PatentDe  


Dokumentenidentifikation EP0971812 28.11.2002
EP-Veröffentlichungsnummer 0971812
Titel VERFAHREN UND GERÄT ZUR HERSTELLUNG EINES EXTRUSIONSERZEUGNISSES UND EXTRUSIONSERZEUGNIS
Anmelder Uponor Innovation AB, Fristad, SE
Erfinder JÄRVENKYLÄ, Jyri, FIN-15870 Hollola, FI;
LAHTINEN, Terho, FIN-00200 Helsinki, FI;
SJÖBERG, Michael, S-723 40 Västeras, SE
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 69624516
Vertragsstaaten AT, BE, CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, LI, LU, MC, NL, PT, SE
Sprache des Dokument EN
EP-Anmeldetag 20.09.1996
EP-Aktenzeichen 969310879
WO-Anmeldetag 20.09.1996
PCT-Aktenzeichen PCT/FI96/00502
WO-Veröffentlichungsnummer 0097010940
WO-Veröffentlichungsdatum 27.03.1997
EP-Offenlegungsdatum 19.01.2000
EP date of grant 23.10.2002
Veröffentlichungstag im Patentblatt 28.11.2002
IPC-Hauptklasse B29C 47/88

Beschreibung[en]

The present invention relates to a method for making an extrusion product, in which method an extrusion material is extruded by an extruder from its extrusion portion through a tool and fluoropolymer is used between the extrusion material and the tool for reducing friction between the extrusion material and the tool.

The present invention further relates to an apparatus for making an extrusion product, which apparatus comprises an extrusion portion for extruding an extrusion material and a tool through which the extrusion material is extruded and fluoropolymer is arranged to be used between the extrusion material and the tool as a slip agent.

The present invention also relates to a product made by the method.

It is essential in the production of crosslinked polyethylene, for example, that the material will flow well against the walls of the tool situated after the screw of the extruder in such a manner that the friction heat generated therein would remain so low that crosslinking cannot start too early. The kinds of polyethylene suitable for producing crosslinked pipes, for example, flow very badly on account of their high molecular weight. On account of low extrusion heat and great viscosity mentioned above, the extrusion process is rather abrupt so that the temperature of the screw and of the cylinder will easily rise too high because of the generated friction heat.

In plastic industry extrusion tools are mainly manufactured of easily machineable hard tool steel or possibly of stainless steel. In order to improve wear resistance required for cleaning processes, for instance, tools are generally chrome plated. EP 0 507 613 discloses that a tool is coated with polytetrafluoroethylene. Polytetrafluoroethylene reduces friction very efficiently and the plastic material will slip steadily along the surface of the tool on account of it. When machining plastics with a high molecular weight, polytetrafluoroethylene will wear off very fast from the surface of the tool during the extrusion process. Therefore it is necessary to halt the extrusion process for adding a new polytetrafluoroethylene layer to the tool. This re-coating has to be carried out even daily. Thus halting the process and starting it again, and wear and addition process of polytetrafluoroethylene will easily raise the costs considerably high. Excessive wear of polytetrafluoroethylene can easily be seen in the final product, too, as the quality of the surface suffers easily. Typically the inner surface of the pipe can become coarse or plastic fluff can be found there. Poor characteristics are not necessarily visible in the outer surface of the pipe, but in microscopic measuring unevenness will become evident. The preamble of the independent claims is based on the document EP 0507613.

WO 94/21441 puts forth a solution to the above-mentioned problem where instead of using polytetrafluoroethylene, a layer of a sacrificial thermosetting material is extruded between the extrusion product and the tool. As in most cases the layer will have to be removed from the surface of the product after extrusion, the invention is complicated and difficult to realize.

WO 92/11125 discloses that a slip agent is added to a plastic material. However, if the slip agent is added to a product which has a high molecular weight, for example, and which requires strong machining, it will result in that on account of its slipperiness, the plastic material will easily become disengaged from the screw in melting zone and the plastic material will come out of the extruder unmolten.

