MXPA00004742A - Paper mill core structure for improved winding and support of paper mill roll - Google Patents

Abstract

Paper mill cores of the invention are structured to allow winding and unwinding chucks to distort the interior diameter and shape of the interior body wall of the core while resisting distortion of the core exterior to prevent center burst failure. The paper mill cores of the invention include a multi-ply zone of high strength, but relatively compliant, paperboard plies within the outer 70%(based on the total body wall thickness) of the body wall having a thickness of at least about 4 mm. An interior zone constituting at least about 25%of the total thickness of the body wall is formed from extremely high strength, extremely high density paperboard plies. The overall wall thickness of the core is preferably at least about 15 mm, and is thus preferably increased, as compared to the wall thickness ofconventional high strength wide paper mill cores formed entirely of extremely high strength, extremely high density, non-compliant paperboard plies.

Description

CARPET NUCLEUS STRUCTURE FOR IMPROVED WINDING AND SUPPORT OF PAPER ROLL FIELD OF THE INVENTION The invention relates to a structure of the cardboard core for winding and supporting heavy rolls of wide and continuous paper sheet. More particularly, the invention relates to a multilayer cardboard core structure having a high crush resistance of the corrugations for winding and supporting rolls of continuous paper sheet having an amplitude exceeding 254 cm, and a diameter of roll typically more than about 127 cm.

BACKGROUND OF THE INVENTION The large and heavy cardboard cores to support the large and heavy paper rolls used in high end applications such as gravure, are built to meet the established demand of resistance requirements including high crush resistance and high resistance dynamic. These and other strength requirements are necessary because the cardboard cores are internally supported at their ends by blows expanded during the winding and unwinding operations in which the roll of the paper wound in the core has about 1, 800 kg, typically reaching or exceeding 4,500 kg, and a space and amplitude typically between about 250 and 4 cm and 356 cm. These cores are currently supplied in two sizes of standard internal diameter (ID) 5 of 76.2 mm and 152.0 mm in the United States, and a standard ID of 150.4 mm in Europe (which corresponds to an ID of 152.0 mm of the core of paper in the United States). The problem known as "core sheath" failure of such heavy and large paper rolls has frustrated the 10-paper manufacturing industry for years. In particular, paper rolls that appear to be perfect when rolled, subsequently fail without an apparent reason in the unwinding operation during printing. The symptoms of central sheath failure are well known and consistent. The paper in the portion of the roll near the core, and at the ends of the roll above the unwinding runners 15, sheath, and patches can be ejected through the sides of the roll. Such patches significantly increase the chances of the network breaking during the printing process resulting in a costly waste of time in the printing room. In the same way, the patches can be found in the upper part of the remaining sheet causing 20 bad impressions and quality problems. Such defective paper rolls that are returned to the papermaking supplier can have a greater impact on profits. - - "- < - &- ** • - * eí ~ > ^» da <, - ^ • "- * -" - 'The exact cause of the central sheath fault has not been identified For example, examination of the cardboard cores that support paper rolls that have central sheath fault defects has not resulted in the identification of correlated defects in the cores.The failure of the central sheath occurs in approximately 1-8% of paper rolls and is known to have increased the frequency of central sheath failure, which has been attributed to the use of larger and heavier rolls of paper. As compared to the fine quality papers of previous decades, today's fine quality papers are often thinner with lower friction surfaces and often have less strength due to a higher recycled fiber content. much more difficult to maintain the tension of vanado and form a uniform structure in the diameter of the paper roll. Said problems have been solved by modifications of the paper winding apparatus to provide continuous monitoring and control of the tension of the paper during the winding together with the application of the torsion, in such a way as to provide a desired profile of the winding tension. . Said modifications form the friction and compression in the wound papermaking roll in order to minimize any possible damage to the paper roll due to the sliding of several layers in the roll in the subsequent loading and unrolling. However, the failure of the central sheath persists and continues to increase without a pattern or predictable cause.

The assignee of the present application has developed various structures and techniques of the cardboard core to solve the specific problems with cardboard cores designated for specific end uses. For example, the patent of E.U.A. No. 5,393,582 issued February 28, 1995 to Yiming Wang, Monica McCarthy, Terry D. Gerhardt, and Charles G. Johnson discloses cardboard tube structures of strength driven crushing of the corrugations. Said structures involve the use of areas or layers of cardboard folds distributed within the wall of the tube, so that the cardboard folds of lower strength and lower density are placed in the outer and inner portions of the tube wall, while Cardboard folds of higher density and superior strength are placed in the middle or central portion of the cardboard tube wall. The patent of E.U.A. No. 5,505,395, issued April 9, 1996 to Yanping Qiu and Terry D. Gerhardt describes structures that solve the problems of internal diameter deformation that arise when the tubes are supported on a mandrel and subjected to substantial radial load loading as result of highly retracted yarns or films wound in the core under high tension. Said core structures involve the use of areas of high strength and high density cardboard folds placed in the outer and lower portions of the tube wall with cardboard folds of lower strength and lower density placed in the middle or central portion of the tube. the cardboard wall. In addition, the factors that influence the radial crush resistance of the cardboard tubes are * - - 4- - * * - * - * • 'describe in T.D. Gerhardt, External Pressure Loading of Spiral Tape Paper Tubes: Theory and Experiment, Journal of Engineering Materials and Technology, Vol. 112, p. 144-150 (1990). Although these and other tube structures and modifications have been proposed to meet the end-use requirements of the specific core carton, the central sheath problem associated with heavy and broad core cores for a wide variety of heavy sheet rolls paper has not been shown to cause any apparent property or defect in the cardboard cores. Furthermore, the extreme weight of the paper rolls and the extreme dynamic stresses applied to the cardboard core during the winding operations dictate that said cardboard cores must show high crush resistance and dynamic resistance, thus limiting the scale of core modifications available to solve the possible core structure variants within the desired wall thickness scale to reduce central sheath failure. Possible modifications of the core are further limited because the inner diameter portions of the cardboard core are formed of cardboard folds of extremely high strength and high density due to the so-called "exit" forces of the impeller applied by the surface of the winding impeller to the inner surface of the core during winding. In fact, due to several of these requirements, the cardboard cores for large and heavy paper rolls are conventionally constructed entirely of cardboard folds of extremely high strength and high density. Typically, the cardboard folds have a density exceeding 0.80 g / cc and a sufficient number of folds are used in the case of a cardboard core with an internal diameter of 150 and 152 mm to provide a wall thickness of about 13. mm, or in the case of the cardboard core, with an internal diameter of 7.62 cm, a wall thickness of around 16 mm. More recently, the assignee of the present application has modified the constructions of the traditional paper winding core to incorporate the crush resistance constructions described in the U.S. patent. No. 5, 393,582, issued on June 28, 1995 to Yiming Wang, Monica McCarthy, Terry D. Gerhardt, and Charles G. Johnson. Accordingly, the current paper winding core constructions of the transferee employ the areas of paperboard folds in the outer and inner portions of the pipe wall in which the bead density lies within the lower portion of the scale. high strength (0.80 to 0.92 g / cc), together with a central zone of folds that have a density in the upper portion of the high resistance scale (0.80 to 0.92 g / cc). The performance of the central sheath of said cores generally exceeds, or is at least comparable, to the performance of the central sheath of competitive conventional paper winding cores. However, in spite of the high strength of the conventional cardboard core structures, and of the modified core constructions of the transferee; and although the winding apparatus has been modified to optimize the construction of rolls of paper, the problems of central sheath failure still persist and have increased.

