WO2012037932A2

WO2012037932A2 - Method for producing three-dimensional objects from recycled plastic waste by pressure intrusion

Info

Publication number: WO2012037932A2
Application number: PCT/DE2011/075183
Authority: WO
Inventors: Klaus Seubert; Lutz Elges; Sebastian Wagner
Original assignee: Reluma Gmbh
Priority date: 2010-08-03
Filing date: 2011-08-02
Publication date: 2012-03-29
Also published as: WO2012037932A3

Abstract

The invention relates to a method for producing three-dimensional objects from plastics by means of an intrusion method. The invention relates in particular to embodiments of the intrusion method in such a way that a first and a second molding mass is used, wherein the second molding mass has an elevated content of polyethylene fractions (HDPE, LDPE, LLDPE) and is added to the first recyclate molding mass in changing proportions. The invention further relates to an additional method step within the method, in which method step the recyclate molding masses are desiccated (dried).

Description

Method for producing three-dimensional objects from recycled plastic waste by pressure intrusion

The invention relates to a pressure-intrusion process for the production of three-dimensional objects, which are produced predominantly from recycled plastic waste. In particular, the invention relates to the design of the method with the aim of producing largely vacuole-free three-dimensional objects.

It is known to produce three-dimensional objects from plastic materials. In this case, unmixed plastic masses are used regularly. They are usually processed by the injection molding or the extruder process.

It is also known that, especially in the case of solid or thick-walled parts, there is the danger of the formation of sink marks or vacuoles. Gas-containing ingredients or adhesions of the plastic masses used during and after plasticizing the gases, which form depending on process parameters, either a zone with numerous small vacuoles or large vacuoles. If molded parts contain large vacuoles, they are usually unusable. For parts that contain small vacuoles in a certain amount, their distribution in the component and the proportion of the reduction in mechanical characteristics is decisive for the usability of manufactured parts.

Therefore, the goal is to produce voluminous or thick-walled components made of plastics as far as possible vacuole-free by means of thermal molding processes. It has long been known that large quantities of plastics are recycled through recycling systems after their intended use. These are mainly the so-called bulk plastics, which were used for packaging, films, containers and the like and are disposed of after use over yellow tons or sacks. A not insignificant Proportion of recycled plastic materials also relates to residues from the production of technical plastic parts, which may at least partly also consist of plastics such as polyethylene, polypropylene and polystyrene. It is known that recycled plastic waste of this type is difficult to access for further processing. On the one hand, this is due to accompanying substances, such as printing inks or the adhesion of foreign substances of various kinds, and, on the other hand, to the moisture penetration or contamination of these plastic wastes. However, recyclers of returned plastic waste are required to process the plastic waste supplied to them by means of processes which, as a result, lead to reusable products.

That this is associated with considerable difficulties is evidenced by the fact that only 77% of plastic-rich waste is currently recycled in Germany, of which approx. 35% is recovered energetically and another approx. 23% is recycled.

However, as there is a considerable energy content in recycled plastic waste, it makes sense to reuse the plastics contained therein as materials. It is possible to produce new products in climate-neutral or even climate-friendly manufacturing processes.

One possible solution has been the production of three-dimensional objects by means of the pressure-intrusion process. Using this method, it is possible to produce moldings that can be used in many fields without the need for time-consuming sorting, separation of substances and expensive cleaning measures with comparatively low energy input. In principle, recycled molding compound supplied in an extruder is plasticized, thereby filling an intrusion mold.

With all the above-mentioned advantages, there are a number of difficulties in carrying out such a pressure-intrusion process, which nullify the success can do. On the one hand, it is known that the plasticate must have good flow properties when filling the mold. In that regard, it is also known that a high proportion of the material polyethylene causes advantageous flow properties of the plasticizer. On the other hand, it is known, in turn, that an excessively high proportion of polyethylene adversely affects the strength properties of the molded parts and therefore precludes their use for certain fields of use.

Thus, there is a need for users of Druckintrusionsverfahrens to minimize the proportion of polyethylene and its derivatives so far that the formation of the moldings in the forms of intrusion is still error-free, on the other hand, however, the mechanical strength reaches high levels.

