DE102005043526A1 - Method and device for treating plastic material and device for conveying and simultaneously heating material, in particular plastic parts - Google Patents

Abstract

The present invention provides a method and an apparatus for treating plastics, such as polyester, in particular for recycling polyethylene terephthalate (PET), e.g. B. from beverage bottles, preferably for the production of food-safe PET, and in particular for the conversion of amorphous plastic material, which is present for example in the form of granules or flakes, in crystalline plastic material. In addition, a device (1) for conveying and simultaneously heating material, in particular plastic parts such as plastic flakes and particles, consisting of a conveying path, means for conveying, means for producing (2, 5) a material-conveying atmosphere mixture and one Source (3) for the irradiation with electromagnetic radiation, in particular infrared radiation, is shown, which can be used, inter alia, as a means for pre-drying, for crystallization and for preheating before the solid post-condensation. With the aid of the present invention, for example, food-grade PET granules can be produced with at least the same high quality, the previous method being simplified and in particular reducing the outlay on equipment, increasing the capacity of existing systems and saving energy.

Description

The The present invention relates to a method of treating plastic material according to the generic term of claim 1, a means for conveying and simultaneous heating of plastic parts according to the preamble of claim 7 and an apparatus for treating plastic material according to the generic term of claim 18.

Plastic materials such as polyesters, especially polyethylene terephthalate (PET), are becoming popular nowadays diverse used, for example for the production of beverage bottles, qualified films and fibers, medical devices, in particular medical syringes and medical containers. Because of a grown ecological consciousness and also increasing economic Interests are reinforced sought after method, these plastic materials according to their intended use continue to use, so possible Completely to lead in the recycling cycle. This is especially true in the above-mentioned fields of application the food packaging and medical technology currently only with extensive Arrangements possible, prevent plastic contaminants from remaining in the plastic.

One effective process for producing recycled PET material, that meets the requirements for food grade PET, d. H. has substantially no contamination is in WO 2004/106025 A1 described. This method comprises the method steps Extrusion and / or granulation under essentially vacuum and the implementation a Feststoffnachkondensation under substantially vacuum, wherein these steps with or without stripping to further remove residual contaminants carried out become. Before extrusion / granulation will be an additional Predrying step and / or between the extrusion / granulation and solid postcondensation an additional crystallization step executed. The pre-drying step leads to a lower water or steam content in the extruder, whereby the viscosity of the PET material does not sink so much in the extrusion or the recycled material a higher one viscosity which, in turn, further processing for example beverage bottles favored. Furthermore promotes the reduced water vapor content in the extrusion process the degassing of Acetaldehyde. The additional Crystallization step leads In addition, in the case of extruded / granulated PET, the partial crystallinity should be reduced by approx. 50% is increased, whereby a sticking of the PET granules is prevented. Thereby the solid post-condensation process can be better and faster be performed. These two measures, which can be performed alternatively or together an efficient process management combined with a very even product quality.

at the method of WO 2004/106025 A1, the disclosure of which fully incorporated herein becomes, sets the present invention, which is another Simplification, especially in terms of equipment required has under a further increase in economic efficiency and consistent product quality this generic method.

These Task is solved by a method of treating plastic material having the features of claim 1, a means for conveying and simultaneous heating of material having the features of claim 7 and a device for treating plastic material having the features of the claim 18. Advantageous embodiments are the subject of the dependent claims.

Of the The present invention is based on the finding that the generic method then simplified, in particular be carried out with less equipment can, if individual steps of a conveyance to a treatment device, for example, to a crystallizer, and the treatment process itself, for example, crystallizing, suitably with each other get connected.

So far, for example, after the extrusion / granulation, the granules were conveyed to a heated Rüttelbett to crystallize there for preferably 15 minutes at 140 ° C. Such crystallization could also be found in one in the EP 0 891 526 B1 described screw conveyor, which has an infrared radiation source. Although a treatment process with a material transport is purely factually associated with these two devices, the connection of these two steps is not yet suitable. On the one hand, the material still has to be conveyed away to such a device and away from it to the next treatment station, since these devices operate adequately only in horizontal operation, but individual treatment stations usually lie on different vertical levels. On the other hand, the material flow with these devices, although continuous but in relation to the material flow, which is necessary for example for filling a solid reactor, in particular a tumble dryer, is not sufficient.