BRIEF DESCRIPTION OF THE INVENTION The invention provides carton core structures that can substantially reduce or eliminate core sheath defects in large and heavy paper rolls. The structures of the cardboard core of the invention are based on the identification of the cause previously without recognizing the failure of the central sheath, and on new modifications of the cardboard cores to counteract the problem recently identified. In particular, the inventors have discovered that the impellers used during the winding operations significantly deform the outer diameter and shape of the cardboard core. The deformation is not apparent, however, because after the winding is completed and the impeller is disengaged, the core normally returns to its original size and shape. Because the diameter and shape of the core is deformed during the winding operation, the compression and friction stresses built into the paper roll are based on the distorted shape of the core during the winding operation. However, when the impellers are disengaged after the winding and the core returns to its original size and shape, a significant portion of the beneficial defects of the compression and friction stresses built up in the paper roll during winding can be lost. The distortion of the cardboard core and the roll of paper constructed during the winding, and the changes related to the structure of the paper roll in the core removal of the winding impellers are complicated by the additional subsequent variable stresses that can be applied to the paper roll by the unwinding runners inserted at the ends of the papermaking core during the unwinding operation. It is believed that the distortions of the paperboard core caused by the pressure of the unwinding rolls during the unwinding operation can, in some cases, aggravate the damaging effects of the distorted stresses generated during winding and / or aggravate the loss of beneficial stresses. in the removal of the core of the winding impellers to increase in this way the possibility of core sheath failure. However, in other cases, the forces applied by the unwinding runners to the ends of the core can counteract, at least in part, the loss of beneficial stresses and / or distorted winding voltages built into the paper roll by the distorted core. during the winding procedure. It is believed that the dependence of core sheath failure in such separate cases associated with winding and unwinding has further interfered with the identification of possible causes of central sheath failure. In accordance with the present invention, the paper cores for the paper roll winding of large and heavy paper rolls are modified to significantly reduce or minimize the outward transmission of the forces applied to the interior of the core by the winding impellers and unwinding. In particular, the papermaking cores of the invention are structured to allow the winding and unwinding runners to distort the inner diameter and the shape of the inner body wall while resisting distortions of the core exterior, i.e. the corresponding distortion of the exterior of the core is significantly less or substantially minimized. Modifications of the papermaking cores according to the invention can be achieved while maintaining the high crush resistance of the corrugations and the dynamic strength properties as required for the paper cores. The core structures of the carton to counter the central sheath failure provided in accordance with the invention include a multi-folds zone of high strength, but relatively complicated, with cardboard folds within 70% (based on the thickness of the total body wall) of the wall or body. The zone of relatively complicated, high-strength cardboard folds has a thickness of at least 4 mm. In addition, the thickness of the general wall of the core is preferably at least about 15 mm, and thus is preferably increased, as compared to the wall thickness for conventional high-strength, high-paper-forming cores formed totally of extremely high strength and extremely high density, non-flexible cardboard folds. Advantageously, the relatively flexible and high-strength cardboard folds have a density between 0.65 and about 0.75 g / cc, more preferably between about 0.67 and 0.73 g / cc. In the case of the inner diameter core of .152 mm (including the 152 mm versions of the EUA and 150 mm European), the area of relatively flexible and high strength cardboard folds is preferably placed in the central portion of the cardboard wall. In the case of cores having an internal diameter of about 76 mm, the area of relatively flexible and high-strength cardboard folds is preferably placed at 50% of the external part of the body wall, and is currently preferred that said area forms 40% of the exterior of the body wall. The improved core structures according to the invention substantially reduce the external diameter changes caused by the winding runners, and also reduce the transfer of damaging forces to the paper roll by unwinding runners. According to the invention, the above is achieved by the confidence in a zone of cardboard folds, in a certain way more flexible, instead of having additional resistance of the core wall for reasons explained in more detail below. The thickness of the preferred increased core wall effectively meets the more flexible and high-strength paperboard crease zone to maintain the crush resistance of the corrugations and dynamic strength of the paperboard core. In addition, preferred increases in wall thickness can also increase the maximum winding speed that is allowed during winding and unwinding operations (known as critical speed). In highly preferred embodiments of the invention, the inner diameter paper core of 150 or 152 mm has a total wall thickness of about 15 mm, more preferably about 16 mm, and thus has an increased wall thickness conforming to it is compared to the 13 mm wall thickness conventionally used in large and high strength cores with an ID of 152 mm. Advantageously, 25.40% of the interior wall thickness of the body is formed of extremely dense and high strength cardboard folds in which the density will vary from about 0.80 to about 0.92 g / cc. The central 30-35% of the thickness of the body wall is preferably formed of high strength and more flexible cardboard folds having a density between about 0.65 and 0.75 g / cc. The outer 30-35% of the core wall is preferably formed of extremely dense and high-strength cardboard used to form the interior zone of the body wall, as described above. In the case of a core of 76 mm inner diameter cardboard according to the invention, it is preferred that 55-65% of the inside wall thickness of the core body be formed of extremely dense and high-density cardboard folds. resistance established previously, and that 35-45% of the outer wall thickness of the diameter core ---; - * - * - • - 76 mm inner is formed of the highest strength and most flexible cardboard folds described above.Coils with a 76 mm ID preferably have a wall thickness of around 17-19 mm when compared to the conventional 15 mm wall thickness used in 5 paper cores with a 76 mm ID According to yet another embodiment of the invention, a portion of the high strength and more flexible cardboard folds can be mixed with cardboard folds of extremely high strength in 30% of the interior of the core body wall, however, in this modality sufficient cardboard folds of extremely high strength are provided in 30% of the interior of the core body wall, so that at least half of the folds in this portion of the body wall are folds with extremely high strength; and substantially all the folds that make up 15% of the interior of the body wall are folds of extremely high resistance. The wall thickness of the total body exceeds about 15 mm; the total thickness of the folds of lower density and high strength, but of flexible scale, exceeds about 5 mm; and the total thickness of the folds in the extremely high density scale exceeds about 9 mm. ^ -fa-ii-M j ^ -j-.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings forming a portion of the original description of the invention; Figure 1 schematically illustrates in partial perspective view a winding impeller, shown in cross section, inserted at the end of the core of the conventional paper supporting a portion of a paper roll, with the ears of the winding impeller being shown distorting the diameter and external shape of the cardboard core in exaggerated detail; Figure 2 schematically illustrates in partial perspective view an unwinding wheel (shown in cross-sectional view) of different configuration compared to the winding wheel shown in Figure 1, inserted at the end of the cardboard core and supporting a portion of a roll of paper, with the ears of the winding impeller shown coupling the inside of the cardboard core in a configuration correspondingly different to the coupling of the winding impeller of figure 1 with the core; Figure 3 illustrates a schematic perspective view of a core of conventional paperboard and illustrates the variant distortion of the outer diameter and shape of the exterior and shape of the core in three different zones along the length of the core as result of the force applied by a conventional winding apparatus; Figure 4 is a partially sectioned cross-sectional view schematically illustrating a preferred cardboard core according to the invention; Figure 5 is a partial cross-sectional view illustrating the interaction between the preferred core shown in Figure 4 and the ears of a winding or unwinding wheel; Figure 6 is a partially sectioned cross-sectional view illustrating another preferred paperboard core according to the invention; Figure 7 is a partially sectioned cross-sectional view illustrating another advantageous paperboard core according to the invention.

