, and the used rod is rod number 9.

0.0001 0.001 0.01 0.1 1 10 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 % MFC µ m /P a s MFC gen 2 MFC gen 1

Figure 15. Air permeability (logarithmic scale) as a funtion of the amount of MFC in the coating.

The MFC concentration during coating affects the air permeability properties. At too high concentration, the viscosity of the dispersion is too high and the coating does not spread out to cover the paper homogeneously. The barrier properties deteriorate most likely due to pinholes formed in the coating layer. The air permeability decreases with decreased amount of MFC. When the viscosity is too low, it is difficult to obtain even coatings, thus affecting the barrier properties. The barrier properties were found optimal at a total concentration of circa 1.2 % MFC for generation 2 and 1.8 % for generation 1, respectively. The difference is due to that the viscosity is higher for generation 2. Figure 15 clearly shows a superior barrier performance of sheets coated with MFC generation 2. These results are most likely linked with an extremely dense structure formed by the carboxymethylated high-charged nanofibrils. The fibril size of generation 2 is smaller than generation 1 MFC, which can explain the difference in barrier properties of the coated sheets.

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The air permeability of the coated paper as a function of the coat weight of MFC is shown in Figures 16 and 17. 0 1 2 3 4 5 6 7 8 0 2 4 6 g/m^2 µ m /P a s

Figure 16. Air permeability as a function of Figure 17. Air permeability (logarithmic scale) coat weight for MFC generation 1. a function of coat weight for MFC generation 2.

For the uncoated 4CC paper, the air permeability was measured to 4.8 µm/Pa s. When the coat weight of MFC generation 2 was increased slightly the air permeability decreased dramatically. For a coat weight for MFC generation 2 of 1.3 g/m2, the air permeance was very low, 0.0006 µm/Pa s. For the coatings with MFC generation 1 the decrease in air permeability is accompanied only with higher coat weights (> 2 g/m2). For a coat weight of 5.8 g/m2 the air permeability is measured to 0.13 µm/Pa s. For lower coat weight for MFC generation 1 the barrier properties is unaffected, or even deteriorated, due to an unknown reason at present. The barrier properties were affected not only by the coat weight, viscosity and the generation of MFC, but also by the type of base paper. Table 2 shows the result from air permeability measurements on different papers. The different result for the different papers can probably be due to the differences in the surface roughness. The air permeability of the uncoated sheets is linked with the porosity in the sheets. Applying MFC decreases the air permeability, which is most significant for MFC generation 2 since the carboxymetylathed MFC most properly forms a denser structure.

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Table 2. Air permeability depending on the type of base paper. Coat weight of the coatings is circa 2 g/m2 (rod number 9 was used). Uncoated [µm/Pa s] MFC gen. 1 [µm/Pa s] MFC gen. 2 [µm/Pa s] Korsnäs SF VIT N 120 g/m2 2.6 2.0 0.0005

Hp home and office 80 g/m2 11.8 2.7 0.0003

Hp everyday inkjet g/m2 11.4 6.6 0.0006

4CC 130 g/m2 4.8 5.2 0.0001

Avery Inkjet + laser paper 80 g/m2 12.5 5.0 0.0006

Yes color copy 100 g/m2 4.3 6.3 0.0004

Tumba svenskt arkiv 80 g/m2 1.2 0.6 0.0001

The air permeability for the MFC-coated papers with incorporated mineral fillers was measured. The air permeability as a function of % Barrisurf LX added is shown in Figure 18. The air permeability seems to be rather independent of the amount of mineral added to the MFC-based coating formulation.

0 1 2 3 4 5 6 0 20 40 60 80 100 % Barrisurf LX µ m /P a s MFC gen 1 + BLX MFC gen 2 + BLX

Figure 18. Air permeability as a function of the amount of Barrisurf LX.

A series of samples with three minerals at different concentrations were measured. The results showed that the best barrier properties were obtained when MFC generation 2 was used in combination with the fillers, see Figure 19. The air permeability measured for these coatings was very low, sometimes outside the measuring range of the permeability tester. The air permeability is equally low regardless on which minerals were incorporated into the MFC-coating.