Now it has surprisingly been found that by the subject matter of the present invention the three steps of transport, treatment (in the case just described crystallization) and further transport can be combined into a single promotion and treatment step in a single institution and so the equipment cost can be considerably reduced. As a result, a cost savings and a reduction in the required footprints are achieved.

The present invention thus provides, on the one hand, a device which simultaneously conveys and heats any material, in particular plastic material, in the form of individual parts of material, namely by irradiating same during the delivery of the plastic parts with radiation in the infrared range. While in the previous technique (Rüttelbett) the heating was done by means of air and the heating was so slow penetrated into the material or the heating was carried out by means of infrared radiation (screw conveyor of the EP 0 891 526 B1 ) and the material had to be circulated tedious, so that all material parts were irradiated and therefore long residence times of the plastic material in a heating apparatus were necessary with these previous techniques, with the inventive device in which the application of electromagnetic radiation is provided, residence times in seconds range is sufficient , This is because this electromagnetic radiation, in particular infrared radiation and preferably radiation in the near infrared, penetrates directly into the plastic material, thereby achieving a depth effect and thus enables the complete heating of the material substantially at once.

It are different frequency ranges of electromagnetic radiation usable. Which type is used depends on the given material and its geometry, that is of which type of radiation most effectively a material part at the same time effective and full body to heat is able.

Important for the Use of electromagnetic radiation for heating while conveying of the plastic material, however, is that every plastic part, So for example, a Kunsstoffflake or a particle, the radiation is directly exposed. The device is according to the invention in addition a conveyor line, Means for conveying and a source for electromagnetic radiation further with means for production a plastic part conveying atmosphere mixture (as conveying atmosphere while the atmosphere within the conveyor line understood), so that the plastic parts are separated and thus essentially irradiates all transported plastic parts become.

Advantageous are in the conveyor according to the invention the conveyor line and the means for producing the material conveying atmosphere mixture summarized realized. This can be done by the fact that the material in a vertical conveyor pipe due to gravity falls down (Gravity feed) and depending on the amount of falling material a mixing ratio between Plastic parts and conveying tube atmosphere, ie creates a specific plastic part density that allows it at a certain pipe section all transported plastic parts over to be irradiated simultaneously with infrared radiation. On the other hand can a common realization of the conveyor line and the means for producing the material conveying atmosphere mixture be realized in that the plastic parts in a conveyor tube, for example vertically from a lower to an upper level, by means of an airflow promotion promoted become. This airflow promotion is preferred over a blower device achieved, however, the use of a suction device is conceivable. Again, this forms a plastic part-Förderrohratmosphären mixture with a certain plastic part density. This density can then, for example, targeted by adjusting the flow rate or the dosing over a metering device is controlled to be influenced.

In an advantageous embodiment are the means for producing a plastic part conveying atmosphere mixture adapted to homogenize its density. Through this homogenization is achieved that all material parts substantially over the same time applied to the substantially same radiation intensity which results in a particularly uniform material quality becomes.

The Plastic part density can be influenced by additional means become. So can For example, suitable screens, turbulators, deflectors, displacement body or fan for adjusting the density, in particular by inhibiting the material flow, be provided, as a side effect also an advantageous homogenization the material density over the conveyor cross section can effect. Thus by the additional Medium no jam in the conveyor pipe results, can furthermore suitable means for shaking be provided which vibrate, for example, a sieve, that always a contingently equal amount of plastic parts passes through the sieve.

