Patent Description:
Cardboard tubes used for winding films, such as extensible or stretchable films often made of plastic, must resist certain forces of radial compression. Cardboard tubes made for winding extensible films rolls are normally made by laminating several plies of cardboard, which are then spiralled at a <NUM>-degree angle until the tubes have the desired width. The width of the spiralled tubes is function of the quality of the film to be wound around the tube, and of the diameter of the film roll.

The main parameters commonly used when developing cardboard tubes are the ring crush resistance of the cardboard used for forming the tube (measured by the force required to crush a cardboard cylinder when exerting an axial crushing force to the edges of the cylinder) and the delaminating resistance of the cardboard (measured by the force required to split a cardboard in two in its thickness). These parameters are commonly used when developing tubes and cores for the winding of paper rolls, and they may not be appropriate for the design of tubes used in applications involving radial compression, as paper rolls exert a linear compression on the tubes, rather than a radial compression. In addition, in spiralled winding cores, a small space is often present between two successive strips (or plies) of paper. This spacing is subject to lead to a break in the core when the core is subject to radial compression.

Until now, cardboard tubes devised for plastic film applications have been made using cardboard that has fibres oriented in multiple directions, as it is generally believed that this arrangement strengthens the tubes. For increasing the strength of spiralled tubes, a known technique requires using of several plies of cardboard, which means that the thickness of the wall of the tube must be increased and be relatively large, even for rolls having small lengths. Another known technique consists of using more resistant cardboard, which generally costs more and thus increases the price of the cardboard tubes.

Spiralled cardboard tubes were originally designed for winding rolls of paper, and their use for the winding of extensible or plastic films mainly comes from the fact that manufacturers of cardboard tubes and cores favoured using a single machine and process when manufacturing the tubes, for obvious economical reasons. However, spiralled tubes may not be the best choice for applications involving radial compression, as they have not been specifically designed to resist to such radial compression.

Straight rolling a web of cardboard is another method of manufacturing cardboard tubes and cores. While this method was commonly used when cardboard tube manufacturing began, it is now less so, because of the difficulty in manufacturing cores of various lengths and because increasing the strength of the tube requires increasing the number of windings, which in turn leads to a significant increase of the diameter and weight of the tube, which may not be either practical or economical.

<CIT> describes a method for reusing rolls that are rejected from paper and cardboard factories by forming them into straight rolled cores for the paper and cardboard industry. While this method provides the advantage of reusing rejected rolls within a paper mill, it suffers from the drawbacks of straight rolls described above.

<CIT> discloses a spirally or convolutely wound multi-layer tube includes one or more plies or layers that have embossments formed therein and projecting from one or both sides of each such ply or layer. The embossments increase the effective caliper and volume of the ply without adding mass. The embossments can abut an adjacent ply or layer of the tube and space such adjacent ply or layer from regions of the embossed ply or layer between the embossments, thereby forming void spaces in the tube wall.

<CIT> discloses a multi-grade spirally wound paperboard winding core of enhance resistance to inside diameter deformation including a plurality of structural paperboard layers having at least two predetermined densities including a lower density and a higher density wherein the lower density is at least about <NUM> % less than the higher density. The cylindrical bodywall is defined in radial cross section by at least one centrally located paperboard layer disposed between at least one radially inwardly located structural paperboard layer and at least one radially outwardly located structural paperboard layer is formed from the lower density paperboard and the inwardly and outwardly located structural paperboard layer are formed from higher density paperboard.

Japanese patent application <CIT> discloses a method and apparatus for forming a tubular body by winding, wherein a makeshift core is held at the turning-back part of running belt so as to be rotated together with the belt in order to feed sheeting material placed on the belt integrally with the belt to the outer periphery of the makeshift core and, after passing through the turning- back part, the belt is moved so as to be apart from the makeshift core in order to separate the sheeting material from the belt and wind it onto the outer peripheral surface of the makeshift core.

Japanese patent application <CIT> discloses a method for producing a composite flat wound paper tube, in which both base papers are rotated simultaneously and continuously by being rotated, and the base papers are overlaid with vertical and horizontal base papers.

Japanese patent application <CIT> discloses a paper cylinder that is wound so that the start and end of each paper are superimposed, with the outer layer being the horizontal paper in which the fibers run in the axial direction and the inner layer being the vertical paper in which the fibers run in the circumferential direction.

<CIT> discloses a spiral paper tube having a structure formed by a method wherein the paper tape has cross-direction fibers at a right angle or an obtuse angle to the longitudinal direction and is wound and bonded in a plurality of layers spirally at a gentle angle of inclination to the center line of a mandrel so that the cross-direction fibers of the paper tape have an angle of inclination opposite to the angle of inclination of the wind of the paper tape.

It would therefore be desirable to provide a cardboard tube specially adapted for the winding of extensible and/or plastic films which can resist radial compression while remaining inexpensive and relatively easy to manufacture.

According to one aspect, there is provided an improved cardboard tube that satisfies at least one of the above-mentioned needs.

