WO2006112781A1 - A thermoplastic product structure for increased creep strain resistance. - Google Patents

A thermoplastic product structure for increased creep strain resistance. Download PDF

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Publication number
WO2006112781A1
WO2006112781A1 PCT/SE2006/000465 SE2006000465W WO2006112781A1 WO 2006112781 A1 WO2006112781 A1 WO 2006112781A1 SE 2006000465 W SE2006000465 W SE 2006000465W WO 2006112781 A1 WO2006112781 A1 WO 2006112781A1
Authority
WO
WIPO (PCT)
Prior art keywords
thermoplastic
outer shell
expanded
product according
thermoplastic material
Prior art date
Application number
PCT/SE2006/000465
Other languages
French (fr)
Inventor
Anders Valentinsson
Original Assignee
Arca Systems Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arca Systems Ab filed Critical Arca Systems Ab
Publication of WO2006112781A1 publication Critical patent/WO2006112781A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D19/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D19/0004—Rigid pallets without side walls
    • B65D19/0006—Rigid pallets without side walls the load supporting surface being made of a single element
    • B65D19/0008—Rigid pallets without side walls the load supporting surface being made of a single element forming a continuous plane contact surface
    • B65D19/001—Rigid pallets without side walls the load supporting surface being made of a single element forming a continuous plane contact surface the base surface being made of a single element
    • B65D19/0014—Rigid pallets without side walls the load supporting surface being made of a single element forming a continuous plane contact surface the base surface being made of a single element forming discontinuous or non-planar contact surfaces
    • B65D19/0016—Rigid pallets without side walls the load supporting surface being made of a single element forming a continuous plane contact surface the base surface being made of a single element forming discontinuous or non-planar contact surfaces and each contact surface having a stringer-like shape
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
    • B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
    • B29C43/18—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles incorporating preformed parts or layers, e.g. compression moulding around inserts or for coating articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
    • B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
    • B29C43/20—Making multilayered or multicoloured articles
    • B29C43/203—Making multilayered articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
    • B29C51/12—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor of articles having inserts or reinforcements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2791/00—Shaping characteristics in general
    • B29C2791/004—Shaping under special conditions
    • B29C2791/006—Using vacuum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/07—Flat, e.g. panels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/12—Articles with an irregular circumference when viewed in cross-section, e.g. window profiles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
    • B29C48/13—Articles with a cross-section varying in the longitudinal direction, e.g. corrugated pipes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/04—Polymers of ethylene
    • B29K2023/06—PE, i.e. polyethylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
    • B29K2023/10—Polymers of propylene
    • B29K2023/12—PP, i.e. polypropylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
    • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/712—Containers; Packaging elements or accessories, Packages
    • B29L2031/7178—Pallets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D2519/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D2519/00004—Details relating to pallets
    • B65D2519/00258—Overall construction
    • B65D2519/00263—Overall construction of the pallet
    • B65D2519/00273—Overall construction of the pallet made of more than one piece
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D2519/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D2519/00004—Details relating to pallets
    • B65D2519/00258—Overall construction
    • B65D2519/00283—Overall construction of the load supporting surface
    • B65D2519/00293—Overall construction of the load supporting surface made of more than one piece
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D2519/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D2519/00004—Details relating to pallets
    • B65D2519/00258—Overall construction
    • B65D2519/00313—Overall construction of the base surface
    • B65D2519/00323—Overall construction of the base surface made of more than one piece
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D2519/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D2519/00004—Details relating to pallets
    • B65D2519/00258—Overall construction
    • B65D2519/00313—Overall construction of the base surface
    • B65D2519/00328—Overall construction of the base surface shape of the contact surface of the base
    • B65D2519/00333—Overall construction of the base surface shape of the contact surface of the base contact surface having a stringer-like shape
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D2519/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D2519/00004—Details relating to pallets
    • B65D2519/00258—Overall construction
    • B65D2519/00398—Overall construction reinforcements
    • B65D2519/00432—Non-integral, e.g. inserts
    • B65D2519/00437—Non-integral, e.g. inserts on the load supporting surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D2519/00—Pallets or like platforms, with or without side walls, for supporting loads to be lifted or lowered
    • B65D2519/00004—Details relating to pallets
    • B65D2519/00547—Connections
    • B65D2519/00552—Structures connecting the constitutive elements of the pallet to each other, i.e. load supporting surface, base surface and/or separate spacer
    • B65D2519/00557—Structures connecting the constitutive elements of the pallet to each other, i.e. load supporting surface, base surface and/or separate spacer without separate auxiliary elements
    • B65D2519/00562—Structures connecting the constitutive elements of the pallet to each other, i.e. load supporting surface, base surface and/or separate spacer without separate auxiliary elements chemical connection, e.g. glued, welded, sealed

Definitions

  • thermoplastic product structure for increased creep strain resistance.
