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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/30—Extrusion nozzles or dies
  • B29C48/32—Extrusion nozzles or dies with annular openings, e.g. for forming tubular articles
  • B29C48/335—Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles
  • B29C48/336—Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles the components merging one by one down streams in the die
• • 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
  • B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
• • 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
  • B29C48/16—Articles comprising two or more components, e.g. co-extruded layers
  • B29C48/18—Articles comprising two or more components, e.g. co-extruded layers the components being layers
  • B29C48/21—Articles comprising two or more components, e.g. co-extruded layers the components being layers the layers being joined at their surfaces

Definitions

• the present invention relates to a method and an article according to the preambles of the independent claims 1 and 7.
• polypropylene is normally forming the main layer of the walls of the containers.
• a barrier layer is as a rule included in the walls and enclosed by layers of polypro ⁇ pylene.
• Polypropylene is selected as it has an excellent capacity to withstand heating without deformation, it is approved by the autho ⁇ rities (e.g. F D ,A) and in addition is a cheap material.
• autho ⁇ rities e.g. F D ,A
• it has the drawback of a bad gloss which might give customers the impression of a bad finish which in turn sometimes incline the custo ⁇ mers to select a package of a different material, such as glass.
• At least one additional layer for gloss such as a layer of polycarbonate, polyamide or polyethylene terephthalate is added.
• the additional layers mean an increase in costs which are of importance in view of the large scale production of containers within the food packaging area.
• the present invention relates to a method and to an article wherein the problems and drawbacks described above are eliminated.
• the aim of the invention is obtained according to the technique defined in the characterising clause of claim 1 and the features defined in the characterising clause of claim 7.
• plastics material with low MFI forms support means for an outer and/or inner layer of plastics material with high MFI.
• plastics material with low MFI forms support means for an outer and/or inner layer of plastics material with high MFI.
• at least about 70 % and preferably at least about 80 % of the weight of the wall is related to plastics material with the low MFI. Said relationship makes certain that the material with the low MFI does not undergo any substantial elongation by influence 5 of the gravity before the extruded tube is enclosed by the mould and expanded to the article.
• the tube layers with the high MFI maintain their lengths.
• the material with the high MFI is heated to a temperature different from the temperature of the material with the low MFI.
• the temperature and the thickness of the material with the high MFI it is possible to improve the gloss properties of the article. If the material with the high MFI is heated to a temperature higher than the temperature of the material with the low MFI, the material is cooled rapidly when abutting the material with low MFI as the thickness of the material with high MFI is relatively small compared 5. to the thickness of the material with the low MFI.
• the material with the high MFI is heated to a 0 lower temperature than that of the material with the low MFI to avoid that the viscosity of the material with the high MFI is changed in such a way that the layer(s) formed varies too much in thickness, becomes too uneven or becomes ruptured.
• a high MFI very often means an improved gloss, again the gloss of for example the outer 5 layer(s) is improved, the layers are properly formed and the gloss of the article is improved.
• Fig. 1 shows an embodiment of an apparatus for coextrusion of a multi-layer tube 40 from which the article is formed.
• the apparatus includes a die head 10 comprising an outer portion 18 and a central 5 body 50.
• the outer portion has a number of channels 11-16 for feeding plastics materials into a main channel 19 which ends in a die 17.
• a circumferen ⁇ tial extended space forms the main channel 19.
• the cross section of the channel increases substantially stepwise each time the channels 12-16 end in the extended space (main channel).
• the central body 50 as well as the outer portion 18 have one or several channels 51 and 60, respectively, for fluid to maintain the central body 50 and the outer portion 18 at adjustable predetermined temperatures.
• the means include insulating members to maintain portions of the means separated by the insulating members at different temperatures. Such insulating members are in some embodiments provided between different channels 11-16. For each such part forming a thermally separated unit the fluid channels form a separate loop. 5
• Fig. 1 also shows a number of extruders 20-23 which are connected to the channels 11-16 by outlet channels 30-33.
• Feeding devices 24-27 shown as hoppers in the figure, are used to charge the extruders.
• Two of the outlet channels are in the disclosed embodiment connected to more than one of the channels 11-16 which in turn are connected to the main channel 19. It is evident to a person skilled in the art that the apparatus includes means (not shown in the figure) to arbitrarily connect a certain outlet channels to one or several of the channels of the outer portion 18. 15
• each additional layer is attached to the last of the layers already formed to form a laminated tube of substantially melted materials.
• the tube travels to the lower portion of the main channel 19 and through the die 17.
