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
  • B29C48/03—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
  • 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
  • B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices
  • B29B7/34—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices
  • B29B7/38—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary
  • B29B7/40—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft
• • 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
  • B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices
  • B29B7/34—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices
  • B29B7/38—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary
  • B29B7/40—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft
  • B29B7/42—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft with screw or helix
• • 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
  • B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices
  • B29B7/34—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices
  • B29B7/38—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary
  • B29B7/46—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with more than one shaft
• • 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
  • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
  • B29C48/395—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die using screws surrounded by a cooperating barrel, e.g. single screw extruders
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/005—Processes for mixing polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene

Definitions

• the present invention relates to the compounding of polymer compositions and more particularly to a method of compounding a multimodal polymer composition compris- ing a low molecular weight ethylene polymer and a high molecular weight ethylene polymer.
• ethylene polymer comprises ethylene homopolymers and ethylene copolymers.
• molecular weight of the polymer is defined by way of its melt flow rate (MFR) according to ISO 1133.
• MFR melt flow rate
• the melt flow rate (which is often erroneously referred to as the melt index) is measured in g/10 min of the polymer dis- charge under specified temperature, pressure and die conditions and is a measure of the viscosity of the polymer, which in turn for each type of polymer is mainly influenced by its molecular weight distribution, but also by its degree of branching etc.
• MFR melt flow rate
• the ingredients thereof such as different polymers, fillers, additives, etc, should be mixed intimately in order to obtain as homogenous a composition as possible. This intimate mixing is done by compounding the ingredients in a compound- ing machine, continuous or batchwise; the former type can be exemplified by an extruder which may be of the single screw of double screw type.
• the composition comprises two or more different polymers these should be so thoroughly mixed with each other that, ideally they form a completely homogenous polymer blend.
• the polymers are mixed with or without external heating so that they are melted and converted into liquids and the liquid polymers are mixed at sufficiently high shear rates .
• the compounding should be carried out at a) a high temperature to transform the polymer components to low viscosity liquids which makes for easier mixing, b) the highest possible shear rate to supply a large amount of mixing energy, and c) during as long time as possible, in order to achieve a homogenous composition, it is on the other hand necessary to restrict the temperature, shear rate and time because of the degradation of the polymers that is caused by too severe conditions .
• the composition is normally compounded by letting the temperature rise as quickly as possible above the melting points of the polymer components and subjecting it to a high shear rate for as short time as possible. Normally, this means compounding the composition in an extruder by heating the composition under conditions such that the rising temperature of the melting ethylene polymer passes the temperature range 130-160°C in well below 10 seconds.
• white spots occur in the compounded material.
• These white spots have a size of about 10-50 ⁇ m and consist of high molecular weight polymer particles that have not been adequately compounded in the composition.
• the white spots may adversely influence the strength of the composition.
• gel particles with a size of about 0.01-1 mm often occur. These gel particles appear as disfiguring inho ogeneities in the finished film and consist of high molecular weight polymer particles that have not been adequately compounded in the composition.
• EP 645 232 is described a way of reducing or obviating this problem by adding into the polymer feed a heat transfer medium, like liquid nitrogen or liquid or solid carbon dioxide.
• the amount of heat transfer medium added ranges from about 5% to 30%, preferably from about 10% to 20% by weight based upon the total feed rate of the polymer.
• Such an addition of a heat transfer medium is, however, a relatively costly way and, in the case of the use of solid carbon dioxide, which is the preferred means, it also presents problems with the working environment .
• the present invention provides a method of compounding, in a single or double screw extruder, at shear rates of at most 100 s _1 in the zone where the major compounding work is performed, of a multimodal polymer composition, comprising a low molecular weight ethylene polymer and a high molecular weight ethylene polymer, without leaving "white spots" or gel particles in the final blend.
• no heat transfer medium is added to the polymer composition and further the residence time in the zone where the temperature in the melt rises from 10 °C below to 10 °C above the melting point of the low molecular weight ethylene polymer is longer than 10 seconds, preferably longer than 15 seconds, more pre- ferably longer than 20 seconds and most preferably longer than 25 seconds.
• the lower melting, high molecular weight ethylene polymer component will first get melted and compounded before the higher melting, low molecular weight component starts to melt, so that the major compounding work will be directed towards the lower melting, high molecular weight, ethylene polymer component.
• the polymer composition compounded according to the present invention is a multimodal, preferably a bimodal polymer composition.
• this expression refers to the form of its molecular weight distribution curve, i.e. the appearance of the graph of the polymer weight fraction as function of its molecular weight.
• the multimodal polymer composition may alternatively comprise at least two different and initially separate ethylene polymer components which are made into a multimodal composition by melt blending or compounding in accordance with the present invention.
• the present invention is restricted to the compounding of a multimodal polymer composition comprising a low molecular weight ethylene polymer and a high molecular weight ethylene polymer.