DETAILED DECRIPTION OF THE PREFERRED MODALITIES The present invention will now be more fully described hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be presented in several different forms and should not be construed as limited to the embodiments set forth herein; on the contrary, said modalities are provided in such a way that this description is complete and complete, and completely transmits the scope of the invention for those - "" - * • experts in the art. Equal numbers refer to like elements in the present. Figure 1 illustrates a winding procedure of the conventional papermaking paper core wherein a portion of a paper roll 10 is shown supported on a conventional paperboard core., which in turn is supported within its inner end portions by a winding impeller 14 which includes a plurality and ears 16 projecting radially. As is well known to those skilled in the art, the ears 16 can be moved radially inwardly and radially outwardly by various well-known mechanisms (not shown) in order to allow assembly of the cardboard core 12 in the impeller 14 and the coupling of the cardboard core 12 by the impeller 14. In particular, when the ears 16 are in a radially retracted position (not shown), the cardboard core can be mounted coaxially on the impeller 14. Retraction on the ears 16 The end of a winding operation also allows the removal of the cardboard core 12 and the entire paper roll 10 from the impeller 14. On the other hand, when the ears 16 extend radially outward, the ears forcefully contact the inner surface of the cardboard core 12, so that the rotation of the impeller 14 also rotates the core 12. The conventional impellers 14 extend axially only from partial area at the ends of the core 12, typically for a length between about 51 mm and about 127 mm. Because the weight • * '* > -. - ,,. »< - ..., .... extremely high of paper roll 10, (for example, exceeding 1, 800 kg, more particularly approaching or exceeding 4,500 kg), and also due to its substantial length (typically between about 2.5 m and 3.5 m), and in addition due to the substantial twisting that must be transmitted from the impeller 14 towards the conventional cardboard core 12, the ears 16 of the impeller 14 are designed to expand radially outwards. The ears 16 are controlled outwardly by pressure from a torsion activation mechanism that forces the ears 16 outwardly at a distance sufficient to engage the inner surface of the core. The conventional paperboard core 12 used for winding paper of large and heavy paper rolls is formed in its entirety from a plurality of cardboard folds of extremely high density and extremely high strength. Typically, the conventional core of 152 mm internal diameter is formed of about 20-25 cardboard folds of extremely high density and has high strength, ie, in the cardboard having a density typically greater than about 0.80 g / cc , varies up to around 0.92 g / cc. It is recognized by the present inventors that the extremely high density of the cardboard folds that are used to form the conventional core for large and heavy paper rolls is of such high density that the absorption of the impeller forces applied to the conventional paperboard core 12, by compression of the wall of the cardboard core 12, is theoretically limited. Accordingly, the inventors designed experiments that apply a plurality of miniature characteristic measurements to the surface of the conventional winding core in order to measure the effects of the conventional winding impeller 14, as illustrated in Fig. 1, for a core of conventional cardboard 12 during a real-time winding operation. As a result of said tests, it was discovered that the outside of the cardboard cores are significantly distorted during the winding process. The distortion of the cardboard core at its ends is illustrated in Figure 1. In particular, the ears 16 interact with the corresponding overlap portion in the conventional cardboard core illustrated in the area 20 shown in Figure 1, so that said portions of the core are folded out causing the shape of the core to unroll into the shape of a frame (or other polygon) as illustrated in figure 1. In this way, due to the extremely high density of the cardboard core, the distortion of the inner shape of the core by the ears 12 produces a corresponding distortion of the outside of the core 12. In turn, the areas 22 of the paper roll 10 that overlap the extended areas 20 of the paper core 12 are forced outwardly to an extension greater than the areas 24 of the roll 10 that does not overlap an ear 16 of the impeller 14. It was also discovered that when the winding operation has been completed and when the roll of pap the fully wound 10 supported in the conventional winding core 12 is removed from the impeller 14, the significant circumferential characteristics observed in the • »-» '> »-« --- *. paper surface 12. As a practical aspect, the above means that the cardboard core 12 returns to its original circular shape. In this way, the areas 22 of the paper roll 10 wound on the top of the extended portions 20 of the cardboard core 12 can lose the beneficial effects of the radial and frictional stresses developed during the winding process, which at It can help maintain the integrity of the roll until the unwinding operation. Furthermore, it is believed that in some cases the areas 22 of the paper roll 10 can also maintain the damaging effects as a result of the differential pressure., which corresponds to the distorted external shape of the cardboard core during winding. With reference to Figure 2, when the paper roll 10 is used by the end user, for example by the printer, the previously distorted cardboard core 12 is supported inside its inner ends by an unwinding wheel 34. However, in several cases, the design and construction of the unwinding runners 34 is completely different from the construction of the winding runners 14. The foregoing is shown for the purposes of illustration only by the illustration of three ears 36 on the unwinding runner 34. as opposed to the four lugs 16 in the winding impeller 14. During unwinding, the expansion of the ears 36 of the unwinding rim 34 applies a substantial radial force to the internal diameter and therefore the OD of the previously distorted paperboard core 12. , as indicated by the force lines 38. Due to the differences between the winding and unwinding runner structures, oe Because of the placement of the roll ends with respect to the lug ears during the different winding and unwinding operations, the outside of the core at the ends may transmit a substantially different force pattern to the paper roll during unwinding, (lustrated in Figure 2 as a triangularly distributed force) when compared to the forces applied to the paper roll by the distorted core during winding. In some cases, the portion of the cardboard core 20 that is distorted outwardly during the winding operation illustrated in Figure 1 may be placed during unwinding at a location identified as location 40 in Figure 2, between two extended ears 36 and which are not longer when overlapping the extended ears as was the case during the winding, i.e., the overlap ears 16 shown in Figure 1. Consequently, significant radial pressure relief may occur in each situation between the core and the paper in the roll in the