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17 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 10 20 30 40 50 60 70 80 % minerals µ m /P a s

MFC gen 2 + Mica MFC gen 2 + BLX MFC gen 2 + BLX

Figure 19. Air permeability as a function of the amount of minerals.

The air permeability increased slightly when the amount of minerals increased over ca. 60 %. This result might be linked with a decreased viscosity of the coating formulation, therefore resulting in an uneven coating of the sheets and higher air permeability.

4.1.2 SEM

The surface structure of the MFC-coated papers was studied using SEM. The resulting micrographs are showed in Figure 20, 21, and 22. The uncoated paper (Figure 20a) shows an open network of fibers. MFC generation 1-coated papers are shown in Figures 20b och 20c. At a coat weight of 2 g/m2 (figure 20b), the network is still open and apparent. When the coat weight increased to ca. 6 g/m2 (figure 20c), the network structure became less apparent and a continuous MFC film was formed. Since the MFC generation1-coating did not cover the fibers completely at coat weight at 2 g/m2, the air permeability of these coatings was not improved compared to uncoated papers.

MFC generation 2-coated papers are shown in Figure 20d and 20e. When the coat weight increased slightly (1.3 g/m2), the network structure of the paper became less apparent (figure 20d). When the coating increased further (4.7 g/m2) a thin film of MFC formed, and the fiber structure in the base paper is hardy visible (figure 20e). The papers coated with MFC generation 2 exhibits a more dense coating, which correlates well with the air permeability measurements.

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Figure 20. SEM micrographs of uncoated 4CC paper (A), MFC-coated papers with MFC generation 1, coat weight of ca. 2 g/m2 (B) and 6 g/m2 (C), and MFC-coated papers with MFC generation 2, coat weight of ca. 1.3 g/m2 (D) and 4.7 g/m2 (E).

Figure 15 show that the MFC concentration during coating affects the air permeability properties. The coating with MFC gen. 1 dispersion at 1.2 % (Figure 21b) can be compared with the MFC coating with concentration of 1.8 % (figure 21c). The fiber network is apparent in both cases, but at a concentration of 1.8 % film partly covered the base paper.

The coating with MFC generation 2 concentration of 0.4 % (Figure 22b) can be compared with the MFC coating with concentration of 1.2 % (figure 22c). Again, the fiber network of the base paper is apparent, but slightly more covered when coating with higher MFC concentration was used.

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Figure 21. SEM micrographs of uncoated 4CC paper (A), MFC-coated papers with MFC generation 1 with concentration of 1.2 % (B) and concentration of 1.8 % (C).

Figure 22. SEM micrographs of uncoated 4CC paper (A), MFC-coated papers with MFC generation 2 with concentration of 0.4 % (B) and concentration of 1.2 % (C).

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4.2 Graphical Coatings

The print coatings were evaluated using contact angle, gloss measurements, surface roughness, surface strength and ink setting.

4.2.1 Surface energy

The surface energy was calculated from the contact angles. The value for the contact angle was read from the resulting graphs when the droplet had spread out to its static value. These times were determined from the reference measurements on the plastic film, see Figures 23 - 25. The curves reached a static value after 0.04 seconds with water, 0.06 seconds with diiodomethane and 0.2 seconds for ethylene glycol.

0.5 1 1.5 2 2.5 3 3.5 4 4.5 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 time [s]

Volume Base Height

Figure 23. The volume, height and base diameter of the drop as a function of time. The liquid was water and the substrate was a plastic film.

0 0.5 1 1.5 2 2.5 3 3.5 0.02 0.04 0.06 0.08 0.1 0.12 time [s]

Volume Base Height

Figure 24. The volume, height and base diameter of the drop as a function of time. The liquid was diiodomethane and the substrate was a plastic film.

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21 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 0.2 0.4 0.6 0.8 1 time [s]

Volume Base Height

Figure 25. The volume, height and base diameter of the drop as a function of time. The liquid was ethylene glycol and the substrate was a plastic film.

The contact angles obtained for calculating the surface energies are collected in Table 3, the graphs are collected in Appendix I. The calculated surface energies are collected in Table 4. Table 3. The contact angles between the coated surface and water, diiodomethane and ethylene glycol respectively.

