NZ720854A - Corrugated medium, paper sheet and a process for the manufacture thereof - Google Patents

Abstract

The present invention relates to a corrugated medium and process for the manufacture thereof that seeks to enhance the bond between the sheets of the corrugated medium and increase creep resistance and ring crush strength. The corrugated medium includes an additive located between the paper sheets that includes clay nano-particles that bond to fibre of the paper sheets, and an adhesive to join the at least two paper sheets together.

Description

CORRUGATED MEDIUM, PAPER SHEET AND A PROCESS FOR THE CTURE THEREOF FIELD OF THE PRESENT INVENTION The present invention relates to a corrugated medium, a paper sheet, and process for the cture thereof. Corrugated medium can be used in a range of applications, including making corrugated board and boxes.

BACKGROUND OF THE INVENTION Corrugated board is a high strength product used in the manufacture of cartons that are used for a range of purposes, including storing fresh food items under moist conditions such as high humidity environments and cold storage. The cartons are also ed to m 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 g humidity environments is the product’s ability to resist "creep", which can be an ant characteristic depending on the circumstances.

Moreover, the performance of the corrugated medium of a corrugated board is ent on a vast number of different variables including, but by no means limited to: quality of the fibre material, particularly virgin fibre versus ed fibre; grammage of the corrugated medium; the flute size and geometry of the corrugated medium; degree of damage resulting from the forces in the corrugating nth, adhesion of the ated medium to the liner boards; moisture resistance of the ated medium; 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 ated medium (both material and structural) plays an important role in the performance of the corrugated medium. Ideally the corrugated medium is as stiff as possible, as this would have the potential to reduce the grammage of the liner board ed to produce a corrugated board. However, the grammage of corrugated medium is generally limited to about 180 gsm. In our experience corrugated medium 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 40 pressure. Delaminating permanently weakens the boards as shear stiffness is greatly reduced. 18245247_1 (GHMatters) P103275.NZ 17/11/21 SUMMARY OF THE INVENTION An embodiment relates to a paper substrate including: at least two layers that are joined together, and an additive that is located between the layers that enhances the bond between the layers together, wherein the additive includes nano-particles that bond to base material of the layers.

The base material may include fibre of the .

The base layer may include cellulose of the layers.

The base layer may include starch of the layers. hout this specification the term "paper , or ions f such as a "sheet of paper" and "sheet" embraces any planar structure including singular ply layer only, and multiple ply sheets. The term "paper sheet" also embraces paper joined to non-paper materials such as polymeric film, metallic foil, coatings of wax and so forth.

Corrugated medium An embodiment s to a corrugating medium 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 and increases creep resistance and ring crush strength compared to a paper sheet having no nano-particles, wherein the additive includes clay nano-particles that bond to fibre of the paper sheets, and an adhesive to join the at least two paper sheets together.

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

Enhancing the bond between the paper sheets may enhance one or more of the performance characteristics of the corrugating . For example, sing the bond between the sheets may increase the ultimate loading point at which the corrugated medium fails when subjected to a load. In some situations, the bending ess or the shear stiffness of the corrugated medium may be increased at any one point in time after manufacture. It will be appreciated however, that an increase 18245247_1 (GHMatters) P103275.NZ 17/11/21 in shear ess and g 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, se the ultimate load point, or even reduce the ultimate load point of the corrugated medium.

When the two paper sheets are joined directly to each other, that is without any additional paper sheet therebetween, the additive may be located at the interface between the sheets, and may penetrate into the sheets to a degree.

In the situation where the corrugated medium includes more than two paper , the additive may be located n any two juxtaposed sheets, i.e., at the interface between the layers.

As well as being present at the ace between the sheets, the additive may also penetrate the sheet to some extent, complete through one or more of the sheets. In one example, the additive may be d to a surface of one of the sheets only, and the additive absorbed to an extent by the other sheet.

The additive may penetrate nearly entirely through each sheet, but may also penetrate only to a smaller extent, for example, up to 50% of the thickness of the sheets, or only up to 30% of the thickness of the sheets.

In one ment, the additive may be absent from the outer face of the paper sheet.

In the situation in which the corrugated medium has three or more , the additive may be present between each of the sheets.

