GB2513226A

GB2513226A - Method and apparatus for manufacture of corrugated paperboard

Info

Publication number: GB2513226A
Application number: GB1402679.3A
Authority: GB
Inventors: Martin Mckenna
Original assignee: INTERPAC Ltd
Current assignee: INTERPAC Ltd
Priority date: 2013-02-14
Filing date: 2014-02-14
Publication date: 2014-10-22
Anticipated expiration: 2034-02-14
Also published as: GB201302572D0; WO2014125297A1; GB201402679D0; GB2513226B; GB2513226C

Abstract

One sheet of paperboard 2 is tensioned while it is bonded to a corrugated sheet 6. The machine to do this has supply rollers 1, 7, 11 for each web, a corrugator 8 and a tensioner 4. Ideally the corrugators are ridged drums 5, 8 with holes and internal vacuum boxes 113. An opposing liner sheet 10 can also be supplied and adhered to the other side of the corrugated sheet. The first sheet and the second sheet can be tensioned by diverging gripper chains during bonding of the second sheet. A PVA glue applicator 9 can be a flanged roller to apply glue in dots along the peak of each corrugation. Adjustably interlocking fingers may adjustably brake the liner, tensioning it. Preferably no steam is involved and the tension is less than that which would tear a dry web but greater than that which would tear a wet web. The machine can adhere multiple lined corrugated sheets together.

Description

Method and apparatus for manufacture of corrugated paperboard

Field of the invention

The present invention relates to a method and apparatus for manufacture of corrugated paperboard, which is conventionally manufactured from paper.

Background to the invention

Corrugated paperboard, sometimes known as corrugated board or simply cardboard, is used throughout the world for the production for cardboard boxes, which provide cheap and practical packaging for a whole range of goods.

However, due to the cost and size of the manufacturing apparatus, only a few, large and expensive factories produce the corrugated paperboard, which is then shipped to the point of use. Whilst not very heavy, the paperboard has a large bulk due to the corrugated nature, and so is disproportionately expensive to ship to the individual factories where it is used to package goods. There is also a detrimental effect to the environment with the carbon footprint associated with the shipping of the corrugated paperboard.

A typical prior art paperboard manufacturing apparatus usually consists of a single facer unit, a conveyor bridge and a double backer unit. A corrugating medium, usually paper, but may also be card or a similar medium, is supplied from a supply roll located conveniently near to the single facer unit. Similarly, a further supply roll supplies an outer liner, again usually of paper, to the single facer unit.

The paper is first usually passed through a series of rollers, at least one of which is heated. This ensures moisture is removed, so that the paper is provided in a consistent state before entering the single facer unit or the double backer unit.

The corrugating medium is then conditioned using hot steam to cause the paper to become pliable, before being ted between a corrugating drum and a corrugating roller. The corrugating drum and roller have interlinking teeth, similar to the meshing of gears, that corrugate the corrugating medium. That is, the paper is forced into the gap between interlocking ridges of the corrugating drum and roller (which is sometimes known as the labyrinth) to form a corrugated layer of paper.

The corrugated layer is sometimes known as fluted web, fluted liner or corrugated liner, and the ridges of the fluted web are sometimes called flutings.

Due to the pliable nature of the freshly steamed corrugating medium, the paper remains held in place of the large corrugating drum as it rotates. A gluing station provides a thin layer of starch glue to the outer ridges or flutings of the fluted web.

The gluing station is typically a bath of glue having a roller constantly touching the surface of the glue, such that a thin layer of glue is transferred onto the roller as it rotates. The glue is then transferred from the roller to the fluted web either directly or via intermediate transfer rollers.

The outer liner is fed through a series of rollers and onto the glued layer of the fluted web, where it bonds to the outer ridges. This combination of corrugated medium bonded to the outer liner is usually known as single faced web. The single faced web, which has poor rigidity, is fed onto the conveyor bridge.

The conveyor bridge is usually run at a slower pace than the output of the single facer unit so that the single face web forms loops on the conveyor bridge to take up the slack of the single faced web. The glue between the fluting web and the outer liner must dry whilst it is on the conveyor bridge before the single face web is fed into the double backer unit.

