AU2016203734A1

AU2016203734A1 - Paper sheet and a process for the manufacture thereof

Info

Publication number: AU2016203734A1
Application number: AU2016203734A
Authority: AU
Inventors: Andrew Conn
Original assignee: Opal Packaging Australia Pty Ltd
Current assignee: Opal Packaging Australia Pty Ltd
Priority date: 2015-06-03
Filing date: 2016-06-03
Publication date: 2016-12-22
Anticipated expiration: 2036-06-03
Also published as: AU2016203734B2; NZ720850A

Abstract

The present invention relates to a paper sheet and a process for making the paper sheet in which the paper sheet includes nano particles. 7809702_1 (GHMatters) P103274.AU 3/06/16 -7-7 fo2 Al ~

Description

1 2016203734 03 Jun2016

PAPER SHEET AND A PROCESS FOR THE MANUFACTURE THEREOF FIELD OF THE PRESENT INVENTION 5 The present invention relates to a paper sheet and a process of making the paper sheet. In particular, the present invention relates to a paper sheet having improved performance, such as any one or a combination of improved bending stiffness, or improved creep resistance to buckling under cyclic or high 10 humidity conditions.

BACKGROUND

The bending stiffness and creep resistance of a sheet of paper is dependent on a number of factors including the weight (or 15 grammage of the paper), the type of fibres used and the amount of starch added to the sheet. For example, the paper sheets used to produce paper based packaging typically have a starch content in the range from 5 to 10%wt. Both chemically modified and unmodified starches can be used to improve the stiffness and 20 strength of paper.

Depending on the product being produced, silicon or compositions containing silicon acting as sizing agents may also be added to increase the hydrophobicity of the paper. The starch material together with the sizing agents help to give the necessary 25 stiffness.

Once the paper sheet has been fully formed and dried, the sheet may also be treated in a coating process to enhance the visual appearance of the sheet, or to laminate the sheet to other materials. For instance, polymeric films and metallised foils 30 have been laminated to the sheet, and in other instances clay has been applied to the outer face of the sheet to form a smooth high gloss surface. The clay may also contribute significantly to the weight of the sheet. 7809702_1 (GHMatters) P103274.AU3/oe/ie 2 2016203734 03 Jun2016

In essence, the clay coating forms a layer in a laminate structure in which the clay coating essentially forms the outer surface of the sheet.

5 SUMMARY OF THE PRESENT INVENTION

The present invention is based on the realisation that nanoparticles can be incorporated in the sheet which can: i) increase the stiffness of the sheet; ii) improve creep resistance of the sheet particularly in cyclic or high humidity 10 environments, and iii) increase hydrophobicity or the moisture barrier property of the sheet.

In one embodiment of the invention relates to a paper sheet including a base material and nano-particles that are bonded to the base material. In a first example, the base material may 15 include any one or a combination of: starch material, cellulosic material, and fibrous material.

In a second example, the base material may include starch material.

In a third example, the base material may include cellulosic 20 material.

In a fourth example, the base material may include fibrous material.

Another embodiment of the invention relates to a paper sheet including nano-particles that can bond to any one or a 25 combination of: starch of the paper sheet, cellulose of the paper sheet, and fibre of the paper sheet.

The bond between the nano-particles and the starch, the cellulose, or the fibre may be in the form of physical bonding, but is ideally a chemical bond. 30 Without wanting to be limited by theory, it is believed that the nano-particles may occupy spaces or voids in the sheet and/or starch coating and thereby define a tortuous path by which moisture is required to take in order to reach the inner core of 7809702_1 (GHMatters) PI03274.AU 3/06/16 3 2016203734 03 Jun2016 the sheet. As a result, one the properties changed is that the sheet may exhibit an increase in the hydrophobicity or the moisture barrier property of the sheet. In addition, the nanoparticles can occupy spaces that would otherwise be voids. 5 Occupying the voids can limit the mobility of the matrix of starch, cellulose and fibre of the paper sheet. It is believed that restricting the matrix mobility on this scale can increase the stiffness and creep resistance of the paper sheet.