In addition, the conveyor line and / or means for producing the Matrial conveying tube atmosphere mixture a larger compared to the conveying section in cross-section container, in particular a cyclone, the same time to Tren tion of the material-delivery atmosphere mixture serves include. In such a container, the electromagnetic radiation source may advantageously be integrated in the lid and / or in the side walls. In order to increase the efficiency of the irradiation, reflectors for the electromagnetic radiation can be provided in the conveying path, so that, for example, even in the case that only over a certain peripheral region of the conveying path radiators are mounted, the vorbeabeförderte material part conveying atmosphere mixture on all sides with radiation is charged.

Farther can the heating effect and thus set in the plastic parts Temperature in addition to a suitable adjustment of the radiation intensity over the conveyor speed be determined. The conveying speed can turn over the blower output, in the conveyor line sieves, swirlers or the like, or in the case of gravity conveying by acting against the fall direction, for example by a fan generated airflow can be adjusted.

In a preferred embodiment of the device according to the invention the device comprises means for stripping the plastic parts For example, in air, steam, inert gases such as nitrogen, or hot air and it is preferred that means for evacuating evolved volatile Products, such as water vapor, contaminants or the like., as they are released inter alia stripping, provided are.

The inventive device to promote and simultaneous heating is now within the scope of the plastic treatment process according to the invention and the plastic treatment device according to the invention but also universally applicable in other methods and devices, because with the help of the application of electromagnetic radiation any material temperatures in the seconds range directly during the conveying are adjustable.

For example may be the device for conveying and simultaneous heating for pre-drying before extrusion / granulation for example, coming from a car wash prepurified PET material used when setting material temperatures of about 150 ° C become. For PET material We recommend the use of infrared radiation, in particular of Near infrared radiation. By heating z. B. plastic flakes this will still stick out of the car wash or inside the flakes water, with residual moisture content of up to 2 wt .-% are common, evaporated and either through the airflow in an air flow promotion dissipated or by suitable means in gravity conveying aspirated. The residual moisture of the device according to the invention to promote and simultaneous heating for extrusion / granulation Material becomes despite the infrared radiation taking place within seconds to values up to <0.2 % By weight lowered. By use of the device according to the invention As a pre-dryer is thus at constant dry performance in turn reduces the expenditure on equipment.

Farther can the device of the invention to promote and simultaneous heating directly to the crystallization of the Extrusion / granulation coming PET granules are used. To this purpose is promoted Material in the device heated by infrared irradiation to 140 ° C, so that the granules also within the short irradiation time in the second range forms a partial crystallinity. This leads that the PET granules are not glued and thus the solid state after-condensation in the solid reactor, for example a tumble dryer, better and done faster can be. This can also be compared to the previous process step, for example, a crystallization on a heated Rüttelbett the equipment costs are significantly reduced.

a Another application is the inventive device for conveying and simultaneous Heating as preheating device to preheat of the semi-crystalline material at a substantially direct filling from an intermediate storage in the solid reactor, for example a tumble dryer. In this process, the semi-crystalline PET granules over the inventive device transported in the tumble dryer and while of promoting at about 200 ° C up to 250 ° C heated, so that the post-condensation process in the tumble dryer after its replenishment can start directly.

Especially, when the device according to the invention to promote and simultaneous heating used simultaneously as a crystallizer and preheater results in a significant reduction of the aparativen expense and at the same time an energy saving.

Additionally poses the present invention is an apparatus for recycling plastics ready. This has at least one extruder, granulator or solid secondary condenser on and at least one pre-dryer or a crystallizer. In this case, the device according to the invention forms to promote and simultaneously heating at least either the pre-dryer, the Crystallizer or before the solid secondary condenser preheating.

In an advantageous embodiment includes the device according to the invention additional funds for filtering the molten PET material, in particular replaceable filter and / or sieve combinations in candle and disk form, the pore size advantageous smaller than 100 μm is.

In a further embodiment includes the device according to the invention At least one stripper leading to an additional removal of volatile Contaminations, in particular of acetaldehyde and oligomers contributes.