The double backer unit glues an inner liner to the single face web to provide the final double faced paperboard. Glue is supplied from a second glue station to the exposed ridges flutings of the fluted web opposite the outer liner. A further roll supplies an inner liner to the double backer unit. The inner liner is fed through a series of rollers and brought into contact with the glued side of the single faced web.

The double faced paperboard is then dried and cooled to provide a three-ply laminated paperboard, which can then be cut to any desired shape ready for use.

The conveyor bridge of the prior art is generally very long, and can be up to one hundred or more metres and may include drying beaters. The conveyor bridge allows a buffer between the single facer unit and the double backer that allows one or the other to be stopped for a short time without the need for stopping the other. In this case the amount of loops of single faced liner stored on the conveyor bridge is increased or decreased.

For example, if a new paper roll was needed to be installed at the double backer unit, the double backer unit could be stopped whilst the paper roll was exchanged. During this time, the single facer unit remains running and so the number of loops that build up on the conveyor bridge increases. Similarly, if a paper roll was changed on the single facer unit, the number of loops of single faced liner stored on the conveyor bridge would decrease.

For this reason, the total amount of paper on the conveyor bridge, and consequently the length of time the single faced liner spends on the bridge can vary considerably, depending on the recent history of the apparatus.

In order that the glue between the outer liner and the fluted web is dry, the conveyor bridge must be very long to ensure that the single faced liner is completely dry and that the single faced liner reaches the double backer in a consistent condition. Of course, at this point, the single faced liner will have lost all heat, and must be preconditioned by using heater units prior being fed into the double backer unit, requiring further energy input.

The corrugated paperboard manufacturing apparatus of the prior art has many disadvantages.

The size of the apparatus is very large, making it unsuitable for use at the point of use, and requiring dedicated large-scale manufacturing premises and a large workforce to keep the apparatus running. This in turn means that the bulky corrugated paperboard needs to be shipped to the point of use, which is both expensive and not environmentally friendly.

The requirement to provide steam to the corrugating medium prior to corrugation requires a large steam boiler to provide enough steam for large manufacturing volumes. This requires very large energy consumption and further increases the size of the facilities needed to house the equipment.

The need to reheat the single faced web after cooling on the conveyor bridge requires still further input of energy.

The untensioned single faced web is left to dry on the conveyor belt, and so is susceptible to varying drying conditions depending on the atmospheric conditions. Therefore, warpage and shrinkage of the single faced web as well as variations and irregularities in the flutings can occur.

For all of the aforesaid reasons, conventional corrugator lines are not as productive and efficient as they might be. Also they do not produce corrugated board of as high a quality as might be desired.

It would be desirable to reduce the size of the equipment to allow the installation of the apparatus at the point of use.

It would be still further desirable to reduce the energy consumption during manufacture of the corrugated paperboard to reduce production costs and to reduce the environmental impact.

Summary of the invention

To address the above-mentioned issues associated with the prior art, the present invention avoids the use of steam in the manufacture of corrugated paperboard and provides a compact corrugated paperboard manufacturing apparatus.

In particular, the invention manufactures the corrugated paperboard in a steam-free method. That is to say, the fluted web is not moistened by steam and is a dry fluted web and neither the corrugating medium nor the fluted web are moistened by steam.

Further, the conveyor bridge is eliminated, and the single faced web can be directed directly into the double backer unit. The single faced web can therefore be kept under tension whilst the inner layer is bonded.

According to the present invention, there is provided an apparatus for manufacturing corrugated paperboard as set out in claim 1 and a method of manufacturing corrugated paperboard as set out in claim 17.

It should be understood that descriptions of embodiment of the apparatus apply equally to embodiments of the method and vice versa.

In the prior art, steam is used to make the corrugating medium more pliable and therefore easier to corrugate. Without the use of steam, the corrugating medium would not remain in a corrugated form after passing through the labyrinth of the corrugating rollers of the corrugator, and would therefore not be corrugated by the time the outer liner was bonded.

According to an embodiment of the present invention, suction can be used to keep the corrugating medium in the ridges of the corrugator after the corrugating medium had passed through the labyrinth. One example of how this could be done is to provide a series of suction holes or pores in the ridges of the corrugator and provide a suction means, such as a vacuum pump, within the corrugator to communicate with the suction holes. Typical range of suction hole diameters are 2.5mm to 3.5mm for paper density in the range of 70 to 80 gm weight, but larger holes may be necessary for higher density papers.

