EP0377650A1 - Procede de production de mousses microcellulaires et mousses microcellulaires en materiaux polymeres semi-cristallins - Google Patents

Procede de production de mousses microcellulaires et mousses microcellulaires en materiaux polymeres semi-cristallins

Info

Publication number
EP0377650A1
EP0377650A1 EP19880908469 EP88908469A EP0377650A1 EP 0377650 A1 EP0377650 A1 EP 0377650A1 EP 19880908469 EP19880908469 EP 19880908469 EP 88908469 A EP88908469 A EP 88908469A EP 0377650 A1 EP0377650 A1 EP 0377650A1
Authority
EP
European Patent Office
Prior art keywords
microcellular
pressure
semi
polymeric material
temperature
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Withdrawn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
EP19880908469
Other languages
German (de)
English (en)
Inventor
Jonathan S. Colton
Nam P. Suh
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.)
Massachusetts Institute of Technology
Original Assignee
Massachusetts Institute of Technology
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 Massachusetts Institute of Technology filed Critical Massachusetts Institute of Technology
Publication of EP0377650A1 publication Critical patent/EP0377650A1/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Withdrawn legal-status Critical Current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
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B7/00—Mixing; Kneading
    • B29B7/74—Mixing; Kneading using other mixers or combinations of mixers, e.g. of dissimilar mixers ; Plant
    • B29B7/7404—Mixing devices specially adapted for foamable substances
    • B29B7/7409—Mixing devices specially adapted for foamable substances with supply of gas
    • B29B7/7428—Methodical aspects
    • 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
    • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
    • B29C44/10—Applying counter-pressure during expanding
    • B29C44/105—Applying counter-pressure during expanding the counterpressure being exerted by a fluid
    • 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
    • B29C44/3469—Cell or pore nucleation
    • B29C44/348—Cell or pore nucleation by regulating the temperature and/or the pressure, e.g. suppression of foaming until the pressure is rapidly decreased