WO 92/19809 discloses a roller for heat treatment of a web of material, in which the web is cooled to a defined, predetermined temperature in a gap between the roller and a mating roller. DE 4412799 discloses a cooling mandrel for cooling extruded plastic foam. The mandrel comprises a frame and a helical element arranged on the frame. The helical element is tubular and the cooling medium flows through it.

The object of the present invention is to provide a method and an apparatus for making an extrusion product where the disadvantages mentioned above can be avoided. A further object is to provide an extrusion product with good characteristics.

The method according to the invention is characterized in that at least the surface of the tool against fluoropolymer is of a material whose thermal conductivity is greater than the thermal conductivity of ordinary tool steel, whereby the friction heat generated is conducted efficiently away from the interface between the tool and the extrusion material towards the tool.

Further, the apparatus according to the invention is characterized in that at least the surface of the tool against fluoropolymer, at least partly at the smallest cross-section, is of a material whose thermal conductivity is greater than the thermal conductivity of ordinary tool steel.

In addition, the product made by the method according to the invention is characterized in that the surface of the product is essentially smooth without transverse microscopic stripes repeated at a specific wave length.

Particular embodiments of the invention are the subject of the respective dependent claims.

The essential idea of the invention is that there is fluoropolymer, such as polytetrafluoroethylene, between the tool and the plastic material to be extruded for reducing friction between the plastic material and the tool and that at least the surface of the tool against fluoropolymer is of a material whose thermal conductivity is greater than the thermal conductivity of ordinary tool steel, whereby the friction heat generated can be conducted fast away from the interface towards the tool. A further idea of one preferred embodiment is that there is a wear resistant coating on the surface of the tool, such as DLC, which comprises pores filled with a fluoro compound, such as polytetrafluoroethylene. The idea of a second preferred embodiment is that there is a slip agent layer essentially comprising a fluoro compound between the coating of the tool and the plastic material. Most preferably the intermediate layer comprises at least partly a fluoro compound, such as fluoro-elastomer, which is supplied into the plastic, and which migrates to abutment surfaces. The idea of a third embodiment is that the fluoro compound forming the slip agent is extruded between the plastic layer and the tool primarily after plastic melting zone just before the nozzle of the tool.

The advantage of the invention is that when at least the surface of the tool is of a material that conducts heat well, the friction heat generated can be conducted efficiently away from the interface of the plastic material to be extruded and the tool, whereby temperature control of the tool will be very good and the temperature will not rise even at the interface too high for polytetrafluoroethylene, for example. It has been unexpectedly found out that by conducting heat away from the interface, the wear resistance of polytetrafluoroethylene, for example, has been considerably improved. In an ordinary tool, although the temperature of the tool is adjusted e.g. to 250°C, polytetrafluoroethylene will wear rather easily from it even though the melting temperature of polytetrafluoroethylene is more than 300°C. Because of friction, the temperature at the interface exceeds the highest temperature allowed for polytetrafluoroethylene, wherefore polytetrafluoroethylene will wear off easily. By means of the method according to the invention, temperature is prevented from rising too high at the interface and thus wear resistance of the tool will improve. DLC is very wear resistant and when its pores are filled with a fluoro compound, the friction between the tool and the plastic material to be extruded will be very small. By forming a slip agent layer between the abutment surfaces of the tool and the plastic material, the material can slip very well along the surface of the tool, but the slip agent layer does not disturb the machining of the actual plastic material, whereby the plastic material may be crosslinked polyethylene that is difficult to machine. By supplying the slip agent between the plastic material to be extruded and the tool primarily after plastic melting zone, the friction heat can also be utilized very efficiently in the melting and machining zone of the actual plastic material.

The invention will be explained in more detail in the accompanying drawings, in which

  • Figure 1 shows a schematic cross-sectional side view of one apparatus according to the invention,
  • Figure 2 shows a schematic cross-sectional side view of a second apparatus according to the invention,
  • Figure 3 shows a schematic cross-sectional side view of a third apparatus according to the invention, and
  • Figure 4a shows a measuring result from the surface of a pipe of an unsatisfactory quality,
  • Figure 4b illustrates Fourier analysis of the measuring according to Figure 4a,
  • Figure 5a shows a measuring result of the surface of a pipe made with the method according to the invention, and
  • Figure 5b illustrates Fourier analysis of the measuring according to Figure 5a.