  • the present invention relates to a product structure made of thermoplastic material, which product structure have a high creep strain resistance.
  • the products are intended for a high mechanical stability.
  • thermoplastic materials can be manufactured by a number of different manufacturing procedures. The most commonly used methods are however, injection moulding, vacuum forming, blow moulding and press moulding.
  • thermoplastic designs most often have to be designed to withstand the highest temperature together with the longest period of time and the highest load that it could be exposed to during its useful life.
  • the creep strain can however be decreased by adding filling or reinforcing additives to the thermoplastic material.
  • filling additives that are commonly used can be mentioned minerals such as lime, glass beads and mica while reinforcing additives that are commonly used are fibres such as glass fibres, steel fibres or carbon fibres.
  • the invention relates to a thermoplastic product with a high creep strain resistance, obtained through the process of moulding an outer shell of a solid thermoplastic material, the moulding method of the outer shell being selected from the group consisting of; vacuum forming, blow moulding, injection moulding or combinations thereof.
  • the outer shell is so composed so as to form an inner void or space.
  • the invention is characterised in that said inner void or space is at least partly filled with an inner structural stabiliser of expanded thermoplastic material.
  • the solid thermoplastic material and the expanded thermoplastic material are compatible materials which are possible to join together by welding.
  • the outer shell and inner structural stabiliser are joined together by means of heat and pressure so that a thermoplastic product having a outer shell of the solid thermoplastic material and an inner void or space at least partially filled with the expanded thermoplastic material is formed.
  • an upper portion of an outer shell and a lower portion of an outer shell is manufactured from sheet shaped solid work pieces, which work pieces are heated so that the thermoplastic material softens.
  • the solid work pieces are then given the desired shape by means of an upper and lower mould half respectively.
  • the inner structural stabiliser is then introduced in the form of a mainly sheet shaped expanded work piece of expanded thermoplastic material.
  • the expanded sheet shaped work piece is arranged between the upper and lower portions of the outer shell whereupon the upper and lower outer shell portions are pressed together to form a unit with each other and with the expanded sheet shaped work piece.
  • the expanded work piece is suitably preheated before being introduced between the upper and lower portion of the outer shell whereby the material of the outer shell and the material of the inner structural stabiliser welds together, thereby forming a good integral bond.
  • the heat stored in the material of the outer shell is enough to also heat the surface of the inner structural stabiliser enough for a good weld between the materials to form.
  • the expanded work piece is according to one embodiment of the invention achieved by means of extrusion moulding. It is also possible to injection mould such an expanded work piece.
  • the latter is especially advantageous if the expanded work piece needs to have a complex shape in order to match the shape and functions of the inner void or space.
  • connection points and bulbs between the upper and lower portions of the outer shell can be mentioned.
  • This is advantageous in for example products like a side wall to a pallet container and a pallet deck.
  • the pallet it is also known that the feet need to be sturdy.
  • the inner structural stabiliser can here be shaped to fill the cavities of the feet. It is also possible to add specially pre-shaped inner structural stabilisers in the feet cavities together with a larger main structural stabiliser covering a larger portion of the void or space.