According to another aspect, there is provided a convolute cardboard tube comprising:
a tubular body having a tubular body wall formed by a plurality of layers of a straight rolled cardboard sheet having a weight equal to or less than <NUM> gsm (<NUM>/ the cardboard m<NUM>), the cardboard sheet including a plurality of fibres, at least a majority of the fibres being substantially aligned in a tangential direction relative to the tubular body to allow the convolute cardboard tube to resist a radial compression force of equal to or greater than <NUM> bar on the tubular body wall.

In at least one embodiment, the wall has a wall thickness of less than <NUM>.

In at least one embodiment, the radial compression force on the tubular body wall is equal to or greater than <NUM> bar.

In at least one embodiment, the wall thickness is less than <NUM> and the radial compression force on the tubular body wall is equal to or greater than <NUM> bar.

In at least one embodiment, all of the fibres are substantially aligned in the direction of the winding of the convolute cardboard tube.

In at least one embodiment, the tubular body has a tensile resistance equal or higher than <NUM>/mm.

In at least one embodiment, the cardboard sheet has a weight equal to or less than about <NUM> gsm (<NUM>/m<NUM>).

In at least one embodiment, the plurality of layers of the straight rolled cardboard sheet include from <NUM> and <NUM> layers.

In at least one embodiment, the cardboard sheet includes a cut edge defining a shoulder on the external surface of the tubular body, the shoulder having a height substantially equal to or less than about <NUM>.

In at least one embodiment, the tubular body has a humidity level equal or lower than <NUM>%, particularly equal or lower than <NUM>%, more particularly substantially equal to <NUM>%.

In at least one embodiment, the cardboard sheet has a sheet width (w) defined in a transversal direction of the cardboard sheet, the sheet width being substantially equal to a length of the tubular body.

In at least one embodiment, the plurality of layers of the straight rolled cardboard sheet are glued together using an adhesive selected from a group consisting of: polyvinyl acetate (PVA), dextrin and silicate.

In at least one embodiment, the tubular body has an inside diameter of between about <NUM> and <NUM>, particularly of between about <NUM> and <NUM>, more particularly of about <NUM>.

In at least one embodiment, the straight rolled cardboard sheet has a sheet thickness of between about <NUM> and <NUM>.

The convolute cardboard tube disclosed hereinafter is less expensive to produce than existing spiralled or straight rolled cardboard tubes since it minimizes the raw materials required to form the tube, while being more resistant to the radial forces exerted on the tube by the extensible film wound around it.

In addition, since the raw materials for forming the convolute cardboard tube come from rolls of trimmed cardboard, that is, rolls of rejected cardboard, manufacturing costs are reduced even further, since trimmed cardboard rolls are less expensive than the rolls normally used for such tubes. Furthermore, using trimmed cardboard rolls as the raw material creates a positive impact on the environment since it does not require the manufacturing of new cardboard rolls, reducing greenhouse effects.

Since trimmed cardboard rolls come in lengths that correspond to the lengths of the tubes generally required for the winding of plastic films, that is, between <NUM> and <NUM> inches (between <NUM> and <NUM>), the cardboard from trimmed cardboard rolls generally does not require any cutting along its length, reducing the steps required to manufacture the convolute cardboard tube of the invention. It also eliminates the need to connect several tubes together to form a convolute tube of the desired length.

While the invention will be described in conjunction with example embodiments, it will be understood that the scope of the invention as claimed is not limited to such embodiments.

In the following description, similar features in the drawings have been given similar reference numerals. For the sake of clarity, certain reference numerals have been omitted from the figures if they have already been identified in a preceding figure.

The resistance of tubes to radial forces can be measured with measuring systems specifically designed for the paper and cardboard industry.

Through several experiments, the applicant uncovered that straight rolled cardboard tubes, or convolute wound cardboard tubes, offer better resistance to radial forces than the commonly used spiralled cardboard tubes.

The term "cardboard" refers to a paper-based material varying in thickness and rigidity according to the purpose for which it is to be used.

The term "convolute cardboard tube" refers to a straight wound or straight rolled tube, as opposed to a spirally wound tube. Each "layer" of the convolute tube's wall refers to a single winding of the cardboard sheet.

Specifically, in at least some circumstances, an improvement of the radial force resistance of at least about <NUM>% between a convolute cardboard tube and a conventional spiralled tube having a same wall thickness has been observed.

It was also found that in some circumstances, the resistance of straight rolled tubes to radial forces may be a function of one or more of the following parameters:.

Further experiments have shown that the resistance of straight rolled cardboard tubes to radial compression is sufficient when the tensile resistance is greater than or equal to <NUM>/mm or about <NUM> bar·mm. The test to determine this ratio consists of attaching the upper end of a sheet of cardboard, for example of <NUM> (width) x <NUM> (length), and of applying a load at its lower opposite end, until the sheet ruptures. The ratio is obtained by dividing the load (in kg) by the thickness (in mm) of the sheet.

By testing the radial compression of several tubes made from different types of cardboard, it was also found that, contrary to the generally held belief that tubes made of cardboard sheets with multidirectional-oriented fibres are more resistant, tubes made of cardboard having a majority of their fibres or all of their fibres substantially oriented in the direction of the winding of the tube - i.e. in a tangential direction relative to the tube - proved to be the most resistant to radial forces.

