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Title:
PAPER SHEET, CORRUGATED PAPER AND A PROCESS FOR THE MANUFACTURE THEREOF
Document Type and Number:
WIPO Patent Application WO/2017/165919
Kind Code:
A1
Abstract:
The present invention relates to a paper sheet and a process of making the paper sheet. In one example, the paper sheet may be a corrugated paper and a process may be a process for making a corrugated paper. Ideally, the paper sheet includes an additive such as a clay nano-particles and/or a plasticising agent. The additive may improve one or more mechanical properties of the paper sheet such as: bending stiffness, crush strength and creep resistance.

Inventors:
CONN ANDREW (AU)
SELWAY JIM (AU)
FALTAS RAFIK (AU)
Application Number:
PCT/AU2017/050273
Publication Date:
October 05, 2017
Filing Date:
March 30, 2017
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ORORA PACKAGING AUSTRALIA PTY LTD (AU)
International Classes:
D21H21/14; B31F1/20; B32B29/08; C09J11/00; D21H17/25; D21H17/68; D21H21/18
Domestic Patent References:
WO2014059413A12014-04-17
WO2012098296A22012-07-26
WO2000029673A12000-05-25
WO2005052256A22005-06-09
Foreign References:
US20140102649A12014-04-17
US4948448A1990-08-14
AU2016203734A12016-12-22
Attorney, Agent or Firm:
GRIFFITH HACK (AU)
Download PDF:
Claims:
CLAIMS

1. A paper sheet including nanoparticles that have been added and that bond to any one or a combination of: starch of the paper sheet, adhesives present in the paper sheet, cellulose of the paper sheet, and fibre of the paper sheet.

2. A paper sheet suitable for use as a corrugating paper including :

at least two paper sheets that are joined together, and an additive that is located between the paper sheets that enhances the bond between the sheets joined together, wherein the additive includes nano-particles that bond to any one or a combination of fibre of the paper sheets, cellulose and starch of the paper sheets.

3. The paper sheet according to claim 1 or 2, wherein the additive includes nano-particles that bond to at least one of the fibres, cellulose and starch within the paper sheet which in turn improves the mechanical properties of the paper sheet. 4. The paper sheet according to any one of claims 1 to 3, wherein the nano-particles include 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.

5. The paper sheet according to any one of claims 1 to 4, wherein the nano-particles include clay nano-particles.

6. The paper sheet according to any one of claims 1 to 5, wherein the additive includes a combination of clay nanoparticles, cellulose nano-particles in which a weight ratio of clay nanoparticles and cellulose nanoparticles is in the ranges of 10 to 90 : 90 to 10 respectively.

7. The paper sheet according to claim 5 or 6, wherein the clay nano-particles are platelets having a thickness in the range of the 1 to 5nm, and suitably approximately 1 nm, and a diameter in the range of 0.1 to ΙΟμτη.

8. The paper sheet according to any one of claims 1 to 7, wherein the additive increases the ring crush strength from 1 to 8% compared to an equivalent paper sheet without the additive.

9. The paper sheet according to any one of claims 1 to 8, wherein the additive slows time dependent deformation (creep) of the paper sheet that is subject to a load in a high

humidity/moisture environment in which the relative humidity is at least 50%, compared to an equivalent paper sheet without the additive .

10. The paper sheet according to any of claims 1 to 9, wherein the additive increases the high humidity load carrying capacity from 1 to 14% compared to an equivalent paper sheet without the additive .

11. The paper sheet according to any one of claims 1 to 10, wherein the nano-particles are distributed throughout the paper sheet .

12. The paper sheet according to any one of claims 1 to 11, wherein the paper sheet has one or more ply layers, and the nano-particles are distributed throughout the or each ply layer. 13. The paper sheet according to any one of claims 1 to 12, wherein the nano-particles are applied to the outer faces of the sheet .

14. The paper sheet according to any one of claims 1 to 13, wherein the nano-particles are distributed to some extent over up to 50% of the thickness of the ply layers.

15. A paper sheet for use as a corrugating paper, the paper sheet including one or more than one ply layer, wherein the paper sheet includes an additive that allows relative movement of the internal structure of the sheet to prevent or reduce fracturing during corrugation of the sheet.

16. A paper sheet for use as a corrugating paper, the paper sheet including:

at least two ply layers that are joined together to form the sheet, and

an additive that is present in the sheet and between the ply layers, wherein the additive facilitates relative movement of the ply layers to prevent or reduce fracturing of the join between the ply layers during corrugation of the sheet.

17. The paper sheet according any one of claims 15 or 16, wherein the additive includes a plasticizing agent that can form a thermoplastic with starch. 18. The paper sheet according to claim 17, wherein the

plasticizing agent includes at least one of glycerol or sorbitol .

19. The paper sheet according to claims 17 or 18, wherein the theromoplastic of the plasticizing agent and the starch is heat softenable during the corrugating forming step.

20. The paper sheet according to claims 17 or 18, wherein the theromoplastic of the plasticizing agent and the starch is heat softenable, thereby allowing the paper sheet to be stored for a period during which the paper sheet can cool, and thereafter heated and optionally moistened, during which the paper sheet can be corrugated in a corrugating forming step. 21. The paper sheet according to any one of claims 15 to 20, wherein the additive includes nano-particles that bond to at least one of the fibres, cellulose and starch within the paper sheet which in turn improves the mechanical properties of the paper sheet.

22. The paper sheet according to any one of claims 15 to 21, wherein the nano-particles include 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.

23. The paper sheet according to any one of claims 15 to 22, wherein the nano-particles include clay nano-particles.

24. The paper sheet according to any one of claims 21 to 23, wherein the additive includes a combination of clay nano- particles, cellulose nano-particles in which a weight ratio of clay nanoparticles and cellulose nanoparticles is in the ranges of 10 to 90 : 90 to 10 respectively.

