Title of Invention

"A METHOD FOR THE CONTINUOUS MANUFACTURE OF EXPANDABLE PLASTIC GRANULATE"

Abstract

Using the method, expandable plastic granulate (G) can be manufactured continuously, with a plastic melt (F) being impregnated using a fluid expanding agent (B) and the impregnated melt being granulated. The method is carried out by means of a plant, which includes the following components: - at least one pressure producing feed apparatus (10) for the melt, which is in particular a volumetrically pumping feed apparatus, - a metering apparatus (9) for the expanding agent, - contacting and homogenising apparatus (2) for the impregnation of the melt, - at least one cooler (3) for the impregnated melt, - an underwater granulator (6) and - a plant control (1). The granulation is carried out using a liquid which is used in the granula- tor as a cooling and transport medium for the granulate. The liquid is in particular water or a brine. An elevated pressure is exerted by the liquid used during granulation, due to which an expanding action of the expand ing agent in the not yet solidified granulate is at least partly suppressed. A regulation of the parameters to be set for the granulation, namely the temperature and pressure of the impregnated melt is effected at the inlet of the granulator. In this regulation, measurements of the named parame ters are made and also measurement values are compared with desired values and deviations from the desired values due to the unit control are used to influence a heat take-up from the impregnated melt by the cooler or coolers.

