SYSTEM AND METHOD FOR PACKAGING VISCOELASTIC MATERIALS

Abstract: A palletized load system for a viscoelastic material and a method for creating such a system by placing a tray (12) on a pallet (13), stacking polymeric, melt processable, film packages (11) of viscoelastic material on the tray and applying a stetchwrap (14) about the periphery of the pallet, the tray and the bags, said wrap overlying and extending down the side supports (13b) of the pallet at least 2,5 cm (one inch) from the edge of the upwardly facing surface of the pallet top (13a). The system inhibits cold flow of the viscoelastic material during shipping and storage and the film packages can be consumed in subsequent viscoelastic material processing operations, thus yielding a reliable, environment-friendly means for transporting and shipping viscoelastic materials.

Description: TITLE SYSTEM AND METHOD FOR PACKAGING VISCOELASTIC MATERIALS CLAIM BENEFIT OF PRIOR APPLICATION This application claims the benefit of U. S. Provisional Application No. 60/055,575, filed August 12, 1997. BACKGROUND OF THE INVENTION Field of the Invention This invention relates to stacked loads of viscoelastic materials in film packages. More particularly, this invention relates to a palletized load and a method of creating a palletized load of stacked film packages containing viscoelastic materials. Background of the Invention Transporting and storing goods on pallets is well known. Various systems and methods have been disclosed for packaging goods on a pallet. In particular, U.S. Patent 5,353,936 to Dockstader et al. ("Dockstader") discloses a protective tray and a method for loading packages of material (such as bags of salt, small rocks or stones, dirt, sugar or fertilizer) on a pallet so as to prevent them from shifting laterally when subjected to a lateral force. The method requires placing a low-friction sheet on the upper surfaces of a pallet. Then a protective fiberboard tray is placed on the sheet and packages of material are stacked in the tray. Finally, a stretch-type plastic wrap is wrapped around the stacked packages so that the lower edge of the wrap overlies the outer periphery of the protective tray but does not overlie the periphery of the pallet. The shifting problem addressed by Dockstader is just one of the obstacles to be overcome when shipping and storing viscoelastic materials. Viscoelastic materials such as polychloroprene polymers flow under conditions of high stress or high temperatures as a result of a phenomenon called "cold flow." Viscoelastic materials lacking crystalline domains such as polychloroprene copolymers made with dichlorobutadiene comonomers, are particularly prone to cold flow. Generally, viscoelastic materials are packaged as chips or pellets which are covered with anti-massing partitioning agents in order to prevent the particulates from massing during shipment and storage. Cold flow exposes new polymer surfaces which in the final packaged materials are not covered with anti-massing partitioning agents and thus can result in massed materials. When the viscoelastic material is a polychloroprene polymer, cold flow couples with the unique property of auto-adhesion possessed by such polymers to cause the material to amass in the package. In the past, cold flow of viscoelastic materials has been inhibited during shipping and storage by packaging the materials in relatively inelastic and stiff packages such as multiwalled paper shipping sacks. These packages are stacked on a pallet and shipped. After the contents are emptied, the packages are disposed of by incinerating, land-filling or recycling. More recently, attention has been focused on developing more environment-friendly packages. One approach is to make packages from a materials that can be consumed in the processing operations to which the package contents are subjected after shipment and/or storage. An example of such packages are the film packages described by Flieger in WIPO Patent Publication WO 93/17067. These packages can be used for shipping and storing melt-processable materials then consumed in the melt-processing operation with the materials contained therein. Unfortunately, while environmentally advantageous, these packages do not adequately inhibit cold flow of melt- processable, viscoelastic materials when used to ship and store such materials on a pallet. When cold flow is not restricted, stacked bags of the viscoelastic material overflow the sides of the pallets on which they are stacked and compromise efficient shipping and/or storage. This phenomenon is illustrated in Figures 2 and 3 wherein bags 11 of viscoelastic material are stacked on pallet 13. After a period of about 48 hours, cold flow is manifested by pushing the outer edges of bags 1 1 substantially laterally beyond the periphery of pallet 13. In Figure 2. the lowermost bags in the stack overhang and sag about the top support, the side supports and side openings of the pallet making it difficult to insert the forklift tines without damaging or shifting some of the bags. In Figure 3. the material has flown to one side, pushing the bags over the edge of the pallet. The material cannot be transported in this condition. The pallet must be reloaded. Applicant has found that existing methods including the Dockstader method for shipping and storing particulate goods do not adequately inhibit cold flow of viscoelastic materials packed in film bags. Accordingly, a need exists for a reliable, environment-friendly system and method for transporting and storing viscoelastic materials on a pallet. SUMMARY OF THE INVENTION In a first aspect, the invention provides a palletized load system for a viscoelastic material comprising: a pallet comprising a generally horizontal top support having an