areas 42 which overlap the previously extended portion of the cardboard core in a similar manner, the areas 44 of the paper roll 10 that overlap the extended ears 36 of the unwinding wheel 34 may correspond to the areas 24 of the roll of paper shown in Figure 1, which are placed between and not above the extended ears 16 of the winding impeller 14. The foregoing may result in the application of characteristics to the paper roll that is distributed circumferentially in a significantly different pattern when compared • > * - '- > - with the characteristics of winding, to aggravate in this way any harmful effect retained in the paper roll as a result of the distorted stresses applied during the winding. On the other hand, if the ears 36 of the unwinding runner 34 are aligned with the paper roll in a manner substantially corresponding to the original alignment of the ears 16 of the winding runner 14 during the winding operation, the stresses applied to the roll of paper by the unwinding wheel 34 can potentially mitigate the damage that results from the loss of the beneficial radial and frictional winding tensions that occur upon uncoupling the winding impellers (as described above). The dynamic tensions applied to the paper roll at its ends during the winding involve the presence of a dynamic cutting standard (axial displacement of the sheet that forms the paper roll between the layers) at the ends of the roll. In addition, because the dynamic stresses are substantially reduced subsequently, 100-200 mm of paper is wound outward in the paper roll, the dynamic cutting standard is generally present only in the inner portions of the paper roll, it is say, the portions of the paper roll in which the paper is damaged in the central sheath failure of a roll of paper during a printing operation. Referring now to Figure 3, the distorted shape of the cardboard core during winding is illustrated. As seen in Figure 3, the broad cardboard core 10 includes three zones along its length. ** "r-! - length, including two end portions 50 and a longer median portion 52. As generally illustrated in Figure 3, the circumferential deformation of the core generally occurs at the end portions 50 of the core while the middle portion 52 of the core is not distorts because the impeller 14, as shown in FIG. 1, extends only in the end portions 50 of the core as illustrated in FIG. 3. In addition, as generally illustrated in FIG. 3, the portions of the core 20 which overlap an extended ear 16 of the winding impeller 14 shown in Figure 1 extend outwards more than in the areas 24 of the end portions 50 of the core which are located between the areas 20. Consequently, the complexity of the forces of The friction and compression applied during the winding to the portion of the paper roll near the core will be apparent from the shape of the distorted core generally illustrated in FIG. Figure 3. Figure 4 illustrates a preferred core structure according to the present invention. The core structure of the invention 100 illustrated in Figure 4 is the presently preferred structure for 150 or 152 mm internal diameter paper cores of the invention. As illustrated in Figure 4, the core wall 100 includes three multi-layer zones 102, 104 and 106 sequentially positioned from the inner portion of the core wall 100 to the outer portion of the core wall 100. Each of the three zones 102, 104 and 106 include a plurality of cardboard folds 102a, 104a and 106a respectively. The folds 102a in the zone 102 are formed of cardboard of extremely high density and extremely high strength, that is, a cardboard having a density exceeding about 0.80 g / cc, advantageously between about 0.80 g / cc and about 0.92. g / cc, and preferably has a density of about 0.82 g / cc or greater, and more preferably a density on the scale of between about 0.82 and about 0.90 g / cc. The densities of the cardboard are determined for the purposes of the subject invention in accordance with the standard tests TAPPI 220 and 411. According to said tests, the cardboard is totally conditioned to 73 ° more or less one degree C and at 50% plus or minus 2% relative humidity until it reaches equilibrium. Subsequently at least 5 cardboard samples are measured for the thickness of the area and weighed. The density is then determined by dividing the weight in grams by the volume in cubic centimeters. 15 Referring now to Figure 4, the multiple folds 106a forming the zone or layer 106 of the core wall 100 as shown in Figure 4, are also advantageously formed of cardboard of extremely high density and extremely high strength, as described above in relation to the zone 102 of figure 4. The creases Multiple manifolds 104a forming the central or middle zone 104 of the wall of the cardboard core 100 are formed of a high strength but relatively flexible cardboard, i.e., a cardboard having the density between about 0.65 and about 0.75 g. / cc, more preferably between "-'-" n l l - - "- -" '~ H_U- around 0.67 and around 0.73 g / cc. The outermost fold or folds 110, which is optional, can be a fold or several folds (ie, one to three folds, typically one or two folds) that are different from cardboard folds of extremely high density and extremely high strength high in zone 102, and also different from the high-strength but relatively flexible cardboard folds of zone 104. In this regard, it should be noted that the external folds of the winding cores are often selected in order to impart various aspects of friction or decorative surface to the outside of the core body; and / or to improve the manufacturing process, that is, a spiral wound or linear stretch process; and / or to improve the addition to the outer fold; as will be apparent to those skilled in the art. Similarly, the innermost fold or folds 111 of the core body may vary in shape and for reasons set forth above with respect to the fold or folds 110. For reasons described below in relation to FIG. 5, the area 104 of the wall of the core illustrated in Figure 4, has a thickness 114 preferably of at least about 4 mm. Even more preferably, zone 104 has a thickness 114 greater than about 4.5 mm, preferably greater than about 5 mm, more preferably between about 4.5 and 6 mm. Currently, it is preferred that the zones 104 have a thickness between about 5 and about 6 mm, more preferably about 5.6 mm. It is also preferred that the zone 104, formed of folds of Flexible and high-strength cardboard, they constitute between about 25 and 40% of the total wall thickness of the core, preferably between about 30 and 35% of the wall thickness. The zones 102 and 106 formed in the extremely high-density, extremely high-density cardboard folds, each have a thickness, 116 and 118 respectively, constituting between about 25 and about 40% of the total wall thickness of the core 100. Preferably, each of the zones 102 and 106 constitutes between about 30 and 35% of the thickness of the total wall of the core 100. Currently it is preferred that each of the zones 102 and 106 have a thickness 116 and 118 respectively, which constitutes about 33% of the total wall thickness of the core 100. Figure 5 illustrates in exaggerated detail how the core structures of the invention interact with the radially expanded ears 16 of a conventional wheel 14. In particular, as seen in FIG. Figure 