EP1478501A1 - Optimisation de l'ecoulement destinee a empecher une percee de la couche centrale - Google Patents

Optimisation de l'ecoulement destinee a empecher une percee de la couche centrale

Info

Publication number
EP1478501A1
EP1478501A1 EP03706008A EP03706008A EP1478501A1 EP 1478501 A1 EP1478501 A1 EP 1478501A1 EP 03706008 A EP03706008 A EP 03706008A EP 03706008 A EP03706008 A EP 03706008A EP 1478501 A1 EP1478501 A1 EP 1478501A1
Authority
EP
European Patent Office
Prior art keywords
interior
flow
stream
velocity
streams
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Withdrawn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
EP03706008A
Other languages
German (de)
English (en)
Inventor
Douglas Sabin
Paul Swenson
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.)
Kortec Inc
Original Assignee
Kortec Inc
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 Kortec Inc filed Critical Kortec Inc
Publication of EP1478501A1 publication Critical patent/EP1478501A1/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Withdrawn legal-status Critical Current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
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/16—Making multilayered or multicoloured articles
    • B29C45/1642—Making multilayered or multicoloured articles having a "sandwich" structure
    • B29C45/1646—Injecting parison-like 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
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/16—Making multilayered or multicoloured articles
    • B29C45/1642—Making multilayered or multicoloured articles having a "sandwich" structure

