US20070283856A1

US20070283856A1 - Load bearing structure

Info

Publication number: US20070283856A1
Application number: US11/796,908
Authority: US
Inventors: Michel Florentine Jozef Berghmans; Robert Stoffa
Original assignee: Nova Chemicals Inc
Current assignee: Nova Chemicals Inc
Priority date: 2006-05-17
Filing date: 2007-04-30
Publication date: 2007-12-13
Also published as: CN101443185A; WO2007136514A1; BRPI0712038A2; JP2009537407A; CA2650615A1; KR20090020619A; TW200812801A; EP2021170A1; MX2008014417A; AU2007254449A1

Abstract

A load-bearing platform that includes a base and a lity of legs extending from one side of the base, the load bearing platform is at least partly made expandable polymer matrix that includes an polymer of a polyolefin and in situ polymerized aromatic monomers.

Description

This application claims the benefit of priority of U.S. Provisional Application Ser. No. 60/801,167, filed May 17, 2006, entitled “Load Bearing Structure”, which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention is directed to novel load-bearing structures, such as pallets, generally used for stacking articles on for storage and/or shipping.
2. Description of the Prior Art
A shipping pallet is a well known load-bearing, moveable platform whereon articles are placed for storage and/or shipment. The pallet usually is loaded with a multiplicity of items, such as cartons or boxes. The loaded pallet is movable, usually with the aid of either a pallet truck or a forklift. Generally, pallets are made from wood.
The weight of the wood pallet is in the range of from forty to seventy pounds. Therefore, the weight of cargo shipped on the wood pallet is reduced by from forty to seventy pounds to provide for the weight of the wood pallet. This severely limits the amount of goods that can be shipped, especially by air.
Further, numerous injuries caused by wood splinters and nails are frequent occurrences among people who handle wood pallets. Additionally, disposal of wood pallets is a frequent concern.
There has been concern among nations about the use of the wood pallet causing an import of wood-boring insects, including the Asian Longhorned Beetle, the Asian Cerambycid Beetle, the Pine Wood Nematode, the Pine Wilt Nematode and the Anoplophora Glapripwnnis. Exemplary of damage caused by imported insects is the fate of the Chestnut Tree in the United States. There was a time when it was said that a squirrel could cross the United States on Chestnut Tree limbs without ever touching the ground. Insect infestation has caused the extinction of the Chestnut Tree in the United States.
Efforts to overcome the disadvantages of wood pallets have lead to molded foam plastic pallets. For example, U.S. Pat. No. 6,786,992 discloses a pallet having an expanded polystyrene core and a layer of high impact polystyrene covering a portion of the core.
U.S. Patent Application Publication No. 2005/0263044 discloses a pallet that includes a shape defining compressible core member, having at least one surface including a convex feature and a core member perimeter; and a thermoplastic shell having a shell interior and a shell edge, where the shell includes a first pliable thermoplastic sheet having an interior shaped by the convex surface of the core member and a first sheet edge extending outside of the core member perimeter, and a second pliable thermoplastic sheet having a second sheet interior and second sheet edge extending outside of the core member perimeter.
Generally, pallets made from plastics, especially foamed plastics, are not as strong as traditional wood pallets and, therefore, break under the load-bearing stress applied during use, making them undesirable.
Therefore, there is a need in the art to provide a lightweight pallet that can withstand the load-bearing stress of repeated use for shipping and/or storing articles traditionally found in wood pallets weight.

SUMMARY OF THE INVENTION

The present invention provides a load-bearing platform that includes a base and a plurality of legs extending from one side of the base, where the load bearing platform is at least partly made of an expandable polymer matrix that includes an interpolymer of a polyolefin and in situ polymerized vinyl aromatic monomers.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a load bearing platform according to the invention; and

FIG. 2 is a bottom perspective view of a load bearing platform according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

