PAPER STRENGTHENING METHODS AND APPARATUS FIELD OF THE INVENTION

The present invention relates to the field of paper production. The present invention will be described with particular reference to paper produced from the pseudostems of banana plants, but is not so limited.

INCORPORATION BY REFERENCE

The entire contents of Australian Provisional Application Nos 2006903588 and

2006905439 are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Relatively high quality paper can be produced from the pseudostems of banana plants, by slicing the pseudostem into one or more thin sheets of fibres. WO2006/ 029469 describes one way of achieving this.

However, the main fibre direction in banana plants is longitudinally up the trunk. Accordingly, the paper produced is composed of generally parallel fibres running the length of the sheet. Therefore, although resistant to tearing in the lateral direction ("across the grain"), the paper is vulnerable to a longitudinal tear ("along the grain").

One method of addressing this problem is to laminate two sheets together such that the fibres of respective sheets run perpendicular to each other. The sheets are then cured, and the resultant two-ply paper is resistant to tearing in either direction. However, this process is relatively expensive and wasteful of the banana plant resources, as two sheets are required to produce a single piece of paper having satisfactory tear resistance.

Furthermore, the thickness of the two-ply paper may result in the paper being undesirably or unusably thick for use in some circumstances.

SUMMARY OF THE INVENTION

In a first aspect, the present invention accordingly provides a method of strengthening a sheet of generally parallel paper fibres to resist tearing in the direction of the fibres, including the step of: (a) laying one or more cross fibres disposed at least partly non- parallel to said generally parallel fibres, to form a single-ply sheet.

These cross fibres provide an increased resistance to tearing along the grain of the sheet, and allow the formation of single-ply paper.

Clearly, whilst at least part of the cross fibres need to cross the generally parallel fibres, the entire cross fibres need not. Accordingly, in some instances, step (a) may be accomplished by bending some of the generally parallel fibres to form said cross fibres. In some embodiments, step (a) may be accomplished by:

(al) breaking some of the generally parallel fibres; and (a2) bending the broken fibres such that they cross over the unbroken generally parallel fibres, thereby providing the cross fibres.

Preferably, steps (al) and (a2) are accomplished by scratching the paper sheets at an angle, thereby breaking and bending some of the fibres to pull them across unbroken generally parallel fibres. Where the paper sheets are formed from a banana plant or similar, the scratching may be performed as the sheets are cut from the plant.

Typically, the broken fibres will be some of the top fibres of the paper sheets, and these will be bent over underlying unbroken fibres.

These steps will all typically be performed when the sheet is wet.

Preferably, the method further includes:

(b) pressing the cross fibres to ensure they remain in position, by applying pressure and heat to the sheet.

Alternatively, step (a) may be accomplished by taking separate fibres from a source other than the sheet itself, and laying them at least partially across the generally parallel fibres. To this end, individual fibres may be extracted from another sheet, or directly from (for example) a banana stem plant, and used as cross fibres.

Where, for example, the fibres are taken from a banana stem plant, step (a) may also be accomplished by spraying or pasting a mash of banana stem fibres onto the sheet. The mash may be obtained by pounding sections of a banana stem until they are separated into a combination of fibre strands and a sticky liquid - i.e. a "mash" for the purposes of this specification.

In a second aspect of the present invention, there is provided single-ply paper comprising a preponderance of generally parallel fibres, and some cross fibres disposed at least partly non-parallel to the generally parallel fibres, thereby providing resistance to tearing of the paper in the direction of the generally parallel fibres.

In a third aspect of the present invention, there is provided apparatus for strengthening a paper sheet of generally parallel fibres to resist tearing in the direction of the fibres, including: breaking means to break some of the fibres; and bending means to bend the broken fibres such that they cross over unbroken fibres.

The breaking and bending means may be separate or provided by the same entity (i.e the breaking and bending means may be integral).