Water [°] Diiodomethane [°] Ethylene glycol [°]

0 pph MFC 0 pph latex 18 ± 0,9 23 ± 0.4 22 ± 1.5 0 pph MFC 3 pph latex 62 ± 3.0 25 ± 1.1 36 ± 4.9 0 pph MFC 5 pph latex 76 ± 1.3 27 ± 1.5 46 ± 4.6 0 pph MFC 7 pph latex 88 ± 0.9 30 ± 1.7 54 ± 3.9 0 pph MFC 9 pph latex 84 ± 0.6 33 ± 1.3 56 ± 3.7 1 pph MFC 0 pph latex 21 ± 2.0 25 ± 0.4 22 ± 1.7 1 pph MFC 3 pph latex 84 ± 1.4 26 ± 0.8 37 ± 4.7 1 pph MFC 5 pph latex 94 ± 0.5 27 ± 1.1 42 ± 4.5 1 pph MFC 7 pph latex 95 ± 0.05 30 ± 1.4 52 ± 4.3 1 pph MFC 9 pph latex 96 ± 0.2 34 ± 1.4 58 ± 3.8 4 pph MFC 0 pph latex 17 ± 2.1 21 ±0.7 18 ± 2.6 4 pph MFC 3 pph latex 62 ± 4.0 22 ± 1.1 28 ± 6.1 4 pph MFC 5 pph latex 90 ± 1.0 24 ± 1.9 43 ± 5.2 4 pph MFC 7 pph latex 96 ± 0.7 27 ± 2.0 50 ± 5.0 4 pph MFC 9 pph latex 106 ± 2.3 28 ± 2.2 64 ± 3.9

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Table 4. The surface energies and acid base parameters estimated in 2 different ways, from all 3 liquids and from only water and diiodomethane. The unit is mJ/m2.

γ LW γ -γ + γ ab γ TOT γ d γ p γ TOT 0 pph MFC 0 pph latex 46.9 27.9 5.9 25.7 72.6 46.9 29.8 76.7 0 pph MFC 3 pph latex 46.1 7.6 2.4 8.6 54.8 46.1 9.3 55.5 0 pph MFC 5 pph latex 45.6 3.0 0.9 3.3 48.9 45.6 3.6 49.2 0 pph MFC 7 pph latex 44.4 0.7 0.3 0.8 45.2 44.4 0.9 45.3 0 pph MFC 9 pph latex 42.9 1.7 0.3 1.6 44.4 42.9 1.7 44.7 1 pph MFC 0 pph latex 46.0 27.2 6.1 25.7 71.7 46.0 29.5 75.5 1 pph MFC 3 pph latex 45.7 0.4 1.2 1.5 47.2 45.7 1.6 47.3 1 pph MFC 5 pph latex 45.5 0.1 0.6 0.5 46.0 45.5 0.09 45.6 1 pph MFC 7 pph latex 44.3 0 0.2 0.03 44.4 44.3 0.08 44.4 1 pph MFC 9 pph latex 42.6 0.03 0.07 0.09 42.7 42.6 0.09 42.7 4 pph MFC 0 pph latex 47.4 27.6 6.2 26.1 73.5 47.4 29.9 77.3 4 pph MFC 3 pph latex 47.1 6.3 2.9 8.6 55.7 47.1 8.9 56.0 4 pph MFC 5 pph latex 46.6 0.03 0.6 0.3 46.9 46.6 0.4 47.0 4 pph MFC 7 pph latex 44.2 0.02 0.2 0.1 44.4 44.2 0.06 44.3 4 pph MFC 9 pph latex 44.7 2.05 0.2 1.4 46.1 44.7 0.4 45.1

The polar contribution to the surface energy, γ ab or γ p, is rather low for the coatings with higher amount of latex. This calculated value was high for the coatings without latex, but it needs to be considered that these coatings absorbed the drop very fast, making it difficult to measure the real value of the contact angle, meaning that this value may not be completely correct. It was obvious that the water drop was not absorbed by the coating as easily when only a small amount of latex was added to the pigment color.