The corrugated medium may also include other adhesives, such as starch and/or PVA to bond the sheets together.

Paper sheet An ment also relates to a paper sheet for use as a corrugating medium, 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 and increases creep resistance and ring crush strength ed to a paper sheet having no nano-particles, wherein the additive includes clay nano-particles that can bond to fibre of the paper sheets and an adhesive to join multiple ply layers together. 18245247_1 (GHMatters) P103275.NZ 17/11/21 Another embodiment also relates to a paper sheet that can be used as a corrugating medium, 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 n the ply layers during corrugation of the sheet and increases creep ance and ring crush strength compared to a paper sheet having no rticles , wherein the additive includes clay nanoparticles that can bond to fibre of the paper sheets and an ve to join multiple ply layers together.

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.

When the two ply layers are joined to each other, that is without any onal 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, the invention es the situation in which the additive is located between any two juxtaposed ply layers, i.e., at the interface between the layers.

The additive may increase the strength of the bond between the , 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 mance teristics of the paper sheet and particularly a corrugated medium 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 medium fails. In some situations, the enhanced bond may increase shear stiffness and bending stiffness of the paper sheet including corrugated mediums made therefrom. It will be appreciated however, that an increase in shear stiffness and bending stiffness does not necessitate an increase in the ultimate g point.

In one embodiment, the additive may be absent from the outer 40 face of the paper sheet. 18245247_1 (GHMatters) P103275.NZ 17/11/21 In one embodiment, the additive may be incorporated into one or more than of the ply layers. For example, the ve 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 wet slurry or in xed 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 ve may migrate from the ply layer having the additive distributed therein to the ply layer in which the additive is not buted therein.

In another 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 yet r embodiment, the additive may be applied to the surface of the paper sheet, and the additive migrates into the paper sheet, including for instance to the interface between the ply layers.

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

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

The additive 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 s 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 40 ply layers themselves within the paper sheet fracturing. 18245247_1 (GHMatters) P103275.NZ 17/11/21 The additive may be 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.

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

The additive may also include starch.

The additive may include a combination of a plasticizing agent and starch at the interface n the ply layers. 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.

An advantage in using a plasticizing agent that can form a thermoplastic with starch is that it is heat able, 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.

Nano-particles The additive may include nano-particles. The nano-particles may e clay nano-particles. Examples of other nano-particles that may be included in the additive include graphite or graphene ets, carbon nanotubes, and ZnO or TiO 2 nano- particles.

The additive may include cellulose nano-particles or derivatives thereof, including nanocrystalline cellulose, cellulose nanocrystals, cellulose whiskers, brillated cellulose, cellulose nanofibrils, microfibrillated ose, carboxymethylated cellulose, microcrystalline cellulose, and cellulose filaments.

The additive may include a combination of clay nano-particles, ose articles and starch.

In one embodiment, the nano-particles may be in the form of clay 40 nano-particles only. 18245247_1 (GHMatters) P103275.NZ 17/11/21 In an embodiment, the nanoparticles may be in the form of ose nano-particles only.

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

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

When the additive includes clay and cellulose articles, the nanoparticles may be provided in any proportion. For instance, the additive 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 nanoparticles and cellulose rticles 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 d 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. articles have a large surface area per unit weight or volume hence significant s of the matrix can be affected.

Restricting the matrix molecule mobility on this minute scale can increase stiffness and in addition e creep performance in cyclic or high humidity ions.

The nano-particles may have a size in the range of equal to, or less than 500nm and may have a size range of equal to or less than 100nm. 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 er in the range of 0.1 to 10µm.

The nano-particles may be any suitable particle for bonding to starch and/or cellulose, and suitably the nano-particles are in the form of clay nano-particles. The nano-particles may also include cellulose nano-particles or derivatives thereof, including nanocrystalline cellulose, cellulose nanocrystals, cellulose whiskers, nanofubrillated ose, cellulose nanofibrils, microfibrillated cellulose, carboxymethylated cellulose, microcrystalline cellulose, and cellulose filaments. 40 The clay articles are ideally in the form of the platelets and may have the size ranges mentioned above. 18245247_1 (GHMatters) P103275.NZ 17/11/21 Examples of other nano-particles that can be included in the corrugated medium include graphite or graphene platelets, carbon nanotubes (fibres/whiskers), ZnO and TiO2 rticles.