In A further advantageous embodiment comprises the device according to the invention Furthermore, means for crushing the plastic material, adapted are to shred the plastic material so that plastic flakes arise, in at least one dimension, a wall thickness less than 2 mm, the wall thickness but in the rest Dimensions be much larger can. Preferably, the means for shredding are adapted so that the plastic flakes a length and / or width in the range 1 to 20 mm, in particular 5 to 12 mm exhibit. This comminution will remove residual contaminants from the plastic material promoted because the diffusion length This contamination is usually greater in the material than 1 mm, so that the contaminations from the maximum 2 mm thick Plastic flakes slightly towards the dimension with the low Wall thickness can escape.

Farther it may also be convenient, instead of crushing Means for fine grinding of the plastic material to plastic particles use, the means are adapted for fine grinding, Plastic particles with an average mean particle size of 0.12 to about 2.6 mm in diameter. Also from these plastic particles it is easier to remove contaminants than uncrushed material.

Further Features, features, and advantages of the present invention will become apparent based on preferred embodiments of the present invention in conjunction with the accompanying drawings become clear. It is purely schematic in

1 a preferred embodiment of the inventive device for conveying and simultaneous heating shown.

In 1 is a preferred embodiment of the inventive device for conveying and simultaneous heating 1 shown. This device 1 , which is designed as a gravity conveyor for plastic parts, comprises a substantially vertical downpipe 2 , which is only partially shown here. Along the circumference is an annular radiator 3 for irradiation with near infrared radiation having a certain width B. This width B is a function of the speed of the falling plastic parts, in particular plastic flakes and particles, and the intensity of the radiator 3 designed so that a single plastic part is applied during a sufficient residence time in area B with the desired temperature, ie about 150 ° C for predrying, 140 ° C for crystallization and 200 ° C to 250 ° C for preheating. In the area of the spotlight 3 has the downpipe 2 an opening 4 so that the radiation can act unimpeded on the conveyed plastic material. To protect the spotlight 3 can the opening 4 be closed by a window of suitable material, such as quartz glass, which allows the radiation to pass through substantially no absorption.

Instead of an annular opening 4 in the downpipe 2 can also be provided a circular segment-shaped opening and a reflector, the inside of the downpipe 2 then covered at the opening in the circumferential direction and for optimum radiation distribution in the downpipe 2 provides.

By additionally in the downpipe 2 above the spotlight 3 appropriate means, such. B. a sieve 5 with adapted to the size of the plastic parts mesh size, a homogenization of the plastic material flow is achieved in the conveyor cross-section and together with the delivery pipe ( 2 ) set the density of the plastic part conveying atmosphere mixture. On the other hand, by a targeted adjustment of the distance of the sieve 5 from the spotlight 3 also the conveying speed of the plastic material can be adjusted and thus the duration of the exposure to the radiation can be determined. The sieve 5 can additionally be shaken by suitable means so that it does not clog but the plastic parts fall through continuously. As a result, the separation of the plastic parts and the homogenization of the plastic part conveying tube atmosphere mixture are also improved. Furthermore, the plastic part density can also be adjusted directly by a rotary feeder (not shown).

For adjusting the conveying speed, a blower (not shown) may additionally be used, which generates an air flow up the downpipe and thus slows down the plastic parts. This air flow also advantageously absorbs volatile products, such as moisture, from the plastic material and transports them, so that, for example, predrying is even more effective. But also volatile contaminants are eliminated faster.

The inventive method will now be described with reference to a preferred embodiment.

In A first step, for example, PET flakes from a Car wash taken. These flakes usually arise through Shredding of PET bottles, which were prewashed in rinse water added with caustic soda, for drinks leftovers and other adhesive contaminants and adhesives from glued on Removing labels and non-similar materials, such as caps or other foreign substances such as other plastics, metal parts and the like were separated.

