EP1112157A1 - Procede et dispositif d'extrusion d'articles en mousse - Google Patents

Procede et dispositif d'extrusion d'articles en mousse

Info

Publication number
EP1112157A1
EP1112157A1 EP99941890A EP99941890A EP1112157A1 EP 1112157 A1 EP1112157 A1 EP 1112157A1 EP 99941890 A EP99941890 A EP 99941890A EP 99941890 A EP99941890 A EP 99941890A EP 1112157 A1 EP1112157 A1 EP 1112157A1
Authority
EP
European Patent Office
Prior art keywords
nucleator
molten mass
molten
plastic
pressed
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP99941890A
Other languages
German (de)
English (en)
Inventor
Hans Overeijnder
Stephan Henricus Maria Koopmans
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Wavin BV
Original Assignee
Wavin BV
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 Wavin BV filed Critical Wavin BV
Publication of EP1112157A1 publication Critical patent/EP1112157A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/468—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length in a plurality of parallel streams which unite during the foaming
    • 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
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/46—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length
    • B29C44/50—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying
    • B29C44/507—Feeding the material to be shaped into an open space or onto moving surfaces, i.e. to make articles of indefinite length using pressure difference, e.g. by extrusion or by spraying extruding the compound through an annular die

Definitions

  • the present invention relates to a method for extruding foamed articles from thermoplastic, in which a molten mass comprising heated, pressurized plastic which is mixed with a foaming agent is pressed through a nucleator and an orifice which shapes the article and is then cooled.
  • a molten mass comprising heated, pressurized plastic which is mixed with a foaming agent is pressed through a nucleator and an orifice which shapes the article and is then cooled.
  • a chemical foaming agent which decomposes in the extruder, such as for example azodicarbonamide.
  • Another option is firstly to melt the plastic in the extruder and then to add a chemical or physical foaming agent and to mix this with the molten mass .
  • plastic foam with small cells which generally has better mechanical qualities than in homogeneous or coarse plastic foam
  • the plastic is essential for the plastic to be intimately mixed with the foaming agent.
  • a physical foaming agent which may be added in the form of a liquid (such as pentane or a chlorofluorohydrocarbon) , a gas (such as nitrogen) or a supercritical liquid (such as carbon dioxide)
  • a molten mass which is as homogeneous as possible and in which the foaming agent is dissolved in the plastic.
  • WO 98/08667 furthermore describes a method (Fig. 14 and the associated description on pages 31 et seq) in which a separate nucleator is not employed, but rather a simple narrowed section of the gap in the extrusion head serves as a nucleator.
  • This method is only suitable for forming thin- walled articles, such as a wire insulation. When this method is used for products with thicker walls, however, it does not produce a microfoam.
  • the object of the invention is to provide a method for extruding foamed articles from thermoplastic, by means of which it is possible to extrude articles with wall thicknesses from one to several tens of millimetres and with a microfoam structure . This object is achieved by means of the method according to claim 1.
  • the invention also relates to an apparatus for extruding foamed articles made from thermoplastic material according to claim 9.
  • Fig. 1 shows a longitudinal section through the end part of an extrusion head with a nucleator mounted thereon
  • Fig. 2 diagrammatically depicts, on a larger scale, detail A from Fig. 1 with a specific embodiment of the nucleator,
  • Figs. 3 and 4 diagrammatically depict, on a larger scale, detail A from Fig. 1 with another embodiment of the nucleator, with different flow patterns of the molten mass,
  • Fig. 5 shows a highly diagrammatic plan view of an extrusion line for the extrusion of foamed articles
  • Figs . 6 and 7 show foam structures which are formed respectively without and with the use of the method according to the invention.
  • Fig. 1 shows a longitudinal section through an end part of an extrusion head, which is denoted overall by 1, for forming a hollow section, in particular a pipe, from foamed plastic.
  • the extrusion head 1 is intended to be mounted on an extruder (not shown here) .
  • the extrusion head 1 comprises an outer cone 2 and an inner cone 3, which delimit an annular channel 4.
  • a molten material which comes out of the extruder and comprises heated, pressurized plastic which is mixed with a foaming agent is pressed through this channel 4.
  • a nucleator assembly 5 is mounted on the outlet side of the extrusion head 1.
  • This nucleator assembly 5 comprises an annular nucleator 6 and a nucleator holder 7, comprising two plates 8 and 9 between which the nucleator 6 is clamped in place.
  • the entire assembly is attached concentrically to the extrusion head 1 by means of bolts 10 .
  • the nucleator 6 comprises a multiplicity of fine channels and preferably comprises 1 or more screens with a mesh width of from 50-500 ⁇ m, preferably 100-300 ⁇ m. If appropriate, coarser screens may be arranged on the outlet side for reinforcement purposes. The number of screens is dependent on the viscosity of the molten material and on the pressure drop which is desired. In the case of a highly viscous molten mass, fewer screens are generally required than in the case of a low-viscosity molten mass.