25. The paper sheet according to claim 24, wherein the nanoparticles are platelets having a thickness in the range of the 1 to 5nm, and suitably approximately 1 nm, and a diameter in the range of 0.1 to ΙΟμτη.

26. The paper sheet according to any one of claims 15 to 25, wherein the additive slows time dependent deformation (creep) of the paper sheet that is subject to a load in a high

humidity/moisture environment in which the relative humidity is at least 50%, compared to an equivalent paper sheet without the additive .

27. The paper sheet according to any one of claims 15 to 26, wherein the additive increases the high humidity load carrying capacity from 1 to 13% compared to an equivalent paper sheet without the additive, in which the relative humidity is at least 50%.

28. The paper sheet according to any one of claims 15 to 27, wherein the additive is located at the interface between the ply layers, and penetrates into the plies to a degree.

29. The paper sheet according to any one of claims 15 to 28, wherein the additive is located entirely through each ply layer.

30. The paper sheet according to any one of claims 15 to 29, wherein the additive is located over up to 30% of the thickness of the ply layers.

31. The paper sheet according to any one of claims 15 to 30, wherein the additive is added to a paper pulp slurry feed to the headbox of a papermaking machine so that the additive is distributed through the ply layer of the headbox.

32. The paper sheet according to any one of claims 15 to 31, wherein the additive is applied to a face of the ply layer that is discharged from a paper machine headbox.

33. A process of manufacturing a paper sheet in the form of a corrugated paper, the process including the steps of:

forming the paper sheet including one or more than one ply layer ;

incorporating an additive in the paper sheet; and

corrugating the sheet into a corrugated form;

wherein the additive facilitates relative movement of internal sheet structure and/or the ply layers to prevent or reduce fracturing of the internal structure and/or join between the ply layers during corrugation of the sheet.

34. The process according to claim 33, wherein the process includes allowing the paper sheet to cool, and thereafter heating the paper sheet prior to and/or during the corrugating step .

35. The process according to claim 33 or 34, wherein the step of corrugating the paper sheet into a corrugated form includes passing the paper sheet between a pair of co-operating rollers having mating surfaces with crests and troughs that impart a corrugated profile.

36. The process according to any one of claims 33 to 35, wherein the step of forming sheet including one or more ply layers includes creating a paper pulp slurry containing the paper fibre, and delivering the slurry onto a travelling wire from a headbox at the wet end of a paper making machine and the step of incorporating the additive in the paper sheet includes any one or a combination of the following:

i) adding the additive to the paper pulp slurry feed to the headbox of a papermaking machine so that the additive is distributed through the ply layer of the headbox; or ii) applying the additive to a face of the ply layer that is discharged from a paper machine head box onto to the wire .

37. The process according to any one of claims 33 to 36, wherein the step of incorporating the additive into the paper sheet includes forming a pool including the additive and conveying the paper sheet through the pool.

38. The process according to claim 33 to 37, wherein the step of incorporating the additive into the paper sheet includes controlling the penetration depth of the additive into the paper sheet.

39. 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; and incorporating nano-particles into the paper sheet, wherein the nanoparticles bond to any one or a combination of: starch of the paper sheet, adhesives present in the paper sheet, cellulose of the paper sheet, and fibre of the paper sheet.

40. The process according to claim 39, wherein forming the paper sheet may include mixing a paper pulp slurry containing the paper fibre, and delivering the slurry onto a travelling wire at the wet end of a paper making machine.

41. The process according to claim 39, wherein the nano- particles are incorporated into the paper sheet by being added to the paper slurry which forms one or more of the ply layers.

42. The process according to claim 39, wherein the nano- particles are incorporated into the paper sheet includes 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. ii) adding the nano-particles in a paper pulp slurry feed to the headbox of a papermaking machine so that the nano- particles is distributed through the ply layer of the headbox; or iii) applying the nano-particles to a face of the ply layer that is discharged from a paper machine head box.

43. A process of manufacturing a corrugated paper, the process including :

locating an additive between two base sheets;

joining the base sheets together with the additive therebetween to form a medium; and

corrugating the medium into a corrugated form;

wherein the additive enhances the bond between the sheets and includes nano-particles that can bond to any one or a combination of the fibre of the paper sheets or starch of the paper sheets .

44. The process according to claim 43, wherein the additive is a wet additive.

45. The process according to claim 43, wherein the additive is applied to one or both of the joined faces of the sheets prior to the sheets being joined together.

46. The process according to claim 45, wherein the additive is applied by means of either: i) spraying the additive onto the paper sheet, or ii) applying the additive by means of roller application .

47. The process according to any one of claims 43 to 46, wherein corrugating the paper sheet into a corrugated form includes passing the paper sheet between a pair of co-operating rollers having mating surfaces with crests and troughs that impart a corrugated profile before drying the additive.

48. The process according to any one of claims 43 to 46, wherein the process includes applying at least one liner board to the corrugated paper after the corrugating step.

Description:
PAPER SHEET, CORRUGATED PAPER AND A PROCESS FOR THE MANUFACTURE THEREOF

FIELD OF THE PRESENT INVENTION

The present invention relates to a paper sheet and a process of making the paper sheet. In one example, the paper sheet may be a corrugated paper and a process may be a process for making a corrugated paper. Corrugated paper can be used in a range of applications, including making corrugated board and boxes.

BACKGROUND OF THE PRESENT INVENTION

Mechanical properties such as bending stiffness, crush strength and creep resistance of a sheet of paper is dependent on a number of factors including the weight (or 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 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 stiffness .

Once the paper sheet has been fully formed and dried, if the paper sheet is going to be used as a liner board for example, the paper 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 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.

