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
  • B29C48/022—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the choice of material
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/06—Condition, form or state of moulded material or of the material to be shaped containing reinforcements, fillers or inserts

Definitions

• the invention relates to a dispersion section, suitable for rotatable incorporation in the barrel of an extruder, of which the enveloping shell has the shape of a cylinder, and in the external surface of said section at least a pair of spirally shaped channels is present, consisting of an inlet channel and an outlet channel, which are each bounded by a first and a second flank, which channels each have an input end and a discharge end, with the input end of the inlet channel of each pair being open and the discharge end closed while of the outlet channel the discharge end is open and the inlet end closed.
• thermoplastic materials are melted and mixed with other materials with the aid of an extruder after which the mixture is brought into in a desired shape.
• An example of another material are fibres which are dispersed in a thermoplastic material in an extruder for manufacturing fibre- reinforced thermoplastic objects.
• DE-A-2,461 ,631 describes the use of a known dispersion section, called Egan dispersion section, in an extruder in a process for manufacturing fibre-reinforced thermoplastic objects. In this publication no further details are given of the dimensions of the dispersion section. Due to the forces occurring, fibre degradation also takes place during dispersion.
• the dispersion of the fibres in the thermoplastic material should be as homogeneous as possible while fibre degradation should be minimal.
• the disadvantage of the known dispersion section is that a very homogeneous dispersion cannot be achieved without the occurrence of fibre degradation that has a strongly adverse effect on the mechanical strength of the material.
• the invention aims to provide a dispersion section that, when incorporated in an extruder screw, gives less fibre degradation than the known dispersion section upon dispersion of the fibres in a thermoplastic material to a certain measure of homogeneity.
• first flank is wider than the second one and with a first radial clearance fits in the extruder barrel, and wherein the ratio of the width of the first flank and the first radial clearance lies between 25 and 750.
• thermoplastic material containing a thermoplastic material and fibres
• a dispersion section incorporated in an extruder screw
• the dispersed material possesses better mechanical properties, such as for example the Izod impact strength, than a corresponding material obtained with the known dispersion section.
• the dispersion section according to the invention is particularly suitable for the homogeneous dispersion of bundles of glass fibres or other fibres, like natural polymeric fibres, in which the bundle as a whole or each of the fibres in it, separately or in smaller subgroups, are surrounded by a thermoplastic material.
• Examples of other fibres suitable for processing with the dispersion section according to the invention are aramid, carbon and steel fibres.
• Such bundles can be manufactured for example by impregnating and/or enveloping a long fibre bundle with melted thermoplastic material and chopping the impregnated and/or enveloped bundle obtained into rod-shaped pieces of suitable length, hereafter indicated as granulate.
• the dispersion section according to the invention fibres with a length between 0.1 mm and a length equal to the length of the first flank of the dispersion section can be processed.
• fibres with a length between 5 and 50 mm are applied, and preferably fibres with a length between 10 and 30 mm.
• thermoplastic materials that can be mixed homogeneously in combination with one or more of the said types of fibres while using the dispersion section according to the invention are polypropylene, polyethylene, polyamides, polyethylene terephthalate, polybutylene terephthalate, polyphenyl sulphide, thermoplastic urethanes, polyoxymethylene and polycarbonate.
• Fig. 1 is an open view of an extruder, in which a dispersion section according to the invention forms part of the extruder screw;
• Fig. 2 is a cross-section of the dispersion section from Fig. 1 along the line A-A;
• Fig. 3 is a development on the dispersion section from Fig. 1 ;
• Fig. 4 is a cross-section along the line B-B in Fig. 3;
• Fig. 5 is a development on a dispersion section, in which the first flank is provided with a raised part running along the inlet channel;
• Fig. 6 is a cross-section along the line C-C in Fig. 5.
• Fig. 1 2 is an extruder with a cylindrical barrel 4 with axis 6 and an extrusion die 8.
• an extruder screw is rotatably incorporated.
• such a screw consists of a number of screw sections capable of rotation around a common axis that each fulfil a specific function or combinations of functions. Examples of such functions are transport, melting, mixing and dispersion.
• barrel 4 in Fig. 1 are shown a transport section 10 and a cylindrical dispersion section 14, which are rotatable around axis 6.
• the enveloping shell of the dispersion section conceived as passing through the points with the largest radial cross-section, is at a first radial distance 16 from shell 4.
• Further 18 is a first channel that forms a pair with a second channel 20.
• the screw direction of the channels relative to the direction of rotation of the screw indicated by arrow 22 and thus to the dispersion section in the extruder has been so chosen that the dispersion section exerts a forward force on the material in the channels and thus also has a transport effect.
