Process for the manufacturing of thermoplastic products with high creep strain resistance

• US 6,458,232 B1
• Filed: 09/09/1999
• Issued: 10/01/2002
• Est. Priority Date: 03/10/1997
• Status: Expired due to Fees

• Current Assignee: Schoeller Arca Systems AB (Schoeller Allibert SASU)
• Original Assignee: Pergo Europe AB (Mohawk Industries Incorporated)
• Inventors: Valentinsson, Anders
• Primary Examiner(s): Ball, Michael W.
• Assistant Examiner(s): Musser, Barbara J.
• Application Number:
  US09/380,314
• Time in Patent Office: 1,118 Days
• Field of Search: 156/308.2, 156/309.6, 156/309.9, 156/2.92, 156/73.5, 156/84, 156/196, 156/242, 156/245, 156/182, 156/304.2, 156/304.6, 156/322, 108/57.27, 108/901
• US Class Current: 156/182
• CPC Class Codes: B29C 2791/001 Shaping in several steps
• CPC Class Codes: B29C 2791/006 Using vacuum
• CPC Class Codes: B29C 2791/007 Using fluid under pressure
• CPC Class Codes: B29C 51/10 Forming by pressure difference, e.g. vacuum
• CPC Class Codes: B29C 51/267 Two sheets being thermoformed in separate mould parts and joined together while still in the mould B29C49/0691 takes precedence
• CPC Class Codes: B29C 65/06 using friction, e.g. spin welding non-plastics elements to plastic elements B29C65/645
• CPC Class Codes: B29C 65/20 with direct contact, e.g. using "mirror"
• CPC Class Codes: B29C 66/1122 Single lap to lap joints, i.e. overlap joints B29C66/45, B29C66/472, B29C66/52272 take precedence
• CPC Class Codes: B29C 66/1142 Single butt to butt joints
• CPC Class Codes: B29C 66/472 said single elements being substantially flat
• CPC Class Codes: B29C 66/54 Joining several hollow-preforms, e.g. half-shells, to form hollow articles, e.g. for making balls, containers; Joining several hollow-preforms, e.g. half-cylinders, to form tubular articles
• CPC Class Codes: B29C 66/543 joining more than two hollow-preforms to form said hollow articles
• CPC Class Codes: B29C 66/71 characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/723 being multi-layered B29C66/7292, B29C66/72941 take precedence
• CPC Class Codes: B29C 66/73921 characterised by the materials of both parts being thermoplastics
• CPC Class Codes: B29C 66/8322 Joining or pressing tools reciprocating along one axis
• CPC Class Codes: B29K 2023/04 Polymers of ethylene
• CPC Class Codes: B29K 2023/06 PE, i.e. polyethylene
• CPC Class Codes: B29K 2023/065 HDPE, i.e. high density polyethylene
• CPC Class Codes: B29K 2023/10 Polymers of propylene
• CPC Class Codes: B29K 2023/12 : PP, i.e. polypropylene
• CPC Class Codes: B29K 2023/18 : Polymers of hydrocarbons having four or more carbon atoms, e.g. polymers of butylene, e.g. PB, i.e. polybutylene
• CPC Class Codes: B29K 2105/26 : Scrap or recycled material
• CPC Class Codes: B29L 2031/7178 : Pallets
• CPC Class Codes: B65D 19/0026 : and each contact surface having a stringer-like shape
• CPC Class Codes: B65D 2519/00034 : Plastic
• CPC Class Codes: B65D 2519/00069 : Plastic
• CPC Class Codes: B65D 2519/00104 : Plastic
• CPC Class Codes: B65D 2519/00293 : made of more than one piece
• CPC Class Codes: B65D 2519/00323 : made of more than one piece
• CPC Class Codes: B65D 2519/00333 : contact surface having a stringer-like shape
• CPC Class Codes: B65D 2519/00373 : whereby at least one spacer is made of one piece
• CPC Class Codes: B65D 2519/00557 : without separate auxiliary elements
• CPC Class Codes: B65D 2519/00562 : chemical connection, e.g. glued, welded, sealed
• CPC Class Codes: Y10T 156/1002 : with permanent bending or reshaping or surface deformation of self sustaining lamina