Corrugated board is a high strength product used in the manufacture cartons that are used for a range of purposes, including storing fresh food items under moist conditions such as high humidity topical environments and cold storage. The cartons are also expected to perform over various time frames from relative short periods such as a few days, to extended periods such as a few months or even years. The ability for a product to resist deterioration or degradation under various environments, particularly high and cycling humidity

environments, is the product's ability to resist "creep", which can be an important characteristic depending on the

circumstances .

Moreover, the performance of the corrugated paper of a

corrugated board is dependent on a vast number of different variables including, but by no means limited to: quality of the fibre material, particularly virgin fibre versus recycled fibre; grammage of the corrugated paper; the flute size and geometry of the corrugated paper; degree of damage resulting from the forces in the corrugating labyrinth, adhesion of the corrugated paper to the liner boards; moisture resistance of the corrugated paper; the humidity of the environment in which the product is being used; the expected life time and so forth.

In practice the shear and bending stiffness of the corrugated paper (both material and structural) plays an important role in the performance of the corrugated paper. Ideally the corrugated paper is as stiff as possible, as this would have the potential to reduce the grammage of the liner board required to produce a corrugated board. However, the grammage of corrugated paper is generally limited to about 180 gsm. Corrugated paper having a grammage greater than this is prone to delaminating during the corrugating process in which the sheet is configured into a cycling wave shape under heat and pressure. Delaminating permanently weakens the boards as shear stiffness is greatly reduced .

SUMMARY OF THE PRESENT INVENTION

The present invention relates to a paper sheet including one or more than one ply layer, wherein the paper sheet includes an additive .

The additive may include a plasticizing agent that allows relative movement of the internal structure of the sheet to prevent or reduce fracturing during corrugation of the sheet.

The additive may include nano-particles that can be incorporated in the sheet which can improve mechanical properties including: i) crush strength; ii) stiffness of the sheet; iii) creep resistance of the sheet particularly in cyclic or high humidity environments, or iv) hydrophobicity or the moisture barrier properties of the sheet.

An embodiment of the present invention relates to a paper sheet for use as a corrugating paper, the paper sheet including:

at least two ply layers that are joined together to form the sheet, and an additive that is present in the sheet and between the ply layers, wherein the additive facilitates relative movement of the ply layers to prevent or reduce fracturing of the join between the ply layers during corrugation of the sheet.

In one embodiment the paper sheet is a corrugating paper or corrugating paper.

In other words, the additive helps prevent or reduce fracturing of the join between the ply/layers compared to an equivalent paper sheet without the additive.

Another embodiment of the present invention relates to a paper sheet suitable for use as a corrugating paper including:

at least two paper base sheets that are joined together, and

an additive that is located between the paper sheets that enhances the bond between the sheets joined together, wherein the additive includes nano-particles that bond to any one or a combination of fibre of the paper sheets, cellulose and starch of the paper sheets.

In one embodiment the paper sheet is a corrugating paper or corrugating paper.

A corrugating paper is a medium that can be imparted with crests and troughs to form a corrugated paper.

In other words, the bond between the base sheets post- corrugation is enhanced compared to an equivalent corrugated paper without the additive between the paper base sheets.

Enhancing the bond between the paper base sheets may enhance one or more of the performance characteristics of the corrugating paper. For example, increasing the bond between the base sheets may increase the ultimate loading point at which the corrugated paper fails when subjected to a load. In some situations, crush strength, the bending stiffness or the shear stiffness of the corrugated paper may be increased at any one point in time after manufacture or setting. It will be appreciated however, that an increase in shear stiffness and bending stiffness does not necessitate an increase in the ultimate load point of the material. Moreover, it is possible that increasing the shear and/or bending stiffness may in fact have no effect on the ultimate load point, increase the ultimate load point, or even reduce the ultimate load point of the corrugated paper. An embodiment of the present invention relates to a paper sheet including nanoparticles that can bond to any one or a

combination of: starch of the paper sheet, adhesives in the paper sheet, cellulose of the paper sheet, and fibre of the paper sheet.

The bond between the nano-particles and the starch, adhesives, and/or cellulose may be in the form of physical bonding, but is ideally in the form of a chemical bond.

The term "adhesives" in the specification embraces materials such as: starch, PVA, and other compatible polymeric materials.

Without wanting to be limited by theory, it is believed that certain types of 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 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 nano-particles can occupy spaces that would otherwise be voids. 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", or variations thereof such as a "sheet of paper" or "sheet" embraces any fibrous or cellulosic containing material and embraces material including a single ply layer, multiple plies and other laminated structures. The term "paper sheet" therefore embraces any one or a combination of a corrugated paper that has been corrugated, corrugating paper prior to being corrugated, namely a flat planar sheet, or paper layers joined together, or optionally joined to non-paper materials such as polymeric film, metallic foil, coatings of wax and so forth.

Nanoparticles

The additive may include nano-particles.

The nano-particles may include 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. Examples of other nano-particles that may be present in the paper sheet include graphite or graphene platelets, carbon nanotubes, and ZnO or Ti0 2 nano-particles.

The nano-particles may include clay nano-particles.

The additive may include a combination of clay nano-particles, cellulose nano-particles and starch. The additive may include any proportion of clay and cellulose nano-particles. For instance, the additive may include from 0% to 100% clay nano- particles and from 100% to 0% cellulose nano-particles, and any mix in between. By way of example, the weight ratio of clay 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.

Without wanting to be limited by theory, nanoparticles have the ability to limit the mobility of molecules for a starch and by bonding to and bridging between adjacent starch particles.

Nano-particles have a large surface area per unit weight or volume hence significant amounts of the matrix can be affected. Restricting the matrix molecule mobility on this minute scale can increase stiffness and in addition improve creep performance in cyclic or high humidity conditions.