In some cases, the humidity level within a cardboard tube may further affect its overall resistance. When performing a flat crush test (during which the tube is placed between two compressing plates which apply pressure on the wall of the tube perpendicularly to a longitudinal axis of the tube), it has been found that a <NUM>% difference in the humidity level of the tube could result in a <NUM> to <NUM>% loss of resistance of the tube to crushing forces. For example, if the level of humidity in the tube is <NUM>%, it will require a pressure of <NUM> bars to flat crush the tube, while when the level of humidity is <NUM>%, the pressure require to flat crush the tube will be around <NUM> bars.

Experiments performed by the applicant have shown that when testing the resistance of tubes to radial compression in which forces are applied to the tube in a radial direction relative to the tube (rather than to straight or perpendicular compression, as described above), a <NUM>% difference in the humidity level of the tube results in a <NUM>%-<NUM>% loss of resistance of the tube. Other experiments performed by the applicants have shown that a tube has sufficient radial compression resistance when the humidity level within the tube is less then <NUM>%, or more specifically of less than <NUM>%, and that its resistance is stabilized when the humidity level is around <NUM>%.

Referring to <FIG>, there is shown a conventional plastic film roll <NUM> comprising a conventional spiralled cardboard tube <NUM> and a plastic film or extensible film <NUM> wound around the tube <NUM>. Because of its extensible properties, the plastic film <NUM> compresses the tube on which it is wound with a radial compression force F which is generally distributed all around the circumference of the tube <NUM> radially relative to the tube <NUM> and towards a central longitudinal axis of the tube <NUM>. By contrast, a tube on which is wound a material with different properties, such as paper which is not substantially extensible, would not be subjected to radial forces. Instead, the main force to which the tube would be subjected would be a downward force from the weight of the paper on the tube, which would tend to compress or bend the tube.

With reference to <FIG>, there is shown a plastic film roll <NUM>. The plastic film roll <NUM> includes a convolute cardboard tube <NUM>, in accordance with one embodiment, and a plastic film <NUM> wound around the convolute cardboard tube <NUM>. Specifically, the plastic film <NUM> forms a plurality of plastic film windings around the convolute cardboard tube <NUM>. The plastic film windings create a radial compression force F on the convolute cardboard tube <NUM>, and the convolute cardboard tube <NUM> is designed to resist this radial compression force F. The convolute cardboard tube <NUM> has a tubular body <NUM> which is defined by a tubular body wall <NUM> formed by several layers <NUM> of a straight rolled cardboard sheet. Specifically, the body <NUM> of the tube <NUM> is made by convoluting or straight winding a continuous sheet of cardboard or paper-based material. The process of "convoluting" or "straight winding" means that each winding after the first winding is superposed over the previous winding in a winding direction which is substantially perpendicular to the longitudinal axis of the tube <NUM>. In this configuration, the thickness of the wall <NUM> of the tube <NUM> therefore substantially corresponds to the thickness of the cardboard sheet multiplied by the number of times the sheet has been wound.

In one embodiment, the straight rolled cardboard sheet has a sheet thickness of between about <NUM> and <NUM>, and the tubular body <NUM> includes from <NUM> to <NUM> layers of the straight rolled cardboard sheet. Therefore, the wall <NUM> may have a wall thickness of less than <NUM>, and more specifically of less than <NUM>. Alternatively, the straight rolled cardboard sheet could have any other suitable thickness and the tubular body <NUM> could include less than <NUM> layers or more than <NUM> layers of the straight rolled cardboard sheet such that the wall <NUM> may have any other suitable wall thickness.

According to the invention, the straight rolled cardboard sheet has a weight equal to or less than about <NUM> gsm or <NUM>/m<NUM>, and more specifically of less than about <NUM> gsm or <NUM>/m<NUM>.

In one embodiment, the tubular body <NUM> has a inside diameter of between about <NUM> and <NUM>, and more specifically of between about <NUM> and <NUM>, and even more specifically of about <NUM>. Alternatively, the tubular body <NUM> may have any other suitable inner diameter.

In the illustrated embodiment, the cardboard sheet includes a cut edge <NUM> which is formed when the cardboard sheet is cut, either prior to forming the convolute cardboard tube <NUM> or after the cardboard convolute tube <NUM> is formed. The cut edge <NUM> corresponds to the end of the outermost winding of the cardboard sheet in the cardboard convolute tube <NUM>. The cut edge <NUM> is secured on the external surface of the tubular body <NUM> and, due to the thickness of the cardboard sheet, defines a step or shoulder <NUM> on the external surface of the tubular body <NUM>. The shoulder <NUM> may therefore have a height which corresponds substantially to the sheet thickness of the cardboard sheet. For example, in one embodiment, the shoulder <NUM> has a height which substantially equal to or less than about <NUM>, or more specifically between about <NUM> and <NUM>. Alternatively, the shoulder <NUM> may have any other suitable height.

In one embodiment, the layers of the cardboard sheet are glued together using an adhesive selected from a group consisting of: PVA, dextrin and silicate. Alternatively, the layers of the cardboard sheet could be secured together using any other suitable adhesive or any other suitable securing technique.