  • the nucleator 6 may also comprise one or more perforated plates with holes of from 50-500 ⁇ m, preferably 100-300 ⁇ m.
  • the holes may be formed by means of laser perforation.
  • the nucleator 6 will often be of planar design, since this leads to the most simple structure.
  • nucleator 6 For example those described in WO 98/08667, may also be used.
  • molten mass comprising heated, pressurized plastic which has been mixed with a foaming agent
  • a foam structure with very small cells is formed in the molten mass. Since the nucleator 6 is located downstream, as seen in the direction of extrusion, of the orifice which is formed by the outer cone 2 and the inner cone 3 of the extrusion head 1 and shapes the article to be extruded, molten material which comes out of the nucleator 6 is now subjected to scarcely any shear forces which could damage the walls of the foam cells.
  • a particularly good and very fine microfoam structure is obtained if the molten material which comes out of the nucleator 6 is subjected to brief compression, during which it is ensured that no shear forces, or only slight shear forces, are generated in the molten mass.
  • This brief compression which helps the small streams of foamed plastic coming out of the nucleator 6 to weld together, can be realized in various ways.
  • a planar nucleator instead of a planar nucleator it is possible to use a curved nucleator, as shown in Fig. 2.
  • This nucleator 6 is of concave design on the outlet side. As a result, the small streams of foamed plastic which come out of the nucleator 6 are pressed forcefully against one another .
  • the welding together of the small streams of foamed plastic which come out of the nucleator 6 can also be improved by guiding the molten mass which comes out of the nucleator 6 through a narrowed section 11 which is relatively short, as seen in the direction of flow.
  • the desired effect can only be achieved without damage to the foam structure if the narrowed section 11 is short.
  • Good results are achieved with a narrowed section of a length of from 3-5 mm for a diameter of the extruded plastic pipe of 50 mm.
  • the narrowed section 11 is used in combination with a planar nucleator 6.
  • Another possibility for improving the welding together of the small streams of foamed plastic which come out of the nucleator 6 without damaging the foam structure consists in axially stretching the molten mass which comes out of the extrusion head 1 and the nucleator 6. This obviously causes the wall thickness of the extruded section to decrease, as depicted in Fig. 4.
  • the axial stretching of the section may, if appropriate, be combined with guiding the extruded article through a narrowed section 11.
  • a pressure drop takes place in the nucleator at a rate of at least 0.05 GPa/sec, and preferably between 0.2 and 1.0 GPa/sec.
  • the pressure itself has to fall from the pressure which prevails in the extrusion head 1, and is often between 10 and 50 MPa, to (virtually) atmospheric pressure.
  • the foamed, optionally stretched section which comes out of the extrusion head and the nucleator 6 is cooled in the conventional way in order to obtain the desired dimensional stability.
  • An extrusion line which is used in tests comprises two single-screw extruders 21 and 22 which are arranged in tandem and have a screw diameter of 120 mm, as extremely diagrammatically depicted in plan view in Fig. 5.
  • the first extruder 21 is used to plasticize the molten mass and to inject the foaming agent, in this case a gas (nitrogen or carbon dioxide) .
  • a feed hopper 23 for feeding the plastic material is mounted on the first extruder 21.
  • the outlet of the first extruder 21 is connected to the second extruder 22 for cooling the molten material and dissolving the gas in the molten material.
  • An extrusion head 24 which is normally used to extrude PVC pipes, is provided, on the outlet side, with a nucleator in the form of three screens with a mesh width of 250 ⁇ m and a wire thickness of 200 ⁇ m.
  • the extrusion line is followed by the conventional equipment such as vacuum calibration and cooling, stretching unit and saw.
  • the extrusion line described above is used to produce a polypropylene microfoam pipe with a diameter of 50 mm and a wall thickness of 4 mm.
  • the conventional polypropylene grade was a standard copolymer.
  • the foaming agent used was nitrogen. At a production rate of 50 kg/h of polypropylene, 0.75% by weight of nitrogen was used.
  • the temperature of the mixture coming out of the first extruder 21 was approx. 210°C.
  • the second extruder 22 the mixture was homogenized and cooled to approx. 180°C. After leaving the extrusion head 24, the pipe was stretched by running the stretching unit at double speed.
  • the diameter of the foam cells varied between 10 and 50 ⁇ m.
  • Figs . 6 and 7 show foam structures which are obtained respectively without and with the use of the method according to the invention.
  • the enlargement factor is 25. It can clearly be seen in Fig. 6 that if the method according to the invention is not used, the result is a coarse, irregular foam structure, while if the method according to the invention is used, the result is a very fine, regular foam structure.
  • thermoplastic materials such as polypropylene, polyethylene, polyvinyl chloride, polystyrene, etc.