Throughout this specification, the term "paper sheet" may refer 10 to any fibrous or cellulosic containing material and embraces material including a single ply, multiple plies and other laminated structures. The term "paper sheet" therefore embraces corrugated medium that has been corrugated, corrugated medium prior to being corrugated, namely a flat planar sheet, and paper 15 layers joined together, and optionally joined to non-paper materials such as polymeric film, metallic foil, coatings of wax and so forth.

The nano-particles may include any one or a combination of clay nano-particles and cellulose nano-particles. 20 Cellulose nano-particles or derivatives thereof including: nanocrystalline cellulose, cellulose nanocrystals, cellulose whiskers, nanofubrillated cellulose, cellulose nanofibrils, microfibrillated cellulose, carboxymethylated cellulose, microcrystalline cellulose, and cellulose filaments. 25 Examples of other nano-particles that may be present in the paper sheet include graphite or graphene platelets, carbon nanotubes, and ZnO or Ti02 nano-particles.

In one embodiment, the nano-particles may be in the form of clay nano-particles only. 30 Irrespective of whether the clay nano-particles are in combination with other nano-particles or not, ideally, the clay nano-particles are present in the paper sheet at a weight in the range of 2.0 to 20.0gsm, and suitably 4.0 to lOgsm. 7809702_1 (GHMatters) P103274.AU 3/06/16 4 2016203734 03 Jun2016

In another embodiment, the nano-particles may be in the form of cellulose nano-particles only.

In yet another embodiment, the nano-particles may include clay nano-particles in combination with the other nano-particles 5 while cellulose nano-particles are absent.

In yet another embodiment, the nano-particles may include cellulose nano-particles in combination with other nanoparticles while clay nano-particles are absent.

The nano-particles may have a size in the range of equal to, or 10 less than 500nm, and even more suitably the nano-particles may have a size in the range of equal to or less than lOOnm.

The nano-particles may have any suitable shape.

In one embodiment, the nano-particles may be platelets. The platelets may have a thickness in the range of 1 to 5nm, and 15 suitably approximately lnm, and a diameter in the range of 0.1 to ΙΟμιη.

In one embodiment, the platelets may be clay platelets. The clay nano-particles may have a platelet shape and may have the size ranges mentioned above. 20 Any combination of clay nano-particles, cellulose nano-particles and starch may be included in the paper sheet. For instance, the nano-particles may include from 0% to 100% clay nanoparticles and from 100% to 0% cellulose nano-particles, and any mix in between. By way of example, the weight ratio of clay 25 nanoparticles and cellulose nanoparticles may be in the ranges of 10 to 90 : 90 to 10 respectively. Specifically, the weight ratio of clay nanoparticles to cellulose nanoparticles may be any one of 50:50, 40:60, 30:70, 20:80, 60:40, 70:30 and 80:20 respectively. 30 The nano-particles, and especially clay nano-particles, provide the synergistic benefit of increased cyclic or high humidity creep resistance, stiffness and possibly the fail strength by forming bonds to starch and/or cellulose, and improving the 7809702_1 (GHMatters) P103274.AU3/oe/i6 5 2016203734 03 Jun2016 moisture barrier property. In other words, the presence of nano-particles in the paper sheet can show a noticeable improvement in paper creep performance in moist or humid environments . 5 The nano-particles may chemically bond to the starch added to the sheet, for example, by hydrogen bonding.

In one embodiment, the nano-particles may be absent from the, or each, outer face of the paper sheet. In another embodiment, 10 the nano-particles may be present on the, or each, outer face of the paper sheet.

The nano-particles may be distributed thought out the paper sheet. Moreover, the nano-particles may be distributed evenly, or uniformly in the paper sheet. 15 When the paper sheet has one ply layer only or multiple ply layers, the nano-particles may be distributed throughout the or each layer. In one embodiment, the nano-particles may be present in at least one outer ply layer of the paper sheet and absent from an inner ply layer of the paper sheet. For 20 instance, the nano-particles may be present in only one of two outer ply layers.