  • twin sheet moulding The process of individually mould two preheated sheets in two mould halves which are facing each other by means of vacuum moulding and then to press these two halves together, thereby forming a hollow product is by the man skilled in the art known as twin sheet moulding.
  • extruded sheet material with a very high molecular weight can be used. Such a material will give a high mechanical strength.
  • One problem is however that it is rather difficult to achieve features like sharp edges, surface structure and the like since the material is very stiff even in molten state and due to the fact that only the pressure of one bar can be used for giving shape to the sheets.
  • the inner structural stabiliser may here serve a second purpose.
  • the inner structural stabiliser is preheated in order to bond with the inner surface of the outer shell.
  • the material of the inner structural stabiliser is expanded, it will be possible to heat only the surface of this part.
  • the inner portions of the inner structural stabiliser will still be rather stiff and can, so to say, act as an inner pressure during the stage where the different parts are joined together. Besides allowing a better reproduction of sharper portions of the mould, it will also ensure a good bond between the inner structural stabiliser and the outer shell.
  • an upper portion and a lower portion of an outer shell through means of injection moulding. Predetermined portions of the inner surfaces, facing the void or space, are then heated. An expanded work piece intended to constitute the inner structural stabiliser is also heated. The upper and lower portions of the outer shell with the expanded work piece arranged in between are then stacked and pressed together so that the respective layers welds together, thereby forming a good integral bond.
  • the thermoplastic product suitably forms a product selected from the group consisting of; a pallet, a pallet deck, a portion of a pallet, a pallet skid, a pallet container, a pallet portion of a pallet container, a side wall of a pallet container, a side wall portion of a pallet container or a combination thereof.
  • a plurality of thermoplastic products are may advantageously be joined together to form a product selected from the group consisting of; a pallet and a pallet container.
  • the plurality of thermoplastic products are suitably joined by any known method of welding.
  • the welding method may be selected from the group consisting of; butt welding, friction welding and filler welding.
  • the thermoplastic product optionally further comprises at least one reinforcing profile arranged in the void or space.
  • This reinforcing profile may be made of metal a thermosetting material or a thermoplastic material.
  • the thermosetting material and/or thermoplastic material is suitably reinforced with fibre selected from the group consisting of; carbon fibre, glass fibre, aramide fibre and combinations thereof.
  • the average density of the thermoplastic material of the inner structural stabiliser is suitably in the range 100 - 700 kg / m 3 .
  • the solid thermoplastic material of the outer shell is constituted of polyethylene while the thermoplastic material of the inner structural stabiliser is constituted of a material selected from the group consisting of; expanded polyethylene and expanded cross linked polyethylene.
  • the solid thermoplastic material of the outer shell is constituted of polypropylene while the thermoplastic material of the inner structural stabiliser is constituted of expanded polypropylene.
  • figure 1 shows in exploded view the different parts of a pallet.
  • the pallet consists of an upper deck portion 13 and pallet skids 14.
  • the upper deck portion 13 is made by an upper portion and a lower portion of an outer shell 11 and 12 respectively and an inner structural stabiliser 20.
  • the upper portion and the lower portion of an outer shell 11 and 12 respectively is manufactured from sheet shaped extruded solid work pieces with a high molecular weight. The work pieces are heated so that the thermoplastic material softens. The solid work pieces are then given the desired shape by means of an upper and lower mould half respectively.
  • the inner structural stabiliser 20 is then introduced in the form of a mainly sheet shaped expanded work piece of expanded thermoplastic material.
  • the expanded sheet shaped work piece is arranged between the upper and lower portions of the outer shell 11 and 12 respectively, whereupon the upper and lower outer shell portions 11 and 12 respectively are pressed together to form a unit with each other and with the expanded sheet shaped work piece.
  • the expanded work " piece is preheated before being introduced between the upper and lower portion of the outer shell 11 and 12 respectively, whereby the material of the outer shell 1 and the material of the inner structural stabiliser 20 welds together, thereby forming a good integral bond.