An advantage in the additive including nano-particles is that the particles can bond to the starch and/or ose of the paper sheets and increase the structural performance of the paper sheet at a minute level to enhance the over performance of the sheet. The bond between the nano-particles and the starch and/or cellulose may be in the form of physical bonding, but is ideally in a chemical bond. The nano-particles may also bond to themselves.

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

The nano-particles, and especially clay nano-particles, also provide the benefit of sed cyclic or high ty creep resistance, stiffness and possibly the fail strength by forming bonds to starch and/or cellulose, and improving the moisture r property. In other words, the presence of nanoparticles , paper creep will show a noticeable improvement in performance in moist or humid environments.

Manufacturing corrugated medium An embodiment also relates to a process of manufacturing a corrugated medium, 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; n the additive es the bond between the sheets and increases creep resistance and ring crush strength compared to a paper sheet having no nano-particles, the ve includes clay nano-particles that can bond to fibre of the paper sheets, and an adhesive to join the at least two paper sheets.

Ideally, the additive is a wet ve. ating 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. 18245247_1 (GHMatters) P103275.NZ 17/11/21 The ve 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 ng the additive by means of roller application.

The process of manufacturing a corrugated medium may also include applying at least one liner board to the corrugated medium after the corrugating step. The ated medium may be bonded to any number of other sheets including liner boards, internal dividing sheets, and other corrugated mediums. The other corrugated mediums may also be made according to the process of the present ion.

Manufacturing a paper sheet An ment also relates to a process of manufacturing a paper sheet that can be used as a corrugated medium, the process including the steps of: forming sheet including one or more than one ply layer; incorporating an additive in the paper sheet including clay nano-particles that can bond to fibre of the paper sheet and an adhesive to join le ply layers together; 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 ure and/or join between the ply layers during corrugation of the sheet and increases creep resistance and ring crush strength compared to a paper sheet having no articles.

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 ated 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 18245247_1 (GHMatters) P103275.NZ 17/11/21 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 g 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 ve 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 e, the play layers may be dried in a drier and the additive applied to the paper sheet in size press. In another e, 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 n the ply layers.

The processes described herein may also include any one of the features of the corrugated medium and the paper sheet described herein. Similarly, the corrugated medium and the paper sheet may also include any one or a combination of the features of the processes described herein.

BRIEF PTION OF THE DRAWINGS A preferred embodiment will now be described with reference to the anying Figures, of which: 40 A preferred embodiment will now be described with reference to the anying s, of which: 18245247_1 (GHMatters) P103275.NZ 17/11/21 Figure 1 is a schematic perspective view of a corrugated medium; Figures 2a and 2b are alternative schematic cross-sectional views of the section shown in the dashed circle in Figure 1; Figure 3 is a tic illustration of a process of making a paper sheet that can be made into a corrugated medium shown in Figure 1 in which the process includes forming two ply layers, g the ply layers er with the additive located at the interface between the layers or incorporated in the ply layers to improve the performance of the corrugated medium; Figures 4a and 4b are schematic illustrations of two processes for applying the additive to the surface of the paper sheet, Figure 4 is representative of the process steps represented by block 20 of Figure 3; Figure 5a is a tic illustration of a corrugating the paper sheet of any one of Figures 1 to 4, in which the paper sheet is heated to soften the plasticising agent of the paper sheet; and Figure 5b is a schematic illustration of a process of making the corrugated medium shown in Figure 1 in which the process es joining two sheets and ng an additive to the interface between the layers to improve the performance of the corrugated medium formed therefrom; Figure 6a is a graph illustrating the improved performance of the single sheet of 100gsm paper that has been treated with starch and nano-clay at a weight of approximately 4.5gsm; Figure 6b is a graph illustrating the improved performance of a sandwich of the two 100gsm sheets of paper in which starch and nano-clay has been applied at a weight of approximately 9gsm bewteen the sheets; and Figure 6c 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 imately 4.5 gsm.