In another embodiment, the nano-particles may be present in an inner ply layer and absent from at least one of the outer ply layers, and suitably both of the outer ply layers. 25 The nano-particles may be incorporated into one or more than one of the ply layers of the paper sheet during the formation of the paper sheet. For example, the nano-particles may be added to a paper pulp slurry feed to the headbox of a papermaking machine so that the nano-particles are distributed throughout the ply 30 layer of the headbox. The nano-particles can be added as a wet slurry or in pre-mixed and dried powered form. The nanoparticles may migrate from the ply layer having the nanoparticles distributed therein to the ply layer in which the nano-particles are not distributed therein. 7809702_1 (GHMatters) P103274.AU3/oe/ie 6 2016203734 03 Jun2016

The nano-particles may be applied to the outer faces of the sheet. It is possible that the nano-particles have been applied to one or both of the outer faces of the sheet.

The nano-particles may be applied to a face of the ply layer 5 that is discharged from a paper machine head box. For instance, the nano-particles may be sprayed onto the ply layer on the wire at the wet end of the paper machine and another ply layer laid on top. The nano-particles may migrate to some extent inwardly from the outer face. 10 For example, the nano-particle may migrate nearly entirely through each ply layer, but may also migrate only to a smaller extent, for example, up to 50% of the thickness of the ply layers, or only up to 30% of the thickness of the ply layers.

For example, although the nano-particles may have been applied 15 to a surface of the one of the ply layers, for example, while the ply layer contains a high water content at the wet end of the paper making machine, or incorporated into the ply layer by being added to the slurry from which the ply layer is made, the nano-particles can migrate away from the interface between the 20 ply layers.

The nano-particles may increase the strength of the bond between the fibres, cellulose and starch within the paper sheet, including within each of the ply layers, and if multiple ply layers are present, between the ply layers. 25 Enhancing the bond between the ply layers and within the ply layers may enhance the performance characteristics of the paper sheet. For example increasing the bond between the ply layers and within the ply layers may increase the ultimate loading point at which the sheet fails. In some situations, the 30 enhanced bond may increase shear stiffness and bending stiffness of the paper sheet. It will be appreciated however, that an increase in shear stiffness and bending stiffness does not necessitate an increase in the ultimate loading point.

Moreover, it is possible that increasing the shear and/or 7809702_1 (GHMatters) P103274.AU3/06/16 7 2016203734 03 Jun2016 bending stiffness may in fact have no effect on the ultimate loading point, increase the ultimate loading point, or reduce the ultimate loading point.

The nano-particles may be applied to the paper sheet after the 5 paper sheet has been formed. For example the nano-particles may be applied at some stage of a dry end of a paper machine, such as in a sizing press. In another example the nano-particles may be applied at some stage after production from a paper machine, for example, in a coating process. 10 The nano-particles may penetrate up to 100 microns from the outer face of the paper sheet during a coating process. The degree of penetration can be controlled to some extent during coating depending on coating viscosity, nip pressure, web moisture, etc. Bending and printing properties can be enhanced 15 if the nano-particles are located predominantly near the surface (as would be suitable for linerboards). While shear properties are enhanced if the nano-particles penetrate to near the centre of the sheet (as would be suitable for corrugating mediums).

The paper sheet may be a corrugated medium having crests and 20 troughs.

One of the benefits of the present invention is that the nanoparticles increase creep resistance of the paper sheet compared to the paper sheet having no nano-particles.

Another benefit of the present invention is that the paper sheet 25 can be made from a reduced amount of virgin fibres, for example, the paper sheet may be made entirely of recycled fibre while maintaining the same or having an improved creep resistance compared to an equivalent paper sheet made from virgin fibres.

It will be appreciated that the term virgin fibres refers to not 30 previously used in paper fibres.

Generally speaking, papers containing recycled fibres, compared to virgin fibre have an inherent increased rate of creep, and therefore, in situations where creep needs to be controlled, higher cost virgin fibres are required. One benefit is that 7809702_1 (GHMatters) P103274.AU3/oe/ie 8 2016203734 03 Jun2016 paper made from solely or predominately from recycled fibres can be used because the nano-particles help to reduce creep. Creep, refers to the undesirable property of paper based packing to deform and weaken over time under load, particularly in humid or 5 cycling humidity environments .