To meet the needs of users who use a recycled plastic compound to perform a pressure-in-extrusion process, the recycling industry has established product specifications for recycled batches of recycled plastic waste as appropriate. In order to make such mixtures of different plastics available for further processing, the German Society for Recycling Economy and Commodities mbH and Duales System Deutschland GmbH have specified product specifications for recycled plastics. The applicable product specifications 04/2009 Fraction number 350 "Mixed plastics" as well as their new version in 03/2010 Fraction number 352 "Mixed plastics" specify the most important types of plastics as well as the possible content of impurities. Thereafter, such a mixed plastic must have only 90 percent by weight of mixed plastic. There are no concrete specifications for the shares of certain types of plastic, since it is only required that the main fraction of 90% should be composed of the plastics PE, PP and PS.

Several other recyclers of recycled plastic waste mainly follow these guidelines, but also supply recycled mixed plastics according to other product specifications, such as 04/2007 Fraction number 310 "Plastic films", 04-01 / 04 Fraction number 321 "PO bottles" and 04 / 2007 Fraction number 322 "Plastic hollow body". The mixed plastics prepared according to the above product specifications are not suitable for processing in the context of an extrusion process using extruders. In addition to far too high levels of impurities, especially the plastics PET and PVC with their variations are decisive for the inapplicability. Further processing of these mixed plastics therefore faces a number of problems. Thus, the proportion of contaminants must be lowered by appropriate measures of re-sorting. Furthermore, the main fraction indicated with 90% can vary so much that a further processing by a pressure-intrusion method is excluded.

Processors can therefore not draw conclusions about the processability of the supplied mixed plastics from deliveries that comply with the product specifications 310, 321, 350 or 352, since the variation ranges for individual components are much too large. You therefore have to re-examine the supplied mixed plastics according to your own criteria and take appropriate measures to produce the processability. As shown above, recyclate plastic materials recycled into the material cycle are never sorted. They have varying proportions of different types of plastics with a predominant proportion of the so-called mass plastics, but also unavoidable proportions of foreign substances inseparably associated with the recyclate plastic compositions, such as coatings with chemicals or printing inks, metallizations, non-or difficult to process plastics and the like.

Such type recycled plastic materials are also subject to impurities that impede further processing or exclude completely. Such impurities can be metallic constituents, adhering residues of packaging contents, dirt or foreign bodies, such as stones, soil or foreign substances. However, the most essential by-product is water that is contained in a high percentage of the blend of recycled plastic pulp with residual residues of ingredients, precipitates, the remainder of cleaning operations, and the like. With regard to the water content, no limit value results from the product specifications mentioned above, since these are based on the solid fractions.

However, there is a need to significantly increase the proportion of recycled plastic masses from recycling processes in the coming years and at the same time limit energy recovery.

It is known that a recycled material from the above-described recycled plastic materials after melting, mixing, shaping and subsequent cooling results in a component having strength characteristics which correspond approximately to those having the plastic type with the lowest strength characteristics. Often they are still over it.

It would be conceivable to process the substance mixture via an extrusion process. However, this possibility is largely eliminated because of uncontrollable rheological conditions.

The recycled plastic waste is adversely affected by adherent moisture on the one hand and by the mixing ratio of the various plastics on the other hand.

The elimination of adhering moisture and, in connection therewith, the discharge of further gassing ingredients has been solved in the prior art by various extruder types which provide a degassing zone. In the processing of recycled plastic materials, the achievable degassing of the molding compositions are insufficient.

In DE 40 21 751 A1 it has been proposed with a different objective to even deliberately add water to the molding compound to be extruded, which is then used as such said entraining agent in the degassing zone of the extruder with the simultaneous entrainment of residual monomer should escape again.

This procedure is completely unsuitable for recycled mixed plastics, since the proportion of moisture and gaseous residues is several times higher and therefore a degassing before the entry of the recycled plastic material in the extruder is necessary.

According to a proposal in DE 42 01 330 A1, the dehumidification is to be achieved in that the extruder is preceded by a further extruder, which plasticizes the molding composition for a first time and then conveys it into a relaxation region. According to this proposal, a predried molding compound is to be plasticized in the upstream extruder and immediately pressed through a filter screen, with the molding compound subsequently being pressed in several strands into a dropping step via a multi-hole die. According to this proposal, the then strand-like molding composition should dissolve into individual drops with a large surface. About a chute, these drop-shaped particles are to fall into the feed opening of the downstream extruder and a blown film can be generated with this and the now dehumidified and solids-free molding compound.

This procedure initially involves washing the plastic waste after it has been crushed. At the same time, the floating fraction is to be removed during the washing process so that ultimately only buoyant plastic particles of HDPE, LDPE, LLDPE and PP are present in the starting material to be processed.