Only the end portion of an extruder portion 1 of an extruder is shown in the appended figure for the sake of clarity in such a manner that the end of a screw portion 1a of the extruder portion 1 and the end of a cylinder portion 1b are visible in the figure. The extruder may be any extruder known per se, an ordinary screw extruder, for example. A tool 2 is arranged to the end of the extruder portion 1. The tool 2 comprises a nozzle outside the extrusion product and a mandrel 4 inside it. The tool 2 can be of any ordinary type, such as a tool having a mandrel carrier provided with a spiral divider, a so-called basket die-head tool having a perforated supporter, a tool having a mandrel carrier secured to the head of a screw, or a so-called crosshead tool. These detailed features have been omitted from the appended figures for the sake of clarity. The extrusion product, a pipe 5 for example, is extruded from between the nozzle 3 and the mandrel 4. The extrusion product can be in addition to the pipe 5 a cable sheath or a film or any such product.

The surfaces of the tool 2 against the plastic material to be extruded are coated with fluoroplastic, most preferably with polytetrafluoroethylene for attaining as good slip characteristics as possible. Before polytetrafluoroethylene is coated, the surfaces of the tool are applied a material whose thermal conductivity is better than that on the other parts of the tool 2 in case the tool 2 is manufactured of tool steel, for example. Thermal conductivity of tool steel is generally about 30 W/mK. Tool steel is easy to machine and also hard enough, thus making it very wear resistant. The coating may be e.g. of beryllium copper alloy whose thermal conductivity is about 200 W/mK or more. By means of this coating, the friction heat caused by friction between the plastic material and the tool 2 may be efficiently conducted away from the interface of the plastic material to be extruded and the tool towards the tool 2. It has also been found in tests that then the temperature at the interface can be dropped as much as 30°C. On account of the dropped temperature, polytetrafluoroethylene does not wear off as fast as in earlier applications. Because of friction heat, temperature at the interface has earlier risen easily too high for polytetrafluoroethylene, even if the tool were cooled at other parts. The tests showed that even a drop of 10°C in this critical zone reduces wear of polytetrafluoroethylene and thus adds significantly to the service life of the tool. The temperature of the interface can be dropped by using coating, for example, with a thermal conductivity of over 100 W/mK. The tool 2 may also be of a material with a better thermal conductivity than tool steel.

In addition to using a material with good thermal conductivity, the tool can be coated e.g. with a thin chromium polytetrafluoroethylene coating or a so-called diamond like coating (DLC) where the pores are filled with a fluoro compound, such as polytetrafluoroethylene. DLC resists wear very well and the fluoro compound, which fills the pores, reduces friction between the plastic material and the tool 2.

The nozzle 3 has a tempering unit 6 provided with oil circulation, for example. A similar tempering unit 6 has also been arranged to the mandrel 4. By means of the tempering units 6, the temperature of the nozzle 3 and the mandrel 4 can be controlled as required by passing heat thereto or removing it therefrom.

The method and the apparatus according to the invention is in principle suitable for all extrusion that requires accurate adjustment of temperature and good slip characteristics. For example, in the drive of polyethylene foam, very low temperatures have to be used and because of exothermic reaction, heat has to be removed efficiently from the process. In orientation processes, for example, a typical melt flow causes disturbances in the actual orientation stage of molecules and thus it is preferable that the friction between the plastic material and the tool is reduced with polytetrafluoroethylene. High temperature is a particular problem especially when making crosslinked polyethylene pipes. It is especially difficult to use a material with a high molecular weight for making the product. The method and the apparatus according to the invention is also suitable to be used for materials whose average molecular weight is more than 200,000 g/mol.