However, without the use of steam, the corrugating medium remains dry throughout the manufacturing process and it has been discovered that the final bonded double faced corrugated paperboard usually has poor rigidity. It is suggested that this is due to the lack of internal strains in the paperboard that would normally be caused by the shrinkage of the corrugating medium during the drying process in the prior art method of manufacturing corrugated paperboard.

Therefore, to provide internal strain to the corrugated paperboard, tensile strain is added to the liners before bonding to the corrugating medium. This was found to produce double faced paperboard with much better rigidity.

Tension is not possible to any significant extent in the prior art manufacturing process for several reasons. Firstly, due to the reduced tensile strength of the paper when wet, for example from the steam, the liners are likely to tear if they are put under any significant tension. However, with the present invention, the paper remains dry throughout the process and so a much more significant tensile strain can be imparted into the paper without risk of damage.

Further, in the prior art, the single faced web is kept slack in loops on the conveyor bridge, therefore it is not possible to strain the outer liner as it enters the double backer unit.

The tension in the present invention could be produced by several means.

Advantageously, the paperboard is pulled from the back of the double backer unit, whilst both movement of the outer liner and the inner liner are resisted. The resistance, could, for example, come from braking mechanisms on the supply ic rollers that dispense the liners. However, one particular advantageous arrangement is the use of tensioning devices between the supply rollers and the gluing stages.

In an example of a tensioning device, the paper is pulled through a series of staggered fingers, or ridges, such that friction between the surfaces of the friction and the liners imparts a tension into the liners. The tension could be controlled by adjusting clamps to adjust the friction caused by the staggered fingers on the paper.

Other similar devices could also be employed to provide tension to the liners. For example, the liners could be forced between two rollers whose rotational speed is controlled to impart a tension in the liners.

The tension is generated by pulling the paperboard out of the double facer against the resistance of the tensioning devices through which the inner and outer liners are fed. This could be done in many ways. In an advantageous example, a gripper chain is used to grip the double faced paperboard at either side and pull it from the double backer unit. The gripper chain has clamping devices that grip either side of the double faced paperboard. As the paperboard is pulled, the liners are pulled tight against the tensioning devices and the liners are put under significant tensile strain.

The amount of strain that is needed depends on the type of paper and the manufacturing process, and the tension might need to be adjusted in order to optimise the strength of the final paperboard. In general, the paper used for the liner will have a tensile strength that reduces when it is wet. In the prior art, the use of steam will cause the liners and the corrugating medium to become damp and they would not be strong enough to be put under this level of strain and would likely tear. Consequently, in the prior art the only tension used is to feed the liner through the assembly. In particular, any tension that may exist in the outer liner whilst being fed through the single facer unit is lost on the conveyor bridge, where the single faced web is allowed to go slack.

With the above arrangement the liners are in tension throughout the drying time of the glue, and this tension provides the finished paperboard with high rigidity and strength without the use of steam.

Further improvements to the quality of the paperboard can be obtained by putting a transverse tensile strain on the liners. This is done by arranging the gripper chains to slightly diverge as they pull the paperboard from the double backer unit. In this manner, as the paperboard is pulled, it is also stretched in a transverse direction producing a transverse tensile strain.

To avoid weakening of the liners, it is preferable not to use starch glue which must be applied liberally and so wets the paper. Instead, other adhesives could be used, for example FVA glue. This should not reduce the strength of the liners significantly, and avoids the liners tearing when under tension.

It would be advantageous to use PVA glue that is designed to cure rapidly at an ambient temperature, to reduce the need for heating and to provide a quick production time.

In the present invention, the liners and the corrugating medium are dry, since they are not conditioned with steam, and so can be very absorbent.

Therefore the PVA glue must be applied very sparingly to avoid the glue being sucked up into the paper like a sponge and overly wetting the paper. In one embodiment, this is achieved by using a specially adapted roller on the gluing station. The roller is provided with radial ridges. In this manner, the glue is applied to the corrugating medium in small spots where the ridges of the gluing roller meet the perpendicular ridges of the corrugating medium rather than being applied along the whole length of each fluting. Therefore, the glue is applied very sparingly to the corrugating medium.