5, the radiated outward expansion of the ears 16 causes the innermost zone 102 formed of cardboard folds of extremely high density and extremely high strength They are deformed out of a cylindrical configuration. In this way, each of the portions 120a of the zone 102 of the wall of the core body is pushed outwards to form "corners or vertices" with a shape similar to a square or similar to a polygon. However, because the multiple folds 104a of the zone 104 are a relatively flexible and less dense cardboard material, the portions 120b of the area 104 that overlap the ears 16 are capable of absorbing a whole portion or a substantial portion of the material. the radiated outward expansion of the portion 120a of the inner zone 102 of the core body wall 100. The portion 120c of the outer zone 106 of the core wall 100 preferably expands radially outwardly to a minimum extent due to a to the absorption of characteristic energy by zone 104. In general, and particularly in the construction of 152 mm inner diameter cardboard cores such as those illustrated in Figures 4 and 5, it is preferred that a zone of extremely high strength and extremely high density cardboard, for example, zone 106 in figure 4, it is placed out of the relatively flexible, high-strength cardboard area 104. It is believed that the above drives the absorption by the area 104 of the radiated expansion effected by the ears 16, without causing substantial external distortion of the body of the core 100. Due to the extremely high density of the cardboard folds forming the inner and outer zones 102 and 106 respectively, of the body wall 100 shown in Figures 4 and 5, the radiated outward expansion of the ear 16 of impeller 14 (as illustrated in figure 5) does not significantly compress the thickness 116 of the inner region 102, or the thickness 118 of the outer region 106 of the body wall. However, because the zone 104 is formed of a relatively flexible and low density board, the thickness 114 of the zone 104 can be compressed, particularly in those portions 120b of the area 104 that overlap the ears that expand outwardly. 16 of the impeller 14. In general, the total thickness and number of folds in the relatively flexible zone 104 are selected to allow the absorption of the expansion distance of the impeller lugs 16. In this way, wherein the cardboard materials of Low density within the lower portion of the preferred scale are selected for the formation of the zone 104, the total thickness of the zone 104 may be less when compared to the situation where the higher density cardboard materials within the preferred scale are selected for the formation of zone 104. In a preferred embodiment, the total number of folds used to form the core body wall 100 as shown in FIG. Figures 4 and 5 will vary from about 25 to about 35 folds, preferably from about 28 to about 32 folds. In general, the higher density folds will typically have a smaller thickness when compared to the lower density folds. For example, the core body wall 100 can advantageously be formed of a plurality of extremely high-density, extremely high-density cardboard folds each having a total thickness of about 0.56 mm, and a plurality of relatively heavy cardboard folds. flexible, high strength that have a thickness of about 0.64 mm. As will be understood by those skilled in the art, the thickness and density of the cardboard folds can vary widely. Preferably, the cardboard folds used in the invention will each have a density of between about 0.65 and about 0.92 g / cc, more preferably between about 0.67 and about 0.90 g / cc. The strength and density of the cardboard will generally vary by varying the pulp treatments, by varying the degree of grip compression and by variations in the raw materials that make up the pulp. The densities and strengths of the paperboard can also be varied by the use of various known additives and reinforcing agents during the papermaking process. The cardboard folds useful herein typically have a thickness within the range of between about 0.51 mm and about 0.89 mm, more typically between about 0.56 mm and about 0.76 mm. In general, the present invention solves a number of previously unrecognized problems and provocation factors associated with the central sheath problem. Significantly, the strength of the extremely high density and extremely high strength cardboard folds such as those normally used to form the body wall of the wide paper cores is derived to a large extent from a high pressure compression of the pulp high quality paper. Nevertheless, the resulting high density and high strength paperboard keeps the capacity for additional compression extremely low, that is, for the additional reduction in thickness. Accordingly, the present invention is based on the use of a plurality of relatively strong cardboard folds, each maintaining additional compressibility and thickness reduction. Therefore, the low density, high strength cardboard folds employed in the present invention are capable of absorbing a substantial amount of radial expansion of the ears of a conventional wheel to counteract the radial expansion that can be transmitted from another form in an amount corresponding to the outside of the cardboard core. Figure 6 illustrates a preferred core structure of the invention as it is applied to a paper core with an internal diameter of 76 mm. The core illustrated in Figure 6 includes two zones, an inner zone 202 and an outer zone 204. The inner zone 202 is formed of a plurality of extremely high-density and extremely high-strength cardboard folds 202a, although the outer zone 204 is form a plurality of high strength but relatively flexible folds 204a. In the structure of the core illustrated in Figure 6, the area of high density but relatively flexible cardboard layers 204 is advantageously placed 50% of the outside of the body wall of the cardboard core. Preferably, the zone 204 has a thickness 214, which constitutes about 30 to about 45% of the thickness of the body wall, more preferably between about 35 and 45% of the thickness of the wall, for example, around 40% of the thickness of the wall. Similarly, the inner zone 204 has a thickness 216, which constitutes about 50% to about 70% of the thickness of the body wall, more preferably between about 55% and 65% of the thickness of the wall, for example, about 60% of the thickness of the wall. When the relatively flexible high strength and density cardboard folds are placed in an area or near the exterior of the body wall, as in the structure illustrated in Figure 6, it is preferred that the total thickness 214 of the zone is at least about 5 mm, preferably about 6 to about 9 mm. A preferred thickness 214 for the zone 204 of the cardboard core structure with a ID of 76 mm illustrated in Figure 6 is from about 6.8 to about 7.2 mm. The thickness of the currently preferred total wall of the cardboard core with a ID of 76 mm illustrated in Figure 6 is from about 17 to about 19 mm. In addition, the core 200 of FIG. 6 may optionally include an outermost crease 210 or folds, which are different from the extremely high density and extremely high strength zone 202 cardboard folds, and also different from the cardboard folds of high strength but relatively flexible of the area 204. The fold or external folds 