Patent Application
20050136204
The present invention relates to support posts for use in packaging an object or group of objects in a carton or the like, the support posts being used for supporting axial loads imposed on the carton, and optionally providing lateral cushioning or protection as well, such as at corners of a packaged object. The invention relates in particular to such support posts formed as tubular structures from paperboard materials.
When packaging one or more objects in a carton or other package that itself does not provide sufficient strength for supporting axial loads and/or for cushioning the object(s) against lateral impacts, particularly at the corners, it is known to include support posts and/or corner protectors in the package to provide the needed axial load support and/or lateral impact protection. Such support posts or corner protectors are commonly made from paperboard materials One known type of corner protector or support post is formed by convolutely winding a sheet of paperboard for a plurality of turns about a mandrel and adhering the adjacent windings together to form a multi-layer tube. The tube while still wet can be deformed into a desired cross-sectional shape and allowed to dry and set.
U.S. Pat. No. 6,186,329 describes a multi-grade convolutely wound corner protector. The corner protector is formed by first preparing a paperboard sheet from three separate pieces of paperboard of different grades. In particular, a first piece of paperboard of relatively higher grade (i.e., higher density and higher stiffness for a given thickness) is joined at one edge to the edge of a second piece of paperboard of relatively lower grade (i.e., lower density and lower stiffness for a given thickness). An opposite edge of the second piece is joined to a third piece of paperboard of higher grade. The paperboard sheet is convolutely wound about a mandrel to build up a plurality of layers or turns, which layers are adhered together. The resulting tube has a wall made up of at least three layers at any given circumferential location, wherein inner and outer layers comprise the higher-grade paperboard and one or more intermediate layers comprise the lower-grade paperboard.
The process of the '329 patent, while effective for producing multi-grade tube structures, is necessarily a batch type of process wherein a single tube is made at a time; the batch process is inherently inefficient, particularly in view of the requirement of preparing the starting sheet from three separate pieces of paperboard. The process would be even less efficient if it were used to produce tubes having more-complicated ply arrangements, such as high/low/high/low/high grade, for example.
The present invention addresses the above needs and achieves other advantages, by providing a multi-ply support post and a method of making multi-ply support posts using a continuous type of production process. In accordance with one embodiment of the invention, there is provided a method for making a multi-ply support post, comprising the steps of:
Thus, the tube is formed continuously on the mandrel and is drawn linearly along the mandrel. At a downstream station, the tube can be cut into desired lengths. The tubes can then be allowed to sit for a period of time to set the adhesive; the setting process can be hastened by heating the tubes in an oven or the like, if desired; the resulting tubes thus have the same cross-sectional shape as the mandrel on which they were formed. Alternatively, while the tubes are still wet, the tubes can be deformed to a different cross-sectional shape (e.g., a generally L-shaped configuration, in the case where the tubes are to be used as corner protectors) and can then be allowed or caused to set. The continuous production process is more-efficient than the batch process used in convolute winding, and also allows substantial freedom in arranging various numbers and grades of plies in various orders in the tube wall.
In some embodiments of the invention, a plurality of intermediate low-grade plies can be included in the tube wall. The low-grade plies can all be contiguous, or alternatively can be separated by intervening higher-grade plies.
The inclusion of lower-grade paperboard material in the tube wall allows the cost of the support post to be reduced. At the same time, the bending stiffness of the tube is not substantially compromised because the lower-grade paperboard material is located in the middle of the tube wall, whereas the primary contributors to bending stiffness are the higher-grade plies located inwardly and outwardly of the low-grade ply or plies.
In another embodiment of the invention, a linear draw support post comprises a plurality of separate paperboard plies wrapped one upon another about an axis and adhered together to form a tube, wherein opposite edges of each ply extend parallel to the axis, and wherein at least one ply located radially between two other plies is embossed with a plurality of discrete embossments spaced apart along length and width directions of the ply for increasing an effective caliper of the ply. The embossments increase the effective caliper of the ply in the tube wall; as a result, the plies on opposite sides of the embossed ply are spaced farther apart, without substantially increasing the mass of the embossed ply relative to a non-embossed ply. The increased spacing between the inner and outer plies contributes to an increase in bending stiffness of the tube, which leads to an increased resistance to buckling of the tube under axial loads, and increased side wall compressive stiffness. The embossed ply can be of the same grade as the other plies in the tube, or can be a relatively lower grade than other plies.
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 inventions 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, these inventions 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.
An apparatus and process for making a multi-grade linear draw support post in accordance with one embodiment of the invention is shown in
Thus, in the illustrated example in
Paper is available in a wide variety of grades. In general, paper stiffness (for a given thickness) can be improved by mechanical refining of paperboard pulps. Thus, a well-beaten pulp generally produces a stiffer grade of paper compared to a lightly beaten pulp, at the same thickness. In addition, paper stiffness can be improved by compressing the paperboard during manufacture by running the web through a set of high-pressure nip rolls. Further, paperboard stiffness is influenced by fiber type and quality. As a general rule, stiffer paperboard sheets have a higher density than less-stiff paperboard sheets, at the same thickness. Stated differently, the above treatments generally result in an increase in paperboard density along with the increase in paperboard stiffness. The higher-density, higher-stiffness papers are also more costly.