Figure 2 shows a schematic cross-sectional side view of a second apparatus according to the invention. The numbers in Figure 2 correspond to those of Figure 1. The extruder according to Figure 2 produces a three-layered product whose outer layer 5b and inner layer 5c preferably form a slip agent layer comprising essentially fluoroplastic, such as polytetrafluoroethylene. Because of these slip agent layers, the extrusion material slips very well along the surface of the tool 2. The coating on the surface of the tool 2, which conducts heat well, causes extra heat to be led efficiently away from the interface, whereby the highest allowed temperature sustainable for the used fluoroplastic will not be exceeded. More preferably, the outer layer 5b and the inner layer 5c comprise at least partly a fluoro compound, such as fluoroelastomer, which is supplied into the plastic, and which migrates to the abutment surfaces of the tool 2 and reduces friction. Differing from the appended figure, the outer layer 5b and the inner layer 5c can be considerably thinner than the middle layer 5a, whereby they form an outer skin and inner skin of the pipe 5. Therefore the slip agent can only be used for thin skins and the effect of the slip agent does not disturb the machining of the material in a middle layer 5a. The middle layer 5a may be crosslinked polyethylene that is difficult to machine.

Figure 3 shows a schematic cross-sectional side view of a third apparatus according to the invention. The numbers in Figure 3 correspond to those of Figures 1 and 2. The extruder contains a first supply channel 7a and a second supply channel 7b, by means of which the outer layer 5b and the inner layer 5c can be supplied to the outside and inside of the middle layer 5a of the extrusion material. The supply channels 7a and 7b are arranged to supply a slip agent layer containing fluoroelastomer or fluoroplastic to the outside and inside of the extrusion material just before the tool 2. In that case, the middle layer 5a can be melted and machined in the extruder portion 1 by using the effect of friction heat very efficiently, as the slip agent layers are supplied to the extruder after plastic melting zone. In Figure 3 the second supply channel 7b is arranged inside the feed screw but it can also be arranged to supply the material from outside through the middle layer 5a. However, forming of a joining seam can be avoided by the solution of Figure 3.

In case the flow of the extrusion material changes so that pure friction flow changes in part into melt flow, transverse stripes are formed in the product, that is, a pattern repeated regularly at distances from about less than a millimetre to some millimetres can be detected in the product. This pattern may not necessarily be visible. In microscopic measurings these transverse stripes can be detected. When handling measuring result mathematically by Fourier analysis, it has been detected that unevenness occurs at regular distances, the distance generally varying between from about less than one millimetre to some millimetres. The method and apparatus of the invention makes the extrusion product slip evenly on the surface of the tool, wherefore unevenness cannot be seen essentially on the surface of the extrusion product.

Figure 4a shows a result of a microscopic measuring from a surface of an unsatisfactory pipe. On X axle the outer surface of the pipe is on a profilometer and the coarseness of the pipe is on Y axle. The unevenness visible in the figure is not necessary visible for the naked eye, but as can be seen in the appended figure, unevenness can be clearly detected in microscopic measuring.

Figure 4b shows a Fourier analysis of measuring according to Figure 4a. Sequentiality of unevenness can be clearly detected in the Fourier analysis, a sequence being 0.81 mm at wave length. Finding a specific wave length proves that the flow of the plastic material is not steady, but pure friction flow has partly changed into melt flow.

Figure 5a shows a microscopic measuring of a pipe made with the method according to the invention. It can be seen in Figure 5a that the surface has been fairly even. A Fourier analysis shown in Figure 5b is also made of the measuring of Figure 5a and it proves that now sequential unevenness cannot be detected.

The drawing and the specification related thereto are only intended to illustrate the idea of the invention. In its details the invention may vary within the scope of the claims.