Definitions

  • Microcellular foams have been made in the past by foaming amorphous polymeric materials such as polystyrene. This process involves cell nucleation at or near the glass transition temperature of the polymer material and is more thoroughly described in U.S. Patent 4,473,665 of Martini-Vvendensky, et al. This patent, however, does not teach foaming of semi-crystalline polymers such as polyethylene and polypropylene. Attempts to produce microcellular foamed articles from semi-crystalline polymers using the . method employed for amorphous polymers have proven to be failures. The three basic problems arising when icrocellularly foaming semi-crystalline polymers result from the polymers* icrostructure. They are as follows:
  • This invention pertains to closed cell micro ⁇ cellular foams of semi-crystalline polymeric materials and a method by which these microcellular foams are produced. More specifically, this invention per- tains to a method for producing closed cell micro ⁇ cellular foams from semi-crystalline polymeric materials comprising the steps of: a) saturating the semi-crystalline polymeric material at an elevated pressure and at a temperature at or above the melting temperature of the material with a uniform concentration of gas; b) shaping the polymeric material at an elevated pressure to substantially prevent cell nucleation within the material; c) reducing the pressure to supersaturate the polymeric material with gas and thereby produce a microcellular structure in said material, and d) lowering the temperature below the melting point of said polymeric material.
  • Polypropylene is used heavily in food container applications because it does not impart any flavor to the food contained within it, and because its thermal properties allow it to be filled with hot items.
  • a microcellular foam of this material would be ideal for food service applications due to its savings in raw materials (polypropylene) , its insulating ability, its strength and its inertness to flavors.
  • FIG. 1 is a schematic representation of a horizontal extrusion die system used in producing microcellular foam from a semi-crystalline polymeric material.
  • Figure 2 is a schematic representation of a vertical extrusion die system used in producing a microcellular foam from a semi-crystalline polymeric material.
  • Figure 3 is a schematic representation of an injection molding apparatus used in producing a microcellular foam from a semi-crystalline polymeric material.
  • This invention relates to microcellular foams of semi-crystalline polymers and a method for producing these foams.
  • the invention involves heating a semi-crystalline polymer to a temperature at or above its melting point.
  • a foaming gas is then supplied to diffuse into the molten polymer.
  • the polymer con- taining the diffused foaming gas is shaped, through extrusion, injection molding or other forming processes.
  • the polymeric body is subjected to a pressure reduction in the atmos ⁇ phere surrounding it which triggers the foaming process. Further cell growth is prevented by reducing the temperature to a point below the melting point of the polymeric material. This may be done, for example, by quenching the material with water.
  • Microcellular foam is a polymeric foam with cell sizes smaller than about 100 micrometers ( ⁇ m) and ideally in the range of about 5 to about 25 ⁇ m. These void diameters are found to be small enough to enhance or at least maintain the mechanical pro- perties of the parent polymer.
  • the crystalline domain of the material is a region in which the molecules have a regular and ordered arrangement. This may be contrasted to the amorphous domains in which the structure is more random and disordered. Due to the absence of polymers with an .absolute crystalline structure, the term semi-crystalline is used here, as in the art, to denote polymeric materials con ⁇ taining crystalline domains.
  • the glass transition temperature is distin ⁇ guished from the melting temperature as follows. Glasses are actually supercooled liquids of very high viscosity. The glass transition temperature is that temperature below which free rotations of the polymer molecules cease because of intermolecular forces. In this state, the material is glassy. Above the glass transition temperature, the polymer is rubbery. All polymers have a glass transition temperature. Semi-crystalline polymers also have a melting temperature above the glass transition temperature, above which the crystalline domains dissolve, leaving a fully amorphous material. Above the melting point, these polymers are viscous or viscoelastic materials.
  • FIG. 1 A schematic representation of a system for forming microcellular foams from crystalline polymers is shown in Figure 1.
  • An extruder 30, is loaded with polymer pellets 1. These pellets are heated to a temperature above their melting point and forced through the extrusion barrel 31 by a screw 32.
  • the molten polymer 10 is forced by the extrusion screw 32 into a horizontal extrusion die 20.
  • the die contains an aperture 22, through which gas at a high pressure can be pumped to allow interaction between the polymer 10 and the gas at the polymer/gas interface 40. At this interface 40, gas will dissolve into the molten polymer.
  • the polymer 10 then passes out of the die at exit 25, at which point foaming begins due to the reduced pressure on the polymer shape.
  • the material may then be quenched with cold water or other fluids to stop the foaming process.