• a mould (not shown in the figure) encloses most of the projecting portion of the tube and separates the enclosed portion from the rest of the tube, whereupon the enclosed portion is expanded against the mould walls to form the article.
• the extruder 23 which is connected to the innermost channel 11 and the outermost channel 16 of the die head is fed with a plastics material of a higher MFI than that of the
• each layer is determined by the cross sections of the channels in the areas where each channel is 0 feeding its material into the main channel. As a consequence the thickness of each layer of the tube is substantially maintained when the layers pass through the main channel towards the die. As the plastics materials are in a melted condition, the materials are attached to each other when abutting.
• the next threee channels 13, 14, 15, which are situated between the channel 12 just mentioned and the outermost channel 16, are used to include barrier layers within the tube being produced.
• the third extruder 21 is connected to two 13, 15 of said three channels, the two channels ending into the main channel upstream and downstream an intermediate channel 14, which is connected to the fourth extruder 20.
• the third extruder 21 is charged with an adhesive and the fourth extruder 20 with the barrier material.
• the adhesive passes from the channel 13 into the main channel it forms an attachment means which connects the barrier material, downstream injected from the intermediate channel 14, to the last layer of plastic material already formed.
• adhesive is injected to the main channel from the next 15 of the channels to form an attachment means between the barrier layer and the outermost layer, fed into the main channel from the outermost channel 16.
• the tube thus formed is travelling downwardly within the main channel and passes through the die 17 to leave the die head.
• the main channel has a continuously reduced cross section at least in the initial portion of the die and/or in an area preceding the die.
• the tube substantially hangs down from the die head. It has to be noted that, while hanging down from the die head, the material of the tube is exposed to stretching forces depending on the gravity.
• the viscosity of the materials and the weight of the depending portion has to be balanced in order to obtain sufficient resistance against the. stretching forces and to avoid any substantial reduction of the thickness of the depending tube wall.
• the melt flow index (MFI) of the material which is used to form at least one of the defining layers of the tube wall, is higher than the MFI of the plastics materials constituting the remaining layers of the tube wall.
• the higher MFI is at last 4 and the lower MFI is equal to or less than 2.0 in case of polypropylene, e.g. homo-polypropylene or copolymer-polypropylene, especially random-copolymer-polypropylene.
• MFI could be as high as 9 and still the extending tube portion is capable of v/ithstanding the gravity without any substantial elongation.
• material with a high MFI has less capability at an increased temperature to withstand stretching forces without elongation, the thickness of the layer or layers with high
• MFI is in some embodiments reduced to let the thickness of the layer or layers consisting of plastics material of low MFI increase, whereby sufficient rigidity against elongation of the extended tube portion is obtained in order to avoid its elongation by means of the gravity.
• the plastics material with the higher MFI forms less than about 30 % of the weight of the article- preferably less than about 20 % of the weight.
• the values of MFI given above are measured at 230°C and at 21.5 N.
• the invention has been practiced for the production of articles by means 0 f coextrusion-parison-blow-moulding and using polypropylene sold by the company Himont under the trademark MOPLE.*!''*.
• H0PLEN EP2 S 12 B was used as the material with the low MFI and MOPLEfl EP2 x 29 G as the material with the high MFI.
• the material with the higher MFI is heated to a temperature which is different from the tempera ⁇ ture of the other materials. Normally, the temperature of the material with the higher MFI is not more than 40°C different from the most near of the increased temperatures of the other materials, preferably not more than 20°C. In some of the embodiments where the outer portion 18 of the die head as well as the central body 5 .
• thermoa- tures are kept such that the temperatures of the materials flowing through the channels 11-16 are either maintained or changed during the flow through said channels.
• the temperatures of the materials which from the outlet of the respective channel are fed into the main channel are set to a value adapted to obtain a good attachment to the already formed layers of the tube and to obtain the firmness or strength of the tube necessary to withstand the gravity when depending from the die head.
• the material with the higher MFI is heated to a temperature which is lower than the temperature of the other mate ⁇ rials and in other embodiments is heated to higher temperatures.
• the material with the higher MFI could be heated to a relatively high temperature to improve the gloss of the material, as the thin layer rapidly assumes the tempe ⁇ rature of the material supporting the material with the higher MFI.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)
• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20370368

Family Applications (1)

Country Status (2)

Cited By (1)

Citations (7)

• 1987
  • 1987-11-24 SE SE8704657A patent/SE8704657L/sv not_active Application Discontinuation
• 1988
  • 1988-11-24 WO PCT/SE1988/000642 patent/WO1989004754A1/en unknown

Patent Citations (7)

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