Patent Application
20090078748
The present invention relates to protective wrappers for rolls to reduce crimping marks on roll ends.
Newsprint and other forms of paper are manufactured and processed as large elongated sheets or webs. As shown in
Various methods have previously been used to wrap paper rolls. One of the most successful methods has been to first wrap the roll in one or two layers of a protective wrapper (
A set of exterior or outside roll headers (somewhat thinner disks typically formed of a kraft paper with a polymer coating on the inside surface) are then attached to the ends of the roll over the crimped edges (
The exterior roll headers are affixed to the ends of the rolls in a typical roll wrapping machine by applying heat and/or pressure in accordance with the properties of the adhesive used. To heat-seal the roll, pressure and high temperature are necessary. This step is known to create crimping marks on the roll ends because of the wrapper crimps that absorb energy from the heat-seal platens.
When the rolls are stacked on end, the crimps crush the edge of the roll and produce indentation. Damage to the paper rolls incurs financial burden to the purchaser, the manufacturer, and/or the transporter.
Crimping marks are generally created during the heat sealing process, the warehousing, the stacking of the rolls and the transportation (mainly due to vibrations and roll dropping). The crimping marks creation varies according to the paper roll density which changes with winding operations and paper grade, the impact stresses due to stacking, the wrapper thickness, the number of wrapper turns, the quality of the crimper and crimp width, the winding quality with offset edge position enhancing crimping marks, the impact strength during roll handling, the stacking procedure, the amount of stacked rolls, the warehousing period, the transportation and restacking, all varying from one mill to another, the transportation mode, rail, boat and truck causing different vibration strengths, the seasonal transportation, the inside headers variations, the position of the roll in the stack (paper roll edge in contact with floor showed more deep crimping marks than those stacked because two roll edges in contact are more compressive than a roll edge in contact with concrete floor). During transportation by a lift truck, the roll is subjected to a clamp force on its sides and by friction along its width as shown in
The cushioning chipboard header is composed of multiple fiber layers. Headers manufacturers can laminate several chipboards together to obtain a thicker header for better cushioning protection. When a pressure is applied on the top of the header, mainly due to the wrapper crimps, some pressure are absorbed by the spongy chipboard and the remaining pressure is transmitted through the chipboard. This is the transmitted pressure which causes the crimping marks.
By increasing chipboard thickness, the pressure absorbed by the spongy chipboard is increased and the transmitted pressure through the chipboard is reduced, providing a better roll edge protection. So far is was the only known technology used to reduce the crimping marks.
Referring back to
The industry has therefore developed typical wrapper design which respect these recommendations. An example of a water-vapour-proof wrapper design protection is two linerboards laminated with a barrier like Polyethylene (PE). A coated linerboard with a similar barrier can also be used. Examples of such wrapper designs are indicated in Table 1 below.
Two wrapper layers around the paper roll with a crimped section is nine wrapper plies for a thickness range of 9 times the wrapper thickness. During the stacking process, the wrapper can be compressed up to 25% as measured on a crimp sample after a long stacking strength (pressure and time).
Also, the wrapper thickness reduction is limited by the minimal wrapper strength needed to wrap a paper roll. For that reason, the reduction of the wrapper thickness is a limited technique to reduce the crimping marks. The stresses involved during the roll transportation (lift, truck, conveyor, etc.) limit the wrapper thickness decreasing since the tearing strength in both the machine direction (MD) and the cross-direction (CD), the tensile strength, the tearing strength, the bursting strength, the TEA and the stiffness are all critical physical properties needed to ensure integrity of the rolls.
It is therefore an aim of the present invention to address the above mentioned issues.