After the point where the paperboard has been assembled, the apparatus could further comprise a series of rolls along the length of a conveyor sited to compress and align the completed assembled board in parallel with a series of heater rolls for the inner liner beneath, which guide the inner liner into position, to heat and dry out prior to the glue application and to assist in the curing process for the now fully assembled corrugated board. The assembly of such a machine may allow the total length of the apparatus to be reduced to less than six metres.

A drive motor attached to gripper chains links up with the conveyor system to pull the assembled corrugated board towards a cutting and stacking stage. To ensure the corrugated board remains in a flat and rigid state, the board is cooled down within the machine before being cut free into selected lengths. Cooling the warm deposits of glue solidifies the whole board. By using exhaust air from a vacuum fan and directing it to the final section of the conveyor, ambient temperature can be achieved, thus eliminating the danger of distortion. As a result of the use of mechanical tensioning systems, specially formulated PVA adhesive and compact positioning of the rollers, which reduce the overall size of the machine and therefore the heat requirements, the apparatus may be run by a single unskilled operator whose sole function is to start and stop the machine.

In a further embodiment, a second corrugator drum is connected with the first to manufacture a double wall corrugate. In practice the second corrugator drum may be positioned above the first to reduce factory footprint.

In adopting the identical procedure of manufacture to the first embodiment two additional reels of an outer liner and a corrugating medium may be sited close to the second corrugator drum; there now being five liners engaged in the manufacturing process, the outer liner and the first corrugating medium being connected to the second corrugator drum and the middle liner, the second corrugating medium and the inner liner connected to the first corrugator drum.

During the manufacturing process all five liners progress towards heater rolls and rollers which change the direction of the liners to keep the factory footprint of the machine as compact as possible.

The top, middle and inner liner each pass through their individual tensioning device before reaching their respective heater rolls, rollers and gluing stations.

After being directed off the second corrugator drum, the conjoined outer liner and corrugating medium, known as single faced web', traverse towards further rollers and gluing trough prior to becoming conjoined on a conveyor system with the middle liner, corrugating medium and inner liner processed from the first corrugator drum, to form a double corrugate.

Gripper chains link up with a conveyor system to pull the assembly ic towards cutting and stacking. To ensure the corrugated board remains in a flat and rigid state, the board is cooled down within the machine before being cut free into selected board lengths.

Cooling the warm deposits of glue solidifies the whole board. By using the exhaust air from vacuum fans and directing it to the final section of the conveyor, consistency of ambient temperature can be achieved, thus eliminating any danger of distortion.

As well as the advantageous discussed above, the apparatus has further advantages, some of which are now highlighted.

The high tension in the inner liner as it contacts the corrugating medium on the corrugator holds the liner tightly against the corrugating medium after the gluing station. This tension will hold the corrugating medium in the corrugations of the corrugator, and therefore suction on the corrugating medium needs only to extend for the short arc-length from the labyrinth to the contact area with the first liner.

In prior art apparatuses, the rotation of the supply rolls has to be carefully monitored and controlled to avoid any undue tension in the liners. In particular, as the amount of paper on the rolls reduces due to it being dispensed, the diameter of the roll reduces. Therefore, without monitoring and careful control, the paper will be dispensed at a lower rate as the paper is used, and so the paper may become strained. In a traditional steam-based apparatus, this could cause damage. However, in embodiments of the present system tensioning devices prior to the gluing stations, the tension in the paper is not controlled by the rotation of the rollers, and so the dispensing system can be much simplified, and the supply rollers may even be freewheeling rather than driven.

By using a suction means to overcome the reduction in pliancy of the corrugating medium before being bonded to the upper liner, the long conveyor bridge is made redundant, and the double backer unit and the single facer unit can be arranged in a much more compact arrangement, and may even be integrated into a single unit.

Brief description of the drawings

The invention may be put into practice in a number of ways and some embodiments will now be described by way of non-limiting example only, with reference to the following figures, in which: Figure 1 shows a schematic diagram an apparatus according to embodiments of the present invention; Figure 2 shows a close-up side schematic diagram according to embodiments of the present invention; Figure 3 shows a schematic diagram of a glue roller according to embodiments of the present invention; Figure 4 shows a side view schematic diagram a spring loaded adjustable tensioning device according to embodiments of the present invention; Figure 5 shows an oblique view of the tensioning device of figure 4 according to embodiments of the present invention; Figure 6 shows a close up side view schematic diagram of an assembly of the apparatus circled in figure 1 according to embodiments of the present invention; and Figure 7 shows a side view schematic diagram of an apparatus for the manufacture of double wall corrugated board according to embodiments of the present invention.