The amount of latex affects the surface energy of the coatings. The contact angle of diiodomethane increased slightly with increased amount of latex, indicating that the dispersive part of the surface energy decreases with increased amount of latex. When the amount of latex increases the contact angle for both water and ethylene glycol increased as well, indicating that the surfaces become more hydrophobic.

The total surface energies decreased with increased amount of latex, but they are generally relatively high. It can for example be compared to polyethylene, which has low surface energy at 33 mJ/m2. A high surface energy is preferable for printing with waterborne ink to enhance the adhesion of the ink.

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4.2.2 Gloss measurements

The resulting value is an average from 3 measurements, collected in Tables 5 - 7. Table 5. The gloss for the coatings with 4 pps MFC.

4 MFC 0 latex 4 MFC 3 latex 4 MFC 5 latex 4 MFC 7 latex 4 MFC 9 latex

20° 60° 75° 20° 60° 75° 20° 60° 75° 20° 60° 75° 20° 60° 75°

1.8 2.7 3.7 1.7 2.7 3.8 1.7 2.7 3.9 1.7 2.7 4.1 1.7 2.7 4.3

Table 6. The gloss for the coatings with 1 pps MFC.

20° 60° 75° 20° 60° 75° 20° 60° 75° 20° 60° 75° 20° 60° 75°

2.1 8.9 23.9 1.8 6.1 17.9 1.8 5 15 1.8 4.2 12.8 1.8 4 12.6

Table 7. The gloss for the coatings with no MFC.

20° 60° 75° 20 ° 60° 75° 20 ° 60° 75° 20° 60° 75° 20° 60° 75° 2.3 20.1 54.3 2 15.3 48.8 2 13.5 46.3 1.8 11.2 42.2 1.8 9.3 39.5

The gloss value is very low (the value is in percentage, where 100 % is highest gloss and 0 % means no reflection at all), meaning that the coatings had very low reflectance and were not glossy. The amount of MFC affected the gloss, when the amount of MFC increased, the gloss value decreased drastically. The coatings with 4 pph MFC obtained very low values for all three angles. It was also obvious that the values decreased with increased amount of latex.

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4.2.3 Surface roughness

The results are collected in Table 8. Table 8. The roughness of the coatings.

Roughness [µm] 0 pph MFC 0 pph latex 1.69 0 pph MFC 3 pph latex 1.77 0 pph MFC 5 pph latex 0.992 0 pph MFC 7 pph latex 0.977 0 pph MFC 9 pph latex 1.04 1 pph MFC gen 1, 3 pph latex 1.66 1 pph MFC gen 1, 5 pph latex 1.39 1 pph MFC gen 1, 7 pph latex 2.60 1 pph MFC gen 1, 9 pph latex 1.78 4 pph MFC gen 1, 3 pph latex 5.84 4 pph MFC gen 1, 5 pph latex 5.65 4 pph MFC gen 1, 7 pph latex 5.57 4 pph MFC gen 1, 9 pph latex 5.49 1 pph MFC gen 2, 3 pph latex 3.32 1 pph MFC gen 2, 5 pph latex 3.06 1 pph MFC gen 2, 7 pph latex 2.63 1 pph MFC gen 2, 9 pph latex 2.37 4 pph MFC gen 2, 3 pph latex 5.81 4 pph MFC gen 2, 5 pph latex 5.96 4 pph MFC gen2, 7 pph latex 6.30 4 pph MFC gen 2, 9 pph latex 6.55

The roughness levels are high and increased with increased amount of MFC. When small amounts (1 pph) were added, the coatings with generation 1 was smother than the coatings with generation 2, but when more MFC were added (4 pph) the coatings obtained about the same roughness for both MFC generation 1 and generation 2, but somewhat higher for generation 2.

The MFC gel was not completely homogenous and consisted of bundles of nanofibers. Due to this, the coatings were not completely homogenous, there were some spots of MFC aggregates in the coating, leading to a higher roughness of the surface.

4.2.4 Strength

The measurements on the both cases with MFC generation 1 and generation 2 were done with the oil with medium viscosity. The calculated picking resistance for coatings with MFC generation 2 and MFC generation 1 are represented in Figure 26 and Figure 27 respectively.