In a fourth aspect of the present invention, there is provided apparatus for strengthening a paper sheet of generally parallel fibres to resist tearing in the direction of the fibres, including: application means to apply cross fibres at least partly non-parallel to said generally parallel fibres.

The application means may be in the form of spraying or pasting means. This may apply a mash of fibres onto the sheet.

In a fifth aspect of the present invention, there is provided apparatus for producing a sheet from the pseudostems of banana plants, including: means for supporting the pseudostem for rotation about its longitudinal axis; means for rotating the pseudostem about its longitudinal axis; and a cutting device for contacting the rotating pseudostem along substantially its entire length; whereby, during rotation, the cutting device removes a continuous sheet of fibres from the pseudostem, breaks some of the fibres, and bends the broken fibres to cross over unbroken fibres.

Preferably, the cutting device includes a serrated blade, which assists in breaking some of the generally parallel fibres and bending the broken fibres to cross over unbroken fibres. The cutting device may be movable in a direction opposite to the rotation of the pseudostem, which increases the force of contact between the cutting device and the pseudostem, and increases the effectiveness of the serrated blade breaking and bending the fibres.

In a sixth aspect of the present invention, there is provided a method of producing a sheet from the pseudostems of banana plants, including: rotating the pseudostem about its longitudinal axis; and contacting the rotating pseudostem along substantially its entire length with a cutting device to remove a continuous sheet of generally parallel fibres from the pseudostem; breaking some of the generally parallel fibres; and bending the broken fibres such that they cross over the unbroken generally parallel fibres, thereby providing cross fibres disposed at least partly non-parallel to said generally parallel fibres to increase the resistance of the sheet to tearing in the direction of the generally parallel fibres.

A detailed description of one or more preferred embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment.

For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention may be practiced without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative embodiment of the present invention will be discussed with reference to the accompanying drawings wherein:

FIGURE 1 diagrammatically displays a preferred method of the present invention used on a sheet of generally parallel paper fibres;

FIGURE 2 displays a paper sheet according to a preferred embodiment of the present invention;

FIGURES 3, 4 and 5 display paper sheets according to other embodiments of the present invention;

FIGURE 6 is a detailed view of a paper sheet being strengthened according to another embodiment of the present invention;

FIGURE 7 depicts part of an apparatus according to an embodiment of the present invention;

FIGURE 8 depicts apparatus according to an embodiment of the present invention;

FIGURE 9 depicts apparatus according to an alternative embodiment of the present invention;

FIGURE 10 depicts a portion of an alternate cutting device for the apparatus shown in Figure 9;

FIGURE 11 displays a pounding and mixing barrel, for producing a mash for use in an embodiment of the present invention;

FIGURE 12 displays apparatus for pasting fibres onto a sheet, according to an embodiment of the present invention; and

FIGURE 13 displays apparatus for spraying fibres onto a sheet, according to another embodiment of the present invention.

DETAILED DESCRIPTION A sheet of paper fibres can be taken from the pseudostem of a banana plant according to known methods, and the invention (although not so limited) will be described with particular reference to these circumstances. The resulting paper sheet consists of generally parallel fibres. Figure 1 depicts such a sheet 10, with the direction of the fibres shown by arrow A.

When taken from the pseudostem, the sheet will generally be wet. It can then be placed on a rubber mat (to prevent slippage) and, with a stiff wire brush, brushed strongly at approximately a 60 degree angle. Arrow B in Figure 1 depicts such a direction of brushing. Of course, it will be understood that other angles may be perfectly acceptable.

On brushing, some of the top fibres in the sheet are broken and bent or pulled across the underlying fibres. These fibres form cross fibres 12, which run at least partly across the grain (A) - i.e. at least partly non-parallel to the direction (A) of the generally parallel fibres of the paper sheet.