For the purpose of the description hereinafter, the terms “upper”, “lower”, “inner”, “outer”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof, shall relate to the invention as oriented in the drawing Figures. However, it is to be understood that the invention may assume alternate variations and step sequences except where expressly specified to the contrary. It is also to be understood that the specific devices and processes, illustrated in the attached drawings and described in the following specification, is an exemplary embodiment of the present invention. Hence, specific dimensions and other physical characteristics related to the embodiment disclosed herein are not to be considered as limiting the invention. In describing the embodiments of the present invention, reference will be made herein to the drawings in which like numerals refer to like features of the invention.
Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties, which the present invention desires to obtain. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10; that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations.
As used herein, the term “expandable polymer matrix” refers to a polymeric material in particulate or bead form that is impregnated with a blowing agent such that when the particulates and/or beads are placed in a mold and heat is applied thereto, evaporation of the blowing agent (as described below) effects the formation of a cellular structure and/or an expanding cellular structure in the particulates and/or beads and the outer surfaces of the particulates and/or beads fuse together to form a continuous mass of polymeric material conforming to the shape of the mold.
As used herein, the term “polymer” is meant to encompass, without limitation, homopolymers, copolymers and graft copolymers.
As used herein, the term “polyolefin” refers to a polymer prepared from at least one olefinic monomer, such as alpha unsaturated C₂-C₃₂linear or branched alkenes, non-limiting examples of which include ethylene, propylene, 1-butene, 1-hexene and 1-octene.
As used herein, the term “polyethylene” refers to and includes not only a homopolymer of ethylene, but also an ethylene copolymer containing units of at least 50 mole %, in some cases at least 70 mole %, and in other cases at least 80 mole % of an ethylene unit and a corresponding proportion of units from a monomer copolymerizable with ethylene, and blends containing at least 50% by weight, in some cases at least 60% by weight, and in other cases at least 75% by weight of an ethylene homopolymer or copolymer with another polymer.
Non-limiting examples of monomers that can be copolymerized with ethylene include vinyl acetate, vinyl chloride, propylene, 1-butene, 1-hexene, and (meth)acrylic acid and its esters.
Polymers that can be blended with ethylene homopolymers or copolymers include any polymer compatible with ethylene homopolymers or copolymers. Non-limiting examples of polymers that can be blended with ethylene homopolymers or copolymers include polypropylene, polybutadiene, polyisoprene, polychloroprene, chlorinated polyethylene, polyvinyl chloride, styrene/butadiene copolymers, vinyl acetate/ethylene copolymers, acrylonitrile/butadiene copolymers, styrene/butadiene/acrylonitrile copolymers, and vinyl chloride/vinyl acetate copolymer.
As used herein, the term “styrenic polymers” refers to homopolymers of styrenic monomers and copolymers of styrenic monomers and another copolymerizable monomers, where the styrenic monomers make up at least 50 mole percent of the monomeric units in the copolymer. Non-limiting examples of styrenic monomers include styrene, p-methyl styrene, α-methyl styrene, tertiary butyl styrene, dimethyl styrene, nuclear brominated or chlorinated derivatives thereof and combinations thereof. Non-limiting examples of suitable copolymerizable monomers include 1,3-butadiene, C₁-C₃₂linear, cyclic or branched alkyl (meth)acrylates (specific non-limiting examples include butyl(meth)acrylate, ethyl(meth)acrylate, methyl (meth)acrylate, and 2-ethylhexyl(meth)acrylate), acrylonitrile, vinyl acetate, alpha-methylethylene, divinyl benzene, maleic anhydride, maleic acid, fumaric acid, C₁-C₁₂linear, branched or cyclic mono- and di-alkyl esters of maleic acid, C₁-C₁₂linear, branched or cyclic mono- and di-alkyl esters of fumaric acid, itaconic acid, C₁-C₁₂linear, branched or cyclic mono- and di-alkyl esters of itaconic acid, itaconic anhydride and combinations thereof.
As used herein, the terms “(meth)acrylic” and “(meth)acrylate” are meant to include both acrylic and methacrylic acid derivatives, such as the corresponding alkyl esters often referred to as acrylates and (meth)acrylates, which the term “(meth)acrylate” is meant to encompass.