Landscapes

  • Extrusion Moulding Of Plastics Or The Like (AREA)

Abstract

Lors de l'extrusion d'articles en mousse, réalisés dans des matières thermoplastiques, on mélange une masse en fusion comprenant une matière plastique chauffée et mise sous pression, avec un agent d'expansion, on comprime ce mélange d'abord à travers un orifice (4), lequel met en forme l'article, puis à travers un dispositif de nucléation (6), et on refroidit ensuite l'article, ce qui permet d'obtenir une structure très fine à microparticules de mousse. On obtient des résultats particulièrement bons si on comprime la matière en fusion pendant une courte période, immédiatement après que celle-ci ait quitté le dispositif de nucléation, cette compression étant exécutée de manière qu'il ne se produise aucune force de cisaillement, ou uniquement des forces de cisaillement légères, dans la masse en fusion.
EP99941890A 1998-09-10 1999-09-07 Procede et dispositif d'extrusion d'articles en mousse Withdrawn EP1112157A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
NL1010057A NL1010057C2 (nl) 1998-09-10 1998-09-10 Werkwijze en inrichting voor het extruderen van geschuimde voorwerpen.
NL1010057 1998-09-10
PCT/NL1999/000552 WO2000015405A1 (fr) 1998-09-10 1999-09-07 Procede et dispositif d'extrusion d'articles en mousse

Publications (1)

Publication Number Publication Date
EP1112157A1 true EP1112157A1 (fr) 2001-07-04

Family

ID=19767789

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99941890A Withdrawn EP1112157A1 (fr) 1998-09-10 1999-09-07 Procede et dispositif d'extrusion d'articles en mousse

Country Status (4)

Country Link
EP (1) EP1112157A1 (fr)
AU (1) AU5536499A (fr)
NL (1) NL1010057C2 (fr)
WO (1) WO2000015405A1 (fr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9522772B2 (en) 2006-04-03 2016-12-20 Lbp Manufacturing Llc Insulating packaging
US9648969B2 (en) 2006-04-03 2017-05-16 Lbp Manufacturing Llc Insulating packaging
US20130303351A1 (en) 2006-04-03 2013-11-14 Lbp Manufacturing, Inc. Microwave heating of heat-expandable materials for making packaging substrates and products
CN104590757B (zh) 2006-04-03 2018-03-30 Lbp制造有限责任公司 可热激发的绝缘包装物
US8404324B2 (en) 2010-04-14 2013-03-26 Braskem America, Inc. Polypropylene compositions
PL2611588T3 (pl) 2010-09-01 2020-06-01 Lbp Manufacturing, Inc. Sposób wytwarzania podłoża wielowarstwowego do opakowania

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1592960A (en) * 1977-12-24 1981-07-15 Sekisui Plastics Process for producing expanded article of thermoplastic resin
DE4422568C1 (de) * 1994-06-28 1996-02-15 Bayer Ag Verfahren und Vorrichtung zur Schaumherstellung mittels unter Druck gelöstem Kohlendioxid
EP0923443B1 (fr) * 1996-08-27 2002-11-27 Trexel Inc. Procede et dispositif pour l'extrusion de mousse de polymeres, en particulier de mousse microcellulaire

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0015405A1 *

Also Published As

Publication number Publication date
WO2000015405A1 (fr) 2000-03-23
NL1010057C2 (nl) 2000-03-13
AU5536499A (en) 2000-04-03

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