For instance, an additive comprising clay nano-particles and additional starch added to the surface of the paper sheet at a weight of up to 5gsm can increase a ring crush strength of the paper sheet from 1 to 8% compared to an equivalent paper sheet without the additive. The additive may, for example, comprise from 85 to 75wt% starch and from 15 to 25wt% clay nano- particles .

The nano-particles may have a size in the range of equal to, or less than 500nm, and even more suitably the nano-particles may have a size in the range of equal to less than lOOnm. Ideally, the nano-particles may be platelets having a thickness in the range of the 1 to 5nm, and suitably approximately 1 nm, and a diameter in the range of 0.1 to ΙΟμτη.

The nano-particles may be have any suitable shape and are suitably platelets shaped nano-particles. Even more suitably, the nano-particles are in the form of clay nano-particles having a platelet shape and may have the size ranges mentioned above. The bond between the nano-particles and the starch and/or cellulose may be in the form of physical bonding, but is ideally a chemical bond.

The nano-particles may chemically bond to the starch of the substrate, for example, by hydrogen bonding.

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 moisture barrier property. In other words, the presence of nano-particles, paper creep will show a noticeable improvement in performance in moist or humid environments.

Ideally, the additive slows time dependent deformation (creep) of the paper sheet subjected to a load in a high

humidity/moisture environment in which the relative humidity is at least 50%, compared to an equivalent paper sheet without the additive. Depending on the preferred conditions, the relative humidity may be at least 65%, and even more preferably at least 75%.

For instance, an additive comprising clay nano-particles and additional starch added to interface between two of the base sheets to from a single sheet at a weight in the range of the 9gsm can increases the high humidity load carrying capacity from 1 to 13% compared to an equivalent paper sheet without the additive. The additive may, for example, comprise from 85 to 75wt% starch and from 15 to 25wt% clay nano-particles.

Plasticizing agent

The additive may include a plasticizing agent that can form a thermoplastic with starch. The starch may be contained within the ply layers, or included in the additive.

The additive may include a combination of a plasticizing agent and starch at an interface between the ply layers of the paper sheet, or between an interface between base sheets. Examples of a plasticizing agent that can be used with starch are glycerol and sorbitol. Glycerol may be included in the additive by itself or in combination with other agents such as sorbitol. Similarly, sorbitol may be included in the additive by itself or in combination with other agents such as glycerol.

Ideally the additive may have an ability to soften when subjected to a temperature above ambient temperature, and harden at temperatures at or below ambient temperatures. Ambient temperature may, for example, be 25, 35 or 45 degrees Celsius. An advantage provided by this aspect is that ply layers can move relative to each other more readily when subject to heat, enabling the sheet to be treated in a corrugating step with a reduced risk of the join between ply layers fractured, or the ply layers themselves within the paper sheet fracturing.

An advantage in using a plasticizing agent that can form a thermoplastic with starch is that the thermoplastic is heat softenable, thereby enabling, for instance the sheet to be heated after being dried to allow the ply layers to move relatively. In one example, the sheet may be manufactured with the additive contained in the paper sheet, and the paper sheet stored for a period during which the paper sheet can cool. The plasticising agent can then be softened, for example by being heated and optionally moistened, and the paper sheet can then be corrugated while heated.

The additive may include one or a combination of the nano- particles, particularly clay nano-particles , cellulose nano- particles, a plasticizing agent, and starch.

Structure

The additive may be located at any section of the paper sheet. For example, and without limitation, the additive may be distributed evenly throughout the entire thickness of the paper sheet, isolated to one of the ply layers of the paper sheet, located in two or more of the ply layers if present, located at the interface between two or more of the ply layers if present in the paper sheet, or located on the outer faces of the paper sheet .

In the situation in which the paper sheet has two ply layers or base sheets that are joined to each other, that is without any additional ply layers therebetween, the additive may be located at the interface between the ply layers, and may penetrate into the plies to a degree.

In the situation where the paper sheet includes more than two ply layers or base sheets, the additive may be located between any two juxtaposed ply layers or base sheets, i.e., at the interface between the layers.

As well as being present at the interface between the ply layers, the additive may also penetrate the ply layers to some extent. For example, although the additive may have been applied to a surface of one of the ply layers 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 additive can migrate away from the interface between the ply layers .

For example, the additive 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.

In addition to being located at the interface between the ply layers. The additive may also be present within the thickness of the paper sheet, i.e., within each of the ply layers. For example, the additive may be distributed throughout the thickness of one of the ply layers. In another example, the additive may be distributed throughout the thickness of two ply layers, and suitably each of the ply layers of the paper sheet.

The additive 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/or between the ply layers.

Enhancing the bond between the ply layers and within the ply layers may enhance the performance characteristics of the paper sheet and particularly a corrugated paper made from 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 or corrugated paper fails. In some situations, the enhanced bond may increase shear stiffness and bending stiffness of the paper sheet including corrugated papers made therefrom. It will be appreciated however, that an increase in shear stiffness and bending stiffness does not necessitate an increase in the ultimate loading point.

In an embodiment, the additive may be absent from the outer face of the paper sheet.

In an embodiment, the additive may be incorporated into one or more than of the ply layers. For example, the additive may be added to a paper pulp slurry feed to the headbox of a

papermaking machine so that the additive is distributed through the ply layer of the headbox. The additive can be added as a wet slurry or in pre-mixed and dried powered form. In this instance, the additive distributed in the ply layer will be present at the interface with an adjacent ply layer that may not have the additive distributed therethrough. The additive may migrate from the ply layer having the additive distributed therein to the ply layer in which the additive is not

distributed therein.