  • the expanded work piece is achieved by means of extrusion moulding. It is also possible to injection mould such an expanded work piece. The latter is especially advantageous if the inner structural stabiliser 20 needs to have a complex shape in order to match the shape and functions of the inner void or space 2. As an example of such shapes and functions, connection points and bulbs between the upper and lower portions 11 and 12 respectively, of the outer shell 1 can be mentioned.
  • twin sheet moulding The process of individually mould two preheated sheets in two mould halves which are facing each other by means of vacuum moulding and then two press these two halves together, thereby forming a hollow product is, by the man skilled in the art, known as twin sheet moulding.
  • extruded sheet material with a very high molecular weight can be used. Such a material will give a high mechanical strength.
  • One problem is however that it is rather difficult to achieve features like sharp edges, surface structure and the like, since the material is very stiff even in molten state and due to the fact that only the pressure of one bar can be used for giving shape to the sheets.
  • the inner structural stabiliser 20 may here serve a second purpose. As stated earlier, the inner structural stabiliser 20 may be preheated in order to bond with the inner surface of the outer shell 1. However, since the material of the inner structural stabiliser 20 is expanded, it will be possible to heat only the surface of this part. The inner portions of the inner structural stabiliser will still be rather stiff and will, so to say, act as an inner pressure during the stage where the different parts are joined together. Besides allowing a better reproduction of sharper portions of the mould, it will also ensure a good bond between the inner structural stabiliser 20 and the outer shell 1. Since a good bond between the inner structural stabiliser 20 and the outer shell 1 is important, conditioning of the inner structural stabiliser 20 to a predetermined temperature is advantageous.
  • the upper deck portion 13 is then joined with pallet skids 14.
  • pallet skids 14 is suitably produced by means on injection moulding, but can also be moulded through means of twin sheet moulding.
  • the skids 14 are suitably joined with the upper deck portion 13 by means of but welding. It is advantageous to condition the different parts in order to avoid problems with warping prior to the joining.
  • process herein described may further be used for achieving other parts such as for example side walls to foldable pallet containers and bases for any type of containers.

Abstract

A thermoplastic product with a high creep strain resistance, obtained through the process of moulding an outer shell (1) of a solid thermoplastic material, the moulding method of the outer shell (1) being selected from the group consisting of; vacuum forming, blow moulding, injection moulding or combinations thereof. Said outer shell (1) is so composed so as to form an inner void or space (2). Said inner void or space (2) is at least partly filled with an inner structural stabiliser (20) of expanded thermoplastic material. The solid thermoplastic material and expanded thermoplastic material are compatible materials which are possible to join together by welding. The outer shell (1) and said inner structural stabiliser (20) are joined together by means of heat and pressure so that a thermoplastic product having a outer shell (1) of the solid thermoplastic material and an inner void or space (2) at least partially filled with the expanded thermoplastic material is formed.

Description

A thermoplastic product structure for increased creep strain resistance.
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a product structure made of thermoplastic material, which product structure have a high creep strain resistance. The products are intended for a high mechanical stability.
2. Description of related prior art
Products made of thermoplastic materials can be manufactured by a number of different manufacturing procedures. The most commonly used methods are however, injection moulding, vacuum forming, blow moulding and press moulding.
In some fields of application a high load carrying capability is required. Carrying designs made of materials such as steel and concrete will be able to handle a load almost irrespective of factors like time and temperature. This is not the case with thermoplastic materials where relatively small loads can cause a remaining deformation when charged for a long period of time. This phenomenon is called creep strain, creep deformation or creepage. This creep strain is accelerated if the temperature is raised. A design made of thermoplastic material will however be able to withstand loads that are tens of times higher without remaining deformation when charged for shorter periods of time. The relation between the amount of creep strain, time and temperature is depending on type and quality of thermoplastic material.