In In a second step, the pre-drying takes place from the car wash coming PET flakes, which consequently still moistened are. This predrying takes place directly in a delivery line by the application of near-infrared radiation more appropriate Intensity, so that in the promoted Flakes sets a material temperature of about 150 ° C, the PET flakes either by Air flow promotion or gravity promoted and the air-particle density is adjusted. The heat spreads in each one Flake immediately within a short time due to the irradiation out. This is enough to get past the flakes, which take a period of time in the range of seconds, at a radiation window to a significant reduction to achieve the residual moisture in and on the flakes.

In in a third step, the flakes become a 1-wave, 2-wave or multi-screw extruder (ring extruder) with a diameter of about 50 mm and a screw speed of about 350 U / min fed, the has several, in particular three degassing zones with Vakuumpumpenständen and in which the material under almost vacuum (<100 mbar) at a temperature of Extruded 280 ° C becomes. Due to the friction and the high temperatures creates a Melt of PET flakes. This melt is made with the help of filters smaller with a pore size 100 μm filtered, thereby freed of dirt particles and then a granulator fed. As a result, granules are produced with a granule size of less than 3 mm.

After this the third step of the extrusion and granulation is finished The granules are transported directly into a silo. With the storage of the Granules in the silo ends the continuous process. After this the silo has a sufficient filling level, to fill the tumble dryer, this is directly during of the fourth step. Also Here the necessary transport takes place of the granules by means of an airflow or gravity conveying with simultaneous separation of the individual granules, the while the singling applied to radiation of the near infrared of appropriate intensity be so that in the granules, a temperature of about 140 ° C. Nevertheless, the irradiation of the individual granules only in seconds this time is sufficient to have a partial crystallinity of about 40 % in the granules. By laying the beginning of the discontinuous process control takes place as well an energy saving.

This semi-crystalline granules is in a fifth step in a solid reactor namely a tumble dryer at temperatures of 200 ° C to 250 ° C and a Condensed pressure less than 1 mbar between 4 and 18 hours, wherein the tumble dryer performs up to 2 revolutions per minute. The so produced PET recyclate has only traces of contamination in the ppm range, leaving it for the food sector can be used.

Advantageous can preheat of the semi-crystalline granules in the tumble dryer of 140 ° C to temperatures from about 200 ° C up to 250 ° C, which are necessary for the postcondensation, also with the aid of inventive device to promote and simultaneous heating done. And especially advantageous if both the crystallization and the preheating at the same time with the device according to the invention when filling tumble dryer happen. This is the previously necessary preheat dispensable, since this intermediate step directly with the filling of the Tumble dryer is coupled. Instead of six process steps so far: removal flakes from car wash, pre-drying, extrusion / granulation, Crystallisation, preheating, Solid state post-condensation, the process is so on five process steps shortened: Removal of the flakes from the washer, pre-drying, extrusion / granulation, Crystal neutralization / preheating, Feststoffnachkondensation. It's not just a heating step, it will also be a promotion step saved, since previously transported before and after the crystallization had, but now the promotion directly during the Crystallization / preheating he follows. Because the beginning of discontinuous process management ago the crystallization has been relocated and the transport routes are reduced a cool down of the crystalline material prevented. This can save energy and the capacity existing facilities increased become.

Of course, the inventive device for conveying and simultaneously heating material not only in the recycling of plastic material but also in converting of amorphous plastic material purchased, for example, in the form of recycled or fresh PET granules or flakes, into semi-crystalline or crystalline plastic material.

in this connection is the procedure only from the steps of crystallization / preheating and solid postcondensation.

Out The above illustration has made it clear that the benefits of the generic method WO 2004/106025 with the aid of the present invention be, with additional Simplifications, especially in terms of equipment, a more efficient Energy use and an increase the capacity existing facilities become.