In an embodiment, the additive may be applied to a face of the ply layer that is discharged from a paper machine headbox. For instance, the additive is sprayed onto the ply layer on the wire at the wet end of the paper machine and another ply layer laid on top.

In the situation in which the paper sheet may include three or more ply layers, the additive is suitably present at the between each of the ply layers.

The ply layers may be joined together by, for example,

laminating the ply layers together. The ply layers may be laminated together without or without an adhesive. In the situation where there is no adhesive, starch may assist in bonding the ply layers together, and the fibre of the ply layers may intertwine to some extent.

In an embodiment, the additive may be applied to one face, and suitably to opposite faces of the paper sheet in a coating step. The additive, such as nano-particles may penetrate up to 100 microns from the outer face of the paper sheet during the coating process. The degree of penetration can be controlled to some extent during coating depending on coating viscosity, nip pressure, web moisture, and so forth. An embodiment relates to controlling the penetration depth of the additive into the paper sheet during the coating step. Bending and printing properties can be enhanced 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 papers) .

The paper sheet may be a corrugated paper having crests and troughs. The corrugated paper may also include other adhesives, such as starch and/or PVA to bond the sheets together.

Another benefit of the present invention is that paper sheet made entirely of recycled fibre can be used to in situations where only virgin (not previously used in paper) fibres may have needed while maintaining the same or having an improved creep resistance can be manufactured.

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 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 cycling humidity environments . An embodiment relates to controlling the creep resistance of the paper sheet by adjusting the weight of additives, in particular, nano-particles in the paper sheet. In one example, the paper sheet may be made entirely of recycles fibre. In another example, the paper sheet may be made of 50% recycled fibre.

Process

An embodiment relates to a process of manufacturing a paper sheet that in a corrugated paper, the process including the steps of:

forming and joining one or more than one ply layer of the paper sheet;

incorporating an additive in the paper sheet; and

corrugating the sheet into a corrugated form;

wherein the additive facilitates relative movement of internal sheet structure and/or the ply layers to prevent or reduce fracturing of the internal structure and/or join between the ply layers during corrugation of the sheet.

The process may include allowing the paper sheet that has been treated with the additive to cool, and thereafter heating the paper sheet prior to and/or during the corrugating step.

Corrugating the paper sheet into a corrugated form may also include passing the paper sheet between a pair of co-operating rollers having mating surfaces with crests and troughs that impart a corrugated profile.

In one embodiment, the process may also include forming the ply layers. Forming the ply layers may include creating a paper pulp slurry containing the paper fibre, and delivering the slurry onto a travelling wire at the wet end of a paper making machine .

While it is possible that the additive may be added to the one or both of the paper pulp slurry that from the ply layers, ideally the additive is applied to one or both of the faces of the ply layers prior to the ply layers being overlaid during joining the ply layers. The step of incorporating the additive in the paper sheet may include any one or a combination of the following.

i) Adding the additive in a paper pulp slurry feed to the headbox of a papermaking machine so that the additive is distributed through the ply layer of the headbox. The additive can be added as a wet slurry, or in pre-mixed and dried powered form. In this instance, the additive distributed in the ply layer will be present at the interface with an adjacent ply layer that may not have the additive distributed therethrough.

ii) Applying the additive to a face of the ply layer that is discharged from a paper machine head box. For instances, the additive may be sprayed onto face of one or more ply layers on a wire at the wet end of the paper machine and another ply layer laid thereover top. iii) Applying the additive to the paper sheet after the ply layers have been joined together. For example, the play layers may be dried in a drier and the additive applied to the paper sheet in size press. In another example, the additive may be applied by meter press roll. According to either example, the additive can migrate into the paper sheet, including to the interface between the ply layers.

An embodiment also relate 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 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 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 both of the ply layers .

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 play layers may be dried in a drier and the nano- particles 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 additive can migrate into the paper sheet. The nano- particles may be applied to the paper as a dispersion that is formed by suspending the nano-particles in water, for example, separating the sheets of the nano- particles in the high shear mixer or 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. ii) Adding the nano-particles in a paper pulp slurry feed to the headbox of a papermaking machine so that the nano- particles is distributed through the ply layer of the headbox. The additive can be added as a wet 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 of one or more ply layers on a wire at the wet end of the paper machine and another ply layer laid thereover top . er embodiment relates to a process of manufacturing a gated paper, the process including:

locating an additive between two sheets of paper;

joining the sheets together with the additive therebetween to form a medium; and

corrugating the medium into a corrugated form;

wherein the additive enhances the bond between the sheets and includes nano-particles that can bond to any one or a combination of the fibre of the paper sheets or starch of the paper sheets .

Ideally, the additive is a wet additive.

Corrugating the paper sheet into a corrugated form may also include passing the paper sheet between a pair of co-operating rollers having mating surfaces with crests and troughs that impart a corrugated profile.

The additive may be applied to one or both of the joined faces of the sheets prior to the sheets being joined together.

The additive may be applied using any suitable means including spraying the additive onto the paper sheet and applying the additive by means of roller application.

The process may also include applying at least one liner board to the corrugated paper after the corrugating step. The corrugated paper may be bonded to any number of other sheets including liner boards, internal dividing sheets, and other corrugated papers. The other corrugated papers may also be made according to the process of the present invention.