For example, when made from predominantly recycled fibres, the paper sheet may include: i) in one embodiment from 50% to 100% recycled fibres, 10 ii) in another embodiment from 70 to 100% recycled fibres; iii) in yet another embodiment from 80 to 100% recycled fibres; and iv) still yet another embodiment from 90 to 100% recycled fibres . 15 The present invention also relates to a process of manufacturing a paper sheet, the process including the steps of: forming a paper sheet including one or more than one ply layer; and incorporating nano-particles into the paper sheet, wherein 20 the nanoparticles bond to any one or a combination of: starch of the paper sheet, cellulose of the paper sheet, and fibre of the paper sheet.

Forming the paper sheet may include mixing a paper pulp slurry 25 containing the paper fibre, and delivering the slurry onto a travelling wire at the wet end of a paper making machine.

The nano-particles may be incorporated into the paper sheet by being added to the paper slurry that forms one or more of the ply layers. 30 The step of incorporating the nano-particles into the paper sheet may include any one or a combination of the following. i) Applying the nano-particles to the paper sheet after the ply layers have been joined together. For example, the 7809702_1 (GHMatters) P103274.AU3/06/16 9 2016203734 03 Jun2016 ply layers may be dried in a drier and the nanoparticles applied to the paper sheet in size press. In another example, the nano-particles may be applied by meter press roll. According to either example, the 5 nano-particles can migrate into the paper sheet. The nano-particles may be applied to the paper as a dispersion that is formed by suspending the nanoparticles in water, for example, separating the sheets of the nano-particles in the high shear mixer or 10 agitator. The dispersion may also include additional agents for treating the web prior to drying. The additional agents include any one or a combination of sizing agents such as silicon, colouring agents such as whitening agents, starch and so forth. 15 ii) Adding the nano-particles in a paper pulp slurry feed to the headbox of a papermaking machine so that the nanoparticles is distributed through the ply layer of the headbox. The nano-particles can be added as a wet 20 slurry, or in pre-mixed and dried powered form. iii) Applying the nano-particles to a face of the ply layer that is discharged from a paper machine head box. For instances, the nano-particles may be sprayed onto face 25 of one or more ply layers on a wire at the wet end of the paper machine and another ply layer laid thereover top .

The process of the present invention may include any one or a 30 combination of the features of the paper sheet described herein. Similarly, the paper sheet may include any one or a combination of the features of the process described herein.

BRIEF DESCRIPTION OF THE DRAWINGS 35 A preferred embodiment will now be described with reference to the accompanying Figures, of which: 7809702_1 (GHMatters) P103274.AU3/o6/i6 10 2016203734 03 Jun2016

Figure 1 is a schematic perspective view of a paper sheet;

Figures 2a, 2b and 2c are alternative schematic cross-sectional views of the section shown in the dashed circle in Figure 1;

Figure 3 is a schematic illustration of a process of making a 5 paper sheet in which the process includes forming two ply layers, in which nano-particles are incorporated in the ply layers, and/or applied to a surface of one of the ply layers of the paper sheet;

Figures 4a and 4b are schematic illustrations of two processes 10 for applying the nano-particles to the surface of the paper sheet, in which Figures 4a and 4b is representative of the process steps represented by block 20 of Figure 3; and

Figure 5a is a graph illustrating the improved performance of the single sheet of lOOgsm paper that has been treated with 15 starch and clay nano-particles at a weight of approximately 4.5gsm;

Figure 5b is a graph illustrating the improved performance of a sandwich of the two lOOgsm sheets of paper in which starch and nano-clay has been applied at a weight of approximately 9gsm 20 between the sheets; and

Figure 5c is a graph illustrating the improved performance of a single sheet of 135gsm paper that has been treated with starch and nano-clay at a weight of approximately 4.5 gsm.

