Patent Application
20070059467
The present invention relates generally to paperboard tube structures. More particularly, the invention relates to paperboard tube structures having a construction promoting an enhanced wall thickness and bending stiffness for a given mass of the tube structure.
Within the paperboard tube industry, it is desirable to minimize the amount of ply material used to manufacture a paperboard tube. Paperboard tube structures are often used in consumer good applications such as paper towel rolls or toilet paper rolls, but they are also used in manufacturing applications such as cores for supporting rolled sheet material or in industrial applications such as forms or templates for columnar structures.
Tube structures must possess structural properties commensurate with their intended applications. Paperboard tube designs and manufacturing procedures preferably should minimize the amount of raw materials needed to achieve the required structural properties for the particular tube structure. By reducing the material needed, the expense of producing the paperboard tube structures will likewise decrease.
The bending stiffness and other strength properties of tube structures depend on a number of factors, including the strength of the individual plies of the tube and the wall thickness of the tube. As a general rule, increasing the wall thickness of a tubular structure will result in a stronger tube. An increase in wall thickness can be brought about by using additional plies and/or using thicker plies. In either case, an additional amount of raw material is required, which increases the cost of the paperboard tube. Tube strength can also be increased by using denser, stronger plies, but such stronger plies are relatively more costly.
Therefore, a need exists for a paperboard tube structure requiring a minimal amount of paperboard material while maintaining adequate tube strength. Furthermore, it would be advantageous for such a structure to be the product of a cost effective process.
The present invention addresses the above needs and achieves other advantages by providing a spirally wound tube having an intermediate zone defining one or more voids and a method of making such a tube. In general, the tube is made by spirally winding a plurality of plies together. More specifically, a plurality of plies form an intermediate zone in the tube having one or more voids, each void having a radial height substantially equal to the radial height of the intermediate zone.
According to one embodiment of the present invention, the tube includes an inner zone, an outer zone, and an intermediate zone. The inner zone is located radially inwardly and includes at least one inner layer. Each inner layer has at least one inner ply. The inner ply or plies are spirally wound to form the inner layer. Similarly, the outer zone is located radially outwardly and includes at least one outer layer. Each outer layer has at least one outer ply. The outer ply or plies are spirally wound to form the outer layer. The intermediate zone is located between the outer zone and inner zone and includes at least one intermediate layer. Each intermediate layer includes more than one intermediate ply. The intermediate plies are spirally wound with gaps between adjacent plies of that intermediate layer. Moreover, the intermediate layers are radially aligned such that the gaps in every intermediate layer are aligned to each other and form voids. Each void has a thickness or radial height substantially equal to the thickness of the intermediate zone.
The width and thickness of the plies may vary. However, according to one preferred embodiment, the thickness of each inner ply, intermediate ply, and outer ply is substantially equal to each other. The width of each intermediate ply is substantially less than the width of each outer ply and inner ply.
In another embodiment of the present invention, the paper tube includes a plurality of paperboard plies spirally wound about an axis and adhered together to form a tube. The wall of the tube comprises an inner zone, an outward zone, and an intermediate zone. The inner zone is located radially inwardly and comprises at least one inner ply. The outer zone is located radially outwardly and comprises at least one outer ply. The intermediate zone is located between the inner zone and the outer zone and comprises a plurality of intermediate paperboard plies. The intermediate paperboard plies are aligned and wound one atop another such that a void exists between adjacent edges of consecutive turns of the intermediate paperboard plies. The thickness or radial height of each void is substantially equal to the thickness of the intermediate zone.
One aspect of the present invention is a method of constructing a paperboard tube with at least one void in its wall. The method includes spirally winding plies about a forming mandrel to form wall zones. In particular, one or more inner plies are spirally wound to form an inner tube wall zone. Two or more intermediate plies are spirally wound and aligned to form an intermediate wall zone with voids between adjacent edges of consecutive turns of the intermediate plies, wherein the radial height of each void is substantially equal to the radial height of the intermediate tube wall zone. Also, one or more outer plies are spirally wound to form an outer tube wall zone. The plies of the inner, intermediate, and outer wall zones are adhered together to form a tube.
According to another embodiment of the present invention, the method includes providing a plurality of plies. The width of each ply is substantially equal. One or more plies are applied to a forming mandrel with nominal gaps between adjacent edges of consecutive turns of each ply to form an inner tube zone. One or more plies are used to form more than one mini-ply. The width of each mini-ply is substantially less than the width of each ply. The mini-plies are applied in a radially aligned fashion to the forming mandrel with gaps between adjacent edges of consecutive turns of the mini-plies to form an intermediate tube zone with voids. The radial height or thickness of each void is substantially equal to the radial height or thickness of the intermediate tube zone. One or more the plies are applied to the forming mandrel with nominal gaps between adjacent edges of consecutive turns of each ply to form an outer tube zone.