The process of the present invention may include any one or a combination of the features 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

A preferred embodiment will now be described with reference to the accompanying Figures, of which:

Figures la and lb are schematic perspective views of a paper sheet and a corrugated paper respectively;

Figures 2a, 2b and 2c are alternative schematic cross-sectional views of the section shown in the dashed circle in Figure la; Figure 3a, 3b and 3c are alternative schematic cross-sectional views of the section in the dashed circle in Figure lb;

Figure 4 is a schematic illustration of a process of making a paper sheet that can be converted into a corrugated paper or a paper sheet shown in Figures la or lb respectively in which the process includes forming two ply layers, joining the ply layers together with the additive located at the interface between the layers or incorporated in the ply layers to improve the performance of the corrugated paper;

Figures 5a and 5b are schematic illustrations of two processes for applying the additive to the surface of the paper sheet, in which Figures 5a and 5b are representative of the process steps of block 20 of Figure 3; Figure 6 is a schematic illustration of a process for

corrugating a corrugating paper (or paper sheet) to form the corrugated paper of any one of Figures lb, 3a, 3b and 3c, in which the paper sheet is heated to soften the thermoplastic of the paper sheet;

Figure 7 is a schematic illustration of a process of making the corrugated paper shown any one of Figures lb and 3a in which the process includes joining two sheets and applying an additive to the interface between the layers to improve the performance of the corrugated paper formed therefrom;

Figure 8a is a graph illustrating the improved performance of the single sheet of lOOgsm paper that has been treated with starch and nano-clay at a weight of approximately 4.5gsm;

Figure 8b 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 bewteen the sheets; and

Figure 8c 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 4.5gsm.

DETAILED DESCRIPTION

A preferred embodiment will now be described with reference to the accompanying figures. To assist in identifying the various features reference numerals have been includes in the text and figures. The same reference numerals have been used on similar or alike features of the various embodiments. However, in order to maintain clarity of the figures, not all of the reference numerals have been used in each of the figures.

With reference to the Figures, Figure la illustrates a paper sheet 10 suitable for a corrugating paper including two base sheets 11 and 12 (or ply layers 11 and 12), with an additive 13 at the interface therebetween. It will be appreciated that the paper sheet 10 may be of any form, including for example, corrugated paper, liner boards for cartons, liner boards for corrugated paper and liner boards for plaster board.

Figures 2a and 2b are schematic cross-section views of the corrugated paper shown in the dashed circle in Figure 1 in which the dots 13 represent the additive in the paper sheet 10. The additive 13 may be present in one or more of the various sections of the paper sheet, including being distributed through the thickness of the paper sheet 10, or on an outer surface and section immediately inward of the outer surface only, or on inner sections of the paper sheet 10 only, for example, at the interface between the base sheets 11 and 12 (or the ply layers 11 and 12) . Figure 2a illustrates the situation in which the additive 13 is present at the interface between the base sheets 11 and 12 (or the ply layers 11 and 12), and has migrated to some extent through the base sheets 11 and 12 (or ply layers 11 and 12) . Figure 2b illustrates the situation in which the additive 13 is incorporated throughout the base sheets 11 and 12 (or ply layers 11 and 12) .

Figure 2c illustrates the situation in which the additive 13 is located on an outside of the paper sheet 10 and has penetrated a small distance into the paper sheet 10.

Figure lb is a schematic illustration of a paper sheet 10 in the form of a corrugated paper having one or more than type of additive 13 that are described herein to improve the performance of the corrugated paper. Figures 3a to 3c are enlarged schematic cross-sectional views of the portion shown in the dashed circle in Figure lb. Specifically, figure 3a illustrates the situation in which an additive 13 is located at the interface between base sheets 11 and 12, and the situation in which the additive 13 has migrate to a small extent into the base sheets 11 and 12. Figure 3b illustrates the situation in which the additive 13 is distributed through the thickness of the base sheets 11 and 12. Figure 3c illustrates the situation in which the additive 13 has been applied to an outside surface of the paper sheet 10 and migrated to an extent into the paper sheet 10.

The additive may include any one or a combination of the following.

a) A plasticizing agent that can form a thermoplastic

starch that is heat softenable. Examples of

plasticizing agents include glycerol and sorbital.

b) Nano-particles , including for example, clay nano- particles and cellulose nano-particles, having a size in the range of equal to, or less than 500nm, and suitably equal to, or less than lOOnm. The nano- particles may have a platelet shape having a thickness in the range of the 1 to 5nm, and suitably

approximately 1 nm, and a diameter in the range of 1 to ΙΟμτη. Clay nano-particles can bond, for example by physical or chemical bonding, to the starch and/or cellulose of the ply layers and, in turn, increase the stiffness of the paper sheet. Examples of other nano- particles that could be used include graphite or graphene platelets, carbon nanotubes (fibers/whiskers), ZnO and Ti0 2 .

A non-exhaustive list of characteristics that may be improved by the additive are as follows.

1. The additive 13 may allow or facilitate relative

movement of the ply layers 11 and 12 (or the base sheets 11 and 12) when the paper sheet 10, for example, is in the process of being corrugated, which typically involves being subjected to heat, pressure and moisture. Advantageously however, after the sheet 10 has been corrugated and cooled, the additive 13 may have an ability to harden and, without wanting to be limited by theory, increase the bond between fibre, cellulose and starch within the base sheets 11 and 12 (or the ply layers 11 and 12), and between the base sheets 11 and 12 (or the ply layers 11 and 12), thereby potentially improving the structure and performance of the sheet 10.

2. The additive 13 may include either one or both of the plasticizing agents and nano-particles and during a corrugating step, the paper sheet and ideally the interface between the ply layers will soften when heated and "slip" avoiding delamination . After the corrugation step is complete, the interface will cool and stiffen.

The additive 13 may produce two practical advantages. Higher grammage ply layers that are inherently stiffer can be used on account that the ply layers are less likely to delaminate, thereby enabling a corrugated paper to be made with a higher stiffness.

Thermoplastic additive can increase the shear stiffness of the paper sheet particularly when cooled and devoid of significant corrugating damage. Furthermore, clay platelet shaped nano-particles can, in addition to allow "slippage" of the ply layer during corrugation, increase the stiffness and creep resistant properties of the paper sheet, and slow moisture uptake which can result in a better resistance to creep in cyclic and high humidity conditions .