DETAILED DESCRIPTION 25 With reference to the Figures, Figure 1 illustrates a paper sheet 15 and nano-particles, preferably either one or a combination of clay nano-particles and cellulosic nanoparticles. It will be appreciated that the paper sheet 15 may be of any form, including for example, corrugated medium, liner 30 boards for cartons, liner boards for corrugated board and liner boards for plaster board.

Figures 2a, 2b and 2c are schematic cross-section views of the paper sheet 15 in the dashed circle in Figure 1 in which the 7809702_1 (GHMatters) P103274.AU3/o6/ie 11 2016203734 03 Jun2016 dots 13 represent the nano-particles 13 in the paper sheet 15. The nano-particles 13 may be present at various sections in the thickness of the paper sheet 15 from an outer surface, to inner sections, and to the interface between ply layers 11 and 12 of 5 the paper sheet 15. Figure 2a illustrates the situation in which the nano-particles 13 are present at the interface between the ply layers 11 and 12 and have migrated to some extent through the ply layers 11 and 12. Figure 2b illustrates the situation in which the nano-particles 13 are incorporated 10 throughout the ply layers 11 and 12 of the paper sheet 15.

Figure 2c illustrates the situation in which the nano-particles 13 are present on the outer face of the paper sheet 13 and may have migrated to some extent inwardly.

The nano-particles 13 suitably including either one or a 15 combination of cellulose nano-particles and clay nanoparticles, having a size in the range of equal to, or less than 500nm, and suitably equal to, or less than lOOnm.

The nano-particles 13 may have a platelet shape having a thickness in the range of the 1 to 5nm, and suitably 2 0 approximately 1 nm, and a diameter in the range of 1 to ΙΟμιη.

Clay nano-particles can bond, for example by physical or chemical bonding, to the starch and/or cellulose of the ply layers and increase the stiffness of the paper sheet 15.

Examples of other nano-particles 13 that may be included in the 25 paper sheet 15 include one or combination of graphite or graphene platelets, carbon nanotubes (fibers/whiskers), ZnO and Ti02 nano-particles.

This will produce two practical advantages. The nano-particles 13 can occupy voids between the starch molecules, cellulose and 30 the fibre of the paper sheet, thereby reducing the mobility of the matrix structure of the paper sheet 15, making the sheet 15 stiffer than equivalent paper sheet 15 without the nanoparticles 13. 7809702_1 (GHMatters) P103274.AU s/oe/u 12 2016203734 03 Jun2016

In addition to making the paper sheet 15 stiffer, the nanoparticles 13 infill voids in the matrix structure of the paper sheet 15, increasing the hydrophobicity of the paper sheet 15.

In turn, the paper sheet 15 will have an increased stiffness and 5 better creep resistant properties in cyclic and high humidity conditions .

The manner in which the nano-particles 13 can be included in the paper sheet 15 can be achieved by several means. Figure 3 is a schematic illustration of the process for making the paper sheet 10 15 in which the process includes forming the ply layers 11 and 12 by delivering sequentially, two suspensions 11s and 12s of paper fibre (paper pulp slurry) onto a wire 17 at the wet end of paper making machine so that the ply layers 11 and 12 are overlaid in a stagewise manner. 15 The nano-particles 13 can be added to the suspensions 11s and 12s, for example, in upstream mixing vessels 21 in which the suspensions 11s and 12s are prepared. It is also possible that the nano-particles 13 can be added directly to the headboxes 18. By including the nano-particles 13 in the suspensions 11s and 20 12s, the nano-particles 13 will be distributed throughout the entire thickness of one or more of the ply layers 11 and 12 delivered from the respective headbox 18.

Figure 3 also illustrates a first ply layer 12 delivered from a first headbox 18 onto the wire 17, and the nano-particles 13 are 25 applied to the upper face of the first ply layer 12 prior to the second ply layer 11 being delivered onto the first ply layer 12. The nano-particles 13 may be sprayed onto the upper face of the first ply layer 12 by a sprayer 19. Thereafter the ply layers 11 and 12 are joined together in a joining step 14. The joining 30 step 14 may include dewatering and drying the paper sheet 15 in a drier.