As used herein, the term “molding” refers to the shaping of a pliable material to assume a new desired shape. Molding can involve the use of specific molding tools such as male and female molding tools, sculptured platens, and the like. It can also include the use of specifically shaped core members including compressible core members that are used to impart a desired shape to at least a portion of a thermoplastic material.
As used herein, the term “expansion factor” refers to the volume a given weight of expanded polymer bead occupies, typically expressed as cc/g.
The present invention provides a load-bearing platform that includes a base and a plurality of legs extending from one side of the base.
The present load-bearing platform is made from an expandable polymer matrix that includes an interpolymer of a polyolefin and in situ polymerized vinyl aromatic monomers and optionally other expandable polymers.
In embodiments of the invention, the interpolymer of a polyolefin and in situ polymerized vinyl aromatic monomers is one or more of those described in U.S. Pat. Nos. 3,959,189; 4,168,353; 4,303,756, 4,303,757 and 6,908,949, the relevant portions of which are herein incorporated by reference. A non-limiting example of such interpolymers that can be used in the present invention include those available under the trade name ARCEL®, available from NOVA Chemicals Inc., Pittsburgh, Pa. and PIOCELAN®, available from Sekisui Plastics Co., Ltd., Tokyo, Japan.
In embodiments of the invention, the interpolymer of a polyolefin and in situ polymerized vinyl aromatic monomers is a particle or resin bead, which is subsequently processed to form the pallets according to the present invention. The interpolymer particles used in the invention include a polyolefin and an in situ polymerized vinyl aromatic resin that form an interpenetrating network of polyolefin and vinyl aromatic resin particles. The interpolymer particles are impregnated with a blowing agent and optionally, a plasticizer.
Such interpolymer particles can be obtained by processes that include suspending polyolefin particles and vinyl aromatic monomer or monomer mixtures in an aqueous suspension and polymerizing the monomer or monomer mixtures inside the polyolefin particles. Non-limiting examples of such processes are disclosed in U.S. Pat. Nos. 3,959,189, 4,168,353 and 6,908,949.
In an embodiment of the invention, the polyolefin includes one or more polyethylene resins selected from low-, medium-, and high-density polyethylene, an ethylene vinyl acetate copolymer, an ethylene/propylene copolymer, a blend of polyethylene and polypropylene, a blend of polyethylene and an ethylene/vinyl acetate copolymer, and a blend of polyethylene and an ethylene/propylene copolymer. Ethylene-butyl acrylate copolymer and ethylene-methyl methacrylate copolymer can also be used.
The amount of polyolefin in the interpolymer resin particles of the invention can be at least 20%, in some cases at least 25%, and in other cases at least 30% and can be up to 80%, in some cases up to 70%, in other cases up to 60% and in some instances up to 55%, by weight based on the weight of the interpolymer resin particles. The amount of polyolefin in the interpolymer resin particles can be any value or range between any of the values recited above.
The amount of polymerized vinyl aromatic resin in the interpolymer resin particles of the invention ranges can be at least 20%, in some cases at least 30%, in other cases at least 40% and in some instances at least 45% and can be up to 80%, in some cases up to 75% and in other cases up to 70%, by weight based on the weight of the interpolymer resin particles. The amount of polymerized vinyl aromatic resin in the interpolymer resin particles can be any value or range between any of the values recited above.
The vinyl aromatic resin can be made up of polymerized vinyl aromatic monomers or the resin can be a copolymer containing monomeric units from vinyl aromatic monomers and copolymerizable comonomers. Non-limiting examples of vinyl aromatic monomers that can be used in the invention include styrene, alpha-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, and isopropylxylene. These monomers may be used either alone or in admixture.
Non-limiting examples of copolymerizable comonomers include 1,3-butadiene, C₁-C₃₂linear, cyclic or branched alkyl(meth)acrylates (specific non-limiting examples include butyl(meth)acrylate, ethyl (meth)acrylate and 2-ethylhexyl(meth)acrylate), acrylonitrile, vinyl acetate, alpha-methylethylene, divinyl benzene, maleic anhydride, itaconic anhydride, dimethyl maleate and diethyl maleate.