  • the pressure can be increased prior to or during the reduction in temperature to further assist in preventing further cell growth.
  • Figure 2 is a schematic representation of a system similar to that depicted in Figure 1; however in Figure 2 the extrusion die 20' is in a vertical rather than a horizontal orientation.
  • the advantage of this orientation lies at the polymer/die seal 100.
  • This seal prevents the diffusion gas from escaping from the die 20* through the die exit 25'.
  • Gravitational force pulls the melted polymer 10 ' to the bottom of the die 20' thereby creating the seal 100 at a point anterior to the die exit 25'. This leads to a more uniform gas diffusion within the melted polymer 10'.
  • the operation of the system is similar to that depicted in Figure 1 and is described as follows.
  • An extruder 30' is loaded with polymer pellets 1*. These pellets are heated to a temperature above their melting point and forced through the extrusion barrel 31* by a screw 32'.
  • the molten polymer 10' is forced by the extrusion screw 32' into a verti ⁇ cally oriented extrusion die 20'.
  • the die contains an aperture 22', through which gas at a high pressure maybe pumped to allow interaction between the polymer 10 ' and the gas at the polymer gas interface 40'. At this interface 40', gas will dissolve into the molten polymer. Below this interface is the polymer/die seal 100 discussed previously.
  • the molten polymer 10' then passes out of the die at the die exit 25', at which point foaming begins due to the reduced pressure on the polymer shape.
  • the material may then be quenched with cold water or other fluids or an increase in pressure to stop the foaming process.
  • Figure 3 is a schematic representation of an injection molding system useful for producing microcellular foams from crystalline polymers.
  • the figure illustrates a number of known elements including an extruder 30'', extrusion barrel 31' ', extrusion screw 32", valve 44, nozzel 46, mold 48 and a clamping hydraulic pressure means 50.
  • the pressure in the mold 48 is maintained above the foaming pressure of the gas at melt temperatures for the given initial saturation.
  • the pressure is dropped and the part is allowed to foam.
  • a pressure substan ⁇ tially equal to that within the extrusion barrel 31" must be maintained within the mold cavity.
  • the pressure can be supplied by a moveable wall 52 under hydraulic pressure for simple part geometries.
  • the mold 48 When the nucleation temperature of the part is achieved the mold 48 is either expanded or cracked to allow the pressure to reach ambient pressure. The part will then expand as the polymer material foams to the final geometry.
  • Many currently existing injec ⁇ tion molding machines may be equipped with a move ⁇ able wall 52 to allow their use in this process.
  • gases can be used to supersaturate the polymeric material.
  • air noble gases (such as argon)
  • nitrogen or carbon dioxide can be used.
  • the pressure of the gas on the raw material should be high enough to provide uniform saturation.
  • Semicrystalline polymers, such as polyethylene and polypropylene, are ideal candidates for foaming due to their low cost and good physical properties. Satisfactory results have been obtained with gas saturation pressures between approximately 750 psig and 2500 psig for polypropylene. Saturation pressures below 750 psig have been found to result in unevenly saturated samples, resulting in uneven nucleation and bubble growth.
  • the foamed material resulting therefrom was found to contain a bubble density on the order of 10 bubbles per cubic centimeter with each bubble of 5 microns in dia ⁇ meter.
  • additives can be employed to enhance cell nucleation.
  • a material such as sodium benzoate can be added to enhance cell nucleation.
  • Foamed discs of semi-crystalline polymeric material were made by injection molding in the following manner.
  • a 2" diameter, 1/16" thick disc of the material to be foamed was placed in a pressure vessel and heated to a temperature above its melting point.
  • a temperature of approximately 173°C was found to be satisfactory.
  • the molten material was then saturated with 1500 psig of nitrogen for approximately 30 minutes.
  • the temperature of the material was then lowered and the pressure was released shortly thereafter. The drop in both temperature and pressure caused a spontaneous cell or bubble nucelation and growth within the material and resulted in a foamed part approximately 1/8" thick.
  • Himont copolymer 7823 polypropylene with 6.9% by weight ethylene
  • United States Steel copolymer polypropylene with 6.9% ethylene
  • Shell nucleated polypropylene 5524 Shell polypropylene 5384
  • Himont 101 polypropylene with 40% talc by weight
  • Microcellular foaming was most successful with the two copoly ers. This is likely the effect of two copolymer characteristics: a) a smaller dropoff of the temperature-viscosity relationship near the melting point, and, b) the existence of internal interfaces at which bubbles can nucleate.
  • the Shell nucleated polypropylene also foamed easily due to the large number of nucelation sites contained within the material.
  • the other Shell polypropylene did foam but not as easily as the others because its interfacial energy is not high enough to provide energy for foaming.
  • the talc-filled Himont was difficult to foam due to the very tight bonding between the talc particles and the polymer which interfered with foaming.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
  • Extrusion Moulding Of Plastics Or The Like (AREA)