5. When the additive 13 includes nano-particles, the nano- particles can occupy voids between the starch molecules, cellulose and the fibre of the paper sheet, thereby reducing the mobility of the matrix structure of the paper sheet 10, making the paper sheet 10 stiffer than equivalent paper sheets at without nano-particles .

6. In addition to making the paper sheet 10 stiffer, the nanoparticles can infill voids in the matrix structure of the paper sheet 10, increasing the hydrophobicity of the paper sheet 10. In turn, the paper sheet 10 will have an increased stiffness and better creep resistant properties in a cyclically and high humidity conditions .

The manner in which the additive 13 is included in the paper sheet 10 can be achieved by several means.

Figure 4 is a schematic illustration of the process for making a paper sheet 10 in which the process includes forming the ply layers 11 and 12 by delivering sequentially, two suspensions lis 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.

The additive 13 can be added to the suspensions lis and 12s, for example, in upstream mixing vessels 21 in which the suspensions lis and 12s are prepared. The suspensions lis and 12s are then fed to the headboxes 18. It is also possible that the additive 13 can be added directly to the headboxes 18.

In another example, part of the additive 13 such as clay nanoparticles can be added to the upstream mixing vessels 21, and another part of the additive 13, such as a plasticizing agent can be added to the suspension in the head boxes 18, or vice versa .

By including the additive 13 in the suspensions lis and 12s, the additive 13 will be distributed throughout the entire thickness of the respective ply layers 11 and 12 discharged from the respective headbox 18, which can product the structures shown in figures 2b and 3b. In some situations, the additive 13 need only be present, and preferably, but not necessarily, at the interface between the ply layers 11 and 12 to benefit the paper sheet 10, as shown in Figure 2a and 3a.

Figure 4 also illustrates a step of applying the additive 13 to the face of the first ply layer 12. Specifically, the first ply layer 12 is discharged from a first headbox 18 onto the wire 17, and the additive 13 is 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. For example, the additive 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 step 14 may include dewatering and drying the paper sheet 15 in a drier.

The additive 13 can be added to the paper sheet 15 by means of either one or a combination of: i) adding the additive to the suspensions lis and 12s in the mixing vessels 21 or the head boxes 18, or ii) applying a solution containing the additive to the surface of one of more of the ply layers using, for example, sprayer 19. Although Figure 4 illustrates the sprayer 19 in a located for applying the additive 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 the additive 13 to the outer face of ply layers 11 and 12. In any event, when the sprayer 19 is used to apply the additive 13, the interface between the ply layers 11 and 12, the structure shown in figures 2a and 3a can result .

As shown in Figure 4, the process may optionally include applying the additive to the outer face of the paper sheet 15 in step 20, which is described in detail below with reference to Figures 5a and 5b. Following step 20 the paper sheet 15 can be rolled into a roll 22 for storage where the paper sheet can cool. The roll 22 can be called from storage for further product as desired.

Figures 5a and 5b illustrate two process steps for treating the surface of the paper sheet 15 with the additive 13. Moreover the processes illustrated in Figures 5a and 5b can be used with, and in addition to the process illustrated in Figure 4. It is possible that the additive 13 may not be included in the suspension lis and 12s, or applied to the surface of the ply layers via sprayer 19 in accordance with Figure 4, but rather, the additive may be applied solely to the outside face of the paper sheet 15 according to the processes shown in Figures 5a and 5b .

The processes of Figure 5a and 5b include forming an aqueous solution of the additive 13, such as plasticising agent and optionally nano-particles , suitably clay nano-particles . A solution of the clay nano-particles is formed by dispersing the nano-particles supplied in a powder/aggregate form in a high shear mixing tank 25. The additive 13 may also include one or more plasticising agents for forming a thermoplastic polymer with starch as described herein. From the mixing tank 25, the dispersion is supplied to a pool 27. The process illustrated in Figures 5a and 5b can be used alternately or in combination.

Figure 5a 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 also include other agents such as addition 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.

Figure 5b illustrates the pool 27 being arranged to feed to meter roller having grooves or indentations on the surface of the metered roller 30 that receives the solution and applies the solution containing the additive to the paper sheet 15. A transfer roller 31 may convey the solution from the pool 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. Moreover, the amount of the additive applied to the sheet 15 passing through the pool 27 can be controlled by adjusting one or more of, the speed of the meter roller 30, the number fo the grooves on the meter roller 30, the residence time of the paper sheet 15 in the pool, or the nip pressure between the rollers 26, or between the rollers 30 and 32. Moreover, the process may include controlling the degree of migration, penetration of the additive into the paper sheet, for example, by adjusting the nip pressure between the rollers 26, or between the rollers 30 and 32.

The processes shown in Figures 5a and 5b can product the structures shown in figures 2c and 3c.

Figure 6 illustrates the process of corrugating the paper sheet 15. The process may include a preliminary heating step 33 for heating the paper sheet 15 and activate the additive 13 prior to corrugating the paper sheet 15. Activating the additive 13, preferably including a plasticising agent, allows the starch to behave in a thermoplastic manner. The paper sheet 15 is then conveyed through a mating pair of rollers 16 that include cooperating crests and troughs to impart a corrugating profile on the paper 15. The paper sheets 15 can also be moistened prior to passing through the corrugation rollers 16 or subjected to any other treatment to ready the paper sheet 15 for corrugation. During the corrugating step, the additive allows the ply layer 11 and 12 to move relative to each other to some extent, reducing the risk of delamination of the ply layers 11 and 12. Figure 6 also illustrates that steps of attaching two liner boards 34 and 35 to the opposite faces of the paper sheet 15 have a corrugated conformation.