Non-limiting examples of vinyl aromatic copolymers that can be used in the invention include those disclosed in U.S. Pat. No. 4,049,594. Specific non-limiting examples of suitable vinyl aromatic copolymers include copolymers containing repeat units from polymerizing styrene and repeat units from polymerizing one or monomers selected from 1,3-butadiene, C₁-C₃₂linear, cyclic or branched alkyl(meth)acrylates (specific non-limiting examples including butyl (meth)acrylate, ethyl(meth)acrylate and 2-ethylhexyl (meth)acrylate), acrylonitrile, vinyl acetate, alpha-methylethylene, divinyl benzene, maleic anhydride, itaconic anhydride, dimethyl maleate and diethyl maleate.
In particular embodiments of the invention, the vinyl aromatic resin includes polystyrene or styrene-butyl acrylate copolymers.
In general, the interpolymer resin particles are formed as follows: The polyolefin particles are dispersed in an aqueous medium prepared by adding 0.01 to 5%, in some cases 2 to 3%, by weight based on the weight of the water of a suspending agent such as water soluble high molecular weight materials, e.g., polyvinyl alcohol or methyl cellulose or slightly water soluble inorganic materials, e.g., calcium phosphate or magnesium pyrophosphate and soap, such as sodium dodecyl benzene sulfonate, and the vinyl aromatic monomers are added to the suspension and polymerized inside the polyolefin particles.
Any conventionally known and commonly used suspending agents for polymerization of vinyl aromatic monomers can be employed. These agents are well known in the art and can be freely selected by one skilled in the art. Initially, the water is in an amount generally from 0.7 to 5, preferably 3 to 5 times that of the starting polyolefin particles employed in the aqueous suspension, on a weight basis, and gradually the ratio of the polymer particles to the water may reach around 1:1.
The polymerization of the vinyl aromatic monomers, which is absorbed in the polyolefin particles, is carried out using initiators.
The initiators suitable for suspension polymerization of the vinyl aromatic monomers are generally used in an amount of about 0.05 to 2 percent by weight, in some cases 0.1 to 1 percent by weight, based on the weight of the vinyl aromatic monomer. Non-limiting examples of suitable initiators include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate and t-butyl perpivalate and azo compounds such as azobisisobutylonitrile and azobisdimethylvaleronitrile.
These initiators can be used alone or two or more initiators can be used in combination. In many cases, the initiators are dissolved in the vinyl aromatic monomers, which are to be absorbed in the polyolefin particles. In other cases, the initiator can be dissolved in a solvent, such as toluene, benzene, and 1,2-dichloropropane.
When the in situ polymerization of the vinyl aromatic monomers is completed, the polymerized vinyl aromatic resin is uniformly dispersed inside the polyolefin particles.
In many cases the polyolefin particles are cross-linked. The cross-linking can be accomplished simultaneously with the polymerization of the vinyl aromatic monomer in the polyolefin particles, and before impregnation of the blowing agent and/or plasticizer. For this purpose, cross-linking agents are used. Such cross-linking agents include, but are not limited to di-t-butyl-peroxide, t-butyl-cumylperoxide, dicumyl-peroxide, .alpha., .alpha.-bis-(t-butylperoxy)-p-diisopropylbenzene, 2,5-dimethyl-2,5-di-(t-butyl-peroxy)-hexyne-3,2,5-dimethyl-2,5-di-(benzoylperoxy)-hexane and t-butyl-peroxyisopropyl-carbonate. These cross-linking agents are absorbed in the polyolefin particles together with the vinyl aromatic monomers by dissolving the cross-linking agent in an amount of about 0.1 to 2 weight % and in some cases 0.5 to 1 weight %, based on the weight of the polyolefin particles suspended in water. Further details of the cross-linking agents and the manner for absorbing the cross-linking agents into the polyolefin particles are provided in U.S. Pat. No. 3,959,189.
In an embodiment of the invention, the interpolymer of a polyolefin and in situ polymerized vinyl aromatic monomers includes a rubber modified styrenic polymer where the rubber constitutes a continuous phase and the styrenic polymer constitutes a dispersed phase in the resin as described in copending U.S. Patent Application Publication No. 2006/0276558, the relevant portions of which are herein incorporated by reference.
In this embodiment, the rubber modified styrenic polymers are prepared by:

- I) forming a dispersion of organic droplets of an organic liquid phase in an aqueous phase, which can be stationary or flowing, where the organic phase contains an organic solution containing one or more elastomeric polymers dissolved in a monomer solution that includes one or more aryl polymerizable monomers, the organic droplets having an average diameter of from about 0.001 mm to about 10 mm, and
- II) polymerizing the monomers in the organic droplets in a low shear flow pattern.

In one aspect of this embodiment, a dispersion of organic droplets is formed by pressure atomizing an organic phase below the free surface of an aqueous phase, which can be stationary or flowing.
In another aspect of this embodiment, a dispersion of organic droplets of an organic liquid phase in an aqueous phase, which can be stationary or flowing, is formed by applying mechanical agitation.
The styrenic polymers can include residues from the polymerization of vinyl aromatic monomers selected from styrene, alpha-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, and isopropylxylene and admixtures thereof.
The elastomeric polymers can include copolymers of one or more conjugated dienes such as but not limited to butadiene, isoprene (i.e., 2-methyl-1,3-butadiene), 3-butadiene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene, one or more of a suitable unsatured nitrile such as acrylonitrile or methacrylonitiles and optionally one or more of a polar monomer such as acrylic acid, methacrylic acid, itaconic acid and maleic acid, alkyl esters of unsaturated carboxylic acids such as methyl acrylate and butyl acrylate; alkoxyalkyl esters of unsaturated carboxylic acids such as methoxy acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, acrylamide, methacrylamide; N-substituted acrylamides such as N-methylolacrylamide, N,N′-dimethylolacrylamide and N-ethoxymethylolacrylamide; N-substituted methacrylamides such as N-methylolmeth-acrylamide, N,N′-dimethylolmethacrylamide, N-ethoxy-methylmethacrylamide and vinyl chloride. These copolymers can also include repeat units from the polymerization of one or more aromatic vinyl monomers such as but not limited to styrene, 0-, m-, p-methyl styrene, dimethylstyrene and ethyl styrene. These types of copolymers are known as “acrylonitrile-butadiene rubbers” or “acrylonitrile-butadiene-styrene rubbers” or collectively as “nitrile rubbers” by those skilled in the art.
In some embodiments of the invention, the nitrile rubbers can be partially hydrogenated in the presence of hydrogen, preferably with a suitable hydrogenation catalyst.
The expandable polymer matrix of the invention can be used as raw materials in producing foamed articles. The blowing agent and/or plasticizer are introduced into the expandable polymer matrix resin particles to form foamable or expandable particles or resin beads, which in turn, are used to mold foamed articles.
The blowing agent should have a boiling point lower than the softening point of the polyolefin and should be gaseous or liquid at room temperature (about 20 to 30° C.) and normal pressure (about atmospheric). Blowing agents are well known in the art and generally have boiling points ranging from −42° C. to 80° C., more generally, from −10° C. to 36° C. Suitable hydrocarbon blowing agents include, but are not limited to aliphatic hydrocarbons such as n-propane, n-butane, iso-butane, n-pentane, iso-pentane, n-hexane, and neopentane, cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, and halogenated hydrocarbons such as methyl chloride, ethyl chloride, methylene chloride, trichlorofluoromethane, dischloro-fluoromethane, dichlorodifluormethane, chlorodifluoro-methane and dichlorotetrafluoroethane, etc. These blowing agents can be used alone or as mixtures. If n-butane, ethyl chloride, and dichlorotetrafluoroethane, which are gaseous at room temperature and normal pressure, are used as a mixture, it is possible to achieve foaming to a low bulk density. Specific types of volatile blowing agents are taught in U.S. Pat. No. 3,959,180. In particular embodiments of the invention, the blowing agent is selected from n-pentane, iso-pentane, neopentane, cylcopentane, and mixtures thereof.
The amount of the blowing agent ranges from about 1.5% to about 20% by weight, in some cases about 1.5% to 15% by weight, and in other cases from 5% to 15% by weight, based on the weight of the expandable polymer matrix.
A plasticizer can be used in combination with the blowing agent and as stated herein above and acts as a blowing aid in the invention.
Suitable plasticizers include, but are not limited to benzene, toluene, limonene, linear, branched or cyclic C₅to C₂₀alkanes, white oil, linear, branched or cyclic C₁to C₂₀dialkylphthalates, styrene, oligomers of styrene, oligomers of (meth)acrylates having a glass transition temperature less than polystyrene, and combinations thereof.
In a particular embodiment of the invention, the plasticizer includes limonene, a mono-terpene hydrocarbon existing widely in the plant world. The known types are d-limonene, 1-limonene, and dl-limonene. D-limonene is contained in the skin of citrus fruits and is used in food additives as a fragrant agent; its boiling point is about 176° C.; and its flammability is low. D-limonene is a colorless liquid, has a pleasant orange-like aroma, is approved as a food additive, and is widely used as a raw material of perfume. Limonene is not a hazardous air pollutant.
The amount of plasticizer can range from about 0.1 to 5 parts and in some cases from about 0.1 to about 1 part, by weight per 100 parts by weight of the expandable polymer matrix.