• the pitch angle that is the angle between the axial direction 6 and the direction of the bounding walls 24 and 26 of the channels, is between 30 and 60°, and preferably between 40 and 50°. This angle is indicated by in Fig. 3 and Fig. 5.
• the channels may have a rectangular cross-section with a flat base, but the channels may also have a curved cross-section, for example in the form of a circle segment.
• One skilled in the art will know how to choose, if the need arises, the shape and area of the cross-section depending on the desired transport capacity of the dispersion section. It is also possible for the cross- sectional area of the channels to vary along their longitudinal direction, for example the depth or the width of the inlet channel can decrease from the open end.
• Inlet channel 18 is open on the inlet side 28 and closed on the outlet side 30.
• Outlet channel 20 is closed on inlet side 32 and open on outlet side 34.
• Open here means that there is a direct connection with a preceding or following element, for example a screw section or extruder die, so that on an open side material can directly enter a channel or material can be discharged from a channel to a following element.
• a preceding or following element for example a screw section or extruder die
• On a closed side such material transport is not possible and with a continuing supply of material from the preceding screw section the material will have to leave the channel and be transported to an adjacent channel through the rotary movement of the dispersion section relative to the extruder barrel over a flank, called the kneading or overflow flank.
• Second flank 40 is higher than flank 38 and fits almost sliding into barrel 4, so that this flank 40 ensures that the material that remains behind in clearance 36 relative to the movement of flank 38 is again scraped off and entrained, the material entering channel 20.
• This flank is bounded by two walls 26 and 24, which slope down to the base of channel 18 and channel 20, respectively. Because outlet channel 20 is open on the outlet side 34, the material can subsequently be discharged through this channel from the dispersion section to the following screw section or, in the case described, to the die 8 of the extruder.
• the material which contains a thermoplastic material and fibres, is thus transported from inlet channel 18 to outlet channel 20 over the first flank 38. Due to the difference in velocity between the material that is in contact with the stationary inside wall and the material that is in contact with the flank 38, which moves relative to the inside wall, shearing of the material takes place. The degree of shearing that takes place should be high enough to ensure that the fibres reaching channel 20 are sufficiently dispersed. This is achieved through a suitable choice of the above-mentioned distance H and the width of the first flank 38. To this end, the width of the first flank 38, which in the development of Fig. 3 and of Fig. 5 is indicated with L, is greater than that of the second flank 40.
• L generally lies between 0.2 and 0.8 x the circumference of the dispersion section.
• the ratio between L and the above-mentioned clearance H, IJH, should be between 25 and 750 and is preferably between 50 and 300. At lower values the shearing that takes place generally appears to be insufficient for bringing about good dispersion of the fibres. At higher values too much fibre degradation occurs so that the reinforcing effect of the fibres in the composition is lost.
• a third relevant dimension of the dispersion section is the length A thereof, which is understood to be the distance from the input end of the inlet channel to the discharge end of the outlet channel measured in the axial direction.
• This length A is preferably chosen to be between 2 and 10 times the diameter D of the dispersion section at the location of the second flank 40.
• the values of A in combination with those of H are preferably so chosen that there is no pressure drop across the dispersion section during the intended operation. For this it is necessary that the transport capacity of the dispersion section is at least equal to the flow rate of the quantity of material supplied by the preceding screw section.
• the transport capacity Q per revolution of the extruder screw over the first flank is calculated with the formula
• v is the peripheral velocity ⁇ .D.n. of the dispersion section and n the number of revolutions per minute of the extruder screw.
• the ratio L/H is a measure of the shearing that is imposed.
• a further advantage of the dispersion section according to the invention now is that through a suitable choice of these quantities L and H the shearing effected by the section can easily be set to a desired value. This can take place for example by first determining the suitable shearing to be imposed in order to obtain a desired dispersion of a certain material as the required numerical value for the IJH ratio using an apparatus by means of which a defined shearing can be imposed on a material, for example a Couette apparatus. Subsequently, in conjunction with the diameter D from that defined value, the suitable values of and H for the dispersion section can be determined.
• the clearance 42 between flank 40 and the barrel 4 of extruder 2 is chosen to be so small that flank 40 fits virtually sliding into barrel 4, which means that at the prevailing pressures, in combination with the viscosity of the material, transport through that space is negligible relative to the transport via the channels over the first flank 38.