Full Text

Sulzer Chemtech AG. CH-8484 Winterthur (Switzerland) A method for the continuous manufacture of expandable plastic granulate. The invention relates to a method for the continuous manufacture of expandable plastic granulate in accordance with the pre-characterising part of claim 1. The invention also relates to a plant for the manufacture of granulate of this kind. A method and also a plant for the manufacture of expandable plastic granulate is known from EP-A- 0 668 (= P.6623). In a special embodiment of the method an impregnated polymer melt is made into pieces in an underwater granulator by means of a shape giving solidification. The melt is extruded through nozzles; the strands which are formed in this way are quenched with water and brought into granulate form by comminution with rotating knives. In this method the polymer melt is pre-cooled prior to entry into the granulator in order to avoid expansion of the strands during extrusion. The provision made for cooling of the impregnated melt to a temperature which lies a few degrees C above the solidification temperature of the melt is problematic. This is because it is very difficult under circumstances such as these to allow the same quantity of melt to flow through all the extrusion nozzles of the granulator which are arranged in parallel. Instabilities in the melt flow arise which can lead to the closing of individual nozzles by the melt solidifying in them. The object of the invention is to provide an improvement on the named method by which the named instabilities can be mastered. Moreover, a more flexible alternative should be found which can be applied more universally, with a combination of two static mixers in which the melt is initially treated with a large shearing action and subsequently with a reduced shearing action in particular no longer being necessary, but can, however, still be an advantageous variant. This object is satisfied by the method defined in claim 1. Using the method, expandable plastic granulate can be manufactured continuously, with a plastic melt being impregnated using a fluid expanding agent and the impregnated melt being granulated. The method is carried out by means of a plant, which includes the following components: - at least one pressure producing feed apparatus (10) for the melt, which is in particular a volumetrically pumping feed apparatus, - a metering apparatus (9) for the expanding agent, - contacting and homogenising apparatus (2) for the impregnation of the melt, - at least one cooler (3) for the impregnated melt, - an underwater granulator (6) and - a plant control (1). The granulation is carried out using a liquid which is used in the granulator as a cooling and transport medium for the granulate. The liquid is in particular water or a brine (or a sols). An elevated pressure is applied with the liquid used during granulation, due to which an expanding action of the expanding agent in the not yet solidified granulate is at least partly suppressed. A regulation of the parameters to be adjusted for the granulation, namely the temperature and pressure of the impregnated melt is effected at the inlet of the granulator. In this regulation, measurements of the named parameters are made and also measurement values are compared with desired values and deviations from the desired values are used by the plant control to influence a heat take-up from the impregnated melt by the cooler or coolers. The dependent claims 2 to 7 relate to advantageous embodiments of the method in accordance with the invention. Plants for carrying out the method in accordance with the invention are the subject of claims 8 to 10. The invention will be explained in the following with the help of the drawings, which show: Fig. 1 a schematic illustration of the plant in accordance with the invention, Fig. 2 a detailed illustration of the underwater granulator which merely appears as a block in Fig. 1, Fig. 3 an illustration of the granulation apparatus of the underwater granulator and Fig. 4 a detailed schematic illustration of a realised plant in accor- dance with the invention and also a diagram with a qualitatively shown plot of temperature and pressure which the melt assumes while flowing through the plant. A method for the continuous manufacture of expandable plastic granulate G can be carried out using a plant in accordance with the invention as schematically illustrated in Fig. 1. In this arrangement a plastic melt F ("Feed") is impregnated with a fluid expanding agent B (Blowing Agent) and the melt F which has been treated in this manner is granulated. The plant includes the following components: at least one pressure producing feed apparatus 10 with which the melt F obtained from a plastic source 80 is volumetrically fed; a source 81 for the expanding agent B, which is fed to the melt F using a metering apparatus 9 (see Fig. 4); a contacting and homogenising apparatus 2 for the impregnation of the melt F; at least one cooler 3 for the impregnated melt; a further homogenising apparatus 5 which is optional; an underwater granulator 6; and also a plant control 1. The granulate G which has been produced is ultimately available as a product in a container 82.The plastic source 80 can consist of a polymerisation reactor for the manufacture of the plastic from a monomer source material and also a degasification apparatus for the polymer. The plastic source 80 can also be a recycling apparatus for recycled thermoplastic of one type and also includes a melting apparatus, in particular a heatable extruder. The plastic source 80 can also simply be a melting apparatus in which a granular thermoplastic is liquefied. The granulation is carried out using a liquid (preferably water, for example also a brine or a sols) which is used in the granulator 6 as a cooling and transport medium for the granulate. An elevated pressure is exerted with the liquid used during granulation, due to which an inflating action of the expanding agent in the not yet solidified granules is suppressed, at least in part. A regulation of the parameters to be adjusted for the granulation at the inlet of the granulator 6, namely the temperature and the pressure of the impregnated melt, is effected using the plant control 1. In this regulation measurements of the named parameters are made and also measurement values are compared with desired values. Deviations from the desired values are used to influence a heat take-up from the impregnated melt by the cooler or coolers 3. The parameters to be adjusted for the granulation are regulated with electronic means using the plant control 1. These means have signal-transmitting connections 19, 110, 13 and 16 to the expanding agent source 81 (metering pump 9), to the feed apparatus 10, to the cooler 3 (or to a plurality of coolers) and to the granulator 6 respectively. The following adjustable parameters are relevant for the impregnation: temperature, pressure and dwell