Carrying thermoplastic designs most often have to be designed to withstand the highest temperature together with the longest period of time and the highest load that it could be exposed to during its useful life. The creep strain can however be decreased by adding filling or reinforcing additives to the thermoplastic material. Among filling additives that are commonly used can be mentioned minerals such as lime, glass beads and mica while reinforcing additives that are commonly used are fibres such as glass fibres, steel fibres or carbon fibres. It is also known to reinforce a thermoplastic product by integrating a metal design with the product. This can for example be constituted by a steel rod applied in a profile in the thermoplastic product. These additives and additions will however decrease some of the good qualities naturally occurring in the thermoplastic material. Among those qualities can be mentioned good impact strength, low weight and being a good electric, acoustic and heat insulator. It will also principally be impossible to recycle the material from a product containing additives. The ability to recycle thermoplastic materials is principally compulsory nowadays. SUMMARY OF THE INVENTION
The above mentioned problems have, through the present invention, been solved whereby a novel thermoplastic product structure with a radically improved creep strain resistance and mechanical stability has been achieved. Accordingly the invention relates to a thermoplastic product with a high creep strain resistance, obtained through the process of moulding an outer shell of a solid thermoplastic material, the moulding method of the outer shell being selected from the group consisting of; vacuum forming, blow moulding, injection moulding or combinations thereof. The outer shell is so composed so as to form an inner void or space. The invention is characterised in that said inner void or space is at least partly filled with an inner structural stabiliser of expanded thermoplastic material. The solid thermoplastic material and the expanded thermoplastic material are compatible materials which are possible to join together by welding. The outer shell and inner structural stabiliser are joined together by means of heat and pressure so that a thermoplastic product having a outer shell of the solid thermoplastic material and an inner void or space at least partially filled with the expanded thermoplastic material is formed.
According to a preferred embodiment of the invention, an upper portion of an outer shell and a lower portion of an outer shell is manufactured from sheet shaped solid work pieces, which work pieces are heated so that the thermoplastic material softens. The solid work pieces are then given the desired shape by means of an upper and lower mould half respectively. The inner structural stabiliser is then introduced in the form of a mainly sheet shaped expanded work piece of expanded thermoplastic material. The expanded sheet shaped work piece is arranged between the upper and lower portions of the outer shell whereupon the upper and lower outer shell portions are pressed together to form a unit with each other and with the expanded sheet shaped work piece. The expanded work piece is suitably preheated before being introduced between the upper and lower portion of the outer shell whereby the material of the outer shell and the material of the inner structural stabiliser welds together, thereby forming a good integral bond. Normally, the heat stored in the material of the outer shell is enough to also heat the surface of the inner structural stabiliser enough for a good weld between the materials to form. However, in some cases it may show advantageous to at least condition the surface of the inner structural stabiliser by a slight preheating. The expanded work piece is according to one embodiment of the invention achieved by means of extrusion moulding. It is also possible to injection mould such an expanded work piece. The latter is especially advantageous if the expanded work piece needs to have a complex shape in order to match the shape and functions of the inner void or space. As an example of such shapes and functions, connection points and bulbs between the upper and lower portions of the outer shell can be mentioned. This is advantageous in for example products like a side wall to a pallet container and a pallet deck. In the latter case, the pallet, it is also known that the feet need to be sturdy. The inner structural stabiliser can here be shaped to fill the cavities of the feet. It is also possible to add specially pre-shaped inner structural stabilisers in the feet cavities together with a larger main structural stabiliser covering a larger portion of the void or space.
The process of individually mould two preheated sheets in two mould halves which are facing each other by means of vacuum moulding and then to press these two halves together, thereby forming a hollow product is by the man skilled in the art known as twin sheet moulding. One of the advantages with this moulding procedure is that extruded sheet material with a very high molecular weight can be used. Such a material will give a high mechanical strength. One problem is however that it is rather difficult to achieve features like sharp edges, surface structure and the like since the material is very stiff even in molten state and due to the fact that only the pressure of one bar can be used for giving shape to the sheets.