In embodiments of the invention, the interpolymer particles can be produced as follows: In a first reactor, the polyolefin particles are suspended in an aqueous medium containing a dispersing agent. The dispersing agent can be polyvinyl alcohol, methylcellulose, calcium phosphate, magnesium pyrophosphate, calcium carbonate, tricalcium phosphate, etc. The amount of dispersing agent employed can be from 0.01 to 5% by weight based on the amount of water. A surfactant can be added to the aqueous medium. Generally, the surfactant is used to lower the surface tension of the suspension and helps to emulsify the water/vinyl aromatic monomer in mixture in the initiator and wax mixes, if used. Suitable waxes include polyethylene waxes and ethylene bistearamide. The aqueous medium is generally heated to a temperature at which the vinyl aromatic monomers can be polymerized, i.e., from about 60° C. to about 120° C. over a period of time, for example, 12 to 20 hours. Over this 12 to 20 hour period, the vinyl aromatic monomers, the vinyl aromatic polymerization initiator, and the cross-linking agent are added to the resulting suspension containing the polyolefin particles, which are dispersed in the aqueous medium. These materials may be added all at one time, or gradually in individual portions.
The interpolymer particles are acidified, dewatered, screened, and subsequently charged to a second reactor where the particles are impregnated with the blowing agent and/or plasticizer.
The impregnation step can be carried out by suspending the interpolymer particles in an aqueous medium, adding the blowing agent and/or plasticizer to the resulting suspension, and stirring at a temperature of, preferably, about 40° C. degrees to 80° C. The blowing agent and/or plasticizer can be blended together and then added to the interpolymer particles or can be added to the interpolymer particles separately.
Alternatively, the blowing agent and/or plasticizer can be added to the first reactor during or after the polymerization process.
The above processes describe a wet process for impregnation of the interpolymer particles. Alternatively, the interpolymer particles can be impregnated via an anhydrous process similar to that taught in Column 4, lines 20-36 of U.S. Pat. No. 4,429,059.
In an embodiment of the invention, the blowing agent can be dosed to the expandable polymer matrix in an extruder to produce resin pellets or beads. The extruder acts to mix the blowing agent into the expandable polymer matrix prior to extruding a strand of the mixture. The strand can be cut into bead or pellet lengths using an appropriate device, a non-limiting example being an underwater face cutter.
The interpolymer resin and/or expandable polymer matrix particles can also contain other additives known in the art, non-limiting examples including anti-static additives; flame retardants; colorants or dyes; filler materials and combinations thereof. Other additives can also include chain transfer agents, non-limiting examples including C_2-15alkyl mercaptans, such as n-dodecyl mercaptan, t-dodecyl mercaptan, t-butyl mercaptan and n-butyl mercaptan, and other agents such as pentaphenyl ethane and the dimer of alpha-methyl styrene. Other additives can further include nucleating agents, non-limiting examples including polyolefin waxes, i.e., polyethylene waxes.
The expandable polymer matrix includes interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers and optionally other expandable polymers. The other expandable polymers include those polymers that can provide desirable properties to the load bearing platform of the invention and that are compatible with the interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers. Non-limiting examples of other expandable polymers that can be used in the present invention include expandable polystyrene (EPS), expandable polyolefins, rubber modified styrenic polymers where the styrenic polymer constitutes a continuous phase and the rubber constitutes a dispersed phase in the resin, rubber modified styrenic polymers where the rubber constitutes a continuous phase and the styrenic polymer constitutes a dispersed phase in the resin as described in copending U.S. Patent Application Publication No. 2006/0276558, the relevant portions of which are herein incorporated by reference, polyphenylene oxide, and combinations and blends thereof.
The expandable polymer matrix can contain 100% interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers, but can also contain up to 99%, in some cases up to 95%, in other cases up to 90%, in some instances up to 80% and in other instances up to 75% based on the weight of the expandable polymer matrix of interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers. Also, the expandable polymer matrix can contain at least 25%, in some cases at least 30%, in other cases at least 40% and in some instances at least 50% based on the weight of the expandable polymer matrix of interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers. The amount of interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers in the expandable polymer matrix can be any value or range between any of the values recited above.
When other expandable polymers are included in the expandable polymer matrix, the other expandable polymers can be present at a level of at least 1%, in some cases at least 5%, in other cases at least 10%, in some instances at least 20% and in other instances at least 25% based on the weight of the expandable polymer matrix. Also, the other expandable polymers can be present in the expandable polymer matrix at a level of up to 75%, in some cases up to 70%, in other cases up to 60% and in some instances up to 50% based on the weight of the expandable polymer matrix. The other expandable polymers can be included in the expandable polymer matrix at any level or range between any of the values recited above.
An embodiment of the load bearing structure according to the invention is shown in FIGS. 1 and 2, where a load bearing structure 8 includes an expanded polymer matrix core 10, which is in the general shape of a rectangular slab with an edge 12 that has a width 14 which can be from 1 to 25 cm, in some cases from 2 to 20 cm and in other cases from 2.5 to 15 cm. Core 10 has a topside 16 that can be from 75 to 150 cm, in some cases from 90 to 140 cm and in other cases from 100 to 130 cm long and from 65 to 140 cm, in some cases from 80 to 130 cm and in other cases from 90 to 120 cm forty inches wide. A bottom side 18 of core 10 includes legs 20-28 from 8 to 15 cm, in some cases from 9 to 13 cm long extending from bottom side 10.