DETAILED DESCRIPTION With nce to the Figures, Figure 1 illustrates a paper sheet 10 in the form of a corrugated medium. The corrugated medium may including two joined paper sheets 11 and 12 with an additive at the interface between the , or two joined ply layers 11a and 12a that form a single a paper sheet, with an additive at the interface between the ply layers 11a and 12a. 18245247_1 ters) P103275.NZ 17/11/21 To assist in illustrating the corrugated medium 10, liner board which is typically applied to the corrugated medium has been omitted from Figure 1.

Figures 2a and 2b are schematic cross-section views of the corrugated medium shown in the circle in Figure 1 in which the dots 13 represent the additive in the paper sheet 10. The additive may be present at various sections in the thickness of the paper sheet from an outer surface, to inner sections, and to the interface between the paper sheets 11 and 12, or the ply layers 11a and 12a. Figure 2a illustrates the situation in which the additive is present at the interface between the paper sheets 11 and 12, or the ply layers 11a and 11b and has migrated to some extent through the ply layers 11a and 11b. Figure 2b illustrates the situation in which the additive is incorporated throughout the paper sheets 11 and 12, or the ply layers 11a and Ideally, the additive includes nano-particles 13 to enhance the bond n the sheets 11 and 12 or the ply layers 11a and 12a, and thereby reduce or eliminate nation of the sheets 11 and 12 or ply layers 11a and 12a, particularly after the corrugating step when the additive has cured.

The additive 13 can also allow and facilitates relative movement of the ply layers 11a and 12a when the paper sheet 10 is in the process of being corrugated, for example, when subjected to heat, re and moisture. Advantageous r, after the sheet has been corrugated and cooled, the additive has the y to harden and, t wanting to be limited by theory, increase the bond n fibre, cellulose and starch within the ply layers 11a and 12a, and between the ply layers 11a and 12a, thereby potentially improving the structure and performance of the sheet.

In the situation in which the corrugated medium is a single paper sheet including two ply layers 11a and 12a joined to together, the ve may include any one or a combination of the following. i) A plasticizing agent that can form a thermoplastic with starch that is heat softenable. Examples of plasticizing agents include ol and al. ii) Nano-particles, including clay nano-particles and 40 cellulose nano-particles, having a size in the range of equal to, or less than 500nm, and suitably equal to, or less than 100nm. The clay nano-particles may 18245247_1 (GHMatters) P103275.NZ 17/11/21 have a platelet shape having a ess in the range of the 1 to 5nm, and suitably approximately 1 nm, and a diameter in the range of 1 to 10µm. Clay nanoparticles 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. Examples of other nano-particles that could be used include graphite or graphene platelets, carbon nanotubes (fibers/whiskers), ZnO and TiO2.

Ideally, the additive will include both plasticizing agents and nano-particles and during the 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 te, the interface will cool and stiffen.

This will 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 medium to be made with a higher stiffness.

In addition, the thermoplastic additive can increase the shear ess of the paper sheet ularly 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 re uptake which can result in a better resistance to creep in cyclic and high humidity conditions.

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

In on, the additive containing nano-particles can penetrate into the paper sheets and thereby enhance the bond between fibre of each sheet, thereby reducing delamination of individual fibres from each other and, in turn, reducing cracking of the corrugated medium during the ation step and particularly after the corrugating step when the additive has cured. In addition, the additive 13 can provide the t of increasing moisture resistance of the corrugated medium 10, and thereby e creep resistance in cyclic or high humidity nments. 40 Figure 3 is a schematic illustration of a process for making the corrugated medium 10 according to an embodiment in which the process includes forming the ply layers 11a and 12a by 47_1 (GHMatters) P103275.NZ 17/11/21 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 11a and 12a are id in stagewise manner.

The additive 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 additive can be added directly to the headboxes 18.

In another example, part of the additive such as clay nano- particles can be added to the upstream mixing vessels 21, and another part of the additive, such as a plasticizing agent can be added to the suspension in the head boxes 18.

By including the ve in the suspensions 11s and 12s, the additive 13 will be distributed throughout the entire thickness of the respective ply layer 11a and 12a delivered from the headbox 18. However, the additive 13 need only be present, and preferably, but not necessarily, at the interface n the ply layers 11a and 12a to benefit the paper sheet 10.