time. The required dwell time depends on the amount of expanding agent B provided for impregnation. A fixed ratio of expanding agent flow to melt flow is set by means of the plant control for each pre-determined proportion of expanding agent B. These flows, which can be variable, are produced by volumetric feeding. The parameters temperature and pressure at the inlet of the granulator 6 are relevant for the granulation.At least one additive can be added before, during and/or after the impregnation of the melt F. Points for the feeding in of additives are shown by Fig. 1 with rhombuses 7a, 7b, 7c and 7d. The feed apparatus 10 is advantageously a gear pump, however it can also be an extruder. Further feed apparatuses (pumps, extruders, screw conveyers) can be used in the plant in accordance with the invention. Possible points for additional feed apparatuses are shown in Fig. 1 as small circles la, Ib and Ic. The manner of operation of the underwater granulator 6 is described with the help of Figures 2 and 3 (see DE-A-35 41 500). The impregnated melt F is granulated in a mechanical apparatus 6' driven by a motor 600. It first passes through a distributor 606 (which forms the inlet of the granulator 6) to a nozzle plate 605, with the melt being extruded through the nozzles 605' of the nozzle plate. An additional feed means at the inlet, namely a screw conveyor 607, is optional. A plurality of nozzles 605' is arranged in ring-like manner on the nozzle plate 605. The plastic strands escaping from the nozzles 605' enter a chamber 603 filled with water (or with another liquid) where the extruded material is brought into the form of granulate by a comminution with rotating knives 604. The knives 604 sit on a holder which is arranged on a shaft 600' leading to the motor 600. The water is directed by a pump 60 through an inlet connection 601 under an elevated pressure (for example 10 bar) into the chamber 603 from which it flushes the granulate, with simultaneous cooling of the granulate G, into a separating apparatus 61 via outlet stubs 602. The granulate G is separated from water in the separating apparatus 61 and discharged into the container 82. The water flows through a cooling apparatus 62 in which it gives off the heat taken up from the freshly produced granulate G into the environment. If the water pressure in the separating apparatus 61 is reduced to ambient pressure, then the water pump 60 is arranged upstream before the cooling apparatus 62. If a brine is used instead of water for example, the cooling of the granulate G can be carried out at lower temperatures ( 0° C for example).In order that the instability problems with the nozzle plate 605 mentioned at the beginning of this specification can be mastered care has to be taken, on the one hand, that the temperatures (temperature fields) are the same for all nozzles. This takes place with not illustrated thermostats. On the other hand the melt F has to assume a temperature in the distributor 606 the value of which has to be adjusted relative to the operating condition of the plant. The pressure results by means of the fall in pressure along the nozzles 605' and the water pressure in the chamber 603. The fall in pressure depends on the mass flow rate of the treated melts and on the viscosity of the melts which has a considerable temperature dependence. The temperature T and the pressure p in the distributor 606 are influenced by the plant control to such an extent that these parameters assume values which are as close as possible to the desired values. The desired values depend on the operating condition and can be presented as mathematical functions or in the form of value tables; they can be determined by means of pilot tests. Fig. 4 shows, in a detailed schematic illustration, a plant in accordance with the invention which has been realised and with which EPS (expandable polystyrene) can be manufactured. A diagram is associated with the same Fig. 4 in which the plot of temperature T and pressure p which the melt adopts on flowing through the plant is shown in correspondence to the plant illustrated in the upper part. In distinction to Fig. 1 the metering pump 9 for the expanding agent B is drawn in in Fig. 4. As a further difference, the contacting and homogenisation apparatus 2 is also composed of two static mixers 2a and 2b arranged in series. The intervals Ha and lib correspond to these mixers 2a and 2b in the diagram. The first interval I corresponds to the pump 10 (gear pump). The cooler 3 - corresponding to the interval III - additionally has a cooling apparatus 30 which circulates a heat transfer medium (thermo oil) in a circuit and gives off the heat taken up in the cooler 3 to a heat sink. In the realised plant the cooler is made of three static mixers (not illustrated) the mixing elements of which are formed as heat exchanger pipes 3'. The interval IV in the diagram corresponds to a second pump 40 which is followed by a static mixer 5 (interval V). A controllable three-way valve 51 which is connected to the plant control 1 (signal line 15) is arranged between the mixer 5 and the granulator 6 (interval VI). Using this when required – this 8 is the case when starting up the plant - melt F can be redirected into an intermediate storage 50. The liquid-filled chamber 603 is indicated in the granulator 6. The signal transmitting connections 19, 110, 13 and 16 have already been described with reference to Fig. 1. Using the two static mixer, a dispersing of the expanding agent B in the melt F and a dynamic holding of the mixture in a pre-determined pressure range and during a dwell time are respectively carried out, with the dwell time having to be greater than a minimum time span. The dispersing occurs by means of static mixing elements at a high shearing of the melt F with fine expanding agent drops being formed. In the subsequent stage of the second mixer 2b the mixture is exposed to a small shearing action, i.e. the mixture is held dynamically. In this arrangement the expanding agent drops dissolve in the melt F. The shearing has to be so large in this arrangement that no de-mixing occurs. In order for the shearing action in the second impregnation stage to be smaller, the second static mixer 2b has a cross-section through which flow takes place which is greater than a corresponding cross-section of the first static mixer 2a. In the diagram the curve 801 shows the melt temperature T as a line drawn through points. The line elements connect the temperature values, which can be respectively measured at the transitions between adjacent plant components and which are illustrated as triangles. In the intervals I, Ha and lib the temperature is about 220°C. The curve 802 shows the course of the melt pressure p. The values of the pressure p illustrated by circles correspond to the temperature values illustrated with triangles. Using the pump 10 the pressure p is increased to over 200 bar. The dynamic holding