Detailed description of embodiments of the invention In figure 1 a schematic embodiment of an improved apparatus for the manufacture of corrugated board is depicted engaged in manufacture with three separate reels of paper rotating about their axes. Their routes are individually configured in such a manner as to create a compact footprint of the apparatus on the factory floor. Gripper chains affixed either side of a conveyor system at the conclusion of the manufacturing process are driven by powered means, which may be a single 2 kW motor, which pulls the attached corrugated board assembly.

The gripper chains are mounted both side of the paperboard on supports and pass over sprockets at each of their ends. As the chain passes over the sprocket at the upstream ends of the supports, the grippers of the chain open in sequence, the paperboard is received within the open gripper and the open gripper closes as the chain leaves the sprocket so as to firmly hold the corrugated board. In this manner, the gripper chain serves to pull the corrugated paperboard through the apparatus. As the grippers of the chain reach the downstream end of the supports, the sprocket causes the grippers to open and to release the board. The width of the grippers can be selected to accommodate the thickness of the corrugated board that is being manufactured.

The single-powered means facilitates the movement of the different paper reels at the beginning of the manufacturing process towards their amalgamation and final assembly towards cutting and stacking. At the centre of each reel is positioned a weighted strap to inhibit any likelihood of over-run of the machine.

The reel supplying the outer liner 1 freewheels about its axis but is pulled by the aforesaid powered means, and feeds outer liner 2 through a series of rollers 3 before being threaded through the tensioning device 4, which may be in an open state during set-up to allow 15 friction-free passage.

At the same time the reel of corrugating medium board 7 freewheels about its axis and feeds corrugating medium 6 through a series of rollers 3 before being directed to reach a toothed cylinder called a corrugating roller 8 which forms the paper into a series of arches called flutes, by compressing between a large corrugating drum 5. The flutes can be pitched at particular intervals relevant to the different strengths of board desired. The corrugating medium is now pulled over the flutes by the aforesaid powered means by gripper chains.

Gluing station 9 facilitates the even distribution of specially prepared adhesive over the corrugating medium 6 to bond with the outer liner 2, which the corrugating medium meets as both liners rotate axially around corrugator drum 5.

The liners are now called a single-faced web and traverse circumferentially.

Without the treatment by steam, the corrugating medium is subject to a spring-back effect and tends to return towards its original state. Consequently, the flutes do not remain in their deformed configuration. Therefore, the present invention may employ suction to maintain the corrugating medium in the ridges of the corrugator as shown in figures 1 and 2. To this end, suction holes (not shown) are formed through the corrugator drum 5 at the bottom of each of the ridges.

Suction holes are formed in each of the recesses along the entire axial length of the corrugator drum 5. In order to create the suction, a vacuum box 113 is mounted within the corrugator drum 5. The vacuum box extends a sufficient distance around the inner circumference of the corrugator drum 5 to apply suction to the corrugating medium in the region between the single facer 8 and the rollers 3, which is approximately 25% of the circumferential extent of the corrugator drum 5 from the point on the corrugator drum 5 where the paper is deformed by the single facer 8.

When a suction fan (not shown) is operated, air is drawn through the suction holes so as to reduce the pressure between the corrugating medium and the corrugator drum 5 and in this way the corrugating medium is retained on the recesses of the surface of the corrugator drum 5 as the drum rotates.

Suction is transmitted to the vacuum box 113 by a central tube 107 which is sealed to the vacuum box by a part-cylindrical recess 115 and suitable seals.

The vacuum box 113 is formed in a number of axially-extending segments separated by walls which are adjustable to allow suction to be applied along different axial lengths of the drum in order to accommodate varying widths of paper. The circumferential region of the vacuum box 113 is provided with seals which seal against the inner circumferential surface of the corrugator drum 5 and also with a part-cylindrical recess adapted to receive the pressure roll 109 and which is sealed to a pressure roll 109 with seals.

The outer liner being pulled by the gripper chains clamps down tightly on the fluting paper, (because of the wrap around effect of the outer liner on the drum created by the tensioning device) to secure the bond. When the glue is applied in dots to the face of the two paper liners, although it is in tiny amounts, it still wets the paper.