As shown is <FIG>, the cardboard sheet <NUM> contains fibres <NUM> that are substantially oriented in the direction of the circumference of the tubular body <NUM>. In other words, the fibres <NUM> are oriented in the direction of the winding of the cardboard sheet <NUM>, or along the length of the unrolled continuous sheet <NUM> (i.e. in a tangential direction relative to the tube <NUM>). The fibres <NUM> are also preferably long, as commonly found in cardboard or paper-based sheets used for boxes and bags. In one embodiment, all of the fibres <NUM> in the cardboard sheet <NUM> are aligned in the direction of the winding of the cardboard sheet <NUM>. Alternatively, not all, but a majority of, the fibres are aligned in the direction of the winding of the cardboard sheet <NUM>.

In the illustrated embodiment, the cardboard used for forming the tube <NUM> is characterized by a tensile resistance ratio substantially equal to or greater than about <NUM>/mm. Alternatively, the cardboard used for forming the tube <NUM> could have a greater or lesser tensile resistance ratio. <FIG> shows an example of a method for measuring the tensile resistance ratio of a cardboard sheet such as the cardboard sheet <NUM>. In this example, the tensile resistance ratio is measured by affixing the cardboard sheet <NUM> or a portion of the cardboard sheet <NUM>, having a predetermined thickness t, length I and width w, at one end and by affixing a load <NUM> at its other end which creates tension in the cardboard sheet <NUM>. The load is increased until the sheet <NUM> breaks or ruptures.

In one embodiment, the humidity level of the convolute cardboard tube <NUM>, measured within the wall <NUM> of the tubular body <NUM>, is substantially equal to or lower than about <NUM>%, and more specifically substantially equal to or lower than about <NUM>%, and even more specifically of <NUM>%. It has been observed that in at least some circumstances, a humidity level below <NUM>%, and more specifically below <NUM>%, provides the tube <NUM> with an improved resistance to radial compressions. Alternatively, the convolute cardboard tube <NUM> could have a humidity level that is above about <NUM>%.

While the cardboard sheet <NUM> used for forming the tube <NUM> may be specifically fabricated for this purpose, the cardboard sheet <NUM> preferably comes from rolls of trimmed cardboard. In other words, the raw material used to form the cardboard tube <NUM> comes from rejected paper from paper mills. This provides a tremendous advantage with regards to the costs of the raw material used to manufacture the cardboard tubes <NUM> for radial compression applications, since it directly reduces the overall cost of the tubes <NUM>. Alternatively, the cardboard sheet <NUM> may not come from rolls of trimmed cardboard and may instead include other types of cardboard.

In one embodiment, the convolute cardboard tube <NUM> has a length Lt and the cardboard sheet <NUM> comes from rolls having a length Lr corresponding to the length Lt. This characteristic of the cardboard sheet <NUM> eliminates the need to cut the sheet along its length when manufacturing the tube <NUM>. It also eliminates the need to connect several tubes together to form a convolute cardboard tube of a desired length. Indeed, rolls of trimmed cardboard Lr generally come in lengths of <NUM> to <NUM> inches (between <NUM> and <NUM>), which advantageously corresponds to the length Lt of cardboard tubes used for winding extensible films.

In another embodiment, the rolls of trimmed cardboard Lr could instead be longer than the required or desired length Lt of cardboard tubes. In this embodiment, an initial cardboard tube could be formed and then cut into one or more cardboard tubes having the required or desired length Lt.

Alternatively, when the length Lr of the cardboard sheet roll does not exactly correspond to the desired length of the convolute cardboard tube <NUM>, the tube <NUM> can be formed by at least two convolute cardboard tubes connected to one another by any suitable manner, such as with adhesive, male-female joints, or by spiralling a finishing band around the joined tubes.

Table <NUM> below contains results of testing performed on a first set of convolute cardboard tubes, compared to results of similar tests performed on conventional spiralled tubes. Specifically, each test was performed on a tube having a length of <NUM>. The test consisted of applying a force radially inwardly in a uniform manner around the entire circumference of the tube and was gradually increased until failure of the tube. The force applied is then divided by the area over which the force is applied to obtain a value of ultimate radial compression strength for the tubes which is independent of the size (i.e. diameter and length) of the tube.

The results in Table <NUM> show that the radial compression strength of the convoluted cardboard tubes is greater than the corresponding spiralled tubes for every cardboard thickness tested. In at least one case (i.e. a cardboard thickness of <NUM>), the convoluted cardboard tube even showed an improvement of about <NUM>% in radial compression strength over the corresponding spiralled tube.

Table <NUM> below contains results of testing performed on a second set of convolute cardboard tubes, again compared to results of similar tests performed on conventional spiralled tubes. The test again consisted of applying a force radially inwardly in a uniform manner around the entire circumference of the tube and was gradually increased until failure of the tube. Conventional spiralled tubes and convolute cardboard tubes with various cardboard thicknesses were selected, and the test was repeated on three convolute cardboard tubes for each cardboard thickness. In this example, both the conventional spiralled tube and the convolute cardboard tube tested were made of cardboard having a weight of <NUM> gsm (<NUM>/m<NUM>) and a humidity level of about <NUM>%.

In this example, in addition to determining the ultimate radial compression strength for each tube as was done in Example <NUM>, the ultimate radial compression strength per unit of thickness was also determined. The results show that the ultimate radial compression strength of the convoluted cardboard tubes configured as disclosed herein in consistently higher than the ultimate radial compression strength of conventional spiralled tube for the same thickness of tube.