Abstract

A process for the manufacturing of thermoplastic products with a high creep strain resistance. The products are free from reinforcing additives. The process includes at least vacuum forming and/or blow moulding of a thermoplastic material such as a polyolefine. A number of product parts are manufactured from a number of preferably tube- or sheet-shaped work pieces. The work pieces are heated so that the thermoplastic material softens whereby they are given the desired shape by means of a mould and the influence of vacuum and/or pressure. The product parts produced are allowed to cool and post-shrink and are hereafter joined to a unit.

Claims

1. A molding process for the manufacture of a product comprising at least a first product part and a second product part from a thermoplastic material selected from the group consisting of polyethylene, polypropylene and polybutylene which product has no reinforcing additives, in a mold having a first mold half and a second mold half, which together includes a shape-giving cavity being a negative depiction of the respective product part, the method comprising:

forming the first product part, comprising;

providing two mold halves, at least one of the mold halves having a projection in the shape-giving cavity thereby forming at least one protrusion in a work piece formed in said mold half;

placing the mold halves so that a space is formed between the two mold halves and so that the shape-giving cavity of each mold half is directed toward each other;

heating two work pieces which constitute an upper half and a lower half of the product part, thereby softening the thermoplastic material;

shaping the work pieces toward the cavity of each mold half with the assistance of vacuum, blowing, and combinations thereof, to form shaped work pieces;

moving the mold halves relatively toward one another and pressing the shaped work pieces together while the thermoplastic material is still hot to form a unitary hollow product part with the upper and lower halves of said product part being joined along their edges and by said at least one protrusion to increase mechanical strength and dimension stability; and

cooling the first product part produced to the point where it can be removed from the mold though still at an elevated temperature; and

further cooling the first product part for 1-2 days until the first product part has reached room temperature and post shrinking has been achieved;

forming the second product part, comprising;

injecting molten thermoplastic material into one or more mold cavities of the mold;

allowing the thermoplastic material to solidify;

opening the mold;

cooling the second product part produced to the point where it can be removed from the mold though still at an elevated temperature; and

removing the product part from the mold;

further cooling the second product part for 1-2 days until the second product part has reached room temperature and post shrinking has been achieved; and

joining the first product part to the second product part and receiving a high creep strain resistant product.

2. The process according to claim 1, further comprising molding at least one additional product part through injection molding by means of a mold comprising one or more mold cavities wherein the mold includes means for injecting a pressurized gas comprising:

injecting molten thermoplastic material into a mold cavity of the mold; and

injecting pressurized gas into the molten thermoplastic material in the mold cavity;

allowing the thermoplastic material to solidify;

evacuating the gas;

opening the mold;

removing the product part from the mold;

allowing the product part to cool completely and post-shrink; and

joining the post-shrunk at least one additional product part to the product.

3. The process according to claim 1, wherein the thermoplastic material is constituted by a polymer with an average molecular mass in the range 200,000-2,000,000.

4. The process according to claim 3, wherein the average molecular mass of the thermoplastic material is greater than 300,000.

5. The process according to claim 1, wherein the thermoplastic material is constituted by a thermoplastic laminate with at least two layers, wherein the layers are constituted by a combination of at least two of the materials selected from the group consisting of virgin solid thermoplastic material, recycled solid thermoplastic material, virgin expanded thermoplastic material and recycled expanded thermoplastic material.

6. The process according to claim 1, wherein said at least one protrusion joining the upper and lower halves of said first product part has a shape selected from the group consisting of a tower or ridge.

7. The process according to claim 1, wherein each work piece is in a form consisting of a sheet.

8. The process according to claim 1, wherein the two work pieces are provided in the form of a two separate sheets prior to said heating.

9. The process according to claim 1, further comprising molding work pieces into at least one product part selected from the group consisting of a pallet deck, a foot and a skid of a pallet;

and a pallet deck, a foot, a side wall and a skid of a pallet container.