An example of a gluing station is shown in figure 3. The gluing stations 9 comprises a glue reservoir 129 which is in the form of a trough. The reservoir 129 may be provided with a comb 131 to remove excess glue from a glue roll 133.

The comb may be adjustable if desired in order to regulate the amount of glue applied to the flutes. The glue roll is formed with circumferential flange-like protrusions 135 at even intervals along the axial length and between teeth of the comb 131. The protrusions 135 have a diameter such that a dot of glue is applied to each apex of the flutings. The glue roll 133 is provided with drive gears 137 which engage with the recesses formed in the surface of the drum and which therefore drive the roll at a rate such that the circumferential speed of rotation of the glue roll is the same as the circumferential speed of the corrugator drum 5.

The glue station may be replaceable with alternative glue stations (or alternative working components) which have a different axial extent of the protrusions, so as to apply a wider or narrower dot of glue, and/or a different number of protrusions, so as to increase or reduce the number of dots of glue applied, according to practical requirements.

Apparatuses of the prior art usually use a starch-based glue and to apply the glue over the entire width of the flutings (that is, the entire length of each corrugation). It is necessary to constantly monitor the consistency and temperature of the glue and it is also necessary to dry the product after the glue has been applied due to the amount of glue that is applied. This, in turn, requires the use of heaters to evaporate excess liquid while the product is constrained to prevent warping. In contrast, the apparatus according to the present invention applies only small amounts of glue, such as FVA adhesive which eliminates the need to dry the product and also eliminates the risk of warping.

Nevertheless, the PVA is absorbed by the paper and therefore the paper can sometimes swell and distort. By applying heat to the paper liners immediately before contact with the glue, the threat of distortion is reduced. The single faced web now travels along the last part of its journey around the circumterence to a further roller 3, which redirects the assembled board to a moving conveyor.

At the same time as the other two reels are being pulled by the same powered means, the final third reel of inner liner board 11, which can treewheel about its axis is also pulled by the same aforesaid powered means and feeds inner liner 10 through a series of rollers 3 before being threaded through the friction fingers of tensioning device 4, which may be in an open state to during set-up to allow friction-tree passage. The inner liner 10 then passes over a series of heaters 12, and conveyor rolls 13, which prepare the inner liner for joining with the single facer to form the complete assembly of corrugated board 15. This part of the apparatus is shown in more detail in figure 5.

Figure 2 features a close up schematic view ot the first part of the production route of the outer liner 2, showing a friction principle ot the adjustable tensioning device 4, heater rollers 3, around which outer liner 2 rotates and meets up and joins with corrugating medium 6 on corrugator drum 5 having passed over gluing trough 9, both types of paper now becoming single faced web. A series of heating rollers 3 to cure the outer liner are positioned around the first part of the perimeter of the corrugator drum 5 close to the entry point of the outer liner on the drum. When the machine stops, or to prevent scorching, the rollers automatically lift away from the surface to allow the paper to be threaded through.

In figure 4, a schematic view is shown of a spring loaded adjustable tensioning device 4 featuring sections 17 and 18, hinged at 15. In practice the device may extend the width of the paper to be tensioned. The device comprises a series of staggered curved surfaces on the end of several fingers 16 arrayed along its length and positioned on opposite sides to facilitate their nesting and to allow sufficient clearance around the nested fingers when the device is closed to be able to create friction of the paper liners in operation as they zig zag' in direction by the manual opening and closing of an adjustable clamp 19 atone end. Of course, the opening and closing of the adjustable clamp 19 can automated and controlled by a controller. Such an adjustable tensioning device may facilitate fine adjustment of the fingers to allow the paper liners to travel between the curved ends of the fingers under appropriately gauged tension to keep the paper liners 2 and 6 individually and separately taut, in their approach to their respective rollers. Such a tensioning system and the resulting tolerance between the fingers may be adjusted to suit the gauge of liners being used (for example top 1 20g, bottom 90g) and aids in the curing of the liners after gluing.

The size of the fingers selected for the tensioning device and their proximity to each other is dependent upon the thickness of the paper liners which are to be manufactured into corrugated board.