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25 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 1 2 3 4 5 6 7 8 9 10 pph latex p ic k in g re s is ta n c e [m /s ] 4 pph MFC gen.2 1 pph MFC gen.2 0 pph MFC

Figure 26. The picking resistance is the strength of the surface on the board coated with MFC generation 2 and latex.

In the measurements on the substrates with 0 parts MFC and 5, 7 or 9 pph latex, and on the substrates with 1 pph MFC and 7 or 9 pph latex, the delamination occurred in the base board before any picking in the coating occurred, and thereby these coatings are definitely strong enough. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 1 2 3 4 5 6 7 8 9 10 pph latex p ic k in g r e s is ta n c e [ m /s ] 4 pph MFC gen.1 1 pph MFC gen.1 0 pph MFC

Figure 9. The picking resistance is the strength of the surface on the board coated with MFC generation 1 and latex.

The final velocity in the measurements on coatings with MFC generation 1 needed to be lower than for those containing generation 2. The final velocity was 0.5 m/s and 1 m/s respectively. In theory this should not affect the calculated picking resistance, but in reality, it has some influence. It shows for the result for the coating with 0 pph MFC. The picking resistance was 0.42 m/s when the final velocity was 1 m/s and 0.32 m/s when the final velocity was 0.5 m/s. However, it is obvious that the coatings with MFC generation 2 are stronger than those containing generation 1. And again the measurements on the substrates

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without MFC and 5, 7 or 9 pph latex gave delamination in the base board and the coatings were therfore strong enough.

Coatings without latex were very weak, the picking started immediately and all the coating was torn off. When the amount of latex increased the picking resistance and strength increased, in a linear relation. For the coatings with 1 pph MFC generation 1 and 3 or 5 pph latex, did the picking started very early, and because of that, there is an uncertainty in the calculated picking resistance for these coatings. This could explain why these points are not on a straight line like the others.

In both cases the coatings became weaker when MFC was added to the color. The force applied to the surface in these tests is dependent on the thickness of the oil layer, and if the coating become very dense when MFC is added, the oil cannot penetrate the coating, resulting in a thicker layer of oil and a different force applied on these coatings. This affects the result and gives a difference in the calculated picking resistance.

4.2.5 Ink setting

The measurements were performed on the coatings with 5, 7 or 9 pph latex, but due to weaknesses in some coatings, some measurements were not successful and no result was collected for these samples.

The force at separation was recorded. The ink tack is due to the binders in the ink film and its value depends on the amount of solvent (ink oil). When the amount of ink oil decreases due to its absorption into the coating the tack value increases and reaches a maximum value. Then the ink film becomes less tacky when more oil is redrawn from the ink film. The curves of tack force against time for the coatings with 0 pph MFC have the typical appearance for a tack force curve, see the tack force curve for coatings with 0 pph MFC and 5 pph latex in Figure 28. (All tack force curves are collected in Appendix II.)

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27 0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 time [s] T a c k f o rc e [ N ] 0 pph MFC, 5 pph latex

Figure 28. The tack force as a function of time.

The setting time is the time it takes before the ink gets so dry that it does not causes set-off, and it is normally when the tack curve reaches 5 N on the decay part of the curve. The setting time and the maximum tack force for the samples without MFC are collected in Table 9. Table 9. Ink setting characteristics. The maximum tack force and the setting time (the time it takes to reach 5N).

Maximum tack force [N] Setting time [s]

0 pph MFC, 5 pph latex 8.9 ± 0.2 69 ± 15

0 pph MFC, 7 pph latex 9.3 ± 0.02 105.5 ± 20

0 pph MFC, 9 pph latex 9.3 ± 0.1 211.5 ± 19

For the coatings containing MFC, the maximum tack force decreased and the resulting curves did not reach or just reach 5 N. Thereby the setting time when it reach 5 N on the decay part of the curve is not a good way to evaluate the results. Instead the time to reach 1.5 N was chosen, which was just before the curves level out, for example see the tack force curve for 1 pph MFC generation 2 and 5 pph latex in Figure 29.