Anspruch[de]
  1. Verfahren zum Herstellen eines Extrusionsprodukts, bei dem ein Extrusionsmaterial mittels eines Extruders aus dessen Extrusionsabschnitt (1) heraus durch ein Werkzeug (2) hindurch extrudiert wird, und zwischen dem Extrusionsmaterial und dem Werkzeug (2) Fluorpolymer verwendet wird, um die Reibung zwischen dem Extrusionsmaterial und dem Werkzeug zu reduzieren,

    dadurch gekennzeichnet, dass mindestens die mit dem Fluorpolymer in Kontakt befindliche Oberfläche des Werkzeugs (2) ein Material aufweist, dessen Wärmeleitfähigkeit höher ist als die Wärmeleitfähigkeit gewöhnlichen Werkzeug-Stahls, wobei die erzeugte Reibungswärme effizient von dem Interface zwischen dem Werkzeug (2) und dem Extrusionsmaterial weg zu dem Werkzeug (2) hin geleitet wird.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Temperatur des Werkzeugs mittels einer Temperierungseinheit (6) wie erforderlich eingestellt wird.
  3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Extrusionsprodukt ein Produkt mit mindestens zwei Schichten ist und dass in dem Kunststoff der mit dem Werkzeug (2) in Kontakt befindlichen Schicht eine Fluorverbindung eingeführt wird, die zu den Anlageflächen des Werkzeugs wandert.
  4. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Extrusionsprodukt ein mindestens drei Schichten aufweisendes Kunststoffrohr (5) mit einer Außenseite und einer Innenseite ist, wobei in den Kunststoff der Außenseite und der Innenseite eine Fluorverbindung, wie z.B. Fluorelastomer, eingeführt wird, die zu den Anlageflächen wandert, und dass eine Mittelschicht (5a) des Rohrs (5) im wesentlichen aus einem Material besteht, das kein Gleitmittel aufweist.
  5. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass ein Gleitmittel, das Fluorelastomer oder der Fluorkunststoff enthält, zwischen dem zu extrudierenden Kunststoffmaterial und dem Werkzeug (2) extrudiert wird, und zwar hauptsächlich hinter der Kunststoffschmelzzone vor dem Werkzeug (2).
  6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Wärmeleitfähigkeit mindestens der mit dem Fluorpolymer in Kontakt befindlichen Oberfläche des Werkzeugs (2) höher als 100 W/mK ist.
  7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Wärmeleitfähigkeit mindestens der mit dem Fluorpolymer in Kontakt befindlichen Oberfläche des Werkzeugs (2) höher als 200 W/mK ist.
  8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, dass mindestens die mit dem Fluorpolymer in Kontakt befindliche Oberfläche des Werkzeugs (2) eine Beryllium-Kupfer-Legierung aufweist.
  9. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass als Extrusionsmaterial ein Kunststoffmaterial mit einem mittleren Molekulargewicht von mehr als 200.000 g/mol verwendet wird.
  10. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Extrusionsprodukt ein vernetztes Polyethylen-Rohr (5) ist.
  11. Vorrichtung zum Herstellen eines Extrusionsprodukts, mit einem Extrusionsabschnitt (1) zum Extrudieren eines Extrusionsmaterials und einem Werkzeug (2), durch das hindurch das Extrusionsmaterial extrudiert wird, wobei zwischen dem Extrusionsmaterial und dem Werkzeug (2) Fluorpolymer als Gleitmittel (2) verwendet wird,