The addition of glue to the surface of each liner will allow stretching and each liner will behave differently. The effect of incorrect tension is that when the glue cures, the board will distort. Current industry practice overcomes this by restricting the board until it is completely cured by passing it through heater plates. Instead of this process, the present invention applies tension as required to each liner and by monitoring the product coming off the end of the conveyor and making adjustments to correct any distortion.

In addition by using the tensioning system in conjunction with heated rollers, wider variations in paper gauges may be used to make corrugated board, for example 1 25g for a outer liner, 70g for a corrugating medium and 70g for a inner liner. The implications of introducing such a tensioning system into this manufacturing process leads to substantial cost savings with no noticeable loss of strength in the manufactured corrugated board.

In figure 5, a tensioning device 4 is shown as a bracket arrangement in three dimensions covering the width of an improved apparatus for the manufacture of corrugated board. Adjustment means 19 may be duplicated either side of the paper liner being tensioned to facilitate even tensioning pressure and to control through-travel of the paper. Fingers 16 extend in a staggered arrangement towards each other from brackets 17 and 18 and range across the full width of paper liner 2 and 6. To facilitate entry of the paper liners the bracket arrangement hinges at 15 to separate the nesting fingers when adjustment means 19 has been released.

Figure 6 shows a detail of the improved apparatus for the manufacture of corrugated board featuring the final stages in the production process which is encircled in figure 1. Inner liner 10 extends appropriately taut out of the second adjustable tensioning device featured in figures 4 and 5 and traverses across guide rollers 3 and heater rollers 12 to loop round 180 degrees and meet single face assembly 14 immediately out of glue receptacle 9 to conjoin with the inner liner and form final corrugated cardboard assembly 15. Conveyer rolls 13 ensure that the final assembly of all three liners is held compressively constant. A further series of heated rollers may be incorporated into the conveyor system to assist in the curing process. The corrugated board assembly traverses along the conveyor to a slitter, or scorer at the so-called dry end' of the machine which cuts and creases the board. Cut-off knives cut the boards to required lengths and an automatic stacker piles them up. When the machine stops heated rollers 12 are automatically released to reduce tension and to avoid scorching, which leads to isolated brittleness across a section of the paper.

In figure 7 a further embodiment of an improved apparatus for the manufacture of corrugated board shows a side view of a schematic drawing of two corrugator drums 20 and 21 positioned within close proximity to each other.

Five liner reels, outer liner 22, first corrugating medium 23, middle liner 24, second corrugating medium 25 and inner liner 26 traverse via location rollers, heated rollers, gluing troughs and three tensioning devices 4 towards their respective corrugated drums, peeling off at appropriate positions on their circumferences by means of rollers in order to meet up and conjoin with each other on a conveyor system, which may then transport the complete assembled double corrugate 27 towards cut-off knives to cut the boards to required lengths and an automatic stacker to pile them up.

The apparatus according to the present invention eliminates the lengthy drying process, resulting in an apparatus that is substantially more compact than the prior art corrugated paperboard manufacturing apparatus. This compactness of the apparatus allows relatively small, and therefore manageable, rolls of paper to be employed. It is also possible to use relatively lightweight paper, especially but not exclusively for the corrugating medium, such as of 70 grams per square metre, or even less, since the paper is not treated with steam which weakens the paper The compact nature of the whole apparatus also allows for a single, unskilled operator to facilitate these means and have complete control over the production process, including the ability to start and stop the machine as necessary, to change the paper for example, or for something as straightforward as a comfort break.

It will be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the ic appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein. The foregoing description details certain preferred embodiments of the present invention and describes the best mode contemplated. Therefore, the description provided herein is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined by the following claims and the full range of equivalency to which each element thereof is entitled.