upwardly facing surface and generally vertical side supports disposed at opposite ends of the top support and extending downward from and supporting the top support; a tray disposed on the upwardly facing surface of the pallet and comprising a bottom panel substantially equal in area to said upwardly facing pallet surface; a load supported on said tray so as not to extend laterally substantially beyond the outer periphery of the top support of said pallet, said load comprising a plurality of polymeric, melt-processable, film packages which contain a viscoelastic material, the packages being stacked in layers; and an outer wrap extending about the periphery of said load, tray and pallet, said wrap overlying and extending down said side supports of the pallet at least one inch from edge of the upwardly facing surface of the pallet and at least partially overlapping the uppermost stacked packages. In a second aspect, the invention provides a method of creating a palletized load of packaged viscoelastic material on a pallet comprising a generally horizontal top support having an upwardly facing surface and generally vertical side supports disposed at opposite ends of the top support and extending downward from and supporting the top support, said method comprising the steps of: placing a tray on the upwardly facing surface of the pallet, said tray comprising a bottom panel substantially equal in area to said upwardly facing pallet surface, placing a plurality of polymeric, melt-processable film packages which contain a viscoelastic material on said tray in stacked layers so as not to extend laterally substantially beyond the outer periphery of the top support of said pallet; and applying an outer wrap circumferentially about the stacked packages, the tray and the pallet such that wrap overlies and extends down said side supports of the pallet to a point at least one inch from edge of the upwardly facing surface of the pallet top and an upper edge of the wrap at least partially overlaps the uppermost stacked packages. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a palletized load of the invention. Figure 2 is a side view of ethylene copolymer packages of viscoelastic material stacked on a pallet wherein the viscoelastic material has undergone cold flow to create a problem of the type overcome by the present invention. Figure 3 is a side view of ethylene copolymer packages of viscoelastic material stacked on a pallet wherein the viscoelastic material has undergone cold flow to create a second problem of the type overcome by the present invention. DETAILED DESCRIPTION OF THE INVENTION Figure 1 depicts a preferred embodiment of the palletized load of the invention. The pallet 13 includes a top support 13a which can be a single piece or a plurality of parallel spaced slats. The top support is conventionally made of suitable strength wood and is fixed at opposite ends, as by nailing or stapling, in transverse relation to side supports 13b. One or more additional runners or stringers, such as the one indicated at 13 c, can be fixed to the top support. The side supports and runners or stringers are also conventionally made of wood. A double-sided reversible pallet can be provided by including a bottom support 13 d, comprising a single piece or a plurality of parallel spaced slats, fixed in transverse relation to the side supports opposite top support 13 a. The top support 13a and bottom support 13d are spaced apart and supported by the side supports 13b and any additional runners or stringers 13c. This spacing creates openings 13e which facilitate entry of the fork tines of a forklift type vehicle to facilitate handling of the loaded pallet. The side supports 13b and any runners or stringers 13c are also formed to facilitate entry and lifting of the pallet by a forklift. Alternative pallet embodiments can be used in the invention. In one such preferred alternative, the side supports and stringer comprise a top board affixed to at least two, and preferably three, blocks. The blocks are positioned at each end of the top board and, if there are three blocks, at the mid-section of the top board. For stability and to facilitate stacking, a bottom board or a plurality of bottom boards may be affixed to the end of the blocks opposite the top boards. This alternative pallet embodiment allows the tines of a forklift to enter and lift the pallet from any of four directions. In assembling the palletized load 10 depicted in Figure 1, a tray 12 is placed on the upper surface of the upwardly facing top support 13 a. The tray comprises a bottom panel substantially equal in area to the upwardly facing pallet surface. In the preferred embodiment depicted in Figure 1, tray 12 further comprises upwardly curved side and end panels secured to an outer rectangular periphery of the bottom panel. Selection of the appropriate tray will depend on the degree of cold flow that the viscoelastic material will undergo. Factors affecting cold flow primarily include: the amount of crystalline domains in the viscoelastic material, the viscosity of the viscoelastic material, and storage and shipping temperatures. More cold flow occurs as the amount of crystalline domains decreases, viscosity decreases and/or shipping or storage temperatures increase. When less cold flow occurs, a substantially flat, bottom panel, comprised of cardboard or plastic, can be used. When more cold flow occurs, the preferred embodiment with its upwardly curved side and end panels should be used. The curved side and end panels help to contain the bottom layer of packages 1 la and, with the outer wrap 14, prevents the bottom layer 11a from flowing over the edge of the pallet 13. The preferred tray 12 is stiff and durable, and may be constructed of wood, cardboard, plastic