Washing necessarily requires a downstream drying process. This alone makes this process more expensive because of the considerable amount of energy to be used.

The method described above may be suitable for producing intrusion moldings instead of blown films. However, the preparation of the starting material always makes the application of this method un- economically. It can no longer be done climate-friendly production of intrusive moldings.

It would also be possible to thermally liquefy or plasticize such mixtures, to fill in molds and thereby to compact. In this case, however, no pore-free body can be generated, which is why they are only partially usable. Ultimately, in this molding process, the dimensional stability of the parts obtained depends on such factors as the density of the starting material, the process temperature and the degree of compaction.

It is known to produce geometrically determined moldings by filling a mold with the aid of an extruder. Depending on the design of the extruder channel forms in such an arrangement, a working back pressure in the extruder, which is at a low level. The quality of the molded three-dimensional objects is therefore dependent in this process, especially on the theological properties of the molding material. At the same time, the filling process of the mold quickly comes to a standstill and shrinkage processes during the cooling cause vacuity-reducing vacuoles in the interior of the three-dimensional objects. Due to the insufficient degree of filling of the molds creates a rugged surface at the same time.

The biggest problem in the processing of mixed plastic molding compounds from recycled plastics results from the moisture content of these materials, since at the usual processing temperatures, which are well above the boiling point of the water, the moisture contained tends to vapor bubble formation. When filling hollow molds, this results in irregular surface structures and so-called vacuoles. If the plasticized molding compound is introduced into a mold with an extruder, a relaxation process of the molding compound takes place immediately after entry into the mold, which enables vapor bubble formation and voids are formed in the area of the flow deltas. At high moisture content vacuoles of different sizes can extend over the entire molded part. In order to suppress this undesirable effect, a so-called pressure-intrusion process has long been in use, in which the molding compound is pressed under increased pressure in the filling nozzle into the molds and once again subjected to the high filling pressure after the end of the filling process. In this way, an attempt is made to generate a high pressure in the resulting vacuoles and thereby bring them to a lower volume.

A major disadvantage of this method, however, is that neither the filling of the mold nor the subsequent cooling process of the molded part in the mold, the formation of the vacuoles is controllable.

This can lead to the formation of large vacuoles, which either accumulate in the upper region of the molded part or extend over wide areas of the molded part. The strength and processing properties of such moldings are reduced to uselessness.

In particular, in order to counteract these effects during the cooling process, it has been proposed in DE 295 13 585 U1 to significantly accelerate the cooling rate of the molded part by using water as the coolant. However, the effects described above are still present.

In DE 42 19 595 A1 it is proposed to reduce the filling speed or the volume flow when casting moldings to such an extent that the enclosed moisture can expand in the molding compound and escape from it, so that a relaxation process becomes possible due to the delayed filling process is and preferably form small volume vacuoles, which should then be distributed substantially uniformly over the cross section of the molding. The resulting reduced throughput affects the economics of this process.

However, the large number of small vacuoles can have a lasting effect on the mechanical strength and the processability of the moldings produced in this way. It has also been proposed to use ventable molds. However, this results in an increased effort, since the venting points must be observed and sealed at the exit of molding material. Furthermore, the formation of internal vacuoles can not be ruled out in this process as well.

According to a further proposal in DE 42 19 595 A1, the formation of vacuoles should be prevented in that the casting molds are subjected to compressed air and the molding material must therefore be filled against the internal pressure in the mold.

However, since the trapped in the molding material moisture has an extremely higher than the boiling point of the water temperature, it comes to explosive relaxation, which can not be avoided by an increased back pressure in the form.

With the measures described above, the formation of vacuoles in the moldings to be cast can be avoided only to a limited extent. There is therefore a need to apply methods in the use of the proportion of moisture in the molding composition significantly reduced and therefore the probability of the formation of vacuoles by gaseous admixtures is reduced from the outset.

It would be possible to dry the supplied recycled plastics before re-plasticizing. When using appropriate drying systems, however, results in a considerable expenditure of energy, energy losses and thus also a poorer energy balance of the shaping process. This counteracts the actual goal of plastics recycling to achieve recycling with a minimized use of energy. Another disadvantage of upstream drying processes is due to other buildup of the recycled plastic masses than water. During the drying process, an odor nuisance may arise, which leads to further follow-up measures. The supplied plastic materials have very different particle sizes and textures. Therefore, they must first be brought to the same particle size as possible with a narrow spread range. Drying processes can only be effective after that. This in turn requires a large-scale design of the plants if the throughputs required for further processing are to be achieved.