Claims

Claims: 1. Apparatus for manufacturing corrugated paperboard, the apparatus comprising: a first supply roller for supplying a first liner; a second supply roller for supplying a corrugating medium; a first tensioning device for providing tension in the first liner; a corrugator for corrugating the corrugating medium to produce a fluted web;and a first bonding assembly for bonding a first side of the fluted web to the first liner, wherein the apparatus is arranged to: direct the corrugating medium to the corrugator; direct the first liner from the first supply roller to the bonding assembly; provide tension to the first liner; and bond the first liner to the first side of the fluted web to form a single faced web.
2. The apparatus of claim 1 wherein the corrugator comprises a corrugator drum which is provided with suction holes arranged at the outer surface of the corrugator drum, and suction apparatus arranged to provide suction via the suction holes for retaining the fluted web on the surface of the corrugator drum.
3. The apparatus of claim 2 wherein the suction apparatus comprises a vacuum box positioned inside the corrugator drum and arranged to provide suction through the suction holes disposed between the corrugating roller and the first bonding assembly.
4. The apparatus of any preceding claim further comprising: a third supply roller for supplying a second liner; a second tensioning device for providing tension in the second liner; and a second bonding assembly for bonding a second side of the fluted web to the second liner, wherein the apparatus is arranged to: direct the second liner from the third supply roller to the second bonding assembly provide tension to the second liner; and bond the second liner to the second side of the fluted web to form a at a point after the corrugator to produce a corrugated paperboard.
5. The apparatus of claim 4 wherein the apparatus is arranged to bond the first liner with the fluted web whilst the fluted web is in contact with the corrugator drum and direct the single faced web under tension from the corrugator drum to the second bonding assembly to bond the second liner to the fluted web.
6. The apparatus of claim 5 further comprising a pulling mechanism for pulling the corrugated paperboard to provide tension in the first and second liners between the pulling mechanism and the first and second tensioning devices, respectively.
7. The apparatus of claim 6 wherein the pulling mechanism are gripper chains.
8. The apparatus of claim 7 wherein the gripper chains are arranged to slightly diverge so that the paperboard is put under transverse tension as it is pulled by the gripper chains.
9. The apparatus of any preceding claim wherein the tensioning devices comprise interlocking fingers arranged so that the liners can pass between the interlocking fingers to cause friction between the surfaces of the fingers and the liners.
10. The apparatus of claim 9 wherein the interlocking fingers are arranged on a clamp, and the tension in the liner is controlled by adjusting clamps to adjust the friction caused by the interlocking fingers.
11. The apparatus of any preceding claim wherein the bonding assemblies comprises a glue roll with circumferential flange-like protrusions, the glue roll arranged to provide adhesive to the fluted web in small dots.
12. The apparatus of any preceding claim wherein the adhesive is PVA glue.
13. The apparatus of any preceding claim wherein the first tensioning device is arranged to provide tension to the first liner that is less than the dry tensile strength of the first liner but greater than the wet tensile strength of the first liner.
14. The apparatus of any preceding claim wherein the first tensioning device is located after the first supply roll and the second tensioning device is located after the second supply roll.
15. The apparatus of any one of claims 4 to 14 wherein the second tensioning device is arranged to provide tension to the second liner that is less than the dry tensile strength of the second liner but greater than the wet tensile strength of the second liner.
16. The apparatus of any preceding claim arranged to manufacture corrugated paperboard having more than one fluted web, the apparatus having a further supply roller for supplying a corrugating medium, bonding assembly, supply roll for supplying a liner and tensioning device for each further fluted web of the paperboard.
17. Method of manufacturing corrugated paperboard, the method comprising the steps of: producing a fluted web from a corrugating medium with a corrugator; providing tension to a first liner; bonding the first liner to a first side of the fluted web whilst the first liner remains under tension.
18. The method of claim 17 wherein the corrugator comprises a corrugator drum and the method further comprises retaining the fluted web on the surface of the corrugator drum using suction.
19. The method of any one of claims 17 and 18 further comprising providing a tension to a second liner and bonding the second liner to a second side of the fluted web whilst the first and second liner remain under tension.
20. The method of any one of claims l7to 19 wherein the tension in each liner is provided between a pulling device and a tensioning device.
21. The method of any one of claims 17 to 20 wherein the method is carried without applying steam to the corrugating medium, the first liner or the second liner.
22. The method of any one of claims 17 to 21 wherein the tension applied to the first liner is less than the dry tensile strength of the first liner but greater than the wet tensile strength of the first liner.
23. The method of any one of claims 19 to 22 wherein the tension applied to the second liner is less than the dry tensile strength of the second liner but greater than the wet tensile strength of the second liner.
24. The method of any one of claims 17 to 23 further comprising the steps of: producing one or more further fluted web from a corrugating medium with one or more further corrugators; providing tension to one or more further liners; bonding the one or more further liners to first sides of the one or more further fluted web whilst the one or more further liners remains under tension.