or a laminate comprising a wooden core between paper outer layers. The stiffness helps maintain the position of the bottom package layer 11a. The durability allows the tray to be reused. Preferably, tray 12 is a SKEE™ slip sheet, made of a hardwood veneer center core bonded between moisture resistant kraft paper, by Elberta Crate & Box Company, Dundee, Illinois. After tray 12 is positioned on pallet 13, packages of viscoelastic material such as bags 11 of material such as polychloroprene polymer, chlorosulfonated polyethylene elastomers, ethylene elastomers, fluoroelastomers, nitrile rubber, hydrogenated nitrile rubber or natural rubber, usually in the form of chips or pellets, are stacked in layers on the tray 12 such as shown in Figure 1. The bags are made of a polymeric film which is compatible with subsequent melt- processing operations for the viscoelastic material. Generally, such melt- processing operations are conducted at temperatures of 80 - 120 °C. Preferably bags 11 are made of a film comprising ethylene copolymers. Alternately preferred bags derived from ethylene vinyl acetate containing 18-28% vinyl acetate and having primary melting point below the temperature of the melt process can be used. The ethylene vinyl acetate resins may be co-extruded with a thin film of ethylene vinyl acetate resins of higher melting points to facilitate opening of the bags during the polymer packaging process. A third preferred material for the construction of the film for making a bag are polyolefins such as Affinity VP-8770, ethylene octene copolymers (The Dow Chemical Company, Midland, Michigan, USA). Polymers of particular interest in this application are those having 1.0 melt index. 0.9 g/cc density and less than 85 °C melting temperatures. Most preferably, bags 11 comprise a film package as disclosed in WIPO Patent Publication WO 93/17067, particularly a package comprising a film of an ethylene copolymer containing 55-90 % by weight ethylene and 15-45% by weight of an unsaturated monocarboxylic acid having 3-8 carbon atoms which is neutralized from 0-40% by at least one metal ion selected from lithium, sodium, magnesium and zinc. An adhesive may optionally be applied to the outer surface of bags 11 to help hold the bags in place relative to each other. Suitable adhesives have a relatively high shear strength so the bags will not slide relative to one another, a low tensile strength so the bags are easily lifted off the low layer, and are chemically compatible with the bags and the viscoelastic materials in the bags. Examples of suitable adhesives include Loc'n Pop Loxit P, (Key Tech, Mukilteo, Washington, USA), Film Grip 33-4044 (National Starch, Bridgewater, New Jersey, USA) and BAM480 (Beardow & Adams, Milton Keynes, England) a hot melt adhesive containing EVA copolymer, synthetic and natural resins and antioxidants. Usually a small amount of adhesive, on the order of 0.2-1.0 grams per 55 pound bag of viscoelastic material, is used. After tray 12 and bags 11 are positioned on pallet 13, an outer wrap 14 is applied circumferentially about the pallet 13, the tray 12 and the stacked bags 1 1 such that wrap overlies and extends down pallet side supports 13b to a point at least one inch from the edge of the upwardly facing surface of pallet top 13a and overlies the upwardly curved side and end panels of tray 12, and an upper edge 14a of the wrap at least partially overlaps the uppermost stacked packages. Applying outer wrap 14 such that it overlies and extends down side supports 13b anchors bags 11 and tray 12 in place on pallet 13. Preferably outer wrap 14 extends around pallet 13 to a point 2-3 inches down side supports 13b as shown in Figure 1. In this preferred embodiment, outer wrap 14 is applied over openings 13e in the pallet. To lift and move the palletized load 10, fork tines of a forklift are inserted into openings 13e, piercing the section of outer wrap 14 overlying said openings. The intact sections of outer wrap 14 in combination with the pleats in the outer wrap, described below, are sufficient to anchor the load in place on pallet 13. Preferably outer wrap 14 comprises a polyolefin stretchwrap. More preferably it is Point Guard, PI3520135, polyolefin stretchwrap (Reynolds Metals Company, Flexible Packaging Division, Appleton, Wisconsin, USA). The stretchwrap should be pre-stretched to 100-200%) elongation before it is applied. Additionally, at least one band of pleats should be formed lengthwise in the wrap. The pleats can be formed using a conventional stretch wrapping machine equipped with a pleating mechanism. The outer wrap is applied such that the pleats are aligned with package layer as shown in Figure 1 wherein pleats 14b align with bag layer 1 lb and pleats 14c align with bag layer 1 lc. Therefore, the preferred number of pleat bands will depend upon the width of the wrap and the approximate distance between midsections of the bag layers being wrapped. Pleating the wrap and aligning the pleats with the mid-section of each bag layer impart strength to the packaging system and help restrict cold- flow. It will thus be appreciated that the palletized load system and method of the present invention provides a stable packaging system for shipping and storing viscoelastic materials with minimal waste disposal requirements. The film packages can be consumed in subsequent viscoelastic material processing operations and the tray can be re-used. Cold flow of the viscoelastic material and its attendant problems are inhibited. While preferred embodiments of the palletized load system and method of the present invention have been illustrated and described, it will be understood that changes and modifications may be made therein without departing from the invention in its broader aspects.