Figure 3 also rates a first ply layer 12a delivered 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 11a being delivered onto the first ply layer 12a. The ve 13 may be sprayed onto the upper face of the first ply layer 12 by a sprayer 19. Thereafter the ply layers 11a and 12a 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 11s and 12s in the mixing vessels 21 or the head boxes 18, or ii) applying a solution ning the additive to the surface of one of more of the ply layers using, for example, r 19. Although Figure 3 illustrates the sprayer 19 in a located for applying the additive to ply layer 12a, it will be appreciated that the sprayer could be arranged to spray the inner face of the play layer 11a. It is also possible that other sprayers could be arranged to apply the additive to the outer face of ply layers 11a and 12a.

As shown in Figure 3, the process may optionally include 40 applying the additive to the outer face of the paper sheet 15 in step 20, which is described in detail below with nce to Figure 4. ing step 20 the paper sheet 15 can be rolled 18245247_1 (GHMatters) P103275.NZ 17/11/21 into a roll 21 for storage where the paper sheet can cool. The roll 21 can be called from storage for further product as desired. s 4a and 4b illustrate process steps for treating the surface of the paper sheet 15 with the additive. er 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 additive may not be included in in suspension 11s and 12s, or applied to the e of the ply layers 11a and 12a via sprayer 19 in accordance with Figure 3, but rather, the additive may be applied solely to the outside face of the paper sheet 15 according to the processes shown n Figure 4a and 4b.

The processes of Figure 4a and 4b include forming and aqueous solution of the ve, such as plasticising agent and optionally nano-particles, ly 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 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 4a and 4b can be 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 also include other agents such as addition starch, sizing agents, ness 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 4b 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 on 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 Figure 5a rates the process of the corrugating the paper sheet 15 having ply layers 11a and 12a. The process may include 40 a preliminary heating step 33 for g the paper sheet 15 and activate the additive prior to corrugating the paper sheet 15. ting the additive, ably including a plasticising agent, allows the starch to behave in a plastic manner. 18245247_1 (GHMatters) P103275.NZ 17/11/21 The paper sheet 15 is then conveyed through a mating pair of rollers 16 that include co-operating crests and s to impart a corrugating profile on the paper 15. The paper sheets can also be moistened prior to g through the corrugation s 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 11a and 12a to move relative to each other to some extent, reducing the risk of delamination of the ply layers 11a and 12a.

Figure 5a 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 5b is a schematic illustration of a process for making the corrugated medium 10 from two preformed sheets 11 and 12 in a rolled formation, joining the sheets 11 and 12, and corrugating together. The rolls can be obtained from any source and may each, for example, have a grammage ranging from 20 to 200 gsm. In one embodiment, the additive 13 is applied to one or both of the surfaces of the preformed sheets 11 and 12 that face each other. Figure 5b illustrates the additive 13 being sprayed onto the surface of the preformed sheets 11 and 12 that face each other. However, it will be iated that any suitable method such as roller application, meter rollers, or even passing the preformed sheets through a bath ning a solution of the additive can be used. ing application of the ve 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 corrugating rollers 16 that include co-operating crests and troughs which impart a corrugated profile to the paper sheet. The corrugated paper sheet 10 can then be cut to lengths as desired.

In other processes (not illustrated in the s of this 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 ed through the 40 corrugating rollers 16, liner board 20 may be , for example using an adhesive, to the undulations one or both of the faces of the corrugated medium 10. 18245247_1 (GHMatters) P103275.NZ 17/11/21 When the nano-particles are present on the outer face of the corrugated medium 10, the articles can also enhance the bond between the corrugated medium 10 and the, or each, of the liner boards 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 ve includes nanoparticles 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 y the clay articles have a size in the range of equal to, or less than 500nm, and suitably equal to or less than 100nm. 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 10µm.

The nanoparticles, particularly clay nano-particles can bond, for example by physical or chemical bonding, to the starch and/or cellulose of the corrugated medium 10 and se the stiffness of the medium 10.