210, when present, vary in shape and for the reasons stated above in relation to the fold or folds 110 of Figure 4, as will be apparent to those experts in the art. Similarly, the innermost fold or folds 211 of the core body 200 of Figure 6 may vary in shape due to the above reasons. Still another embodiment of the invention is illustrated in Figure 7. The paper core of Figure 7 is advantageously a paper core with an ID of 150 mm or 152 mm. The core illustrated in Figure 7 includes five zones, an interior zone 302, an exterior zone 312, a central zone 306, and two zones 304 and 308 positioned respectively between the inner and central zones, and between the external and central zones. In the structure of the paper core of Figure 7, the inner zone 302 is formed of a plurality of cardboard folds of extremely high density and extremely high strength 302a, although the outer zone 312 is also formed of a plurality of extremely high strength cardboard folds 312a. Similarly, the central zone 306 is formed of a plurality of cardboard folds of extremely high strength and extremely high density. The zones 304 and 308 are each formed of a plurality of relatively flexible low density and high strength cardboard folds 304a and 308a, respectively. In the structure of the cardboard core illustrated in Figure 7, the extremely high strength cardboard zones and the internal and external density 302 and 312, respectively, each constitute about one-sixth of the total thickness of the wall structure. Similarly, each of the cardboard zones 304 and 308 formed from the relatively flexible, low density, high strength cardboard folds constitute about one sixth of the total thickness of the cardboard body wall. The central area 306, formed of extremely high strength, extremely high density cardboard folds, preferably have a thickness of about one third of the thickness of the body wall. The body wall preferably has a total thickness of at least about 15 mm. The core 300 of Figure 7 may optionally include an outermost fold or folds 310, which are different from the extremely high density and extremely high strength cardboard folds of the areas 302, 312 and 306 and are also different from the folds of the folds. high strength but relatively flexible cardboard of the areas 304 and 308. The fold or outer folds 310, when present, vary in shape and for the reasons stated above with respect to the fold or external folds of Figures 4 and 6, as will be apparent to those skilled in the art. Similarly, the innermost fold or folds 311 of the body of the core 300 of Figure 7 may vary in shape and due to the above reasons. The structure of the cardboard core illustrated in Figure 7 is not currently preferred; however, it provides considerable strength properties although a substantially decreasing distortion of the core exterior in the application of significant radial force to the interior of the core. The broad-strength, high-strength cardboard cores of the invention generally have a length greater than about 2.5 m, typically greater than about 3 m, more typically at about 3.6 m or greater. Advantageously, the cardboard cores have a minimum body wall thickness of about 13 mm and preferably have a total body wall thickness of at least about 15 mm or greater. More preferably, the total body wall thickness will exceed the thickness of the conventional body wall used for a high strength cardboard core with a corresponding ID. In this way, the thickness of the body wall between the core with an ID of 152 mm illustrated in Figures 4 and 5 will preferably exceed about 15 mm, thus exceeding the thickness of the body wall of 13 mm standard. Similarly, the thickness of the core body wall with a ID of 76 mm illustrated in Figure 6 will preferably exceed the conventional 15 mm body wall thickness for cores with an ID of 76 mm. The use of a total body wall thickness that exceeds the thickness of the body wall of a broad, conventional high-strength core of the same or comparable ID provides several significant benefits and advantages. In particular, the increase in the thickness of the body wall compensates for the use of a lower amount (i.e., a lower number of folds) of cardboard folds of extremely high density and extremely high strength, when compared to conventional structures, although a crush resistance of the corrugations is not provided, which is comparable to or exceeds the crush resistance of the corrugations of conventional structures. In general, the cardboard cores of the present invention will have an extremely high crush resistance of at least about 3,500 N / 100 mm. For example, a high strength cardboard core with a 15.24 cm ID formed entirely of extremely high density and extremely high strength cardboard folds has a crush resistance of about 3.500 N / 100 mm. A cardboard core with a preferred 15.24 cm ID as illustrated in Figures 4 and 5 can easily have a total wall thickness of 16 mm and thus thicker than the conventional structure in an amount of about 3 mm , thus representing a 23% increase in wall thickness. However, only about 65-70% of the thickness of the total wall in this case the board of extremely high strength and extremely high density is formed; in this way the structure illustrated in Figures 4 and 5 is preferably formed only of about 80% of the board of extremely high strength and extremely high density as that which is used to form the conventional structure. However, the structure of the preferred cardboard core illustrated in Figures 4 and 5 can easily have a crush resistance of corrugations of about 3.850 N / 100 mm. In addition, the preferred structure illustrated in Figures 4 and 5 reduces the amount of core space OD for the impeller coupling by about 30% compared to a conventional core. Similarly, the preferred structures for 76 mm inner diameter cores as illustrated in Figure 6 can easily have a 25% core sheath improvement (reduction in the amount of core OD expansion for the impeller coupling) as it is compared with the conventional wall thickness structure of 15 mm. However, the crush resistance of the corrugations of the preferred structures illustrated in Figure 6 can easily be about 5%., 425 N / 100 mm when compared with the crush resistance of conventional corrugations for a wall thickness of 15 mm, core with an ID of 76 mm, of around 5,250 N / 100 mm. In addition, the dynamic strength properties of the cardboard core illustrated in Figure 6 preferably compares or exceeds the dynamic strength of the core with a conventional comparable ID. The use of a higher thickness of the wall according to the present invention also allows to achieve a higher allowable rotational speed, or "critical speed". Accordingly, the preferred cardboard cores according to the invention can rotate at speeds of about 3 to about 5% greater than the critical rotation speed of conventional core structures. Preferably the increase in rotational speed is achieved by the use of a total body wall thickness greater than about 15 mm in any embodiment of the invention. The thickness of the major wall associated with the preferred structures increases the OD of the core. The increased OD results in a lower rotational speed for any network speed during winding and unwinding. In this way, the performance of the critical speed is improved.