Figure 2 depicts the resultant paper sheet formed from strengthening according to the method of the present invention. Whilst only three cross fibres 12 are shown in Figure 2, this will be understood to be for clarity purposes only, and in practice there will likely be many more cross fibres 12. As shown, the resulting angle of the cross fibres 12 need not be perpendicular to the grain. Furthermore, some of the cross fibres may not be broken at all (see the fibre 12' on the right of Figure 2), and may simply be extracted at the edge of the sheet and bent across the grain.

These cross fibres 12 will increase the resistance of the resultant paper to tearing along the grain. As some of the generally parallel fibres have been broken, some sacrifice may be made to the resistance to tearing across the grain. However, banana paper in particular has a high resistance to tearing across the grain, and this sacrifice is practical where it results in an increased resistance to tearing along the grain.

Nonetheless, in further embodiments, fibres 14 can be taken from a different source, such as the centre of the core of the banana plant stalk, and used as cross fibres. The centre of the core of the banana plant stalk is not currently used in the banana paper making process as it is too difficult to slice, and the present invention can make use of what would otherwise be a waste product. Fibre can also be taken from any other part of the banana stalk, and used as cross fibres.

These fibres 14 can then be laid on the sheet, and pressed into position by applying pressure and heat to the sheet. Examples of possible resulting paper sheets are shown in Figure 3 (where the fibres 14 are laid approximately perpendicular to the grain), Figure 4 (where the fibres 14 are arranged in a pattern), and Figure 5 (where shorter fibres 14 are scattered generally randomly).

The number and concentration of fibres 14 may be varied according to preference. To achieve paper of increased strength, the fibres 14 may be laid close together. On the other hand, if smoother paper is desired, the fibres 14 may be laid far apart.

These fibres 14 may also be dyed prior to being laid on the sheet 10. The patterns and/ or colours of the fibres 14 could be changed to suit particular customers.

The method for laying the fibres 12 taken from the same sheet (referring to Figure 2) will naturally be different to laying the fibres 14 taken from another source (as described above and shown in Figures 3, 4 and 5). To produce a sheet 10 as shown in Figure 2, a stiff wire brush may be used to break and bend fibres 12. As described previously, the brush strokes would be in the direction of arrow B. In some embodiments, long brush strokes may be used. However, short sharp brush strokes may also be used, followed by a lifting of the brush and returning to a position a little forward of the original position. This can be achieved by moving the sheet 10 of paper fibres under the brush. Accordingly, in a production line, the fibre may be placed on a rubber topped conveyer belt. A cylindrical brush could be used to continuously brush the paper, or alternatively a flat brush could be used, with a short action which then lifts and returns the brush to its starting point for another stroke.

Brushing the sheet in this manner may have the added benefit of reducing the appearance of flaws in the resultant paper and making the end product smoother without the need to sand, or otherwise smooth, the paper.

The brushing process may also be repeated on the other side of the sheet 10, with the brush strokes crossing the fibres in a direction opposite to the first side. However, this step should not be taken to be essential to the invention.

An alternative means is shown in Figure 6, which displays a magnified section of the sheet 10. In this alternative, the fibres 12 in the sheet 10 can be cut and lifted with a number of narrow blades 20 digging laterally into the sheet 10. Clusters of fibres 12 are then pulled out so they point upwards.

These fibres 12 might then be scraped to either side with a rubber implement.

However, whilst this implementation of the present invention may give greater strength, it might also result in rougher paper.

Figures 7 and 8 depict another implement that may be used as part of an apparatus to perform the method of the present invention. Here, there is shown a small (e.g. lcm) brush 24 which is generally circular in shape, similar to brushes seen in floor polishing machines and the like. These brushes 24 can be set in rows on a backpiece 26, which is then used to brush the sheet 10 of paper fibres. These brushes 24 may increase tearing of the fibres 12, but they may also tangle the fibres 12 together and therefore further increase the resistance of the resultant paper to tearing along the grain.