This can provide two practical ages. Firstly, higher grammage paper sheets that are inherently stiffer and previously t unsuitable can be used on account that the sheets are less likely to nate, thereby enabling a ated medium to be made with a higher stiffness.

In addition, clay nano-particles can increase the creep resistant properties of the corrugated medium, and slow moisture up take which can result in a better resistance to creep in cyclic and high humidity conditions.

Figure 6a is a graph illustrating the improved performance of the single sheet of 100gsm paper that has been treated with starch and nano-clay at a weight of approximately . To provide a control, untreated paper is first tested according to the 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 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 40 the sample collapses. The sample is pre-conditioned in a controlled environment having a 50% relative humidity at 23°C. 18245247_1 (GHMatters) P103275.NZ 17/11/21 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 use measured (i.e. creep test) iii) Step ii) is repeated for a series of different loads. iv) The load required to survive one full three-hour ve humidity cycle is estimated ( via the exintercept of log-load(N) versus log-life(at number of relative humidity cycles) a plot). v) The load is used as a measure of Cree performance in a site click high humidity environment.

As can be seen in figure 6a, the RCS of a single 100gs a 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.

Figure 6b is a graph illustrating the improved performance of a sandwich of the two 100gsm sheets of paper in which starch and nano-clay has been applied at a weight of approximately 9gsm n the sheets. The RCS of the sandwich does not increase significantly; however, the HHLCC of the same sample of paper increases by approximately 13%.

Figure 6c is a graph illustrating the improved mance of a single sheet of 135gsm paper that has been treated with starch and nano-clay at a weight of approximately 4.5 gsm. The RCS of the single sheet ses by proximally 5%, and the HH else of the same sample increases by approximately 4%.

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 articles by up to 115%, and ly 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 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 ly in the range of 103 to 18245247_1 ters) P103275.NZ 17/11/21 105% 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 clay nanoparticles, and ii) starch, clay nanoparticles and cellulose nanoparticles.

Table 1 Paper l Starch and Starch, clay Composition (Starch clay nanoparticles and additive nanoparticles cellulose Only) nanoparticles Pulp Fibre % 95 92 85 Starch % 5 5 5 Clay 0 3 5 nanoparticles % cellulose 0 5 5 nanoparticles% Ring Crush 100 range from range from 112 to Strength* % 104 to 110, 125, (relative to lly 108 typically 120 control) High Humidity 100 range from range from 112 to Load Carrying 105 to 115, 125, Capacity * % typcially 113 lly 120 (relative to control) 18245247_1 (GHMatters) P103275.NZ 17/11/21 One of the benefits of the present invention is that the performance characteristics, such as ultimate load strength, shear stiffness and bending ess can be improved by the additive. This means that a corrugated medium containing a higher percentage of the ed 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 of the t compared to other corrugated medium 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. 18245247_1 (GHMatters) P103275.NZ 17/11/21

Claims (6)

1. 1. CLAIMS 5 1. A corrugating medium 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 and increases creep resistance and ring crush strength 10 compared to a paper sheet having no nano-particles, wherein the additive includes clay nano-particles that bond to fibre of the paper sheets, and an adhesive to join the at least two paper sheets together.

2. The corrugated medium according to claim 1, wherein the nano- 15 particles are located at the interface between the sheets and has penetrated into the sheets to a degree.

3. The corrugated medium ing to claim 1 or 2, wherein the nano-particles are platelets having a thickness in the range of

4. 0.5 to 5.0nm and a er in the range of 0.1 to 10.0µm. 20 4. The corrugated medium according to any one of the preceding claims, wherein the nano-particles e cellulose nanoparticles.

5. A process of cturing a corrugated medium, the process 25 locating an additive between two sheets of paper; joining the sheets together with the ve therebetween to form a medium; and corrugating the medium into a corrugated form; wherein the additive es the bond between the sheets 30 and increases creep resistance and ring crush strength compared to a paper sheet having no nano-particles, the ve includes clay nano-particles that can bond to fibre of the paper sheets, and an adhesive to join the at least two paper sheets together. 35

6. The process according to claim 5, wherein corrugating the paper sheet into a corrugated form es passing the paper sheet between a pair of co-operating rollers having mating 18245247_1 (GHMatters) P103275.NZ