Claims: What is claimed is: 1. A palletized load system for a viscoelastic material comprising: a pallet comprising a generally horizontal top support having an upwardly facing surface and two generally vertical side supports disposed at opposite ends of the top support and extending downward from the top support; a tray disposed on the upwardly facing surface of the pallet and comprising a bottom panel substantially equal in area to said upwardly facing pallet surface; a load supported on said tray so as not to extend laterally substantially beyond the outer periphery of the top support of said pallet, said load comprising a plurality of polymeric, melt-processable, film packages which contain a viscoelastic material, the packages being stacked in layers; and an outer wrap extending about the periphery of said pallet, tray and load, said wrap overlying and extending down said side supports of the pallet at least one inch from edge of the upwardly facing surface of the pallet top, and at least partially overlapping the uppermost stacked packages. 2. The palletized load system of claim 1 wherein the outer wrap is pleated and the pleats are substantially aligned with the mid-section of each package layer. 3. The palletized load system of claim 2 wherein the tray further comprises upwardly curved side and end panels secured to an outer rectangular periphery of the bottom panel and the outer wrap overlies said upwardly curved side and end panels of the tray. 4. The palletized load system of claim 3 wherein the tray comprises a material selected from wood, cardboard, plastic, and a laminate comprising a wooden core and a paper outer layer on opposite sides of the wooden core. 5. The palletized load system of claim 4 wherein the viscoelastic material comprises a polychloroprene polymer. 6. The palletized load system of claim 5 wherein the melt-processable ethylene copolymer package comprises a film of an ethylene copolymer containing 55-90 % by weight ethylene and 15-45% by weight of an unsaturated monocarboxylic acid having 3-8 carbon atoms which is neutralized from 0-40% by at least one metal ion selected from lithium, sodium, magnesium and zinc. 7. The palletized load system of claim 5 further comprising an adhesive at least one point between the layers of stacked packages. 8. The palletized load system of claim 5 wherein the outer wrap overlies and extends down the side supports of the pallet to a point about 2-3 inches from edge of the upwardly facing surface of the pallet top. 9. A method of creating a palletized load of packaged viscoelastic material on a pallet comprising a generally horizontal top support having an upwardly facing surface and generally vertical side supports disposed at opposite ends of the top support and extending downward from and supporting the top support, said method comprising the steps of: placing a tray on the upwardly facing surface of the pallet, said tray comprising a bottom panel substantially equal in area to said upwardly facing pallet surface; placing a plurality of polymeric, melt-processable, film packages which contain a viscoelastic material on said tray in stacked layers so as not to extend laterally substantially beyond the outer periphery of the top support of said pallet; and applying an outer wrap circumferentially about the pallet, the tray and the stacked packages such that wrap overlies and extends down said side supports of the pallet to a point at least one inch from edge of the upwardly facing surface of the pallet top and an upper edge of the wrap at least partially overlaps the uppermost stacked packages. 10. The method of claim 9 wherein the outer wrap is pleated and applied about the stacked packages such that the pleats are substantially aligned with the mid-section of each package layer. 11. The palletized load system of claim 10 wherein the tray further comprises upwardly curved side and end panels secured to an outer rectangular periphery of the bottom panel and the outer wrap overlies the upwardly curved side and end panels of the tray. 12. The palletized load system of claim 11 wherein the tray comprises a material selected from wood, cardboard, plastic, and a laminate comprising a wooden core and a paper outer layer on opposite sides of the wooden core. 13. The method of claim 12 wherein the viscoelastic material comprises a polychloroprene polymer. 14. The method of claim 13 wherein the melt-processable ethylene copolymer package comprises a film of an ethylene copolymer containing 55-90 % by weight ethylene and 15-45% by weight of an unsaturated monocarboxylic acid having 3-8 carbon atoms which is neutralized from 0-40% by at least one metal ion selected from lithium, sodium, magnesium and zinc. 15. The method of claim 13 further comprising the step of applying an adhesive to at least one point on a surface of at least one package layer such that the adhesive bonds the package layer to the underlying tray or package layer or to the overlying package layer. 16. The method of claim 13 wherein the outer wrap overlies and extends down the side supports of the pallet to a point about 2-3 inches from edge of the upwardly facing surface of the pallet top.

Inventors: POWELL GLEN ELLIS, POWELL, GLEN, ELLIS
Applicants: DUPONT DOW ELASTOMERS LLC, POWELL GLEN ELLIS, DUPONT DOW ELASTOMERS L.L.C., POWELL, GLEN, ELLIS
Application year: 1998
Main classification: B65D71
IPC codes: B65D71