10. The process according to claim 1, further comprising molding one or both work pieces into at least one shape selected from the group consisting of a pallet deck, a foot and a skid of a pallet;

and a pallet deck, a foot, a side wall and a skid of a pallet container.

11. The process according to claim 1, wherein the two work pieces are part of a single tube, having a circumferential surface, wherein said circumferential surface serves as both the first and the second work piece.

12. The method of claim 1, wherein the first product part is a first hollow pallet deck and the second product part is at least one hollow pallet skid.

13. The method of claim 12, further comprising molding a second hollow deck member and wherein the product comprises three second product parts, wherein each of the second product parts a hollow pallet skid.

14. The method according to claim 1, wherein said joining of the first product part to the second product part is by welding.

15. The process according to claim 14, wherein said welding of the hollow pallet deck and the hollow pallet skids includes welding selected from the group consisting of butt welding, friction welding and filler welding.

16. The process according to claim 14, wherein said welding of the hollow pallet deck and the hollow pallet skids includes welding selected from the group consisting of butt welding, friction welding and filler welding.

17. The process according to claim 14, wherein said welding is selected from the group consisting of ultrasonic welding, low frequency welding and rotation welding.

18. A molding process for the manufacture of a product comprising a hollow pallet deck and a at least one hollow pallet skid from a thermoplastic material selected from the group consisting of polyethylene, polypropylene and polybutylene, which product has no reinforcing additives, in a mold having a first mold half and a second mold half, which together includes a shape-giving cavity being a negative depiction of the respective product part, the method comprising:

forming one of either the pallet deck or the at least one skid, comprising;

providing two mold halves, at least one of the mold halves having a projection in the shape-giving cavity thereby forming at least one protrusion in a work piece formed in said mold half;

placing the mold halves so that a space is formed between the two mold halves and so that the shape-giving cavity of each mold half is directed toward each other;

heating two work pieces which constitute an upper half and a lower half of the product part, thereby softening the thermoplastic material;

shaping the work pieces toward the cavity of each mold half with the assistance of vacuum, blowing, and combinations thereof, to form shaped work pieces;

moving the mold halves relatively toward one another and pressing the shaped work pieces together while the thermoplastic material is still hot to form a unitary hollow product part with the upper and lower halves of said product part being joined along their edges and by said at least one protrusion to increase mechanical strength and dimension stability; and

cooling the first product part produced to the point where it can be removed from the mold though still at an elevated temperature; and

further cooling the first product part for 1-2 days until the first product part has reached room temperature and post shrinking has been achieved;

forming the other of the pallet deck or at least one skid, having a high creep strain resistance, no reinforcing additives, a mold, the mold having a first mold half and a second mold half, which together includes a shape-giving cavity being a negative depiction of the respective product part, the method comprising;

providing two mold halves, at least one of the mold halves having a projection in the shape-giving cavity thereby forming at least one protrusion in a work piece formed in said mold half;

placing the mold halves so that a space is formed between the two mold halves and so that the shape-giving cavity of each mold half is directed toward each other;

heating two work pieces which constitute an upper half and a lower half of the product part, thereby softening the thermoplastic material;

shaping the work pieces toward the cavity of each mold half with the assistance of vacuum, blowing, and combinations thereof, to form shaped work pieces;

moving the mold halves relatively toward one another and pressing the shaped work pieces together while the thermoplastic material is still hot to form a unitary hollow product part with the upper and lower halves of said product part being joined along their edges and by said at least one protrusion to increase mechanical strength and dimension stability; and

cooling the second product part produced to the point where it can be removed from the mold though still at an elevated temperature; and

further cooling the second product part for 1-2 days until the second product part has reached room temperature and post shrinking has been achieved; and

joining the hollow pallet deck and hollow pallet skids together.

19. The method of claim 18, comprising forming two hollow pallet decks and three hollow pallet skids.

20. The process according to claim 18, wherein said joining of the pallet deck and skid is by welding.

21. The process according to claim 20, wherein said welding is selected from the group consisting of ultrasonic welding, low frequency welding and rotation welding.