    dadurch gekennzeichnet, dass mindestens die mit dem Fluorpolymer in Kontakt befindliche Oberfläche des Werkzeugs (2) zumindest an dessen kleinstem Querschnitt ein Material aufweist, dessen Wärmeleitfähigkeit höher ist als die Wärmeleitfähigkeit gewöhnlichen Werkzeug-Stahls.
  12. Vorrichtung nach Anspruch 11, dadurch gekennzeichnet, dass das Werkzeug (2) eine Temperierungseinheit (6) zum Steuern der Temperatur des Werkzeugs (2) aufweist.
  13. Vorrichtung nach Anspruch 11 oder 12, dadurch gekennzeichnet, dass an mindestens einigen Stellen die Oberfläche des Werkzeugs in der axialen Richtung eine Chrom-Polytetrafluorethlyen-Beschichtung oder eine DLC-Bechichtung aufweist, in der Poren mit einer Fluorverbindung gefüllt sind.
  14. Vorrichtung nach einem der Ansprüche 11 bis 13, dadurch gekennzeichnet, dass die Vorrichtung eine Einrichtung zu Herstellung eines dreidimensionalen Produkts ist.
  15. Vorrichtung nach Anspruch 14, dadurch gekennzeichnet, dass die Vorrichtung eine Einrichtung aufweist, um ein Gleitmittel, das Fluorelastomer oder Fluorkunststoff enthält, zwischen dem zu extrudierenden Kunststoffmaterial und dem Werkzeug (2) zu extrudieren, und zwar hauptsächlich hinter der Kunststoffschmelzzone vor dem Werkzeug (2).
  16. Vorrichtung nach einem der Ansprüche 10 bis 15, dadurch gekennzeichnet, dass die Wärmeleitfähigkeit mindestens der mit dem Fluorpolymer in Kontakt befindlichen Oberfläche des Werkzeugs (2) höher als 100 W/mK ist.
  17. Vorrichtung nach Anspruch 16, dadurch gekennzeichnet, dass die Wärmeleitfähigkeit mindestens der mit dem Fluorpolymer in Kontakt befindlichen Oberfläche des Werkzeugs (2) höher als 200 W/mK ist.
  18. Produkt, hergestellt durch das Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Oberfläche des Produkts im wesentlichen glatt und frei von sich mit einer bestimmten Wellenlänge wiederholenden querverlaufenden mikroskopischen Streifen ist.
  19. Produkt nach Anspruch 18, dadurch gekennzeichnet, dass das Produkt ein mindestens drei Schichten (5a,5b,5c) aufweisendes Rohr (5) ist, wobei mindestens die äußeren und inneren Schichten (5b,5c) ein Gleitmittel aufweisen, das eine Fluorverbindung enthält.
  20. Produkt nach Anspruch 19, dadurch gekennzeichnet, dass die äußere Schicht (5b) und die innere Schicht (5c) eine Außenseite und eine Innenseite des Rohrs (5) bilden.
  21. Produkt nach Anspruch 19 oder 20, dadurch gekennzeichnet, dass die mittlere Schicht (5a) ein Material aufweist, dessen mittleres Molekulargewicht mehr als 200.000 g/mol beträgt.
  22. Produkt nach Anspruch 21, dadurch gekennzeichnet, dass die mittlere Schicht (5a) hauptsächlich im wesentlichen vernetztes Polyethylen aufweist, das kein Gleitmittel enthält.
Anspruch[en]
  1. A method for making an extrusion product, in which method an extrusion material is extruded by an extruder from its extrusion portion (1) through a tool (2) and fluoropolymer is used between the extrusion material and the tool (2) for reducing friction between the extrusion material and the tool, characterized in that at least the surface of the tool (2) against fluoropolymer is of a material whose thermal conductivity is greater than the thermal conductivity of ordinary tool steel, whereby the friction heat generated is conducted efficiently away from the interface between the tool (2) and the extrusion material towards the tool (2).
  2. A method according to claim 1, characterized in that the temperature of the tool is adjusted as required with a tempering unit (6).
  3. A method according to claim 1 or 2, characterized in that the extrusion product is a product with at least two layers and that a fluoro compound is supplied into the plastic of the layer against the tool (2) the fluoro compound migrating to the abutment surfaces of the tool (2).
  4. A method according to any one of the preceding claims, characterized in that the extrusion product is a plastic pipe (5) with at least three layers comprising an outer skin and an inner skin, whereby a fluoro compound, such as fluoroelastomer, is supplied into the plastic of the outer skin and the inner skin, the fluoro compound migrating to the abutment surfaces, and that a middle layer (5a) of the pipe (5) is essentially of a material that does not contain a slip agent.
  5. A method according to any one of the preceding claims, characterized in that a slip agent containing fluoroelastomer or fluoroplastic is extruded between the plastic material to be extruded and the tool (2) primarily after plastic melting zone before the tool (2).
  6. A method according to any one of the preceding claims, characterized in that the thermal conductivity of at least the surface of the tool (2) against fluoropolymer is greater than 100 W/mK.