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28 0 1 2 3 4 5 6 0 20 40 60 80 100 120 140 160 time [s] T a c k f o rc e [ N ] 1 pph MFC gen 2, 5 pph latex

Figure 29. The tack force as a function of time.

The time to reach 1.5 N on the decay part of the curve, and the maximum tack force for all samples are collected in Table 10.

Table 10. Ink setting characteristics. The maximum tack force and the time it took to reach 1.5 N.

Maximum tack force [N] Time to reach 1.5 N [s]

0 pph MFC, 5 pph latex 8.9 ± 0.2 69 ± 15 0 pph MFC, 7 pph latex 9.3 ± 0.02 105.5 ± 20 0 pph MFC, 9 pph latex 9.3 ± 0.1 211.5 ± 19 1 pph MFC gen 2, 5 pph latex 5.7 ± 0.3 23 ± 5.3 1 pph MFC gen 2, 7 pph latex 5.3 ± 0.4 65.3 ± 19 1 pph MFC gen 2, 9 pph latex 5.6 ± 0.08 73 ± 21 1 pph MFC gen 1, 9 pph latex 6.3 ± 0.6 25.2 ± 0.6 4 pph MFC gen 1, 7 pph latex 3.8 ± 0.06 10.8 ± 1.06 4 pph MFC gen 1, 9 pph latex 3.6 ± 0.06 16.2 ± 2.0

The maximum tack force decreased when the amount of MFC increased. The splitting occurs at the weakest link, which could be either cohesive in the ink or the coating, or adhesive at any interface. In normal cases the splitting should be cohesive in the ink, but if, as in this case, the coatings are weaker, the splitting probably occured both in the ink, in the interface between the ink and the coating, and in the coating. This explains why the maximum tack force decreased for the coatings containing MFC.

The setting time, or the time to reach 1.5 N became longer when the amount of latex increased. The setting time is dependent on the properties of the ink, and the absorption ability of the paper. The time to reach 1.5 N is also affected by the amount of MFC, when the amount of MFC increases, the time to reach 1.5 N is shorter. This means that when the amount of MFC is increasing, the absorption ability increases.

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5 Conclusions

Papers coated with MFC generation 2 shows excellent barrier properties already at very low coat weights. For coatings with MFC generation 1 the barrier properties are unaffected, or even deteriorated unless the coat weight is very high. The air permeability decreased even at low coat weights when MFC generation 2 was used. MFC generation 2 forms much denser film structure upon coating.

Addition of minerals did not enhance the barrier properties of the coatings. However, it was shown that high amounts of minerals could be added without reducing the barrier properties. This means that minerals could be added to the coating to lower the viscosity of the coating dispersion and thereby lower the cost of the coating process, and without any significant changes of the good barrier properties of MFC-coated papers.

The print quality depends on how the ink interacts with coating. These pigment coatings did have a relatively high surface energy, which is preferable for printing with waterborne ink. It was also shown that the absorption abilities increased when the amount of MFC was increased. However, MFC in coating colors did not in present work improve the printability in offset printing. Offset printing demands high surface strength. And despite the fact that MFC itself has very high strength, when added to coating colors with pigment and latex binder, the surface strength of the coatings become too weak. MFC does not seem to be compatible with the latex, and cannot be added to the coating color with this composition. More work need to be done to completely determined if MFC can improve printability.

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6 Future work

 Oxygen transmission rate on barrier coatings to confirm that it is proportional to the air permeability.

 Oxygen transmission rate on barrier coatings at different humidity to see if the addition of mineral clays decreases the moist sensitivity of the MFC coatings.

 Evaluate the printability for another print method that does not have as high demands on surface strength.

 Improve the preparation of coating color with MFC so it gets more homogeneous and evaluate if this aggregation of MFC in the coatings affects the surface strength.

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7 Acknowledgment

I would like to thank Innventia AB for the opportunity to perform my Master Thesis at their institution. A special thanks to my supervisors Christian Aulin and Göran Ström for all guidance and support during this project.

Futher, I would like to thank everyone at Innventia for giving me help and support. A special thanks to Anne-Chatrine Hagberg for all your guides and help in the printability lab. Thanks to Jolanta Borg for helping me with the PPS-measurements.