The nano-particles 13 can be added to the paper sheet 15 by means of either one or a combination of: i) adding the nanoparticles 13 to the suspensions 11s and 12s in the mixing 7809702_1 (GHMatters) P103274.AU3/oe/ie 13 2016203734 03 Jun2016 vessels 21 or the head boxes 18, or ii) applying a solution containing the nano-particles 13 to the surface of one of more of the ply layers 11 and 12 using, for example, sprayer 19. Although Figure 3 illustrates the sprayer 19 located for 5 applying the nano-particles 13 to ply layer 12, it will be appreciated that the sprayer 19 could be arranged to spray the inner face of the ply layer 11. It is also possible that other sprayers could be arranged to apply a solution containing the nano-particles 13 to other faces of ply layers 11 and 12. 10 As shown in Figure 3, the process may include applying the nanoparticles 13 to the outer face of the paper sheet in step 20, which is described in detail below with reference to Figure 4. Following step 20 the paper sheet 15 can be rolled into a roll 21 for storage. 15 Figures 4a and 4b illustrate process steps for treating the surface of the paper sheet 15 with the nano-particles 13. Moreover the processes illustrated in Figures 4a and 4b can be used with, and in addition to the process illustrated in Figure 3. It is possible that the nano-particles may not be included 20 in in suspension 11s and 12s, or applied to the surface of the ply layers 11 and 12 via sprayer 19 in accordance with Figure 3, but rather, the nano-particles may be applied solely to the outside face of the paper sheet 15 according to the processes shown in Figure 4a and 4b. 25 The processes of Figures 4a and 4b include forming an aqueous solution of the nano-particles. The solution may be formed by dispersing the nano-particles 13 supplied in a powder/aggregate form in a high shear mixing tank 25. From the mixing tank 25, the dispersion is supplied to a pool 27. The process 30 illustrated in Figures 4a and 4b can be carried out alternately or in combination.

Figure 4a illustrates the pool 27 formed in a size press comprising two engaging rollers 26 with the paper sheet 15 being conveyed through the nip of the rollers 26. The pool 27 may 7809702_1 (GHMatters) P103274.AU 3/οβ/ιβ 14 2016203734 03 Jun2016 also include other agents such as starch, sizing agents, brightness enhancers and so forth. After being conveyed through the size press, the paper sheets 15 can be dried in an after drier 28 and rolled. 5 Figure 4b illustrates the pool 27 being arranged to feed a meter roller 30 having grooves or indentations on the surface of the metered roller 30. The grooves receive the solution and apply the solution containing the nano-particles 13 to the paper sheet 15. A transfer roller 31 may convey the solution from the pool 10 27 to metered roller 30. A backing roller 32 may be used to ensure adequate contact between the paper sheet 15 and the meter roller 30.

Figure 5a is a graph illustrating the improved performance of the single sheet of lOOgsm paper that has been treated with 15 starch and nano-clay at a weight of approximately 4.5gsm (i.e., apporximately 4.5wt%). To provide a control, untreated paper is first tested according to a ring crush strength test (RCS) and a high humidity load carrying capacity test (HHLCC).

The RCS test method involves a compression force being exerted 20 on a sample of paper held in a ring form in a sample holder that is placed between two platens of a compression machine in which platen is driven toward a rigid platen at a uniform speed until the sample collapses. The sample is pre-conditioned in a controlled environment having a 50% relative humidity at 23°C. 25 The HHLCC test method is the same as the RCS test method described above, save for the additional following steps: 30 i) The sample is exposed to a changing environment in which the humidity changes stepwise between 50% relative humidity and 90% relative humidity over a three hour cycle . ii) A constant load is applied and the time taken for the sample to collapse is measured (i.e. creep test). iii) Step ii) is repeated for a series of different loads. 7809702_1 (GHMatters) P103274.AU3/oe/ie 15 2016203734 03 Jun2016 iv) The load required to survive one full three-hour relative humidity cycle is estimated using a plot comprising the ex-intercept of log-load(N) versus log-life (at number of relative humidity cycles). 5 v) The load is used as a measure of Cree performance in a site click high humidity environment.