of the melt F in the second static mixer 2b (interval lib of the diagram) takes place at a falling pressure p from approximately 100 to 80 bar. The plant control 1 causes the heat take-up from the impregnated melt to be influenced by the cooler or coolers 3 by means of the regulation in accordance with the invention. The curve 801' shown as a broken line shows an altered course of the curve which is to be expected with increased cooling power. Since the viscosity of the melt increases when the temperature is lowered, a greater fall in pressure occurs downstream following the cooling. The pressure curve is correspondingly displaced upwards: dotted curve 802'. Since the pump 10 pumps volumetrically, the pressure increases when the flow resistance increases due to a larger viscosity. In the case of an alteration in operation the temperature T and the pressure p have to be adapted at the granulator 6. Alterations in operation are: starting up the plant; alteration of the quality of the infed melt F; alteration of the feed quantity (rate); alteration of the proportion of expanding agent; alteration of the composition of the additive. In the case of alterations such as these the regulation has to become active by means of the plant control 1. Once a steady state operating condition has been reached, then the control is only necessary with regard to disturbing influences from the environment. Apart from polystyrene, another thermoplastic can also be used as a plastic. Examples are: styrene-copolymers, polyolefines, in particular polyethylene and also polypropylene or a mixture of these named substances. HaO, CO2, N2, a low boiling hydrocarbon, in particular pentane, or a mixture of the named substances can be used as an expanding agent. Diverse forms of granulate can be produced (depending on the cross-section of the nozzles 605', on the rotational speed of the knives 604 and on the water pressure in the chamber 603). In particular, the granulate can be produced in the form of "pellets" or "beads" or as a partially foamed granulate. Patent Claims 1. A method for the continuous manufacture of expandable plastic granulate (G) by impregnation of a plastic melt (F) using a fluid expanding agent (B) and also granulation of the impregnated melt by means of a plant which includes as components at least one pressure-producing feed apparatus (1) for the melt, in particular a volu-metrically pumping feed apparatus, a metering apparatus (9) for the expanding agent, contacting and homogenising apparatus (2) for the impregnation of the melt, at least one cooler (3) for the impregnated melt, an underwater granulator (6) and a plant control (1), wherein the granulation is carried out using a liquid which is used in the granulator as a cooling and transport medium for the granulate, in particular using water or a brine, characterised in that an elevated pressure is applied with the liquid used during granulation, on the basis of which a blowing action of the expanding agent in the not yet solidified granulate is at least partly suppressed and in that a regulation of the parameters to be set for the granulation, namely the temperature and pressure of the impregnated melt at the inlet of the granulator is effected using the plant control, with measurements of the named parameters being made and also measurement values being compared with desired values and deviations from the desired values being used by the plant control in the said regulation to influence a heat take-up from the impregnated melt by the cooler or coolers. 2. A method in accordance with claim 1 characterised in that static mixers are used as contacting and homogenising apparatuses (2) and/or the cooler or the coolers (3) are likewise static mixers, the mixing elements of which are in particular designed as heat exchanger tubes. 3. A method in accordance with claim 1 or claim 2, characterised in that the feed apparatus (10) for the melt is a gear pump or an ex truder, the feeding power of which can be influenced by the plant control (1) with respect to a variable offer of the melt (F) to be im pregnated , with the metered supply of expanding agent (B) being controlled. 4. A method in accordance with any one of the claims 1 to 3, charac terised in that the expanding agent (B) is dispersed in the melt (F) in a first stage of the contacting and homogenising apparatuses (2), in particular by means of strong shearing action in a static mixer (2a), and in that the mixture which is obtained in this way is fed to a sec ond stage (2b), in which the mixture is held dynamically, within a predetermined pressure range and also during a dwell time within a predetermined time interval. 5. A method in accordance with any one of the claims 1 to 4, charac terised in that polystyrene, styrene-copolymers, polyolefines, in par ticular polyethylene and also polypropylene or a mixture of the named materials are used as a plastic (F); and in that HbO, COa, N2, a low boiling hydrocarbon, in particular pentane, or a mixture of the named substances is used as an expanding agent (B). 6. A method in accordance with any one of the claims 1 to 5, charac terised in that at least one additive is mixed in before, during and/or after the impregnation. A method in accordance with any one of the claims 1 to 6, charac terised in that one of diverse granulate forms is produced, with the granulate (G) being produced in particular in the form of "pellets" or "beads" or as a partially expanded granulate. 7. A plant for the manufacture of expandable plastic granulate (G) in accordance with any one of the claims 1 to 7. 8. A plant in accordance with claim 8, characterised in that it includes the following components arranged in series: a first gear pump (10) or an extruder (10) for a melt which is to be impregnated; a static mixer (2) with an inlet connection to a metering pump (9) for ex panding agent (B); a cooler (3) or a series of coolers, the heat ex changers of which are designed as static mixing elements; a second gear pump which is arranged within the series of coolers or down stream of and following the cooler or coolers; a further static mixer (5); an underwater granulator (6); and an electronic plant control (1) which is provided for the regulation of the parameters to be set for the granulation and which has for this purpose signal transmitting connections (110, 13, 16, 19) to the feed means, i.e. to the named pumps or extruder, to the cooler or to a plurality of coolers and also to the granulator. 9. A plant in accordance with claim 9, characterised in that the static mixer (2) which follows the first geared pump, is a first static mixer (2a) which is followed by a second static mixer (2b), in that mixing elements in the first static mixer create greater shearing effects than in the second one and in that in particular the second static mixer as a flow cross-section which is larger than a corresponding cross-section of the first static mixer.