The papermaking winding cores currently preferred according to the invention have the constructions set forth below.

CONSTRUCTION 1 ID: 150.4 mm OD: 182.4 mm Thickness of the wall (estimated): 16 mm Plieque Density (g / cc) Thickness (microns) Internal * around 0.78 600 Folds 2-10 0.9 550 Folds 11-18 0.72 620 Folds 19- 27 0.9 550 Fold 28 ** 0.68 740 External fold NA 220 * The internal fold is provided for the consideration ** Fold 28 and outer fold are provided for manufacturing and decorative considerations.

CONSTRUCTION 2 ID: 78.7 mm OD: 110.7 mm Thickness of the wall (estimated): 17 mm Plieque Density (q / cc) Thickness (microns) Internal * around 0.72 620 Folds 2-18 0.9 550 Folds 19-29 0.72 620 Fold 30 ** 0.68 740 External fold NA 220 * The internal fold is provided for manufacturing considerations ** Fold 30 and internal fold are provided for manufacturing and decorative considerations.

CONSTRUCTION 3 ID: 76 mm OD (estimated): .94 mm Thickness of the wall (estimated): .18 mm Plieque Density (q / cc) Thickness (cm) Internal * 0.76 0.0635 Folds 2-21 0.82 0.055 Fold 22-32 0.68 0.0635 External fold NA 0.033 * The internal fold is provided for manufacturing considerations ** The external fold is provided for considerations of manufacture and decorative.

CONSTRUCTION 4 ID: .152 mm OD (estimated) .168 mm Wall thickness (estimated): .160 mm Plieque Density (q / cc) Thickness (cm) Internal * 0.76 0.0635 Folds 2-11 0.9 0.055 Folds 1-31 0.76 0.0635 Folds 32-37 0.9 0.055 Fold 38 ** 0.76 0.0635 External Fold NA 0.033 * The internal fold is provided for manufacturing considerations ** Fold 38 and outer fold are provided for manufacturing and decorative considerations.