The following convolute tube manufacturing apparatus is not according to the invention and is present for illustration purposes only.

Now turning to <FIG>, there is shown a convolute tube manufacturing apparatus <NUM> for manufacturing a convolute wound tube such as the convolute cardboard tube <NUM>, in accordance with one embodiment. In this embodiment, the apparatus <NUM> includes a frame <NUM> having an input end <NUM> at which paper is provided to the apparatus <NUM> and an output end <NUM> located opposite the input end <NUM>. The frame <NUM> is configured to receive a paper roll <NUM> at the input end <NUM> to feed paper towards the output end <NUM>. Specifically, the paper roll <NUM> is rotatable about a roll axis R<NUM> to unwind a length of paper, or unwound cardboard sheet <NUM>, from the paper roll <NUM>. The unwound cardboard sheet <NUM> includes an end edge <NUM> (best shown in <FIG>) which is moved in a machine direction M towards the output end <NUM> by a plurality of intermediate rollers <NUM> disposed between the input and output ends <NUM>, <NUM>. In one embodiment, the intermediate rollers <NUM> are further movable selectively upwardly and downwardly by corresponding actuators to allow the user to set a desired tension in the unwound cardboard sheet <NUM>.

The "machine direction" M refers to a direction of travel of the unwound cardboard sheet <NUM> through the apparatus <NUM>, from the input end <NUM> to the output end <NUM>. This direction is also tangential to the paper roll, and perpendicular to the roll axis R<NUM>. The "transversal direction" T refers to a direction which is substantially perpendicular to the machine direction.

The apparatus <NUM> further includes a tube forming roller <NUM> which is rotatably connected to the frame <NUM> and is rotatable about a tube roller axis R<NUM>. The tube forming roller <NUM> is configured for engaging the end edge <NUM> of the paper roll <NUM> and rotates to wind or convolute the paper roll <NUM> around the tube forming roller <NUM>. Specifically, the apparatus <NUM> includes a prehension mechanism <NUM> for engaging the end edge of the unwound sheet of paper. This allows the end edge <NUM> of the unwound sheet of paper to be guided along a circular path around the tube forming roller <NUM> to form the first winding of the convolute tube. Once the first winding of the tube is formed, the end edge <NUM> is wedged under the unwound sheet of paper which is being wound over it and therefore the prehension mechanism <NUM> can be disactivated. Alternatively, the prehension mechanism <NUM> could remain activated during an entire forming of the convoluted cardboard tube <NUM>.

The tube forming roller <NUM> has a diameter which is substantially equal to an inner diameter of the convolute cardboard tube <NUM>. In one embodiment, the tube forming roller <NUM> has a diameter of between about <NUM> and <NUM>, and more specifically of between about <NUM> and <NUM>, and even more specifically of about <NUM>. Alternatively, the tube forming roller <NUM> could have a larger or smaller diameter.

In this configuration, both the unwinding of the paper from the paper roll <NUM> and the winding or convoluting of the unwound cardboard sheet <NUM> around the tube forming roller <NUM> can therefore be performed in one, continuous motion. Specifically, the tube forming roller <NUM> is oriented such that when the paper roll <NUM> is received on the frame <NUM>, the tube roller axis R<NUM> and the roll axis R<NUM> are parallel to each other. The unwound cardboard sheet <NUM> therefore keeps moving in the machine direction as it is unwound from the paper roll <NUM> and as it is wound around the tube forming roller <NUM> to form the convolute cardboard tube <NUM>.

In an embodiment in which the convolute cardboard tube includes a plurality of fibres of which at least a majority are aligned in a tangential direction relative to the convolute cardboard tube <NUM>, the paper roll <NUM> is selected such that the cardboard on the paper roll includes fibres which are also oriented in a tangential direction relative to the paper roll <NUM>, i.e. in the machine direction. The fibres therefore remain aligned in the machine direction M as the unwound cardboard sheet <NUM> travels from the input end <NUM> to the output end <NUM>.

In the illustrated embodiment, the apparatus <NUM> further includes an adhesive application assembly for applying adhesive to the unwound cardboard sheet <NUM> being wound on the tube forming roller <NUM>. In one embodiment, the adhesive application assembly is configured to apply adhesive on an underside of the unwound cardboard sheet <NUM>, upstream of the tube forming roller <NUM>, such that as the unwound cardboard sheet <NUM> is wound to form a winding over a previous winding underneath, the unwound cardboard sheet <NUM> is simultaneously glued on the previous winding. In another embodiment, the adhesive application assembly could instead be configured to apply adhesive on an outer side of each winding as it makes a full rotation around the tube forming roller <NUM> and is moved underneath the unwound cardboard sheet <NUM> which forms a new winding over it, thereby gluing the winding to the underside of the unwound cardboard sheet <NUM>. In one embodiment, the adhesive could be selected from a group consisting of PVA, dextrin and silicate. Alternatively, the adhesive could include any other suitable adhesive.