The inner structural stabiliser may here serve a second purpose. As stated earlier, the inner structural stabiliser is preheated in order to bond with the inner surface of the outer shell. However, since the material of the inner structural stabiliser is expanded, it will be possible to heat only the surface of this part. The inner portions of the inner structural stabiliser will still be rather stiff and can, so to say, act as an inner pressure during the stage where the different parts are joined together. Besides allowing a better reproduction of sharper portions of the mould, it will also ensure a good bond between the inner structural stabiliser and the outer shell.
It is according to one embodiment then advantageous to pre-shape the expanded work piece to fit predetermined portions of the inner void or space of the-outer shell.
It is, according to an alternative embodiment of the invention possible to achieve an upper portion and a lower portion of an outer shell through means of injection moulding. Predetermined portions of the inner surfaces, facing the void or space, are then heated. An expanded work piece intended to constitute the inner structural stabiliser is also heated. The upper and lower portions of the outer shell with the expanded work piece arranged in between are then stacked and pressed together so that the respective layers welds together, thereby forming a good integral bond. According to the invention, the thermoplastic product suitably forms a product selected from the group consisting of; a pallet, a pallet deck, a portion of a pallet, a pallet skid, a pallet container, a pallet portion of a pallet container, a side wall of a pallet container, a side wall portion of a pallet container or a combination thereof. A plurality of thermoplastic products are may advantageously be joined together to form a product selected from the group consisting of; a pallet and a pallet container. The plurality of thermoplastic products are suitably joined by any known method of welding. The welding method may be selected from the group consisting of; butt welding, friction welding and filler welding.
In extreme cases, where the case of load is very unfavourable, either due to the extent of time, increased temperatures, unfavourable application of load or a combination of the above, the thermoplastic product optionally further comprises at least one reinforcing profile arranged in the void or space. This reinforcing profile may be made of metal a thermosetting material or a thermoplastic material. The thermosetting material and/or thermoplastic material is suitably reinforced with fibre selected from the group consisting of; carbon fibre, glass fibre, aramide fibre and combinations thereof.
The average density of the thermoplastic material of the inner structural stabiliser is suitably in the range 100 - 700 kg / m3.
According to one embodiment of the invention the solid thermoplastic material of the outer shell is constituted of polyethylene while the thermoplastic material of the inner structural stabiliser is constituted of a material selected from the group consisting of; expanded polyethylene and expanded cross linked polyethylene.
According to another embodiment .of the invention the solid thermoplastic material of the outer shell is constituted of polypropylene while the thermoplastic material of the inner structural stabiliser is constituted of expanded polypropylene.
DESCRIPTION OF AN EMBODIMENT EXAMPLE
The invention is further described together with enclosed drawing showing a selected embodiment of the invention, wherein, -figure 1 shows in exploded view the different parts of a pallet according to the invention.
Accordingly, figure 1 shows in exploded view the different parts of a pallet. The pallet consists of an upper deck portion 13 and pallet skids 14. The upper deck portion 13 is made by an upper portion and a lower portion of an outer shell 11 and 12 respectively and an inner structural stabiliser 20. The upper portion and the lower portion of an outer shell 11 and 12 respectively, is manufactured from sheet shaped extruded solid work pieces with a high molecular weight. The work pieces are heated so that the thermoplastic material softens. The solid work pieces are then given the desired shape by means of an upper and lower mould half respectively. The inner structural stabiliser 20 is then introduced in the form of a mainly sheet shaped expanded work piece of expanded thermoplastic material. The expanded sheet shaped work piece is arranged between the upper and lower portions of the outer shell 11 and 12 respectively, whereupon the upper and lower outer shell portions 11 and 12 respectively are pressed together to form a unit with each other and with the expanded sheet shaped work piece. The expanded work" piece is preheated before being introduced between the upper and lower portion of the outer shell 11 and 12 respectively, whereby the material of the outer shell 1 and the material of the inner structural stabiliser 20 welds together, thereby forming a good integral bond. The expanded work piece is achieved by means of extrusion moulding. It is also possible to injection mould such an expanded work piece. The latter is especially advantageous if the inner structural stabiliser 20 needs to have a complex shape in order to match the shape and functions of the inner void or space 2. As an example of such shapes and functions, connection points and bulbs between the upper and lower portions 11 and 12 respectively, of the outer shell 1 can be mentioned.