In accordance with the above-mentioned possibilities and their disadvantages, it should be noted that the production of three-dimensional objects from recycled plastic waste with a pressure-intrusion method has not been satisfactorily solved so far. In particular, the following issues remain unresolved by the proposed procedures and annexes:

- The recycled plastic masses must be largely free from gaseous admixtures or buildup prior to the onset of the print intrusion to minimize the chance of vacuole formation.

With regard to their flow properties, the plasticates produced from the recycled plastic materials in the extruder must be able to completely fill both large-volume and pressure-intrusion molds provided with deposits and / or mold undercuts without defects or vacuoles being able to arise.

- The stochastically distributed proportions of various plastics in the recycled plastic waste supplied are to influence the flowability of the plastic and optionally also depending on the object to be produced so that an article is formed, the highest possible component strength at the same time acceptable surface of the molded articles Has. The above-mentioned requirements can not be met with the solutions described in the prior art. It is therefore the object of the invention to propose methods for producing three-dimensional objects from recycled plastic waste by means of the pressure intrusion method, which allow control of the flow properties of the produced plasticate in order to achieve fully formed and largely vacuole-free three-dimensional objects with at the same time high component strength are easily controllable and create conditions in terms of energy expenditure to produce the molded objects climate-neutral or climate-positive. This object above is achieved with a method for producing three-dimensional objects from recycled plastic waste with the features of claim 1. Secondary and subordinate claims describe embodiments of the method according to the invention, without limiting the scope of the invention to these.

In the following description, embodiments and claims, the following terms are used with the following meaning: Recycled waste plastics are waste plastics which consist of a collection system or of industrial plastic wastes and contain a high proportion of polyolefins. The recycled plastic waste can comply with the product specifications 310, 321, 322, 350 and 352 of the recycling industry and contain about 90 percent by weight mixed plastic, especially polyethylene, polypropylene and polystyrene.

Recyclate plastic compound - is a recycled mixture of recycled plastic waste. Plasticized molding compound mixture is a recycled plastics material heated above the plasticizing temperature and, in extruders, agglomerators, pelletizers, heating tunnels or similar devices, at least modifying the initial shape of the particles in a changing manner. Druckintrusionsform- is a negative mold with the ability to connect to a filler neck, which is filled for the purpose of filling with the plasticized molding composition, then shut off against the filler and is subjected to a longer cooling cycle, at the end of the Entform- the object is.

According to the invention, recycled waste plastics, which are to be processed into new three-dimensional objects by means of a pressure-intrusion process, are prepared in such a way that optimum results are achieved when plasticizing the molding material mixture and filling the pressure-curing mold.

That is, an optimum is sought between the strength of the molded three-dimensional article, the proportion and size of vacuoles and its surface finish.

In this case, the invention takes into account that the flowability of the plasticized molding composition substantially depends on the proportion of the plastic polyethylene in the plasticized molding composition. Also, that depends on this proportion, the surface quality of the three-dimensional objects to be achieved.

The invention also takes into account that the proportion of polyethylene further depends on the strength characteristics of the molded three-dimensional objects. According to the invention, therefore, the pressure-intrusion process is controlled so that the plasticized molding material just contains the required amount of polyethylene, which leads to the full formation of the three-dimensional objects. If an improved surface structure is required, the proportion of polyethylene in the plasticized molding composition can be adjusted.

The invention takes into account that delivered recycled plastic waste can have a stochastically distributed proportion of polyethylene components. This may vary according to the product specifications of the recycling industry. between 0 and 90%, but will probably be about one third of the recycled plastic mass.

Greater fluctuations in the recycled plastic masses delivered make it possible to separate out batches with a significantly higher proportion of polyethylene before processing.

For this purpose, the content of polyethylene is first determined in the delivered recycled plastic waste. The test result is decisive for the further treatment of the recycled plastic waste.

Batches with a high content of polyethylene can be separated from the delivered recycled plastic waste. As a result of the investigation to be carried out, a first mixture with a known proportion of polyethylene is present for further processing.

In the case of the discarded batches, the proportion of polyethylene is then determined again, so that measures for their further treatment can be determined.

By means of the discarded batches and possibly using almost sorted polyethylene waste a second recycled plastic mixture is prepared, which has an increased polyethylene content.