Definitions

  • This invention relates to an injection molding process, and in particular, a method and apparatus for preventing an interior layer from breaking through a flow front made up of at least one inner and one outer layer in an injection molding process.
  • plastic articles are formed by injection molding processes. These articles include common items such as test tubes and pre-forms for forming items such as beer and ketchup bottles. Many of these articles are produced from injection molding machines having the ability to inject multiple plastic layers at the same time (i.e., co- injection). Thus, the injection-molded articles may have two or more layers of plastic in their final form (i.e., multi-layer plastic articles).
  • a common configuration of multi-layer plastic articles includes an interior or "core" plastic layer, which is surrounded on substantially all sides by an outer plastic layer.
  • core plastic layer For example, see U.S. Pat. Nos. 5,914,138 and 6,187,241, both assigned to Kortec, Inc. The disclosures of both of these patents are incorporated herein by reference.
  • the interior (core) layer is formed of a material such as Ethyl Vinyl Alcohol (EVOH), and the inner and outer layers are formed from a material such as Polyethylene Terephtholate (PET) or Polypropylene (PP).
  • EVOH Ethyl Vinyl Alcohol
  • PET Polyethylene Terephtholate
  • PP Polypropylene
  • a common problem in multi-layer molding is maintaining a uniform penetration of the leading edge of the interior layer when the interior layer is not near the zero gradient of the velocity profile of the flowing polymer stream as it flows through the hot runner nozzle and/or in the mold cavity forming the molded article. This problem particularly occurs when there are reasons to form a multi-layer article wherein the interior layer is not centered on the mid-plane of the article.
  • three-layer molding when molding a tube shaped article with one closed end containing the part gate, it may be desirable for the leading edge of the interior layer to be very close to the far end of the article.
  • the container closure is applied to the open end it is desirable to minimize the area of the container below the seal, which does not contain interior layer. This is particularly true if the interior layer is a high barrier material with permeation rates that are less than 10% of the skin. In this case any area of the container without interior layer barrier material, can become a significant leak and raise the total container permeability.
  • U.S. Patent 4.751,035 describes a method in which the interior layer is folded over by the sequential injection of materials across the zero-velocity-gradient streamline. In fold over the core (interior) material will break through when it reaches the flow front, hi this method, some portion of the interior is always on the zero-velocity- gradient streamline.
  • a method of co-extruding a plurality of plastic material flowing streams into a mold cavity to produce a molded product is provided.
  • Inner and outer streams of covering plastic materials are combined with at least one interior stream that is to serve as an interior core layer of a resulting molded plastic product.
  • the combined streams are forced to flow along annular flow paths, with the interior stream encased within the inner and outer annular covering plastic material stream layers.
  • the flows of the interior stream and the inner and outer streams are controlled so that: the interior stream has a flow velocity that is greater than an average velocity of the combined streams, and the interior core stream does not flow along or across a zero-velocity-gradient streamline of the combined streams.
  • Figure 1 is a cross sectional view of an injection molding system according to a first exemplary embodiment of the present invention.
  • Figure 2 shows a velocity profile for the injection molding system of
  • Figure 3 shows the injection of material in an article before the interior flow catches up with the flow front.
  • Figure 4 shows the injection of material in the article of Figure. 3 shortly after the interior flow catches up with the flow front.
  • Figure 5 shows the injection of material in the article of Figure. 4 some time after the interior flow catches up with the flow front.
  • One exemplary embodiment provides a method and apparatus for extruding plastic articles to change the relative volumetric flow rate of the skin layers and the interior core layer, so that no part of the interior layer is on the zero-velocity gradient of the combined flow thereby preventing break though of the interior (core) layer tlirough the flow front formed by the inner and outer skin layers.
  • the interior layer By moving the interior layer away from the zero velocity gradient to a slower moving streamline that has a velocity that is greater that the average velocity, the interior layer can "catch up" to the fountain flow and wrap over, creating uniform coverage of the molded part.
  • the interior layer may be located either inside or outside the location of the zero-velocity gradient creating wrap over toward the inside or outside of the part, respectively.
  • Figure 1 shows a cross section of an injection molding system according to a first exemplary embodiment of the present invention.
  • Figure 1 shows the velocity profile 120 at the end of the nozzle 100 having a throttle pin 110.
  • Figure 1 also shows the velocity profile 160 near the flow front 140 in an article 130, such as a container perform.
  • the flow front moves* at an average velocity V avg .
  • Figure 3 shows an injection molding system where a interior layer is disposed to flow on an offset streamline through a nozzle and into the a mold cavity.
  • Core breakthrough may occur during the sequential injection of materials that are injected across the zero-velocity gradient.
  • the zero velocity gradient occurs at the point where the velocity of the flow is greatest. Because the flow at the zero velocity gradient point is greater than the average velocity of the flow front, the interior material injected at the zero velocity gradient point can, under some circumstances, "catch up” to and pass the flow front and break through the skin, even if injection of the interior material begins after injection of the PET or PP inner and outer layers.
  • the interior (core) material will breakthrough when the interior material reaches the flow front at the zero velocity gradient.
  • FIG. 1 also shows the velocity profile 160 near the flow front 140 in article 130. Because the interior (core) material 170 is injected along a streamline having a velocity greater than the average flow velocity, but less than the velocity Vmax at the zero velocity gradient 150, the interior flow 170 wraps around near the flow front 140. [0022] This method creates good part coverage, because the leading edge is uniform due to the fact that no portion of the interior layer is on the zero-velocity gradient.
  • the interior (core) layer is placed so that no portion of the interior (core) layer is on the zero velocity gradient and so the interior (core) layer is on a streamline that has a velocity higher than the average flow velocity V avg . If the interior layer is on a streamline having a velocity lower than the average flow velocity, the interior layer can never catch up to the flow front, and does not wrap around. So long as the interior layer is in between the streamline having the average velocity and the zero velocity gradient streamline, then the interior layer can catch up to the flow front, but will wrap around on itself, instead of breaking through the flow front.
  • the hatched area shows the acceptable location for interior layer placement that is both greater than the average velocity and off the zero velocity gradient. This area will wrap the layer to the inside of the part. From the graph we can see that the flow fraction of the inside layer can be in a range from 0.1 to 0.45.
  • the flow fraction of the outside layer can be from 0.9 to 0.55.
  • the interior layer thickness can be as thick as 0.45.
  • the interior layer 170 has just reached the fountain flow region adjacent to the flow front 140 and has begun to wrap around to form a "hook" shapel71.
  • the interior layer is inside the zero velocity gradient line, so the interior layer 170 wraps around towards the inside of the article.
  • the interior layer wrap method is distinct from other multi-material processes creating fold over because it us created by a interior stream of material following in a streamline that wraps when it reaches the fountain flow portion at the flow front. Additionally, because no portion of the interior layer that is wrapping is on the zero-velocity gradient the interior layer will theoretically never break through the skin. This method creates uniform part coverage because a non-uniform leading edge can wrap when it reaches the flow front staying close to the flow front without breaking through. [0030] Because the interior layer is displaced from the maximum velocity streamline, the interior layer never catches up to and passes the flow front. Injection of the interior layer can begin at the same time as, or very shortly after, the skin layer material.
  • the interior layer injection should begin soon enough after the skin injection so that the interior layer catches up to the flow front. Once the interior layer catches up with the flow front and wraps around, the "hook" portion of the interior layer propagates forward and stays close to the flow front, so that the portion of the interior layer doubled upon itself elongates without breaking through the skin layers.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)