Documents:

469-del-2006-Abstract-(12-03-2013).pdf

469-del-2006-Abstract-(21-09-2012).pdf

469-del-2006-abstract.pdf

469-del-2006-Claims-(12-03-2013).pdf

469-del-2006-Claims-(21-09-2012).pdf

469-del-2006-claims.pdf

469-del-2006-Correspondence Others-(12-03-2013).pdf

469-del-2006-Correspondence Others-(23-11-2012).pdf

469-del-2006-Correspondence Others-(27-01-2014).pdf

469-del-2006-Correspondence Others-(28-01-2013).pdf

469-del-2006-Correspondence-Others-(30-07-2013).pdf

469-del-2006-correspondence-others.pdf

469-del-2006-Description (Complete)-(21-09-2012).pdf

469-del-2006-Description (Complete)-(30-07-2013).pdf

469-del-2006-description (complete).pdf

469-del-2006-Drawings-(21-09-2012).pdf

469-del-2006-drawings.pdf

469-del-2006-Form-1-(21-09-2012).pdf

469-del-2006-form-1.pdf

469-del-2006-Form-2-(21-09-2012).pdf

469-del-2006-form-2.pdf

469-del-2006-Form-3-(21-09-2012).pdf

469-del-2006-form-3.pdf

469-del-2006-form-5.pdf

469-del-2006-GPA-(21-09-2012).pdf

469-del-2006-gpa.pdf

469-del-2006-Petition-137-(21-09-2012).pdf

469-del-2006-Petition-137-(27-01-2014).pdf

469-del-2007-correspondence-others-1.pdf

469-del-2007-form-18.pdf