In the illustrated embodiment, the piece of cardboard sheet forming the convolute cardboard tube <NUM> is only separated from the rest of the unwound cardboard sheet <NUM> once the convolute cardboard tube <NUM> has been formed. Specifically, the apparatus <NUM> further includes a cutting assembly located upstream of the tube forming roller <NUM>, towards the input end <NUM>. Once the unwound cardboard sheet <NUM> has been wound a desired number of times to form a desired number of windings and a desired thickness of the convolute cardboard tube <NUM>, the cutting assembly may be moved towards the unwound cardboard sheet <NUM> to separate the formed convolute cardboard tube <NUM> from the rest of the unwound cardboard sheet <NUM>. In this configuration, the apparatus <NUM> therefore manipulates a single piece of paper, i.e. the unwound cardboard sheet <NUM>, instead of multiple separate pieces, which simplifies the manufacturing process.

Alternatively, the piece of cardboard sheet forming the convolute cardboard tube <NUM> which is used to form the convolute cardboard tube <NUM> may be separated from the rest of the unwound cardboard sheet <NUM> prior to forming the convolute cardboard tube <NUM>.

Now turning to <FIG>, the prehension mechanism <NUM> includes a plurality of suction openings <NUM> defined in the tube forming roller <NUM>. Specifically, the tube forming roller <NUM> is hollow and includes an inner channel <NUM> in fluid communication with the suction openings <NUM>. The inner channel <NUM> is further operatively connected to a vacuum source such as a pump or the like to create suction through the suction openings <NUM>. Specifically, the suction created is sufficient to hold the end edge <NUM> against the tube forming roller <NUM>.

In the illustrated embodiment, the suction openings <NUM> are aligned with each other substantially parallel to the tube roller axis R<NUM>. Alternatively, the suction openings <NUM> could be disposed in any other suitable pattern. Still in the illustrated embodiment, each suction opening <NUM> is substantially circular, but alternatively, the suction openings <NUM> could be elongated or have any other shape.

In the illustrated embodiment, the prehension mechanism <NUM> further includes a plurality of suction nozzle members <NUM>. Each nozzle member <NUM> is received in a corresponding suction opening <NUM> and is movable relative to the tube forming roller <NUM>. Specifically, each suction nozzle member <NUM> is selectively movable between an extended position in which the suction nozzle member <NUM> extends partially outwardly from the corresponding suction opening <NUM> and a retracted position in which the suction nozzle member <NUM> is fully retracted within the tube forming roller <NUM>.

In the illustrated embodiment, each suction nozzle member <NUM> is connected to a nozzle member actuator <NUM> such as a solenoid actuator or an electromagnet which, when activated, moves the suction nozzle member <NUM> from the retracted position to the extended position. Still in the illustrated embodiment, the suction nozzle member <NUM> is further connected to a spring member <NUM> which biases the suction nozzle member <NUM> towards the retracted position. In this embodiment, when the nozzle member actuator <NUM> is deactivated, the spring member <NUM> moves the suction nozzle member <NUM> from the extended position back to the retracted position. Alternatively, the nozzle member actuator <NUM> could instead include a two-way actuator which could both move the suction nozzle member <NUM> from the retracted position to the extended position and from the extended position to the retracted position.

As shown in <FIG>, the suction nozzle member <NUM> is first in the extended position to engage the end edge <NUM> or the unwound cardboard sheet <NUM> proximal the end edge <NUM>. In this position, the vacuum source is further activated to provide suction through the suction nozzle member <NUM>. As the tube forming roller <NUM> is rotated forward, as shown in <FIG>, the suction nozzle member <NUM> maintains the unwound cardboard sheet <NUM> against the tube forming roller <NUM>. The tube forming roller <NUM> is then further rotated until the end edge <NUM> is tucked under the unwound cardboard sheet <NUM> and the first winding is formed, as shown in <FIG>. At this point, the vacuum source could be deactivated and the suction nozzle members <NUM> could be moved to the retracted position as the remaining windings are formed. In one embodiment, the vacuum source could remain activated and the suction nozzle members <NUM> could remain in the extended position as the first few windings are formed to ensure that there is sufficient friction between the windings to prevent the windings from becoming undone from the tube forming roller <NUM> before moving the suction nozzle members <NUM> in the retracted position.

In one embodiment, the tube forming roller <NUM> is rotated at a first rotation speed when forming the first winding or the first few windings, and then rotated at a second rotation speed greater than the first rotation speed when forming the remaining windings. Alternatively, the tube forming roller <NUM> could instead be rotated at constant speed through the forming of all the windings.

Still in the illustrated embodiment, the apparatus <NUM> further includes an upper holding roller <NUM> rotatably connected to the frame <NUM> and disposed above the tube forming roller <NUM>. Specifically, the upper holding roller <NUM> extend generally parallel to the tube forming roller <NUM> and is movable substantially vertically. The upper holding roller <NUM> is further operatively connected to an upper holding roller actuator for selectively moving the upper holding roller <NUM> between an idle position in which the upper holding roller <NUM> is spaced upwardly from the tube forming roller <NUM> and a holding position in which the upper holding roller is lowered towards the tube forming roller <NUM> to hold the unwound cardboard sheet <NUM> against the tube forming roller <NUM>. Alternatively, the apparatus <NUM> may not incudes an upper holding roller <NUM>.