An aspect of the invention provides a wrapper for wrapping on a roll of length L having two opposed roll ends. The wrapper comprises an interior layer of a length Wi and of an interior layer basis weight, adapted to be adjacent the roll when the wrapper is wrapped on the roll; an exterior layer of a length We longer than the length Wi of the interior layer forming at least one end strip of width S and of an exterior layer basis weight, adapted to be outside of the roll when the wrapper is wrapped on the roll. The interior layer basis weight is different from the exterior layer basis weight. The end strip of the exterior layer is adapted to be folded on a corresponding one of the roll ends during crimping following wrapping of the wrapper on the roll.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
Referring now to the drawings and, more particularly, to
The roll 20 is wrapped with a protective wrapper 30 having a width W1, longer than the length L1, in a manner such that longitudinal edge strips 32a, 32b of the wrapper 30 extend outwardly beyond the roll ends 24. The edge strips 32a, 32b of the wrapper 30 typically extend between three to ten inches and, preferably, between four to nine inches, beyond the roll ends 24 but they can be wider or narrower.
The edge strips 32a, 32b are crimped using a crimping wheel which hammers the edge strips 32a, 32b onto the ends 24 of the roll 20. It will appreciated that any other suitable technique can be used to crimp the extending edge strips 32a, 32b. Each of the edge strips 32a, 32b of the wrapper 30 overlaps onto itself on the roll ends 24 during the crimping procedure. As the edge strips 32a, 32b are crimped over the roll ends 24, ridges 36 are produced and part of the wrapper 30 overlaps onto itself forming overlapped areas 38 (
An exterior roll header 42 (
Referring now to
The roll headers 34, 42 are disks formed of corrugated cardboard, chipboard, or laminated kraft paper, for example. The roll headers 34, 42 can have adhesive properties on a face. For example they can be coated with a heat sensitive adhesive such as polyethylene. For the interior roll header 34, the adhesive is on the face opposite to the face in contact with the roll 20, i.e. the face in contact with the crimped edge strips 32. For the exterior roll header 42, the adhesive is on the face in contact with the crimped edge strips 32. Therefore, when activated, if necessary, the adhesive bonds the roll headers 34, 42 to the crimped edge strips 32a, 32b, as it will be described in more details below.
Referring back to
If the basis weight of the interior layer is greater than the basis weight of the exterior layer and only the exterior layer is crimped, the crimping marks will be induced by the layer with the smallest thickness and therefore will be reduced when compared to a standard design wrapper where both layers of identical thickness are crimped. It should be noted, however, that even if the basis weight of the interior layer is smaller than the basis weight of the exterior layer and only the exterior layer is crimped, the crimping marks will still be reduced when compared to a standard design wrapper where both layers of identical thickness are crimped because only one layer of the wrapper is crimped.
In some cases, the interior layer of a width W2 will be slightly larger than the width of the roll L1 and the interior layer will therefore be slightly crimped when the exterior layer is crimped. This will protect the edges of the roll, will not create unacceptable damages to the roll and will still reduce the crimp marks with respect to standard wrappers.
A third layer, with or without moisture barrier properties, can be laminated in between the interior and exterior layers of the wrapper. The third layer may have a width of W1 or W2 or any width in between W1 and W2 and will therefore be completely crimped with the exterior layer, will not be crimped at all or will be partially crimped, respectively.
Referring back to Table 1, examples of typical wrapper designs include two or three layers of materials with a thickness range from 325 to 575 microns.
These standard wrapper designs follow the recommendations of the TAPPI. However, a single layer of 126 g/m2 does not follow these recommendations since it has a tensile CD force of 4 to 7 kN/m, a Burst force of 450−650 kPa and a Tear CD force of 1.8-2.2 N. However, if it is crimped and sealed on a header (having a composition of 200 g/m2, for example), the single layer of 126 g/m2 becomes laminated with the header and therefore stronger, yielding a tensile CD force of 15-17 kN/m, a Burst force of 1400-1650 kPa and a Tear CD force of 6.8-7.9 N.
An asymmetrical wrapper design with a total composition of about 252 g/m2 would therefore yield the same acceptable protection for the length of the roll. Similarly, other compositions could be designed to yield a total of about 269 or 322 g/m2. Such an asymmetrical wrapper design could be as follows.