I would also like to thank my examiner Thomas Ederth for the helpful discussion during the work.

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References

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(2009). Nanocelluloses: A new Family of Nature-Based materials. Green nanomaterials.

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Appendix I

This appendix collects all the curves for the contact angles with the different liquids water, ethylene glycol and diiodomethane.

0 20 40 60 80 100 120 0 5 10 15 20 25 time [s] C o n ta c t a n g le w it h w a te r [° ]

0 pph MFC, 0 pph latex 0 pph MFC, 3 pph latex 0 pph MFC, 5 pph latex 0 pph MFC, 7 pph latex 0 pph MFC, 9 pph latex

Figure 27 The contact angle with water.

0 20 40 60 80 100 120 0 5 10 15 20 25 time [s] C o n ta c t a n g le w it h w a te r [° ]

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34 0 20 40 60 80 100 120 0 5 10 15 20 25 time [s] C o n ta c t a n g le w it h w a te r [° ]

Figure 29 The contact angle with water.

0 10 20 30 40 50 60 70 80 90 0 5 10 15 20 25 time [s] C o n ta c t a n g le w it h e th y le n g ly c o l [° ]

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35 0 10 20 30 40 50 60 70 80 90 0 5 10 15 20 25 time [s] C o n ta c t a n g le w it h e th y le n g ly c o l [ °]

Figure 31 The contact angle with ethylene glycol.

0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 time [s] C o n ta c t a n g le w it h e th y le n g ly c o l [ °]

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36 0 5 10 15 20 25 30 35 40 45 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 time [s] C o n ta c t a n g le w it h d ii o d o m e th a n e [° ]

Figure 33 The contact angle with diiodomethane.

0 5 10 15 20 25 30 35 40 45 50 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 time [s] C o n ta c t a n g le w it h d ii o d o m e th a n e [ °]

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37 0 10 20 30 40 50 60 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 time [s] C o n ta c t a n g le w it h d ii o d o m e th a n e [ °]

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Appendix II

The tack force curves from ISIT are collected in this appendix.

0 1 2 3 4 5 6 0 50 100 150 200 time [s] T a c k f o rc e [ N ]

I pph MFC gen 2, 9 pph latex, #1 I pph MFC gen 2, 9 pph latex, #2

Figure 36 The tack force as a function of time.

0 1 2 3 4 5 6 0 50 100 150 200 time [s] T a c k f o rc e [ N ]

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39 0 1 2 3 4 5 6 7 0 50 100 150 200 time [s] T a c k f o rc e [ N ]

0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 500 600 time [s] ta c k f o rc e [ N ] 0 pph MFC, 9 pph latex, #1 0 pph MFC, 9 pph latex, #2

(46)

40 0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 500 600 time [s] T a ck fo rce [ N ] 0 pph MFC, 7 pph latex, #1 0 pph MFC, 7 pph latex, #2

0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 500 600 time [s] T a c k f o rc e [ N ] 0 pph MFC, 5 pph latex #1 0 pph MFC, 5 pph latex #2

Nanocellulose in pigment coatings : Aspects of barrier properties and printability in offset

Department of Physics, Chemistry and Biology

Master's Thesis

Nanocellulose in pigment coatings

- Aspects of barrier properties and printability in offset

Sofie Nygårds

2011-06-07

LITH-IFM-A-EX--11/2533--SE

Department of Physics, Chemistry and Biology

Nanocellulose in pigment coatings

- Aspects of barrier properties and printability in offset

Sofie Nygårds

Thesis work done at Innventia AB, Stockholm

2011-06-07

Supervisor

Christian Aulin and Göran Ström, Innventia

Examiner

Thomas Ederth

Abstract

Sammanfattning

Table of contents

1 Introduction

2 Theory

3 Experimental details

Type

Number Wire diameter (mm) Wet film deposit (µm)

Close wound

1

0,08

6

2

0,15

12

3

0,31

24

4

0,51

40

6

0,76

60

8

1,27

100

9

1,50

120

Spirally wound

300

0,51

300

500

1

500

4 Results and discussion

5 Conclusions

6 Future work

7 Acknowledgment

References

Appendix I

Appendix II