In the illustrated embodiment, the apparatus <NUM> further includes a tube removal assembly <NUM> for removing the convolute cardboard tube <NUM> from the tube forming roller <NUM> once formed. Specifically, the tube removal assembly <NUM> includes a carriage <NUM> movable along a travel path parallel to the tube roller axis R<NUM> and an abutting element <NUM> secured to the carriage <NUM> and located proximal to the tube forming roller <NUM>.

As shown in <FIG> and <FIG>, the carriage <NUM> is operatively mounted on a carriage track <NUM> which extends underneath the tube forming roller <NUM> and is movable therealong. The abutting element <NUM> is connected to the carriage <NUM> via a support member <NUM> which extends substantially vertically between the carriage <NUM> and the abutting element <NUM>. In the illustrated embodiment, the abutting element <NUM> includes an annular member <NUM> extending coaxially around the tube forming roller <NUM>. Specifically, the annular member <NUM> has an inner diameter which is smaller than an outer diameter of the formed convolute cardboard tube <NUM>. In this configuration, movement of the carriage <NUM> along its travel path on the carriage track <NUM> causes the annular member <NUM> to move along the tube forming roller <NUM> and to push the formed convolute cardboard tube <NUM> towards one end of the tube forming roller <NUM> until it is completely removed from the tube forming roller <NUM>. The carriage <NUM> can then move back to its initial position and a new convolute cardboard tube <NUM> can then be formed on the tube forming roller <NUM>.

It will be appreciated that the apparatus <NUM> described above provides a relatively fast and completely automated way of manufacturing convolute cardboard tubes such as the convolute cardboard tube <NUM>. For example, in some embodiments, the apparatus <NUM> could be configured to wind the unwound cardboard sheet <NUM> to form the convolute cardboard tube <NUM> at a speed of about <NUM>/s to about <NUM>/s, and to form on average about three convolute cardboard tubes <NUM> per minute. Moreover, by using a paper roll which includes fibres of which at least a majority are aligned in a tangential direction, i.e. in the machine direction M, the formed convolute cardboard tube <NUM> includes a plurality of fibres of which a majority is also aligned in a tangential direction, which, as explained above, provides enhanced radial compression resistance to the convolute cardboard tube <NUM>.

Moving the unwound cardboard sheet <NUM> in a single direction, i.e. the machine direction M, as opposed to cutting the unwound cardboard sheet <NUM> which are then moved independently laterally for example, further simplifies and accelerates the manufacturing process.

The following convolute tube manufacturing process is not according to the invention and is present for illustration purposes only.

Turning now to <FIG>, there is shown a method for manufacturing a convolute cardboard tube such as the convolute cardboard tube <NUM>, in accordance with one embodiment. Although the following method is described in connection with the apparatus <NUM> described above, it will be understood that this is provided an example only and that the method could instead be performed with a different apparatus.

A paper roll such as the paper roll <NUM> is first provided and unwound. Specifically, the paper roll includes cardboard which has been preselected according to one desired characteristic. For example, the paper roll <NUM> includes a preselected cardboard which comprises a plurality of fibres which are aligned substantially in a tangential direction relative to the paper roll <NUM>.

In the illustrated embodiment, the paper roll <NUM> is installed on the frame <NUM>, towards the input end <NUM>, as shown in <FIG>. The paper roll <NUM> can then be unwound in the machine direction M to form the unwound cardboard sheet <NUM>. The end edge <NUM> is then moved towards the output end <NUM> until it engages the tube forming roller <NUM>.

The unwound cardboard sheet <NUM> can then be straight rolled or convoluted to form the convolute cardboard tube <NUM> such that the convolute cardboard tube <NUM> includes the fibres aligned in the machine direction M. In one embodiment, the unwound cardboard sheet <NUM> can be wound at a speed of between about <NUM> and <NUM>/s. Alternatively, the unwound cardboard sheet <NUM> could be wound at a lower or higher speed.

Referring to <FIG>, to convolute the unwound cardboard sheet <NUM> to form the convolute cardboard tube <NUM> according to one embodiment, the end edge <NUM> is positioned above the tube forming roller <NUM>. The upper holding roller <NUM> is in the idle position such that it is spaced upwardly from the tube forming roller <NUM> and the end edge <NUM> is positioned between the tube forming roller <NUM> and the upper holding roller <NUM>.

As shown in <FIG>, the upper holding roller <NUM> is then lowered to the holding position, in which it abuts the unwound cardboard sheet <NUM> above the tube forming roller <NUM>. The vacuum source is then engaged to create suction through the suction openings <NUM> to hold the end edge <NUM> against the tube forming roller <NUM>. The suction nozzle members <NUM> may further be positioned in the extended position.

As shown in <FIG>, the tube forming roller <NUM> may then be rotated forwardly to form the first winding, with the end edge <NUM> remaining held against the tube forming roller <NUM>. The tube forming roller <NUM> may then further be rotated, at the same speed or at a greater speed, to form the remaining windings, during which time the vacuum source may be deactivated and the suction nozzle members <NUM> may be moved back to the retracted position. Adhesive such as PVA, dextrin or silicate is further provided as the tube forming roller <NUM> is rotated, as described above. In one embodiment, the tube forming roller is rotated in total from <NUM> to <NUM> times to form a convolute cardboard tube <NUM> having from <NUM> to <NUM> layers of cardboard. Alternatively, the tube forming roller could be rotated in total less than <NUM> times or more than <NUM> times.