Figure 9 displays yet another apparatus 30 for use in performing the present invention, which is adapted for removing sheets from the pseudostems of banana plants. A pseudostem 40 of a banana plant 40 is held in place by a skewer 32 and two rollers 34. In use, the rollers 34 are rotated, which in turn rotates the pseudostem 40 about the skewer 32. A cutting tool 36 is positioned with a cutting edge 37 against the pseudostem 40. As shown in the figures, the cutting edge 37 of this device is serrated, having a series of teeth 38. A spacing roller 42 is positioned between the cutting tool 36 and the pseudostem 40, to ensure the cutting tool 36 cuts at a constant depth.

Rotation of the pseudostem 40 by means of rollers 34 causes the cutting tool 36 to contact the pseudostem 40 and to separate a sheet of fibres from it. The spacing roller 39 ensures that the cutting tool 36 separates the sheet of fibres at the desired depth. The cutting tool 36 is also moved in a direction opposite the rotation the pseudostem 40. This action increases the force with which the teeth 38 of the cutting edge 37 contact the pseudostem, and therefore increases the number of fibres that will be broken and bent to form cross fibres.

The cutting tool 36 can then be pulled back in the same direction as the rotation of the pseudostem 40, and pushed forward for another stroke, to repeat the separating, breaking and bending of fibres. This movement is shown by arrow C in Figure 10.

Referring in more detail to Figure 10, in this embodiment, some teeth 39 of the cutting edge 37 protrude out of the plane of the blade of the cutting tool 36, thereby pushing into the pseudostem 40. This has the effect of pushing a greater number of fibres 12 across the grain. Some of the protruding teeth can be sharp, in order to cut through the fibres 12 (thereby shortening them and making them easier to move), while other protruding teeth 39 will be blunt in order to push fibres 12 without breaking them.

While the cutting tool 36 is on the backwards part of the cycle, it be moved sideways (as shown by arrow D) in order to locate the protruding teeth 39 at different parts of the pseudostem 40. This would have the effect of varying the position on the sheet at which the fibres 12 are cut and pushed.

In another form, the protruding teeth 39 may extend on both sides of the blade of the cutting tool 36 to cut and push the fibres 12 on both the top and bottom of the fibre sheet.

Alternatively, the cutting tool may comprise two blades, facing each other, so a greater variety of cutting, slicing and pushing movements can be achieved. In this form, the two blades would have protruding teeth extending in opposite directions.

Alternative embodiments of the method of the present invention will now be described. In particular, whilst Figures 3 to 5 and the corresponding description referred to the use of extracted fibres (extracted from, for example, the central core of a banana plant), it would also possible to use a mash of fibres. This mash could be produced from core material or leaf petoile sheath material of banana plants.

To this end, a "mash" of short banana stem fibres may be produced by cutting a banana stem into sections, and pounding these sections until the banana stem sections are separated into a combination of fibre strands and a sticky liquid - i.e. a "mash" for the purposes of this specification. In this mash, there will be a large number of fibres aligned at different angles to each other. It is important not to pound the stems so hard that the fibres are damaged or broken, but hard enough that the fibre strands are separated into individual strands or small groups of softened strands.

Producing a banana stem mash

Figure 11 depicts apparatus for pounding and mixing the banana stems.

Banana stems can cut into sections, which are put into a rotating barrel 26.

Inside the barrel are metal or stone mashing balls 27. As the barrel rotates, these mashing balls 27 are caught on wire guides 29 attached to a paddle 28, and are moved up the side of the barrel until the wire guides 29 tip the mashing balls 27 out. The mashing balls 27 then fall onto the banana stems, softening them and separating the fibres.

The banana stem sections and partially mashed banana stem material that were on the same paddle 28 as the said mashing balls 27, are then taken further up the side of the barrel and then tipped out. Because they are moved further up the barrel than the mashing balls 27, the banana stem sections and partially mashed banana stem material will land closer to the opposite side of the barrel than the mashing balls 27, and thus will be rotated into the landing area of the said mashing balls 27 as the barrel turns. The rotating action of the barrel 26 combined with the mixing action of the paddles 28 also serve to mix the banana stem fibres. This ensures that the resulting short fibres do not align substantially parallel to each other.