In yet another embodiment, the method includes forming more than one intermediate layer. Each layer is formed by spirally winding a plurality of mini-plies. For example, the method includes forming four mini-plies out of one ply and spirally winding the four mini-plies to form one intermediate layer such that a gap exists between adjacent mini-plies. Further, the mini-plies in a given intermediate layer are radially aligned to form voids. Each void has a radial height substantially equal to a radial height of the entire intermediate zone.
Another aspect of the present invention is the forming of the mini-plies out of the one or more of the plies. The forming of the mini-plies may be accomplished using a variety of methods. For example, according to the preferred embodiment, the method further includes a step of perforating one or more of the plies to facilitate the forming of the mini-plies. More specifically, according to this embodiment, the forming of the mini-plies is accomplished by separating one or more of the plies into mini-plies along a perforation line. Alternatively, the forming of the mini-plies may be accomplished by using a water jet cutter or other means known in the art.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
As used herein, a “layer” is a region of the tube 10 delimited by an outer radius ro and an inner radius ri that respectively correspond to an outer surface and inner surface of a “ply” of that layer. A “ply” is a unitary sheet of material that, when wound into the tube 10, constitutes at least a part of a single layer of the tube 10. Thus, in accordance with the present invention, a layer can comprise more than one ply occupying the region bound by ro and ri as best seen in
According to one embodiment of the present invention and as shown in
Similarly, the outer zone 40 includes one layer 140 comprising one ply also referred to herein as an outer ply 1040 due to its location within the outer zone 40. The outer ply 1040 is wound so that nominally it has no substantial gaps between its adjacent edges along the length of the tube 10.
It should also be noted, as further described in U.S. Pat. No. 6,851,643, it is known from geometrical considerations applicable to spiral winding that to achieve a perfect butt joint, the width of ply, the diameter of the ply, and the spiral wind angle are related. Basically, the width, the angle, or both must increase as the diameter of the ply increases. Therefore, one in the art would appreciate that either the spiral wind angle, the width of the ply, or both may vary between layers to account for the above-mentioned geometrical considerations.
The intermediate zone 30 has one layer 130 comprising more than one mini-ply. For example purposes only and as seen in
In an alternative embodiment, shown in
Wound tubes 10 having either the above-described 2-spoke core or the above-described 4-spoke core were constructed and tested for inner diameter stiffness. One in the art would appreciate that inner diameter stiffness is generally the resistance of the inner diameter to changes to its size due to radial pressure applied to the outer diameter. Inner diameter stiffness is described in more detail in U.S. Pat. No. 6,851,643 to Qiu et al. Typically, inner diameter stiffness is measured by psi per 0.001 inches, i.e., how much psi is required on the outer diameter to change the inner diameter by 0.001 inches.
The tested 4-spoke cores were constructed according to
The tested 2-spoke cores were constructed according to
One in the art would appreciate that the tested 4-spoke cores and 2-spoke cores as generally described-above have substantially the same weight and substantially the same amount of volume of voids. However the test results, shown in the table below, indicated that the 2-spoke cores had a higher inner diameter stiffness.
(The test results take into account an 8% moisture content within the tubes.)
Another embodiment of the 2-spoke core was tested against a solid core. In general, a solid core, as referred to within this present specification and appended claims, is a conventional tube constructed without any mini-plies or significant gaps or voids between adjacent plies. However the solid core is constructed generally with the same material as the 2-spoke core and has substantially the same inner diameter and outer diameter. The 2-spoke cores and the solid cores were tested for inner diameter stiffness.
The results of the test are shown in the following table:
(Again, the test results take into account an 8% moisture content.)
The results show that the 2-spoke core outperformed the solid core in inner diameter stiffness. Also, as indicated, the 2-spoke core is approximately 20% lower in weight compared to a solid core.
Another aspect of the present invention is a method or process of forming the tube 10. In general, the tube 10 is formed by spirally winding a plurality of plies about a mandrel 100, adhering the plies together, and severing portions or sections of the spirally wound plies to form individual tubes 10.
As shown in
The forming of mini-plies from one wider ply is one aspect of the present invention. This can be accomplished in several ways, for example with the use of water jet cutting. However, the preferred method is by perforating the plies. More specifically, one or more perforation lines, as best seen in
Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