Figure 7 is a schematic illustration of a process for converting two preformed paper base sheets 11 and 12 into a corrugated paper 10. The preformed paper sheets 11 and 12 may be provided in a roll formation and can be obtained from any source and may each, for example, have a grammage ranging from 20 to 200 gsm. As shown in figure 7, the additive 13 may be applied to one or both of the surfaces of the preformed sheets 11 and 12 that face each other using a spray box 19. However, it will be

appreciated that any suitable method such as roller application, meter rollers, or even passing the preformed sheets through a bath/pool containing the additive can be used.

The amount of the additive 13 applied to the paper sheets 11 and 12 can be controlled. For example, controlling the amount of additive 13 applied may include adjusting the rate at which the additive solution is sprayed from the sprayer 19, or adjusting the speed of the paper sheets 11 and 12 passing the sprayer 19. In addition the degree of the penetration of the additive into the base sheets 11 and 12 can be controlled by adjusting the nip pressure between the rollers 14 and the amount of the additive solution sprayed onto the base sheets 11 and 12.

The following application of the additive 13, the two sheets 11 and 12 are then joined together. The joining step may include pressing the sheets 11 and 12 together, for example, by passing through a nip of a pair of pressure rollers 14 to form an intermediate sheet 15. The intermediate sheet 15 is then corrugated by passing between a mating pair of co-operating rollers 16 that include co-operating crests and troughs which impart a corrugated profile to the paper sheet. The corrugated sheet 10 can then be cut to length as desired.

In other processes (not illustrated in the figures of the specification), the pressure rollers 14 may not be required and the sheets 11 and 12 may be simultaneously joined and corrugated between the corrugating rollers 16.

Once the intermediate sheet 15 has been conveyed through the corrugating rollers 16, liner board 20 may be bonded, for example using an adhesive, to the undulations of one or both of the faces of the corrugated paper 10.

When an additive in the form of nano-particles is present on the outer face of the corrugated paper 10, the nano-particles may, in addition to affecting the mechanical properties of the corrugated paper 10, enhance the bond between the corrugated paper 10 and the liner board 20.

The additive may be included in a solution that is applied to one or both of the sheets 11 and 12 prior to the sheets being joined and corrugated. Ideally, the additive includes nano- particles such as either one or a combination of clay

nanoparticles and cellulose nano-particles . However, the additive may also include other types of the nano-particles such as those mentioned herein.

Ideally the clay nano-particles have a size in the range of equal to, or less than 500nm, and suitably equal to or less than lOOnm. Ideally, the nano-particles may be platelets having a thickness in the range of the 1 to 5nm, and suitably

approximately 1 nm, and a diameter in the range of 1 to ΙΟμτη. The nanoparticles, particularly clay nano-particles can bond, for example by physical or chemical bonding, to the starch and/or cellulose of the corrugated paper 10 and increase the stiffness of the paper 10.

Trials

A set of trials have been carried to measure the performance of a paper sheet that has been treated according to a preferred embodiment. The standard test methods we used are a ring crush strength (RCS) test, and a high humidity load carrying capacity (HHLCC) test. Both tests are standard test methods and were carried out on i) untreated paper for use a control, and a paper treated with an additive in accordance with the embodiments described herein. The RCS test method involves a compression force being exerted 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.

The HHLCC test method is the same as the RCS test method described above, save for the additional following steps:

i) The sample is exposed to an 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 to collapse

measured (i.e. creep test) iii) The load and time to collapse is used to determine and measure creep performance in a cyclic high humidity environment .

Trial one

A lOOgms paper sheet was surface treated using a mixture of starch and nano-clay at a weight of 4.5gsm. The mixture may be applied to the surface of the paper sheet using the size press methodology shown in figures 5a and 55, or sprayed onto the surface of the paper sheet. The treated paper sheet had a structure as shown in figure 3c and the mixture comprised starch and nano-clay in proportions of 85% starch and 15% nano-clay.

Figure 8a shows the test results of the treated and untreated paper sheets. As can be seen, the RCS of the paper sheet increased by approximately 8% and the HHLCC of the same paper sheet increased by approximately 13%. This is considered to be a considerable improvement.

Trial two

Two layers, each of lOOgms, where sandwiched together using a mixture of starch and nano-clay that was applied at a weight of approximately 9gsm between the sheets. The mixture may be applied to either dry or wet layer, for example by means of the spray boxes 19 in figures 4 and 7, or by suitable means such as roller application, meter rollers, or even passing the preformed sheets through a bath containing the additive. In any event, the layers may form a paper sheet having the structure shown in figures 2a or 3a. The mixture comprised 25% nano-clay and 75% starch .

Figure 8b is a graph illustrating the improved performance of the sandwich paper sheet. The RCS of the sandwich does not increase significantly, however, the HHLCC of the same sample of paper increases by approximately 13%.

Trial three

A 135gms paper sheet was surface treated using a mixture of starch and nano-clay at a weight ratio of 4.5gsm. The mixture may be applied to the surface of the paper sheet using the size press methodology as shown in figures 5a and 55, or sprayed onto the surface of the paper sheet. In any event, the paper sheet had a structure as shown in figure 3c and the mixture comprised 85% starch and 15% nano-clay. Figure 6c is a graph illustrating the improved performance of the paper sheet. Specifically, the RSC of the paper sheet increased by approximatly 5%, and the HHLLC of the same sample increases by approximately 4%.

One of the benefits of the present invention is that the performance characteristics, such as ultimate load strength, shear stiffness and bending stiffness can be improved by the additive. This means that a corrugated paper containing a higher percentage of the recycled fibres can be produced with characteristics more akin to a product made from virgin fibre. Similarly, when applied to a paper sheet comprising virgin fibre, the embodiments could further improve the performance o the product compared to other corrugated paper of similar grammage made of the virgin fibre.

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.