Abstract

Cette invention concerne un procédé de co-extrusion d'une pluralité de flux de matière plastique dans une cavité de moule en vue de l'obtention d'un produit moulé. A cette fin, on utilise à l'extrémité de la buse (100) un profil de vitesse d'écoulement (120) doté d'un doigt d'étranglement (110), dont un profil de vitesse d'écoulement (160) près du front d'écoulement (140) dans un article (130) lorsque le front d'écoulement (140) se déplace à vitesse moyenne. La matière centrale (170) est injectée selon une ligne de flux dont la vitesse est supérieure à la vitesse moyenne des flux combinés, mais inférieure à la vitesse maximum de gradient zéro (150), le flux intérieur ne s'écoulant pas le long ou en travers de la ligne de flux de gradient zéro des flux combinés.
EP03706008A 2002-01-31 2003-01-31 Optimisation de l'ecoulement destinee a empecher une percee de la couche centrale Withdrawn EP1478501A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US35359602P 2002-01-31 2002-01-31
US353596P 2002-01-31
PCT/US2003/002867 WO2003064133A1 (fr) 2002-01-31 2003-01-31 Optimisation de l'ecoulement destinee a empecher une percee de la couche centrale

Publications (1)

Publication Number Publication Date
EP1478501A1 true EP1478501A1 (fr) 2004-11-24

Family

ID=27663229

Family Applications (1)

Application Number Title Priority Date Filing Date
EP03706008A Withdrawn EP1478501A1 (fr) 2002-01-31 2003-01-31 Optimisation de l'ecoulement destinee a empecher une percee de la couche centrale

Country Status (2)

Country Link
EP (1) EP1478501A1 (fr)
WO (1) WO2003064133A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2544870B1 (fr) 2010-03-08 2018-05-09 Milacron LLC Procédés de moulage d'articles polymères multicouches commandant la percée de la couche centrale
CA2802328C (fr) 2010-07-16 2019-06-04 Kortec, Inc. Impermeabilite au gaz amelioree pour contenants moules par injection
WO2012071497A1 (fr) 2010-11-24 2012-05-31 Kortec, Inc. Procédé permettant d'éviter l'échec d'un scellage à chaud, et article
US8491290B2 (en) 2011-10-21 2013-07-23 Kortec, Inc. Apparatus for producing non-symmetric multiple layer injection molded products

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4174413A (en) * 1976-07-27 1979-11-13 Asahi-Dow Limited Multi-layered molded articles
US6063325A (en) * 1996-08-22 2000-05-16 Continental Pet Technologies, Inc. Method for preventing uncontrolled polymer flow in preform neck finish during packing and cooling stage
US5914138A (en) * 1996-09-27 1999-06-22 Kortec, Inc. Apparatus for throttle-valving control for the co-extrusion of plastic materials as interior core streams encased by outer and inner streams for molding and the like
CA2253042C (fr) * 1998-11-05 2007-04-17 Jobst Ulrich Gellert Methode de moulage par injection a trois couches avec co-injection sequentielle et simultanee

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO03064133A1 *

Also Published As

Publication number Publication date
WO2003064133A1 (fr) 2003-08-07

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