In accordance with the invention, the inner ply 10 and the outer ply 16 comprise paperboard of relatively high stiffness and high density, also referred to as high-grade paperboard. Through theoretical calculations and empirical testing, it can be shown that the lengthwise bending stiffness of a multi-layer tube is largely a function of two factors, namely, the stiffness of the ply or plies nearest the inner and outer surfaces of the tube, and the radial spacing between these plies. The stiffness of the plies, for a given thickness, correlates with the paperboard grade; thus, a given ply of high-grade paperboard has a greater stiffness than an otherwise equivalent ply of lower-grade paperboard. Placing high-grade plies toward the inside and outside of a tube tends to maximize the contribution these plies make toward the bending stiffness of the tube.
On the other hand, the stiffness of the intermediate plies in the middle of the tube wall tends to contribute only weakly toward the overall bending stiffness of the tube, but these plies do serve the important function of spacing the high-grade inner and outer plies apart from each other. The intermediate plies thus are roughly analogous to the web of an I-beam, which spaces apart the two flanges that contribute most of the bending stiffness of the beam. All other things being equal, the farther apart the inner and outer plies are spaced, the greater will be the bending stiffness of the tube. Accordingly, in accordance with the invention, one or more of the intermediate plies are selected to be lower-grade paperboard, since the contribution these plies make to the tube's stiffness is relatively slight compared with the inner and outer plies' contributions.
Thus, one or both of the intermediate plies 12 and 14 comprise paperboard of relatively lower stiffness and density, i.e., low-grade paperboard. The usage of such low-grade paperboard in the middle of the tube wall does not substantially impair the bending stiffness of the tube, relative to a tube formed entirely of higher-grade paperboard, and can result in significant cost savings.
The tube 20, once formed on the mandrel M, is linearly advanced along the mandrel to a downstream cutting station (not shown), where the tube is cut into desired lengths. The resulting tubes can then be held to allow the adhesive to set, such that the tubes have the same shape as when they were removed from the mandrel. The tubes can be used as support posts in a package for carrying axial loads exerted on the package, such as when multiple packages are stacked upon one another.
Alternatively, after the tubes have been cut into lengths, or during the cutting process, and while the adhesive is still wet, the tubes can be deformed into a different cross-sectional shape and then allowed to dry. As an example,
The invention is not limited to four-ply support posts, nor is it limited to posts having only one high-grade ply radially inward and radially outward of the intermediate low-grade ply or plies. Support posts in accordance with the invention can have from one to a plurality of high-grade plies located radially inward of the low-grade ply or plies, and can have from one to a plurality of high-grade plies located radially outward of the low-grade ply or plies. As noted, one or more intermediate low-grade plies can be included. When a plurality of low-grade plies are included, such plies can all be contiguous, or alternatively there can be intervening high-grade plies between them.
In another aspect of the invention, the radial spacing between inner and outer plies in a support post can be enhanced with virtually no addition of mass to the support post, by embossing one or more of the intermediate plies.
A paperboard ply can be embossed using a process diagrammatically represented in
As noted, the invention is not limited to support posts having a single embossed ply.
In the practice of the invention, a ply can be drawn from a supply roll as an ordinary unembossed ply and can be embossed using a process similar to that shown in
Embossing is not the only way that can be used, in accordance with the invention, to “artificially” increase the effective thickness of intermediate plies in a support post. A similar result can be achieved by corrugating one or more plies. To maximize the axial stiffness of the ply or plies, the corrugations or flutes should extend parallel to the axis of the post.
It is also within the scope of the invention to reinforce one or more particular regions of a support post wall with one or more paperboard plies having a narrower width than the other plies making up the post, so that the region is thickened relative to other portions of the wall.
Based on the foregoing description, it will be appreciated that the continuous linear draw production process of the invention is more-efficient than the batch convolute winding process used in the prior-art, and also allows substantial freedom in arranging various numbers and grades of plies in various orders in the tube wall. The multi-grade linear draw support posts of the invention enable axial load-bearing strength to be substantially maintained while substituting a proportion of less-costly low-grade paperboard for the more-costly high-grade paperboard that might otherwise be required. Additionally, the linear draw support posts having one or more embossed or corrugated plies also allow a reduction in the amount of paperboard material required to form a support post. The use of narrow reinforcing plies in a support post allows specific regions of a post to be reinforced for greater bending stiffness and/or cushioning.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.
Therefore, it is to be understood that the inventions are 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.