First and second mixture are each prepared separately to a recycled plastic mass by a size fractionation is carried out, foreign components (stones, metal objects, etc.) are sorted out and, if necessary, difficult to process plastics, such as polyvinyl chloride and polyethylene terephthalate are additionally discarded. The latter ingredients may remain in the mixture to some extent. However, if this is too high, the pressure-intrusion process is disturbed and the proportion of these materials must be lowered by targeted removal from the mixture. The treatment of the two mixtures after comminution or sorting refers in particular to the removal of gaseous constituents, such as water, remaining buildup of contents of recycled packaging and the like.

The elimination of such buildup occurs, if necessary, prior to the production of a plasticized molding compound mixture. In this case, process steps which initiate a drying process are preferred.

The two recycled plastic mixtures are subsequently mixed in a ratio which, in accordance with the criteria described above, is suitable for reliably forming the three-dimensional objects to be produced. For this purpose, first the proportion of polyethylene in the first recycled plastic mass is determined and then adjusted by metered addition of the second recycled plastic mixture of the required for further processing polyethylene content. Subsequently, the recycled plastic mixture is fed to an extruder, which plasticizes the same and filled via a filler neck the Druckintrusionsform.

Due to the performance of the extruder, the filling of the pressure-in-mold takes place over a longer time interval. It comes by contact of the molding compound with the walls of the mold to partial cooling and an incipient cooling process from outside to inside.

Towards the end of the filling process, the pressure of the inflowing molding compound is increased via the filler neck, in order to fully mold the surface structure of the three-dimensional object and at the same time minimize the volume of gas bubbles contained in the molding compound. Completely filled Druckintrusionsformen be closed and separated from the filler neck. Subsequently, they are subjected to a cooling process, at the end of which the three-dimensional object is demolded. The procedure described above can be adapted in various ways to circumstances, as far as this results from the particularities of the recycled plastic waste used, from plant-specific features o- special features of auszuformenden with the three-dimensional objects. For example, it may be provided that the recycled plastic waste supplied to the process is already sorted according to specifications that place significantly higher demands on the product specifications explained in the prior art.

It is also possible to introduce recycled plastic waste already in a pre-plasticized, agglomerated, pelletized or granulated form into the process according to the invention, provided that after delivery as the second step, the determination of the polyethylene content.

Furthermore, it can be provided to shred the recycled plastic waste before or after a rough cleaning. In this case, all commonly used methods and systems can be used.

It can be envisaged to temporarily store both the recycled plastic waste delivered and the recycled plastic materials produced during processing.

For the cleaning of the recycled plastic waste, everything can be used in procedures and facilities, which allows the success of a measure to be carried out to remove certain admixtures. So manual as well as automatic sorting can be considered.

With regard to transports between delivery and processing or between preparation, dehumidification (drying) as well as between dehumidification (drying) and plasticizing, all conceivable conveying means can be used come. This applies, for example, to manual conveyance, mechanical, pneumatic conveyors, hoists or material handling equipment.

An advantageous embodiment of the method according to the invention arises when the selection criterion for the mixing ratio between the first and second recycled plastic mass is the recognized flowability of the plasticizer. About the final share of polyethylene fractions, especially of individual polyethylene grades, the flowability of the plasticized material is determined. It can also be provided to apply the number and / or size and / or distribution of vacuoles or the resulting surface quality of the molded three-dimensional objects as a selection criterion for the mixing ratio of first and second recycled plastic mass. A particularly advantageous embodiment of the method according to the invention arises when a particularly high proportion of low-pressure polyethylene (LDPE) is provided in the production of the second recycled plastic mass.

Particularly advantageous is an increased proportion of linear low-density polyethylene (LLDPE).

The mixing of the first and the second recycled plastic mass may take place in a mixer, a conveyor, an agglomerator, a hot pelletizer or an extruder.

It can be provided an operation after which a dehumidification (drying) is provided at least by heating the recyclate plastic compositions above a temperature of 373 ° K prior to the preparation of the plasticized molding material.

For the dehumidification (drying), various facilities, such as drying tunnels, agglomerators, Heißpelletierer, presses or extruders may be provided. If the recycled plastics material already dehumidifies sufficiently after dehumidification (drying), it can be fed directly to the extruder.

A preferred form of dehumidification arises when, by way of increasing the temperature, it is ensured, in particular, that moisture contained passes into the vapor phase and moisture contained in the recycled molding composition can be removed in this way with little expenditure of energy. In particular, the energy required for dehumidification can thus be significantly reduced. Particularly suitable for such a method step are a microwave-producing drying unit or a cascade of two extruders with a relaxation section arranged between the two extruders.