Claims (19)

Process for treating plastic material, such as polyester, in particular for recycling polyethylene terephthalate (PET), eg from beverage bottles, preferably for the production of food grade PET, and in particular for converting amorphous plastic material, for example in the form of granules or flakes, into crystalline plastic material, with at least one of the process steps extrusion, granulation or solid postcondensation, wherein before the extrusion / granulation a predrying step and / or prior to solid postcondensation a crystallization step is performed, characterized in that plastic parts of the plastic material, in particular plastic flakes or granules, at least during the predrying step, during the crystallization step or the preheating of the plastic material during or before the Feststoffnachkondensationsschritt simultaneously be conveyed and heated, said heating by irradiation with electromagnetic radiation, in particular infrared radiation, preferably near infrared radiation, takes place and the plastic parts are separated during conveying to effect by producing a plastic part conveying atmosphere mixture, so that substantially each plastic part is irradiated and thus heated. Method according to claim 1, characterized in that the crystallization step and the preheating step take place simultaneously. Method according to claim 1 or 2, characterized in that the promotion and production of the Plastic part delivery atmosphere mixture due to gravity Dropping the plastic parts are carried out in a downpipe. Method according to claim 1 or 2, characterized in that the promotion and production of the Plastic part conveying atmosphere mixture by a Air flow promotion he follows. Method according to one the claims 1 to 4, characterized in that the plastic parts during the conveying be slowed down. Method according to one the claims 1 to 5, characterized in that the density of the plastic part conveying atmosphere mixture while of promoting adjusted and homogenized. Facility ( 1 ) for conveying and simultaneously heating material, in particular plastic parts, such as plastic flakes, plastic granules, plastic particles or the like., Preferably made of polyester, in particular of polyethylene terephthalate (PET), with a conveyor line ( 2 ) and means for conveying, characterized by a radiation source ( 3 ), which irradiates and heats the material at least along a part of the conveying path with electromagnetic radiation, in particular with infrared radiation, preferably near infrared radiation, and means for producing ( 2 . 5 ) of a material conveying atmosphere mixture, so that substantially each material part is irradiated with infrared radiation and thus heated. Device according to claim 7, characterized in that the conveyor line a delivery pipe ( 2 ). Device according to claim 7 or 8, characterized in that the means for promoting a blowing device or a suction device, which the material parts in the air flow promoted. Device according to one of claims 7 to 9, characterized in that the conveying pipe as a substantially vertical downpipe ( 2 ) is carried out, so that the transport takes place by the action of gravity on the material parts. Device according to one of claims 7 to 10, characterized in that the means for producing ( 2 . 5 ) of the material-delivery atmosphere mixture are adapted to adjust the density and homogenize, so that all parts of the material are exposed to substantially the same time with the substantially same radiation intensity. Device according to one of claims 7 to 11, characterized in that the means for producing the material conveying atmosphere mixture of at least one of the elements sieve ( 5 ), Swirler, deflector, displacer or Ge include blower. Device according to claim 12, characterized in that the means for producing the material conveying atmosphere mixture further means for shaking, in particular of the sieve ( 5 ). Device according to one the claims 7 to 13, characterized in that the conveying path and / or the means for preparing the Matrial conveying tube atmosphere mixture a container, in particular a cyclone. Device according to one the claims 7 to 14, characterized in that in the conveying path reflectors for the electromagnetic radiation are provided. Device according to one the claims 7 to 15, characterized in that further comprises means for stripping the material parts provided in air, steam, inert gases or hot air are. Device according to one the claims 7 to 16, characterized in that further comprises means for suction arising volatile Products, for example of water vapor, contaminants or the like., are provided. Device for treating plastic material, such as polyester, in particular for recycling polyethylene terephthalate (PET), eg from beverage bottles, preferably for producing food-grade PET, and in particular for converting amorphous plastic material, for example in the form of granules or flakes, into crystalline plastic material, with at least one extruder, a granulator or a solid reactor, for example a tumble dryer, and at least one pre-dryer, a crystallizer or a heating apparatus, which preheats the plastic material before or in the solid reactor, characterized in that at least the pre-dryer, the crystallizer or the heating apparatus as means ( 1 ) is designed for conveying and simultaneous heating according to one of claims 6 to 15. Device according to claim 18, characterized in that the crystalliser and the preheater are collectively referred to as a device ( 1 ) are carried out for conveying and simultaneous heating according to one of claims 6 to 15.