• the molecular weight of the polymer is defined by way of its melt flow rate.
• the low molecular weight ethylene polymer has a MFR 2 .i 6 of about 0.1-5000 g/10 min, preferably about 50-500 g/10 min
• the high molecular weight ethylene polymer has a MFR 21 . 6 of about 0.01-10.0 g/ 10 min, preferably about 0.1-5.0 g/10 min.
• the density of the low molecular weight ethylene polymer should lie in the range from about 0.935-0.970, preferably from about 0.940-0.965 g/ cm 3
• the density of the high molecular weight ethylene polymer should lie in the range from about 0.875-0.945, preferably from about 0.875-0.935 g/cm 3
• the low molecular weight ethylene polymer is a high density type polyethylene (HDPE) and the high molecular weight ethylene polymer is a linear low density type polyethylene (LLDPE) .
• the polymer composition is subjected to compounding for an extended period of time in a temperature range from about 10°C below to about 10°C above, preferably from about 5°C below to about 5°C above the melting point of the low molecular weight ethylene polymer.
• This temperature range under the conditions used in the extruder, will cover the range from where the high molecular, low melting, ethylene polymer component has started significantly to melt until also a major part of the low molecular, higher melting, ethylene polymer component has melted and been worked into the blend.
• the viscosity of the low molecular weight ethylene polymer to the viscosity of the high molecular weight ethylene polymer should preferably lie within the range from about 5:1 to about 1:5, more preferably from about 3:1 to about 1:3. It has been found that it becomes increasingly difficult to achieve a good distribution and dispersion of the polymer components if the viscosity ratio lies outside this range.
• the viscosity ratio should amount to at most about 5:1, i.e. the viscosities of the polymer components should not differ too much in order to obtain a good dispersion of the components.
• the high molecular weight ethylene polymer which has the lower melting point thus starts at first to melt while the low molecular remains solid.
• the viscosity difference between the two polymer components becomes inverted in that the viscosity of the high molecular weight ethylene polymer, from under normal conditions being higher than that of the low molecular weight ethylene polymer suddenly drops when the high molecular weight ethylene polymer melts and becomes lower than that of the low molecular weight, still solid ethylene polymer.
• This "inverted" viscosity relation remains until the low molecular weight ethylene polymer component has melted, because in liquid phase and at the same temperature the high molecular weight ethylene polymer has a higher viscosity than the low molecular weight ethylene polymer. Therefore, as the tem- perature rises the difference in viscosity between the polymer components gets reversed back into normal when both polymer components are completely melted.
• the two materials are relatively close in stiffness/viscosity and thus a good mixing and homogeneity can be obtained.
• the compounding should be carried out for as long time as possible in the crossover area, i.e. from a temperature in the melt of about 10 C below to about
• the time of compounding in the crossover area is longer than 10 seconds, preferably longer than 15 seconds, more pre- ferably longer than 20 seconds and most preferably longer than 25 seconds.
• the time in the crossover area should not be more than about 1 minute. This is in contrast to conventional compounding which normally strives to melt the composition as quickly and completely as possible and compound it as a liquid at a high temperature.
• the melting points lie at about 125-140°C.
• the temperature at which the melting starts is dependent on the rate of heating and at high rates of heating, such as about 300-400 C/min which may occur during compounding a polymer composition in an extruder, the temperature at which the melting starts may increase to about 140-155°C.
• the melting of the high molecular weight ethylene polymer is delayed more than that of the low molecular weight ethylene polymer. This means that in practice the crossover area or temperature range within which the com- pounding according to the invention is carried out roughly lies between 125-155°C depending on the polymers and on the heating rate.
• shear rate Another factor of importance is the shear rate to which the polymer composition is subjected during the compounding. Although in principle a more effective mixing should be obtained by increasing the shear rate, a too high shear rate leads to degradation of the polymer. At the present invention the shear rate, in the zone where the major compounding work is performed, should therefore be at most about 100 s _1 , preferably about 10-100 s _1 . A shear rate below about 10 s _1 tends to be ineffective, while shear rates above about 100 s "1 involve a risk of degrading the polymer.
• the expression "in the zone where the major compounding work is performed” takes into account that during the compounding in an extruder different parts of the polymer composition are exposed to different shear rates.
• the major part of the composition is compounded in the helical screw channel between the screw lands at a lower shear rate.
• This shear rate which could also be said to be the average shear rate, that should be at most about 100 s -1 at the present invention.
• the method according to the present invention may in principle be carried out in a conventional compounding apparatus, e.g. of the single screw or double screw type, preferably of the counter rotating double screw type. However, additional cooling may be necessary in order to keep the composition at the prescribed temperature range during the prescribed compounding time.
• the polymer composition When the polymer composition has been compounded according to the present invention it may, when required be further compounded according to conventional compounding techniques. This means that the composition may be subjected to an additional compounding step at an in- creased temperature of about 150-300°C, preferably about 160-250°C and a shear rate of about 200-1000 s "1 . This optional, supplementary compounding may be carried out in direct connection with the compounding according to the invention or separately at a later time.
• each step implies a separate compounding operation in a mixer or extruder.

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• 1996
  • 1996-10-09 SE SE9603683A patent/SE506754C2/sv not_active IP Right Cessation
• 1997
  • 1997-10-03 WO PCT/SE1997/001659 patent/WO1998015591A1/en not_active Application Discontinuation
  • 1997-10-03 CN CN97198698A patent/CN1066469C/zh not_active Expired - Fee Related
  • 1997-10-03 JP JP10517447A patent/JP2001502370A/ja active Pending
  • 1997-10-03 AU AU46413/97A patent/AU4641397A/en not_active Abandoned
  • 1997-10-03 EP EP97945139A patent/EP0931106A1/de not_active Withdrawn

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