Legs 20-28 and bottom side 18 define spaces 42, 44, 46, and 48 proximate to edge 12. Spaces 42, 44, 46, 48 separate legs 26-28, legs 20, 23, 26, legs 20-22 and legs 22, 25, 28, respectively, from the edge 12. In an embodiment of the invention, spaces 42, 44, 46, 48 are adapted to receive the tongues of a forklift truck. As a non-limiting example, a first tongue of a forklift can be placed under and along the length of bottom side 18 between leg 20 and leg 23, leg 21 and leg 24 and/or between leg 22 and leg 25 and a second tongue of a forklift can be placed under and along the length of bottom side 18 between leg 26 and leg 23, leg 27 and leg 24 and/or between leg 28 and leg 25. When the forklift truck lifts the first and second tongues, a surface of each tongue contacts the surface of bottom side 18 and acts to lift load bearing structure 8 and any articles stacked on topside 16.
Because core 10 is made from the above-described expanded polymer matrix, it has sufficient structural strength to be used as a load bearing platform.
In order to provide a desirable surface finish and/or texture and/or to minimize where and tear from repeated use, a suitable layer material can be applied to topside 16 and optionally edge 12.
Suitable layer materials that can be applied include rubber modified styrenic polymers, polyamides, such as nylon, polypropylene, polyethylene, and combinations thereof.
The density of the expanded polymer matrix in core 10 can be at least 5, in some cases at least 10 and in other cases at least 15 kg/m³and can be up to 40, in some cases up to 35 and in other cases up to 30 kg/m³. In embodiments of the invention, the density of the expanded polymer matrix in core 10 corresponding to the portions proximate spaces 42, 44, 46, 48 is higher than the density of the expanded polymer matrix in the remainder of core 10. This feature aids in preventing stress breakage at the thinnest portions of load bearing structure 8.
The load bearing structure can be prepared by heating beads of the expandable polymer matrix using a heating medium such as steam. Depending on the desired density in any portion of the load bearing structure, the beads are expanded to an expansion ratio (the ratio of expanded bead volume/initial bead volume) of from 5 to 100, in some cases from 10 to 90, in other cases from 20 to 80, in some instances from 30 to 75 and in other instances from 40 to 70.
The beads of the expandable polymer matrix according to the invention can be formed into a load bearing structure of a desired configuration by pre-expanding the beads and further expanding and shaping them in a mold cavity. The resulting load bearing structure has superior thermal stability, chemical resistance (e.g., oil resistance), and flexural strength compared to EPS pallets.
In an embodiment of the invention (not shown), a groove or channel can be molded or cut into the surface of topside 16 such that the groove or channel follows the perimeter of topside 16 and a first edge of the groove or channel is spaced apart from edge 12. The spacing of the groove or channel from edge 12 can be at least 1 cm, in some cases at least 2 cm and can be up to 10 cm, in some cases up to 8 cm. The groove or channel can be continuous or discontinuous.
In a particular embodiment of the invention, the groove or channel has a width and depth adapted to receive a foam panel. The foam panel can form an angle or arc to conform to a corner section of topside 16 directly above a portion of leg 20, 22, 28 and/or 26. Alternatively, the foam panel can extend along the sides of topside 16 beginning above leg 20 and terminating above leg 22, beginning above leg 22 and terminating above leg 28, beginning above leg 28 and terminating above leg 26, and/or beginning above leg 26 and terminating above leg 20. The length of the panels will conform to the dimensions of load bearing platform 8 as described above. The height of the panels can be at least 5 cm, in some cases at least 10 cm and in other cases at least 15 cm and can be up to 450 cm, in some cases up to 400 cm, in other cases up to 350 cm and in some instances up to 310 cm. The height of the panels can be any value or range between any of the values recited above.
In a further embodiment, a top panel can be included that roughly matches the width and length of load bearing structure 8. The top panel includes a groove or channel matching the groove or channel in topside 16 and is adapted to receive a top surface of the panels.
When assembled, the load bearing structure, panels and top panel form a box or open-box structure. Buckles or appropriate fasteners can be used to secure the panels and structure together. Alternatively, shrink wrap can be applied around the outside perimeter of the box or open-box structure to secure the parts in position.
In an embodiment of the invention, the top panel can be a load bearing structure 8 that includes a groove or channel that passes along a corresponding bottom surface of legs 20, 21, 22, 25, 28, 27, 26, and/or 23.
In another embodiment of the invention, the panels and top panels are made from the expandable polymer matrix described herein.
In other embodiments of the invention, the panels and top panels are made of one or more other expandable polymers as described above.
The panels and/or top panel prevent articles placed or stacked on topside 16 from sliding or otherwise leaving the surface of topside 16 when load bearing structure 8 is moved.
The present invention has been described with reference to specific details of particular embodiments thereof. It is not intended that such details be regarded as limitations upon the scope of the invention.