The process of individually mould two preheated sheets in two mould halves which are facing each other by means of vacuum moulding and then two press these two halves together, thereby forming a hollow product is, by the man skilled in the art, known as twin sheet moulding. One of the advantages with this moulding procedure is that extruded sheet material with a very high molecular weight can be used. Such a material will give a high mechanical strength. One problem is however that it is rather difficult to achieve features like sharp edges, surface structure and the like, since the material is very stiff even in molten state and due to the fact that only the pressure of one bar can be used for giving shape to the sheets.
The inner structural stabiliser 20 may here serve a second purpose. As stated earlier, the inner structural stabiliser 20 may be preheated in order to bond with the inner surface of the outer shell 1. However, since the material of the inner structural stabiliser 20 is expanded, it will be possible to heat only the surface of this part. The inner portions of the inner structural stabiliser will still be rather stiff and will, so to say, act as an inner pressure during the stage where the different parts are joined together. Besides allowing a better reproduction of sharper portions of the mould, it will also ensure a good bond between the inner structural stabiliser 20 and the outer shell 1. Since a good bond between the inner structural stabiliser 20 and the outer shell 1 is important, conditioning of the inner structural stabiliser 20 to a predetermined temperature is advantageous. This temperature is very much decided by the design and the thickness of the outer shell 1, so trials with different conditioning is necessary for each design. If the inner structural stabiliser is heated too much, a good bond cannot be ensured as the pressure it exerts on the inner surface of the outer shell, during the joining phase, will be lowered as the structural integrity of the expanded material is weakened. As the man skilled in the art will easily recognise, properties like outer shell 1 wall thickness and design, temperature of outer shell 1, thickness and design of the inner structural stabiliser 20 and density and temperature of the inner structural stabiliser 20 will affect the result. Also the difference between the thickness of the inner structural stabiliser 20 and the free height between the inner surfaces of the outer shell 1 plays an important role.
The upper deck portion 13 is then joined with pallet skids 14. These pallet skids 14 is suitably produced by means on injection moulding, but can also be moulded through means of twin sheet moulding. The skids 14 are suitably joined with the upper deck portion 13 by means of but welding. It is advantageous to condition the different parts in order to avoid problems with warping prior to the joining.
As will be recognised by the man skilled in the art, the process herein described may further be used for achieving other parts such as for example side walls to foldable pallet containers and bases for any type of containers.
The invention is not limited by the embodiments shown since these can be varied in different ways within the scope of the invention.

Claims

WE CLAIM
1. A thermoplastic product with a high creep strain resistance, obtained through the process of moulding an outer shell (1) of a solid thermoplastic material, the moulding method of the outer shell (1) being selected from the group consisting of; vacuum forming, blow moulding, injection moulding or combinations thereof, said outer shell (1) being so composed so as to form an inner void or space (2), that said inner void or space (2) is at least partly filled with an inner structural stabiliser (20) of expanded thermoplastic material, that said solid thermoplastic material and said expanded thermoplastic material are compatible materials which are possible to join together by welding, that said outer shell (1) and said inner structural stabiliser (20) are joined together by means of heat and pressure so that a thermoplastic product having a outer shell (1) of the solid thermoplastic material and an inner void or space (2) at least partially filled with the expanded thermoplastic material is formed.
2. A thermoplastic product according to claim 1 wherein an upper portion (11) of an outer shell (1) and a lower portion (12) of an outer shell (1) is manufactured from sheet shaped solid work pieces, which work pieces are heated so that the thermoplastic material softens whereby they are given the desired shape by means of an upper and lower mould half respectively whereupon the inner structural stabiliser (20) is introduced in the form of a mainly sheet shaped expanded work piece of expanded thermoplastic material, that the expanded sheet shaped work piece is arranged between the upper and lower portions (11 and 12 respectively) of the outer shell (1) whereupon the upper and lower outer shell portions (11 and 12 respectively) are pressed together to form a unit with each other and with the expanded sheet shaped work piece.