Abstract

Procédé de production d'une mousse microcellulaire à partir d'un matériau polymère semi-cristallin. Le matériau est chauffé jusqu'à son point de fusion élevée puis il est saturé avec une concentration uniforme d'un gaz. La pression est ensuite abaissée pour provoquer une nucléation de bulles et une croissance dans le matériau. Le matériau est ensuite refroidi pour empêcher qu'il mousse davantage. Des bulles d'un diamètre de l'ordre de 5um sont produites, leur densité étant approximativement de 1010 bulles/cm3.
EP19880908469 1987-07-29 1988-07-28 Procede de production de mousses microcellulaires et mousses microcellulaires en materiaux polymeres semi-cristallins Withdrawn EP0377650A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US7925187A 1987-07-29 1987-07-29
US79251 1987-07-29

Publications (1)

Publication Number Publication Date
EP0377650A1 true EP0377650A1 (fr) 1990-07-18

Family

ID=22149362

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19880908469 Withdrawn EP0377650A1 (fr) 1987-07-29 1988-07-28 Procede de production de mousses microcellulaires et mousses microcellulaires en materiaux polymeres semi-cristallins

Country Status (2)

Country Link
EP (1) EP0377650A1 (fr)
WO (1) WO1989000918A2 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2803478A2 (fr) 2014-09-02 2014-11-19 Mondi Consumer Packaging Technologies GmbH Feuille à plusieurs couches en plastique
EP2815879A2 (fr) 2014-09-02 2014-12-24 Mondi Consumer Packaging Technologies GmbH Feuille de coextrusion en polyéthylène

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US5182307A (en) * 1990-11-21 1993-01-26 Board Of Regents Of The University Of Washington Polyethylene terephthalate foams with integral crystalline skins
US5158986A (en) 1991-04-05 1992-10-27 Massachusetts Institute Of Technology Microcellular thermoplastic foamed with supercritical fluid
US5223545A (en) * 1992-02-03 1993-06-29 The Board Of Regents Of The University Of Washington Polyethylene terephthalate foams with integral crystalline skins
NL9401055A (nl) * 1994-06-24 1996-02-01 Corell Resin Technology Bv Werkwijze voor het vervaardigen van een kunststof blad, alsmede met die werkwijze verkregen blad.
EP0692358A1 (fr) 1994-06-24 1996-01-17 Corell Resin Technology B.V. Procédé pour fabriquer une plaque en matière plastique et plaque ainsi obtenue
DE59607975D1 (de) * 1995-07-14 2001-11-29 Hennecke Gmbh Verfahren zur Herstellung von Polyurethanschaumformkörpern
WO1997006935A1 (fr) * 1995-08-14 1997-02-27 Massachusetts Institute Of Technology Dispositif d'etranglement a engrenage en tant que dispositif de nuceation dans un systeme d'extrusion en continu d'un materiau microcellulaire
US6884377B1 (en) 1996-08-27 2005-04-26 Trexel, Inc. Method and apparatus for microcellular polymer extrusion
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
US6884823B1 (en) 1997-01-16 2005-04-26 Trexel, Inc. Injection molding of polymeric material
AU742749B2 (en) * 1997-01-16 2002-01-10 Trexel, Inc. Injection molding of microcellular material
ATE226171T1 (de) * 1997-06-26 2002-11-15 Trexel Inc Mikrozellularer behälter und verfahren zum bewahren von produkten bei niedriger temperatur in diesem behälter
US6235380B1 (en) 1997-07-24 2001-05-22 Trexel, Inc. Lamination of microcellular articles
US6706223B1 (en) 1997-12-19 2004-03-16 Trexel, Inc. Microcelluar extrusion/blow molding process and article made thereby
EP1040158B2 (fr) 1997-12-19 2012-04-18 Trexel, Inc. Procede de moulage par extrusion/soufflage de materiaux micro-cellulaires et article obtenu
US6231942B1 (en) 1998-01-21 2001-05-15 Trexel, Inc. Method and apparatus for microcellular polypropylene extrusion, and polypropylene articles produced thereby
US6322347B1 (en) 1999-04-02 2001-11-27 Trexel, Inc. Methods for manufacturing foam material including systems with pressure restriction element
WO2001005569A1 (fr) * 1999-07-16 2001-01-25 Wavin B.V. Procede de formage d'un article comprenant une micromousse a alveoles fermees issue de thermoplastique
IT1319887B1 (it) * 2000-02-07 2003-11-12 Guala Dispensing Spa Chiusura per contenitori, in particolare tappo per bottiglie.
UA74582C2 (uk) * 2000-06-06 2006-01-16 Thermaflex Internat Holding B Спосіб одержання фізично спінених пінополіолефінів та пінополіолефіни, одержані цим способом
CN1189303C (zh) 2000-06-14 2005-02-16 旭化成株式会社 热塑性树脂的注射成型法
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ES2301388B1 (es) * 2006-10-17 2009-06-22 Jose Fernando Lopez Diaz Procedimiento y medios para la fabricacion de tuberias moldeadas con estructura craneal microcelular.

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2803478A2 (fr) 2014-09-02 2014-11-19 Mondi Consumer Packaging Technologies GmbH Feuille à plusieurs couches en plastique
EP2815879A2 (fr) 2014-09-02 2014-12-24 Mondi Consumer Packaging Technologies GmbH Feuille de coextrusion en polyéthylène

Also Published As

Publication number Publication date
WO1989000918A2 (fr) 1989-02-09
WO1989000918A3 (fr) 1989-03-09

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