Of course, a number of paddles 28 with wire guides 29 would be built into the rotating barrel. They would preferably be at equidistant intervals around the

barrel and positioned so that the mashing balls do not land on them. The pounding action of the mashing balls 27 might be varied in a number of ways. The mass of the balls might be changed by using different materials, or by making the balls hollow. The speed that the balls hit the banana stem material might be changed by adjusting the angle and shape of the wire guides 29, so that the balls fall from a higher or lower position. Changing the size of the barrel mixer might also accomplish this change of ball speed. A larger rotating barrel mixer will generally mean that the said mashing balls 27 will fall from a greater height. Conversely, a smaller rotating barrel will generally mean that the said mashing balls 27 will fall from a lower height.

The purpose of adjusting the said pounding action of the said mashing balls 27 is to ensure that the fibres are mashed well, but without damaging the fibres. A heavier ball may have a stronger pounding action whereas a lighter ball might have a weaker pounding action. Similarly a ball that strikes the mash from a greater height and thus a faster velocity might have a stronger pounding action whereas a ball falling from a lower height might have a weaker pounding action. A stronger pounding action will result in well "mashed" fibres - i.e. short discrete fibres aligned at different angles to each other - whereas a weaker pounding action would be less likely to damage the fibres, but may not mash the fibres as thoroughly.

A banana stem mash might also be produced using a blender, such as a household blender or an industrial machine of a similar nature. In this method, banana plant material (including from the central core and/ or leaf petiole material) might be cut into small sections of a size similar to bark chips, thus making banana stem chips, using a mulcher or similar device. These chips can then be placed into the blender, and blended until a suitable mash is produced. Using a blunt blender blade (rather than a sharp blade) may help ensure that the fibres are not cut too short. If the fibres are too

short, they may not provide sufficient tear resistance along the grain of the sheet of fibres.

Spraying or pasting tlte mash onto a siieet In this particular embodiment, the applicant considers that it would be best to use short sections of banana stems, and also use the sawdust created when cutting the banana stem sections, in order to make a mixed banana stem mash with very short fibres. A possible range of fibre lengths is lmm to 5mm.

Figure 12 depicts a process whereby a flat sheet 10 is moved on a conveyer belt 57 underneath a wood block 55. The block 55 has a rubber squeegee 56 connected to it. A mash 17 is placed on the sheet 10 adjacent the rubber squeegee 56, and is pressed into the said sheet 10 by the pressing action of the said rubber squeegee 56. Accordingly, in this way, the mash 17 is pasted onto the sheet 10.

Figure 13 depicts a process whereby a flat sheet 10 is sprayed with a mash via spray nozzles 59. The sheet 10 is moved on a conveyer belt 58 underneath the spray nozzles 59. The mash is sprayed onto the sheet 10 from the spray nozzles 59.

Of course, although the sheet 10 is shown moving along conveyor belts 57, 58, it would be within the scope of the present invention to instead move the application means (i.e. the spray nozzles 59 or squeegee 56) to apply the mash (and accordingly apply the cross fibres).

After using either of the processes described in Figures 12 or 13, the sheet 10 with the added mash 17 (and accordingly added cross fibres) can be rolled and dried to produce a sheet of paper.

Although a preferred embodiment of the present invention has been described in the foregoing detailed description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention. Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention.

For example, although the present invention has been described with particular reference to banana paper, the present invention may be applied to any type of paper which includes generally parallel fibres, and so is vulnerable to tearing along the grain.

This example is not intended to be exhaustive, and is only intended to be indicative of other embodiments still in accordance with the present invention.

Throughout this specification and the claims that f ollow unless the context requires otherwise, the words 'comprise' and 'include' and variations such as 'comprising' and 'including' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.