Especially in the latter case, a period is provided in the process which gives the already plasticized molding material an opportunity that after the exit from the extruder contained in the molding compound vapor or gas inclusions can diffuse to the surface of the molding compound and escape from the same.

It may further be provided to divide the exiting plasticized molding material flow by measures to increase the surface area, to generate a particle flow or to provide a prolonged expansion phase.

Even before the solidification process can begin, an increase in the filling pressure, at least to three times the filling pressure, takes place immediately following the filling. This ensures that the mold is completely filled, that no voids form in the molding and thus the moldings can be demolded after cooling dimensionally stable and dimensionally stable.

After completion of the high-pressure filling phase, the mold is closed, separated from the second extruder and transported into the cooling zone. The cooling process can take place after its beginning over a longer period, wherein the molding can remain in the mold until it reaches the ambient temperature. It is possible to accelerate the cooling process by using cooling media.

A preferred embodiment of the method is that the molding material is brought into the mold via a pressure-intrusion process. In this case, care is taken that an increased pressure is built up in the feed channel, wherein the pressure level should expediently be at least 20 bar. Thus, on the one hand, a largely laminar flow and at the same time a high flow velocity are ensured in the feed channel.

A further preferred embodiment of the method is that at the end of filling the mold both in the mold and in the feed channel of the extruder, a pressure increase takes place, which is at least three times the filling pressure. The increased pressure is then maintained and the mold is separated from the extruder, thereby largely avoiding the formation of vacuoles in the three-dimensional article.

With the method described above, three-dimensional objects can be produced which have a cylindrical, a rectangular or a polygonal cross-section.

It is also possible to incorporate a profiling of the surface into the mold. It is also possible to make conical shapes. The manufactured three-dimensional objects can be used for a wide variety of applications. Thus, applications such as pegs, posts, railway sleepers, sheet piling, supports, for tubular parts or masts are possible. If the three-dimensional object is to be used as a pole, it can taper off at its end face and its tip can be formed of the same material.

It is possible to introduce inserts into the mold and in this way to make recesses in the three-dimensional objects during the initial molding process. bring to. These are also flowed around by the inflowing molding compound and thus molded virtually negative.

Preference is given here to the approximately coaxial arrangement of inserts, which make it possible to produce a cavity in the center of the shaped three-dimensional objects. This cavity can be available for other tasks when using the three-dimensional objects, as is the case, for example, with antenna or lampposts through the electrical installation located in the interior.

A preferred embodiment of the method is to accelerate the cooling in the area of the inserts of the shape such that the solidification process of the three-dimensional object takes place from the inside and thus cools the three-dimensional object substantially without tension. It does not matter in which way the cooling is effected, which cooling medium is used and how the cooling process is otherwise configured. Ultimately, this is an optimization task determined by the three-dimensional object to be generated. In the production of hollow molds, it is possible that in the shell of the three-dimensional object recesses are additionally formed.

One form of use of such a hollow profile with an additional recess for connection to the inside is a lamp post, which tapers upwards regardless of its external shape.

The three-dimensional objects produced by the method according to the invention described above are sufficiently strong, stable, insensitive to the effects of weathering, seawater-resistant and rot-proof for the above-mentioned uses. Furthermore, they are climate-neutral and ecologically harmless. In addition, at the end of their life cycle, they can be recycled back into the raw material cycle and thus serve again as a raw material base for three-dimensional objects to be produced according to the method described above. The invention will be explained in more detail below with reference to some embodiments and drawings. Showing:

Fig. 1- is a schematic representation of an intrusion process, as in

State of the art is carried out with known systems. the inventive method, illustrated by a comparison with FIG. 1 Modified schematic representation. 2 shows a schematic representation of the sequence of a further preferred embodiment of the method according to the invention according to FIG.

According to the methods known in the prior art, the processors can be according to step 1. deliver recycled plastic waste that can comply with product specifications 310, 321, 322, 350 or 352. It may also be separately collected packaging residues, residues of technical plastic parts or the like. A proportion of foreign substances is also regularly included.

The delivered recycled plastic waste is shredded after delivery according to step 2. and then sorted according to step 3., where both processing steps can be exchanged with each other in the order or even linked together.