• This clearance as a rule lies between 10 "4 x D and 0 "2 x D and is very suitably chosen between 0.3 x 10 "3 x D and 3 x 0 "3 x D.
• the dispersion section is preferably provided with upright edges 44 and 46 along the circumference of the ends, which leave only such small clearances 16 between these edges and the extruder barrel that transport through that space is negligible at the prevailing pressures in combination with the viscosity of the material.
• edges 44 and 46 usually provide the bearing of the dispersion section in the extruder barrel.
• the clearances 16 are chosen in the same area as defined above for the clearance 42.
• the size H of the clearance 36 may also increase, in general virtually proportionally. If this results in H getting a size comparable to the diameter of the granulate used in the unmelted state, the granulate can be transported in unmelted condition over flank 38 so that the desired dispersion of the fibres is not achieved.
• a raised part indicated by 50 in Figs. 5 and 6, can be provided, which leaves a clearance between that raised part and the extruder barrel that is smaller than the diameter of the unmelted granulate. Suitable values range from 0.1 to 0.8 x the diameter of the granulate.
• clearance 36 Preferably the above-mentioned clearance is between 0.3 and 0.5 x the diameter of the unmelted granulate.
• This design allows melted material and fibres to pass, while insufficiently melted granulate cannot. That is thus forced to remain in inlet channel 18 and will after some time be melted completely there, following which the melted material can as yet pass the raised part and, while passing the first flank 38, be subjected to the desired shearing.
• the width L of the first flank 38 can also increase, preferably almost proportionally to the increase in said diameter. If this width now becomes larger than is necessary for bringing about the required shearing, the introduction of a second pair of channels can be considered, each pair then preferably covering half of the surface area of the circumference of the dispersion section.
• the dimensions described above then apply to each pair of channels and associated flanks separately.
• the material to be dispersed can enter the dispersion section through two inlet channels, from each of which the material can overflow to the associated first flank, from there enter the corresponding second channel and thus exit from the dispersion section along two outlet channels. This considerably increases the transport capacity in comparison with the situation in which only one pair of channels with associated flanks is present in a dispersion section that is otherwise equally large.
• Fig. 2 48 indicates the direction of rotation of the screw.
• 18 and 20 indicate the inlet channel and the outlet channel.
• the material fed into inlet channel 18 will reach clearance 36 and further outlet channel 20 over flank 38.
• Fig. 5 the reference figures have the same significance as in the preceding figures. 50 indicates a raised part that prevents the entry of unmelted material into clearance 36.
• the invention also relates to a process for dispersing fibres in a thermoplastic material with the aid of an extruder that is provided with a screw composed of one or more screw sections, which comprises feeding the fibres and the thermoplastic material to the extruder and transporting and processing the total of the supplied fibres and the thermoplastic material with the aid of the screw sections.
• thermoplastic material ratio is already present in the enveloped fibres or fibre bundles supplied.
• the mixture homogeneously dispersed in the extruder can be processed into fibre-reinforced objects according to techniques known in themselves.
• techniques known in themselves are injection moulding, with the material being injected directly into a mould from the extruder die, or extrusion compression moulding, with the material being able to flow freely from the extruder and a suitable quantity of extruded material always being taken up, placed in a mould and compressed therein to give it the desired shape.
• the material can also be processed using other methods known for the processing of thermoplastic materials.
• the invention relates to an extruder, provided with a screw composed of one or more screw sections, in which at least one of the screw sections is a dispersion section according to the invention.
• a glassfibre-filled polypropylene was processed.
• a part of the mixture flowing out as a strand from the extruder was compressed in a Fontijne ® press at a pressure of 8 MPa and a moulding temperature of 40°C in a time of 1 minute to form a flat sheet with a thickness of 2.3 mm.
• the Table shows that when use was made of the dispersion section according to the invention a material was obtained that, with the same quality of the dispersion, has better mechanical properties than the material that was obtained with the known mixing section.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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ID=19771608

Family Applications (1)

Country Status (3)

Cited By (1)

Citations (5)

• 2000
  • 2000-06-27 NL NL1015542A patent/NL1015542C2/nl not_active IP Right Cessation
• 2001
  • 2001-06-20 AU AU2001267928A patent/AU2001267928A1/en not_active Abandoned
  • 2001-06-20 WO PCT/NL2001/000462 patent/WO2002000416A1/en active Application Filing

Patent Citations (5)

Non-Patent Citations (1)

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