Claims

1. A load-bearing platform including a base and a plurality of legs extending from one side of the base, wherein the load bearing platform comprises an expandable polymer matrix that includes an interpolymer of a polyolefin and in situ polymerized vinyl aromatic monomers.

2. The load-bearing platform according to claim 1, wherein the expandable polymer matrix comprises other expandable polymers.

3. The load-bearing platform according to claim 1, wherein the polyolefin is selected from the group consisting of low density polyethylene, medium density polyethylene, high density polyethylene, an ethylene vinyl acetate copolymer, an ethylene/propylene copolymer, a blend of polyethylene and polypropylene, a blend of polyethylene and an ethylene/vinyl acetate copolymer, and a blend of polyethylene and an ethylene/propylene copolymer, ethylene-butyl acrylate copolymer, ethylene-methyl methacrylate copolymer and combinations thereof.

4. The load-bearing platform according to claim 1, wherein the vinyl aromatic monomers are selected from the group consisting of styrene, alpha-methyl-styrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, and isopropylxylene and admixtures thereof.

5. The load-bearing platform according to claim 1, wherein the polyolefin is present in the interpolymer resin particles at a level of from 20% to 80% by weight based on the weight of the interpolymer resin particles and the vinyl aromatic monomers or resulting polymers are present in the interpolymer resin particles at a level of from 20% to 80% based on the weight of the interpolymer resin particles.

6. The load-bearing platform according to claim 1, wherein the expandable polymer matrix comprises a blowing agent and/or plasticizer.

7. The load-bearing platform according to claim 2, wherein the other expandable polymers are selected from the group consisting of expandable polystyrene, expandable polyolefins, rubber modified styrenic polymers where the styrenic polymer constitutes a continuous phase and the rubber constitutes a dispersed phase in the resin, rubber modified styrenic polymers where the rubber constitutes a continuous phase and the styrenic polymer constitutes a dispersed phase in the resin, polyphenylene oxide, and combinations and blends thereof.

8. The load-bearing platform according to claim 2, wherein the expandable polymer contains from 25 to 99% based on the weight of the expandable polymer matrix of interpolymers of a polyolefin and in situ polymerized vinyl aromatic monomers and from 1 to 75% based on the weight of the expandable polymer matrix of other expandable polymers.

9. The load-bearing platform according to claim 2, wherein the load bearing platform is in the shape of a rectangle and has an edge of from 1 to 25 cm, a length of from 75 to 150 cm and a width of from 65 to 140 cm.

10. The load-bearing platform according to claim 1 comprising a layer material applied to a topside of the platform.

11. The load-bearing platform according to claim 1, wherein a continuous or discontinuous groove or channel is molded or cut into a surface of a topside of the base such that the groove or channel follows the perimeter of the topside and a first edge of the groove or channel is spaced apart from an outer edge of the base.

12. The load-bearing platform according to claim 11 comprising a plurality of panels adapted to fit into the groove or channel.

13. The load-bearing platform according to claim 12 comprising a top panel that matches the width and length of the load bearing structure and includes a groove or channel matching the groove or channel in the topside and is adapted to accept a top surface of the panels to form a box or open box structure.

14. A load-bearing platform including a base and a plurality of legs extending from one side of the base, wherein the load bearing platform comprises an expandable polymer matrix that includes rubber modified styrenic polymers wherein the rubber constitutes a continuous phase and the styrenic polymer constitutes a dispersed phase.

15. The load-bearing platform according to claim 14, wherein the styrenic polymers comprise residues from the polymerization of vinyl aromatic monomers selected from the group consisting of styrene, alpha-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylbenzene, and isopropylxylene and admixtures thereof.

16. The load-bearing platform according to claim 14, wherein The elastomeric polymers are selected from the group consisting of copolymers comprising one or more conjugated dienes and one or more of unsatured nitrites, one or more polar monomers, alkyl esters of unsaturated carboxylic acids, alkoxyalkyl esters of unsaturated carboxylic acids, acrylamide, methacryl-amide; N-substituted acrylamides, vinyl chloride; aromatic vinyl monomers, and combinations thereof.

17. The load-bearing platform according to claim 14, wherein the expandable polymer matrix comprises a blowing agent and/or plasticizer.

18. The load-bearing platform according to claim 14, wherein the load bearing platform is in the shape of a rectangle and has an edge of from 1 to 25 cm, a length of from 75 to 150 cm and a width of from 65 to 140 cm.

19. The load-bearing platform according to claim 14 comprising a layer material applied to a topside of the platform.