By the aforementioned steps, a recycled plastic material is produced, which is either further processed directly or, if necessary, according to step 4. stored in silos, sacks or large containers. In a direct way or from the interim storage facility, the recycled plastic mass is further processed into a plasticized molding compound in accordance with process step 5 via an extruder, and this is filled with an intrusion mold connected to the extruder in accordance with step 6.

The filled intrusive mold can be removed from the extruder after filling and stored intermediately. In the intermediate storage is carried out according to step 7. the cooling process of the molded parts, wherein after reaching a certain component temperature the same, as indicated in step 8, can be removed from the mold.

The demolded part can then be stored temporarily or, if necessary, subjected to a machining operation.

The inventive method, however, provides that after the with 1. This means that when the recycled plastic waste is handed over in an intermediate step 1 .1. the content of the delivered masses of the polyethylene fractions HDPE, LDPE and LLDPE is determined.

It may be another intermediate step 1 .2. be provided in the identified batches with particularly high levels of polyethylene fractions from the delivered recycled plastic waste are discarded. A special feature may be that - if possible - delivered batches that fully comply with product specification 321 are also sorted out without determining the content of PE fractions.

An embodiment of the method may consist in the fact that with the delivery of recycled plastic waste a separation of batches with high PE contents already in step 1. he follows. Likewise, PE industrial waste and the like can be accepted in this step. In the subsequent step 2, the recycled plastic waste shredded and sorted in a step 3., whereby both steps can be interchanged or linked together in the process of the invention.

However, it is essential that delivered recycled plastic waste with "normal" content of PE be processed as the first recyclate plastic mass.

Separate batches with high PE content and optionally PE residues are processed in the same way, but separately, to a second Recyclat- plastic mixture, that is crushed and sorted.

First us second recyclate plastic mixture can be stored temporarily or further processed directly.

When carrying out the intrusion process, the production of the first and second recycled plastic mixtures is usually synchronous with the production of the three-dimensional objects. During filling of the intrusion mold, therefore, the flow behavior of the plasticized molding compound is observed during filling of the molds and decisions are derived from the results obtained, in which way the flow behavior by increasing or decreasing the proportion of the second recycled plastic mixture is required.

Alternatively or additionally, information about this can be obtained by evaluating already formed three-dimensional objects and also influencing the proportion of the second recycled plastic mixture to be admixed.

A preferred embodiment of the method provides that, after the work steps 2, 3 or 4, the proportion of PE fractions in the total mixture is already determined on the first recycled plastic mixture. From the results of the tests and in connection with any proportions of other plastics that may have been detected, the necessary proportion of PE fractions can be deduced and an adaptation can be achieved by varying the addition amounts of the second recycled plastic mixture.

A preferred embodiment of the method according to the invention additionally provides, after the 4th working step, for dehumidifying the recyclate plastic mass which is to be processed. This can be done by means of agglomerators, hot pelletizers or by an extruder cascade. The recycled plastic mass is heated above the plasticizing temperature, whereby a large part of the moisture contained in the vapor phase passes and escapes from the molding compound.

If an extruder cascade is used in this case, it is designed in such a way that the extruder charged with the recycled plastic mass initially plasticizes it and conveys the plasticized molding mass flow back into the open. By plasticizing takes place on moistened plastic mass particles, a temperature increase, which also leads during the plasticization to an isochor-adiabatic pressure increase and the inclusion in the form of vapor bubbles in the molding composition. After the molding compound has been discharged to the outside, a large part of the moisture can escape through the then possible expansion of the trapped water vapor.

The period of relaxation can be optimized by choosing the time duration, by increasing the surface of the molding compound and by the transport speed of the molding material.

Dehumidifying operation 5 may also be carried out by means which are particularly suitable for vaporizing water contained in the molding compound. Typically, this can be done using microwaves.

Other options include heating up the molding compound with the aid of hot or hot air, direct heat supply via heaters or infrared radiation, so that the water contained in it escapes. Through the extruder screw, the plasticized molding compound is conveyed into the filling channel of the extruder, which tapers strongly up to the outlet opening. This ensures that the molding mass flow when flowing through the filling channel builds up a pressure greater than 20 bar and enters the mold with this pressure level. This pressure intrusion ensures complete filling of the mold.