The laminated asymmetrical wrapper of example 3 has a composition of 161 g/m2+barrier+90 g/m2, wherein 161 g/m2+barrier is the crimping zone thickness. The laminated asymmetrical wrapper of example 4 has a composition of 90 g/m2+barrier+161 g/m2, wherein 90 g/m2+barrier is the crimping zone thickness. In some applications, the fact that the crimping zone thickness will be composed of the 90 g/m2+barrier layers will be sufficient to yield the appropriate strength for the application, In other applications, a higher thickness for the crimping zone will be required and then the crimping zone thickness composed of the 161 g/m2+barrier layers can be used. Other combinations of thicknesses of layers can also be used as will be readily apparent to one skilled in the art and examples 3 and 4 are solely exemplary.
Table 2 below shows examples of the wrapper thickness ranges, crimp thickness ranges (which are 3 times the wrapper thickness range) and crimp section thicknesses when the wrapper is compressed by a maximum of 25% in thickness and, for the new designs, the edge thickness with its compressed thickness ranges.
The edge strips 32a, 32b of the wrapper 30 can further have an exposed strip 46 of a material with adhesive properties on one or both faces. The adhesive strip can be provided on the wrapper 30 either prior to wrapping the roll 20 or once the roll 20 is wrapped. Reference is made to co-pending US published patent application no. 2006/0277866 for a detailed description of embodiments of this exposed strip 46 with adhesive properties. When wrapping the roll 20, the exposed strip 46 can be located on the face of the wrapper 30 in contact with the interior roll header 34 and/or the end 24 of the paper roll 20 and/or in contact with the exterior roll header 42, if any, i.e. the outer face of the wrapper 30.
For protecting the roll 20 from external moisture, the atmosphere, and physical abrasions, the wrapper can have moisture proof properties along its widths W1, W2 or any width in between. The paper layers can be laminated with a material having moisture barrier properties such as PE, wax, an appropriate polymer or any other appropriate material.
Referring now to
The roll 20 can be any type of rolled paper including coated printing paper. However, it will appreciate that the above described technique and wrapper can be applied to any rolled material that needs to be wrapped and protected from liquids and/or moisture infiltration.
The wrapper can be manufactured on existing roll wrap extruders, laminators, and coater-laminators and can be applied to the roll 20 with existing roll wrapping equipments.
It will appreciate that the roll 20 can be wrapped one turn or more by the wrapper depending upon the physical properties of the wrapper.
Seventeen paper rolls were wrapped with standard design wrappers and with asymmetrical wrappers. Different header thicknesses were used. Prior to wrapping the rolls, all packaging materials (heat sealable outside headers, chipboard inside headers, wrappers) were also conditioned to 23 deg.C and 50% of relative humidity. The purpose was to keep the same compressibility of the different packaging materials. The rolls were stacked in a conditioned room at 23 deg.C and 50% of relative humidity, and with the same stacking weight being applied on each paper rolls. The stacking period was 30 days. A paper roll without inside chipboard headers was wrapped and used as the reference for the standard wrapper. After the stacking period, the wrapper and the header, if any, on each paper roll was removed and, with a laser beam vernier, the crimping marks depth were accurately measured. In some areas of the roll edge, typically near the center, almost no crimping occurred and the edge has remained damage free. In areas closer to the outside perimeter of the roll edge, crimping has occurred and has created depressions in the roll edge surface. The highest point on the roll edge was determined to be at a position where no crimping occurred. Then, a comparative measurement was done between that point and the lowest point where crimping occurred and created a depression on the roll edge. That distance is the crimping marks depth measured.
Table 3 below shows the average crimping marks depth obtained for the laminated standard wrapper of type 1, with a composition of 126 g/m2-barrier-126 g/m2 wherein all layers are crimped, the laminated asymmetrical wrapper of example 3, with a composition of 161 g/m2+barrier+90 g/m2, wherein 161 g/m2+barrier is the crimping zone thickness and the laminated asymmetrical wrapper of example 4, with a composition of 90 g/m2+barrier+161 g/m2, wherein 90 g/m2+barrier is the crimping zone thickness. The average (avg) and standard deviation (s.d.) (in italics) crimping marks depth, in μm, was measured to be as follows in Table 3, for each header thickness tested and for each wrapper design.
The embodiments of the invention described above are intended to be exemplary only. Several alternatives are possible. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.