3. A thermoplastic product according to claim 2 wherein the expanded work piece is preheated before being introduced between the upper and lower portion (11 and 12 respectively) of the outer shell (1) whereby the material of the outer shell (1) and the material of the inner structural stabiliser (20) welds together, thereby forming a good integral bond.
4. A thermoplastic product according to claim 2 wherein the expanded work piece is achieved by means of extrusion moulding.
5. A thermoplastic product according to claim 2 wherein the expanded work piece is achieved by means of injection moulding.
6. A thermoplastic product according to claim 4 wherein the expanded work piece is pre-shaped to fit predetermined portions of the inner void or space (2) of the outer shell
(1).
7. A thermoplastic product according to claim 5 wherein the expanded work piece is pre-shaped to fit predetermined portions of the inner void or space (2) of the outer shell
(1).
8. A thermoplastic product according to claim 1 wherein an upper portion and a lower portion (11 and 12 respectively) of an outer shell (1) is achieved through means of injection moulding, that predetermined portions of the inner surfaces, facing the void or space (2), are heated, that an expanded work piece intended to constitute the inner structural stabiliser (20) is heated and that the upper and lower portions (11 and 12 respectively) of the outer shell (1) with the expanded work piece arranged in between are stacked and pressed together so that the respective layers welds together, thereby forming a good integral bond.
9. A thermoplastic product according to any of the claims 1 - 8 wherein the thermoplastic product forms a product selected from the group consisting of; a pallet, a pallet deck, a portion of a pallet, a pallet skid, a pallet container, a pallet portion of a pallet container, a side wall of a pallet container, a side wall portion of a pallet container or a combination thereof.
10. A thermoplastic product according to claim 9 wherein a plurality of thermoplastic products are joined together to form a product selected from the group consisting of; a pallet and a pallet container.
11. A thermoplastic product according to claims 9 wherein the plurality of thermoplastic products are joined by any known method of welding.
12. A thermoplastic product according to claim 11 wherein the welding method is selected from the group consisting of; butt welding, friction welding and filler welding.
13. A thermoplastic product according to claim 9 wherein the thermoplastic product optionally further comprises at least one reinforcing profile arranged in the void or space (2).
14. A thermoplastic product according to claim 13 wherein the reinforcing profile is made of metal.
15. A thermoplastic product according to claim 13 wherein the reinforcing profile is made of a thermosetting material.
16. A thermoplastic product according to claim 15 wherein the thermosetting material is reinforced with fibre selected from the group consisting of; carbon fibre, glass fibre, aramide fibre and combinations thereof.
17. A thermoplastic product according to claim 13 wherein the reinforcing profile is made of a thermoplastic material.
18. A thermoplastic product according to claim 17 wherein the thermoplastic material is reinforced with fibre selected from the group consisting of; carbon fibre, glass fibre, aramide fibre and combinations thereof.
19. A thermoplastic product according to any of the claims 1 - 8 wherein the average density of the thermoplastic material of the inner structural stabiliser is in the range 100 - 700 kg / m3.
20. A thermoplastic product according to any of the claims 1 - 8 wherein the solid thermoplastic material of the outer shell (1) is constituted of polyethylene while the thermoplastic material of the inner structural stabiliser (20) is constituted of a material selected from the group consisting of; expanded polyethylene and expanded cross linked polyethylene.
21. A thermoplastic product according to any of the claims 1 - 8 wherein the solid thermoplastic material of the outer shell (1) is constituted of polypropylene while the thermoplastic material of the inner structural stabiliser (20) is constituted of expanded polypropylene.
PCT/SE2006/000465 2005-04-22 2006-04-21 A thermoplastic product structure for increased creep strain resistance. WO2006112781A1 (en)

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