  7. A method according to any one of the preceding claims, characterized in that the thermal conductivity of at least the surface of the tool (2) against fluoropolymer is greater than 200 W/mK.
  8. A method according to claim 7, characterized in that at least the surface of the tool (2) against fluoropolymer is of beryllium copper alloy.
  9. A method according to any one of the preceding claim-scharacterized in that a plastic material with an average molecular weight of more than 200,000 g/mol is used as the extrusion material.
  10. A method according to any one of the preceding claims, characterized in that the extrusion product is a polyethylene pipe (5) that is crosslinked.
  11. An apparatus for making an extrusion product, which apparatus comprises an extrusion portion (1) for extruding an extrusion material and a tool (2) through which the extrusion material is extruded and fluoropolymer is arranged to be used between the extrusion material and the tool (2) as a slip agent, characterized in that at least the surface of the tool (2) against fluoropolymer, at least partly at the smallest cross section, is of a material whose thermal conductivity is greater than the thermal conductivity of ordinary tool steel.
  12. An apparatus according to claim 11, characterized in that the tool (2) comprises a tempering unit (6) for controlling the temperature of the tool (2).
  13. An apparatus according to claim 11 or 12, characterized in that at least in some places the surface of the tool comprises in the axial direction a chrome polytetrafluoroethylene coating or DLC where pores have been filled with a fluoro compound.
  14. An apparatus according to any one of claims 11 to 13, characterized in that the apparatus comprises means for making a three-layered product.
  15. An apparatus according to claim 14, characterized in that the apparatus comprises means for extruding a slip agent containing fluoroelastomer or fluoroplastic between the plastic material to be extruded and the tool (2) primarily after plastic melting zone before the tool (2).
  16. An apparatus according to any one of claims 10 to 15, characterized in that the thermal conductivity of at least the surface of the tool (2) against fluoropolymer is greater than 100 W/mK.
  17. An apparatus according to claim 16, characterizedin that at least the surface of the tool (2) against fluoropolymer is of beryllium copper alloy whose thermal conductivity is more than 200 W/mK.
  18. A product made by the method according to claim 1, characterized in that the surface of the product is essentially smooth without transverse microscopic stripes repeated at a specific wave length.
  19. A product according to claim 18, characterized in that the product is a pipe (5) comprising at least three layers (5a, 5b, 5c), whereby at least the outer and inner layers (5b, 5c) comprise a slip agent containing a fluoro compound.
  20. A product according to claim 19, characterized in that the outer layer (5b) and the inner layer (5c) form an outer skin and an inner skin of the pipe (5).
  21. A product according to claim 19 or 20, characterized in that the middle layer (5a) comprises a material whose average molecular weight is more than 200,000 g/mol.
  22. A product according to claim 21, characterized in that the middle layer (5a) primarily comprises essentially crosslinked polyethylene that does not contain a slip agent.
Anspruch[fr]
  1. Procédé de fabrication d'un produit extrudé, dans lequel procédé un matériau pour l'extrusion est extrudé par une extrudeuse dans sa partie extrusion (1) à travers un outil (2) et un fluoropolymère est utilisé entre le matériau à extruder et l'outil (2) destiné à réduire la friction entre le matériau à extruder et l'outil, caractérisé en ce qu'au moins la surface de l'outil (2) contre le fluoropolymère est constituée d'un matériau dont la conductivité thermique est supérieure à la conductivité thermique de l'acier ordinaire pour outils, moyennant quoi la chaleur de friction est évacuée de façon efficace de l'interface entre l'outil (2) et le matériau à extruder vers l'outil (2).
  2. Procédé selon la revendication 1, caractérisé en ce que la température de l'outil est ajustée en fonction des besoins à l'aide d'une unité de régulation thermique(6).
  3. Procédé selon la revendication 1 ou 2, caractérisé en ce que le produit extrudé est un produit ayant au moins deux couches et en ce qu'un composé fluoré est fourni dans le plastique de la couche contre l'outil (2), le composé fluoré migrant vers les surfaces de butée de l'outil (2).