As can be seen in figure 5a, the RCS of a single lOOgs a paper sheet increased by approximately 8% and the HHLCC of the same 10 paper sheet increased by approximately 13%. This is considered to be a considerable improvement.

Figure 5b is a graph illustrating the improved performance of a sandwich of the two lOOgsm sheets of paper in which starch and clay nano-particles have been applied at a weight of 15 approximately 9gsm between the sheets (i.e., approximatekly 4.5wt%). The RCS of the sandwich does not increase significantly; however, the HHLCC of the same sample of paper increases by approximately 13%.

Figure 5c is a graph illustrating the improved performance of a 20 single sheet of 135gsm paper that has been treated with starch and clay nano-particles at a weight of approximately 4.5 gsm (i.e., approximately 3.3wt%). The RCS of the single sheet increases by proximally 5%, and the HH else of the same sample increases by approximately 4%. 25 In other words, the addition of clay nano-particles and starch can increase creep resistance of the paper sheet compared to the paper sheet having no nano-particles by up to 115%, and suitably up to 113%, and even more suitably in the range of 105 to 110% when the starch and nano-particles together are applied in an 30 amount in the range of 3 to 5 wt%.

In other words, the additon of the addition of clay nanoparticles and starch can increase the ring crush strength of the paper sheet compared to the paper sheet having no nano-particles by up to 108%, and even more suitably in the range of 103 to 7809702_1 (GHMatters) P103274.AU3/06/16 16 2016203734 03 Jun2016 105% when the starch and nano-particles together are applied in an amount in the range of 3 to 5 wt%.

Set out below in Table 1 is a set of data showing the performance increases from combinations including: i) starch and 5 clay nanoparticles, and ii) starch, clay nanoparticles and cellulose nanoparticles .

Table 1

Paper Composition Control (Starch additive Only) Starch and clay nanoparticles Starch, clay nanoparticles and cellulose nanoparticles Pulp Fibre % 95 92 85 Starch % 5 5 5 Clay nanoparticles % 0 3 5 cellulose nanoparticles% 0 5 5 Ring Crush Strength* % (relative to control) 100 range from 104 to 110, typcially 108 range from 112 to 125, typically 120 High Humidity Load Carrying Capacity * % (relative to control) 100 range from 105 to 115, typcially 113 range from 112 to 125, typically 120

One of the benefits of the present invention is that the 10 performance characteristics, such as ultimate load strength, shear stiffness and bending stiffness can be improved by the nano-particles. This means that the paper sheet may contain a higher percentage of the recycled fibres, yet have the 7809702_1 (GHMatters) P103274.AU 3/06/16 17 2016203734 03 Jun2016 characteristics akin to a product made from virgin fibre. Moreover, the nano-particles can improve the performance of the paper sheet, particular in terms of the stiffness and creep resistance in high or cyclic humid conditions. 5 It will be understood to persons skilled in the art of the invention that many modifications may be made to embodiments described above without departing from the spirit and scope of the invention. 7809702_1 (GHMatters) P103274.AU 3/οβ/ιβ

Claims

1. A paper sheet including a base material and nano-particles bonded to the base material.

2. The paper sheet according to claim 1, wherein the base material includes any one or a combination of: fibrous material, cellulosic material or starch material, and the nano-particles can be bonded to at least one of the fibrous material, the starch material or the cellulosic material.

3. The paper sheet according to claim 1 or 2, wherein the nanoparticles include any one or a combination of clay nanoparticles and cellulose nano-particles.

4. The paper sheet according to claim 1 or 2, wherein the nanoparticles are in the form of clay nano-particles only.

5. The paper sheet according to claim 3 or 4, wherein the clay nano-particles are present in the paper sheet at a weight in the range of 2.0 to 20.0gsm, and suitably 4.0 to lO.Ogsm.

6. The paper sheet according to claim 1 or 2, wherein the nanoparticles are in the form of cellulose nano-particles only.

7. The paper sheet according to any one of claims 2 to 6, wherein the cellulose nano-particles are present in the paper sheet at a weight in the range of 2.0 to 20.0gsm, and suitably 4.0 to 10.Ogsm.