<FIG> shows the convolute cardboard tube <NUM> formed around the tube forming roller <NUM>, with the upper holding roller <NUM> abutting the convolute cardboard tube <NUM>. As shown in <FIG>, the upper holding roller <NUM> is then raised back to its idle position. The unwound cardboard sheet <NUM> is cut in a widthwise direction, proximal to the tube forming roller <NUM>, to separate the convolute cardboard tube <NUM> from the rest of the unwound cardboard sheet <NUM>. In one embodiment, the unwound cardboard sheet <NUM> is cut before the upper holding roller <NUM> is raised, but alternatively, it could be cut after the upper holding roller <NUM> is raised.

As shown in <FIG>, the convolute cardboard tube <NUM> can then be removed from the tube forming roller <NUM>. In the illustrated embodiment, the convolute cardboard tube <NUM> is removed using the tube removal assembly <NUM>. Specifically, the carriage <NUM> is moved along the carriage track <NUM> such that the annular member <NUM> pushes the convolute cardboard tube <NUM> towards an end of the tube forming roller <NUM> and entirely off the tube forming roller <NUM>.

It will be appreciated that the location at which the unwound cardboard sheet <NUM> was cut now defines a new end edge of the unwound cardboard sheet <NUM>, which can then be engaged by the prehension mechanism <NUM> to form a new convolute cardboard tube <NUM>.

In one embodiment, the adhesive is then set. Specifically, the adhesive could be set merely by waiting a certain amount of time. Alternatively, the adhesive could be set or cured using an active adhesive setting technique such as using ultraviolet light, heat or any other suitable technique.

In one embodiment, the convolute cardboard tube <NUM> may also be dried to reduce its humidity level to a desired humidity level, which could be substantially equal to or lower than about <NUM>% and more specifically of about <NUM>%. The drying could be performed by letting the convolute cardboard tube <NUM> sit in a relatively dry environment for a certain amount of time, or could be performed using a drying apparatus. Alternatively, the convolute cardboard tube <NUM> may not be dried.

In one embodiment, a film such as the plastic film <NUM> can then be wound around the convolute cardboard tube <NUM> to form the plastic film roll <NUM>. Specifically, the winding of the plastic film <NUM> around the convolute cardboard tube <NUM> could be performed in the same facility, i.e. a plastic film roll manufacturing facility, as the manufacturing of the convolute cardboard tube <NUM>. For example, if the convolute cardboard tube <NUM> is manufactured using the apparatus <NUM>, the apparatus <NUM> may be provided at the plastic film roll manufacturing facility. This may contribute to maintaining the convolute cardboard tube <NUM> are the desired humidity level by reducing the time, the number of manipulations and the potential changes in environment between the manufacturing of the convolute cardboard tube <NUM> and the manufacturing of the plastic film roll <NUM>. Alternatively, the convolute cardboard tube <NUM> could be manufactured at a first facility such as a convolute cardboard tube manufacturing facility and later transported to a second facility such as a plastic film roll manufacturing facility where the plastic film <NUM> is wound around the convolute cardboard tube <NUM>.

As it can be appreciated, the convolute tube <NUM> of the invention is less expensive to manufacture than those known in the art, not only because it uses trimmed or reject cardboard as its raw material (indeed, rolls of trimmed cardboard, or reject rolls are relatively inexpensive relative to the cost of cardboard used up to now for manufacturing convolute or spiralled winding tubes or mandrels), but also because less material is required to form the tubes, thanks to the selection of cardboards with specific properties (weight, tensile resistance, humidity level, orientation of the fibres). The invention also helps to reduce greenhouse effects by using trimmed cardboard as its raw material, rather than requiring the manufacture of cardboard specifically for the purpose of creating tubes. It is also particularly adapted to the needs of applications involving radial compression, such as those using extensible or plastic films. Advantageously, because there are no spacing between to successive wounded strips or plies, as it is the case in spiralled cores, the core is less subject to breaking when being radially compressed.

Moreover, the fact that the convolute cardboard tube can resist the same radial compression force than a corresponding conventional spiralled tube while having a thinner wall than the corresponding conventional spiralled tube may have additional advantages. For example, wound cardboard tubes often experience a "rebound" effect in which the cut edge of the cardboard tube in the final wound layer may tend to move before the adhesive has fully set because of the slight tension that may have been created in the windings when the tube forming roller is rotated. It has been observed that forming a tube having a lower wall thickness reduces this rebound effect and thereby contributes to preventing movement of the cut edge relative to the rest of the tube while the adhesive sets.

Claim 1:
A convolute cardboard tube (<NUM>) comprising:
a tubular body (<NUM>) having a tubular body wall (<NUM>) formed by a plurality of layers (<NUM>) of a straight rolled cardboard sheet (<NUM>);
characterized in that the cardboard sheet (<NUM>) has a weight equal to or less than <NUM> gsm (<NUM>/m<NUM>)
and includes a plurality of fibres (<NUM>), at least a majority of the fibres being substantially aligned in the direction of the winding of the convolute cardboard tube (<NUM>) to allow the convolute cardboard tube (<NUM>) to resist a radial compression force (F) equal to or greater than <NUM> bar on the tubular body wall.