  4. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le produit extrudé est un tube en plastique (5) ayant au moins trois couches comprenant une peau extérieure et une peau intérieure, moyennant quoi un composé fluoré, tel que le fluoroélastomère, est fourni dans le plastique de la peau extérieure et de la peau intérieure, le composé fluoré migrant vers les surfaces de butée, et en ce qu'une couche médiane (5a) du tube (5) est essentiellement constituée d'un matériau qui ne contient pas d'agent lubrifiant.
  5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce qu'un agent lubrifiant contenant du fluoroélastomère ou du fluoroplastique est extrudé entre le matériau plastique à extruder et l'outil (2) principalement après la zone de fusion du plastique avant l'outil (2).
  6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la conductivité thermique au moins de la surface de l'outil (2) contre le fluoropolymère est supérieure à 100 W/mK.
  7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la conductivité thermique au moins de la surface de l'outil (2) contre le fluoropolymère est supérieure à 200 W/mK.
  8. Procédé selon la revendication 7, caractérisé en ce qu'au moins la surface de l'outil (2) contre le fluoropolymère est constituée d'alliage de béryllium et de cuivre.
  9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce qu'un matériau plastique ayant un poids moléculaire moyen supérieur à 200 000 g/mol est utilisé comme matériau à extruder.
  10. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le produit extrudé est un tube en polyéthylène (5) qui est réticulé.
  11. Appareil de fabrication d'un produit extrudé, lequel appareil comprend une partie extrusion (1) pour extruder un matériau à extruder et un outil (2) à travers lequel le matériau à extruder est extrudé et un fluoropolymère est disposé pour être utilisé entre le matériau à extruder et l'outil (2) comme agent lubrifiant, caractérisé en ce qu'au moins la surface de l'outil (2) contre le fluoropolymère, au moins partiellement au niveau de la plus petite section transversale, est constitué d'un matériau dont la conductivité thermique est supérieure à la conductivité thermique de l'acier ordinaire des outils.
  12. Appareil selon la revendication 11, caractérisé en ce que l'outil (2) comprend une unité de régulation thermique (6) pour le contrôle de la température de l'outil (2).
  13. Appareil selon la revendication 11 ou 12, caractérisé en ce que, au moins à certains endroits, la surface de l'outil comprend, dans la direction axiale, un revêtement de polytétrafluoroéthylène chrome ou DLC dans lequel les pores ont été remplis avec un composé fluoré.
  14. Appareil selon l'une quelconque des revendications 11 à 13, caractérisé en ce que l'appareil comprend les moyens pour fabriquer un produit à trois couches.
  15. Appareil selon la revendication 14, caractérisé en ce que l'appareil comprend les moyens pour extruder un agent lubrifant contenant du fluoroélastomère ou du fluoroplastique entre le matériau en matière plastique à extruder et l'outil (2) principalement après la zone de fusion du plastique avant l'outil (2).
  16. Appareil selon l'une quelconque des revendications 10 à 15, caractérisé en ce que la conductivité thermique au moins de la surface de l'outil (2) contre le fluoropolymère est supérieure à 100 W/mK.
  17. Appareil selon la revendication 16, caractérisé en ce qu'au moins la surface de l'outil (2) contre le fluoropolymère est en alliage de béryllium et de cuivre dont la conductivité thermique est supérieure à 200 W/mK.
  18. Produit fabriqué par le procédé selon la revendication 1, caractérisé en ce que la surface du produit est essentiellement lisse sans rayures microscopiques transversales répétées à une longueur d'onde spécifique.
  19. Produit selon la revendication 18, caractérisé en ce que le produit est un tube (5) comprenant au moins trois couches (Sa, 5b, 5c), moyennant quoi au moins les couches externe et interne (5b, 5c) comprennent un agent lubrifant contenant un composé fluoré.
  20. Produit selon la revendication 19, caractérisé en ce que la couche externe (5b) et la couche interne (5c) forment une peau extérieure et une peau intérieure du tube (5).
  21. Produit selon les revendications 19 et 20, caractérisé en ce que la couche médiane (Sa) comprend un matériau dont le poids moléculaire moyen est supérieur à 200 000g/mol.
  22. Produit selon la revendication 21, caractérisé en ce que la couche médiane (Sa) comprend principalement du polyéthylène essentiellement réticulé qui ne contient pas d'agent lubrifiant.






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