8. The paper sheet according to any one of the preceding claims, wherein the nano-particles have a size in the range of equal to, or less than 500nm, and suitably the nano-particles have a size in the range of equal to or less than lOOnm.

9. The paper sheet according to any one of the preceding claims, wherein the nano-particles are platelets having a thickness in the range of 0.5 to 5.Onm and a diameter in the range of 0.1 to 10 . Ομιη.

10. The paper sheet according to any one of the preceding claims, wherein the platelets are clay platelets.

11. The paper sheet according to any one of the preceding claims, wherein the paper sheet includes starch, clay nanoparticles and cellulose nano-particles, in which the weight ratio of clay nano-particles to cellulose nano-particles is in the range of 10 to 90 : 90 to 10 respectively.

12. The paper sheet according to any one of the preceding claims, wherein the nano-particles are absent from at least one outer face of the paper sheet.

13. The paper sheet according to any one of the preceding claims, wherein the nano-particles are present on at least one outer face of the paper sheet.

14. The paper sheet according to any one of the preceding claims, wherein the nano-particles are distributed throughout the paper sheet.

15. The paper sheet according to any one of the preceding claims, wherein the paper sheet has at least two ply layers and the nano-particles are present in only one of the ply layers.

16. The paper sheet according to any one of the preceding claims, wherein the paper sheet has at least one outer ply layer and at least one inner ply layer, and the nano-particles are absent from an inner ply layer of the paper sheet.

17. The paper sheet according to any one of the preceding claims, wherein the addition of clay nano-particles and starch increases creep resistance of the paper sheet compared to the paper sheet having no nano-particles by up to 115%, and suitably up to 113%, and even more suitably in the range of 105 to 110%.

18. The paper sheet according to any one of the preceding claims, wherein the addition of clay nano-particles and starch increases the ring crush strength of the paper sheet compared to the paper sheet having no nano-particles by up to 108%, and even more suitably in the range of 103 to 105%.

19. The paper sheet according to any one of the preceding claims, wherein the paper sheet includes a combination of starch, cellulose nano-particles and clay nanoparticles range the high humidity load carrying capacity ranges 112 to 125% relative to the paper sheet having starch only, and typically 120%.

20. The paper sheet according to any one of the preceding claims, wherein the paper sheet includes a combination of starch, cellulose nano-particles and clay nanoparticles range the ring crush strenght range from 112 to 125%, and typically 120%.

21. The paper sheet according to any one of the preceding claims, wherein the paper sheet may include from 50% to 100% recycled fibres yet retain the same creep resistance as the paper sheet made from virgin fibres.

22. A process of manufacturing a paper sheet, the process including the steps of: forming the paper sheet including one or more than one ply layer comprising a base material; and adding nano-particles to the paper sheet, wherein the nanoparticles bond to the base material.

23. The process according to claim 22, wherein the base material includes any one or a combination of: fibrous material, cellulosic material or starch material, and the nano-particles are bonded to at least one of the fibrous material, the starch material or the cellulosic material

24. The process according to claim 23, wherein forming the paper sheet includes mixing fibrous material, cellulosic material or starch material so as to form a paper pulp slurry and delivering the slurry onto a travelling wire at the wet end of a paper making machine, and adding the nano-particles to the paper pulp slurry includes adding the nano-particles into the pulp slurry.

25. The process according to claim 23, wherein the nanoparticles are added to a paper pulp slurry feed to a headbox of a papermaking machine so that the nano-particles are distributed through a ply layer that is delivered by the headbox onto the travelling wire.

26. The process according to claim 23, wherein the nanoparticles are contained in a liquid that is sprayed onto face of one or more ply layers on a wire at the wet end of the paper machine .

27. The process according to claim 23, wherein incorporating the nano-particles into the paper pulp slurry includes applying the nano-particles to the paper sheet after ply layers of the paper sheet have been joined together.

28. The process according to claim 26, wherein the nanoparticles are applied to the paper sheet in a size press.

29. The process according to claim 26, wherein the nanoparticles are applied to the paper sheet by meter press roll.