CONSTRUCTION 5 ID: .152 mm OD: (estimated): .168 mm Wall thickness (estimated): .160 mm Plieque Density (q / cc) Thickness (cm) Internal * 0.76 0.0635 Folds 2-11 0.82 0.055 Folds 12-31 0.68 0.0635 Folds 32-37 0.82 0.055 Folds 38 ** 0.76 0.0635 Outer fold 0.65 0.033 * The inner fold is provided for manufacturing consk ** The fold 38 and outer fold are provided for manufacturing and decorative considerations. Various modifications and other embodiments of the invention will become apparent to those skilled in the art to which the invention pertains, having the benefit of the teachings presented in the foregoing descriptions and the related drawings. Therefore, it should be understood that the invention is not limited to the specific embodiments described and that the modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a generic and descriptive manner only and not for purposes of limitation.

Claims (15)

NOVELTY OF THE INVENTION CLAIMS

1. - A multi-layer paperboard core for supporting a continuous, broad paper sheet roll, comprising: a multi-layer paperboard core having a length exceeding approximately 255 cm and which is defined by a generally cylindrical body having a thickness of at least about 15 mm; said body wall including a radially inner multi-layered zone constituting at least about 25% of the total thickness of the body wall and consisting essentially of layers of cardboard, each having a density exceeding 0.80 g / cm3; and a second multi-layer zone within 70% of the total thickness of the body wall will consist essentially of layers of cardboard having each a density of between about 0.65 and about 0.75 g / cm3, said area having a thickness of at least about 4 mm.

2. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll, according to claim 1, further characterized in that the cardboard layers in said radially inner multiple layer zone have a density of between approximately 0.82 and 0.90 cm3.

3. - The multi-layer cardboard core for supporting a continuous, broad paper sheet roll according to any of the preceding claims, further characterized in that said cardboard layers in the second multi-layer zone have a density of between about 0.67. and 0.73 g / cm3.

4. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll according to any of the preceding claims, further characterized in that the inner multi-layer zone constitutes between approximately 30 and 35% of the total thickness of the body wall.

5. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll according to any of the preceding claims, further characterized in that the second multi-layer zone has a thickness of between about 40 and about 50. % of the total thickness of the body wall.

6. The multi-layer cardboard core to support a continuous, broad paper sheet roll according to any of the preceding claims, further characterized in that the core has an internal diameter of 150 to 152 mm and said layer zone radially inner manifold constitutes from about 25% to about 35% of the total thickness of the body wall and will comprise a third multilayer zone radially outwardly of the second zone, the third zone consisting essentially of layers of cardboard having a density which exceeds about 0.80 g / cm3 and constitutes between about 30% and about 35% of the total thickness of the body wall, and said layers within the zone constituting between about 35% and about 45% of the total thickness of the wall of the body. body.

7. The multi-layer cardboard core for supporting a continuous, wide sheet of paper roll, according to claim 6, further characterized in that the inner multiple layer zone constitutes approximately 33% of the total thickness of the body wall .

8. The multi-layer cardboard core for supporting a continuous, broad paper web roll, comprising: a multi-layer cardboard core having a length exceeding approximately 255 cm and defined by a generally cylindrical body having a thickness of at least about 15 mm, and an internal diameter of about 76.2 mm; said body wall including a radially inner multi-layered zone constituting at least about 50% of the total thickness of the body wall and consisting essentially of layers of cardboard, each having a density exceeding 0.80 g / cm3; and a second multi-layer zone within 50% of the thickness of the body wall will consist essentially of layers of cardboard having each a density of between about 0.65 and about 0.75 g / cm 3, said area having a thickness of at least less about 5 mm.

9. - The multi-layer cardboard core for supporting a continuous, broad paper sheet roll, according to claim 8, further characterized in that said layers of paperboard in the layers in the radially inner multilayer zone each have a density between 0.82 and 0.90g / cm3.

10. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll according to any of claims 8-9, further characterized in that said cardboard layers in the second multiple layer zone have a density between about 0.67 and 0.73 g / cm3.

11. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll according to any of claims 8-10, further characterized in that said inner multilayer zone constitutes from about 55 to about 65% of the total thickness of the body wall.

12. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll, according to claim 11, further characterized in that the second multi-layer zone has a thickness of between about 35 and about 45% of the total thickness of the body wall.

13. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll according to any of claims 8-12, further characterized in that the body wall has a total thickness of approximately 16 mm or greater .

14. The multi-layer cardboard core for supporting a continuous, broad paper web roll, comprising: a multi-layer cardboard core having a length exceeding approximately 255 cm and defined by a generally cylindrical body having a thickness of at least about 15 mm, and an internal diameter of 150-152 mm; said body wall including a radially inner multi-layered zone constituting from about 25% to about 35% of the total thickness of the body wall and consisting essentially of layers of cardboard, having a density such that at least substantially all the layers forming the radially inner 15% of the body wall have a density exceeding approximately 0.80 g / cm 3, and substantially all other layers in said radially inner multiple layer zone have a density of between about 0.67 and 0.73 g / cm3; a second multi-layered zone within 70% radially inner of the total thickness of the body wall consisting essentially of layers of cardboard each having a density of between about 0.65 and about 0.75 g / cm3, the second zone having a thickness of at least about 4 mm of the total thickness of the body exceeding about 15 mm; and the paperboard core comprises a total thickness exceeding 5 mm formed of paperboard layers having a density between about 0.67 and 0.73 g / cm, and a total thickness exceeding 9 mm formed of layers of paperboard having a density that exceeds approximately 0.80 g / cm3.

15. The multi-layer cardboard core for supporting a continuous, broad paper sheet roll, according to claim 14, further characterized in that it comprises a third multi-layer zone located radially outwardly of said zone, constituting approximately 25% to about 35% of the total thickness of the body wall and essentially consisting of layers of cardboard, having a density such that at least substantially all of the layers forming the radially inner 15% of the body wall have a density which exceeds approximately 0.80 g / cm 3, and substantially all other layers in said radially inner multilayer zone have a density between about 0.67 and 0.73 g / cm 3.