At the beginning of the filling process, the plasticized molding compound shoots into the mold as a homogeneous mass flow. Subsequently, the mass flow first relaxes and the molding material swells up. Upon contact with the wall, solid particles solidify, accumulate near the wall, but are still heated by the incoming mass flow. This results in the mold during filling a comparatively rapid formation of a solidified outer skin, while still flowing in the interior of molding compound with a higher temperature. After the mold volume is largely filled, further molding compound is pressed through the extruder, wherein an increase in pressure takes place at least to five times the filling pressure. This measure ensures that the mold fills completely and no defects can form. Furthermore, it is achieved that inside the moldings during the subsequent cooling phase no voids can arise. At best, a formation of small bubbles may occur in the core area.

Another embodiment of the method according to the invention relates to the cooling phase.

The mold to be filled is additionally equipped with a deposit to produce moldings with a cavity. In the contact area of the insert with the outer shape, the outer shape is broken, so that the interior of the insert access is possible.

After filling the mold using the procedure described above, compressed air or water is fed into the interior of the insert via a supply line. The accumulated heat in the interior of the insert is thus eliminated and at the same time increased heat extraction is achieved. Due to the increased removal of heat, a reversal of the cooling process can be achieved, wherein initially the particles of the molding compound in contact with the insert solidify and the solidification process can take place from the inside to the outside.

Once this solidification process has started, it will also run until the ambient temperature is reached. Depending on the rate of cooling, the molding can be cooled more or less quickly and more or less stress-free. Ultimately, this is an optimization task.

The three-dimensional objects produced by the method according to the invention can be embodied with a cylindrical, a rectangular or a polygonal cross-section. Likewise, hollow shapes, such as tubular, box-shaped or the like can be executed.

It has been found that preferably elongate moldings are to be produced by the method according to the invention. Preferred embodiments are therefore cylindrical moldings, pegs or piles, boards or planks, beams, sleepers and molds, such as columns with conical holes, rectangular blocks with conical holes and antenna or lampposts, which are also conical on their outer contour.

A particularly preferred use are lamp posts with a lateral recess for the installation of the electrical system.

In the manufacture of piles, an embodiment is preferred in which the end to be driven is already made pointed in the form.

When profiled boards are used, molds having profiling on at least one of the outer surfaces formed by the molding are used. Since the method according to the invention advantageously makes it possible to produce elongated bodies, cuts are made in the production of railway sleepers by a separating process which correspond to the length of the railway sleepers.

When filling the mold is carried out by the method of pressure intrusion. That is, the pressurized molding compound shoots with overpressure in the mold and distributed after the release in the mold cavity immediately immediately. Furthermore, a continuous flow then forms inside the mold space, while in areas near the mold wall a cooling and hardening process already takes place. The already in cooling particles of the molding material at the same time form a heat insulating jacket through which the molding compound flowing in the interior is largely maintained at temperature and forms a flow channel within the mold, which allows the filling of very long shapes without the molding mass flow solidifies.

A preferred embodiment of the invention consists in the production of hollow profiles. In the process, a sufficiently conically shaped core is inserted in the interior of the mold so that a channel which is sufficient for the molding material flow remains on each side.

When filling the mold with molding compounds, a solidifying layer is also formed on the inserted mold core, which at the same time isolates the molding compound from the environment.

In this embodiment of the method, hollow profiles, such as conical tubes, light poles, shaft inlets and the like can be produced. It is also possible to achieve lateral recesses in the molded part by inserting inserts into the mold which bridge the distance between the outer jacket and the inserted core. Another preferred form of the method provides that the core to be inserted is hollow inside and offers the possibility of introducing cooling media. In this case, for example, with compressed air increased heat removal during cooling of the molding achieved and thus the curing of the molding from the inside out are possible.

It has been found that distortion-free hollow body can be produced in this way, in which by the cooling from inside to outside a permanent de-stressing is achieved.

The moldings produced in this way can be used as conical tubes, after boring as conventional tubes, as light poles or the like.

If the shape is that of a lamppost, insertions in the form can at the same time be used to form the shape for the installation opening.

The inventive method thus has the advantage that on the one hand at least sufficient flow properties of the plasticized molding composition by mixing a first and a second molding compound and on the other hand, a reduction in the moisture content or the content of other gassing substances causes and thus conditions are created, intrusive moldings to significantly reduce the risk of malformations and inappropriate levels of vacuoles.

Claims

claims

1 . Method for producing three-dimensional objects from recycled plastic waste by pressure intrusion, which is subdivided into the following procedural sections:

- preparation of a mixture of recycled plastic waste in order to obtain a processable recyclate plastic mass,

Treatment of the recycled plastic mass with the aim of freeing it of admixtures and / or adhesions,

Plasticizing the recycled plastics material to a molding material mixture,

Filling a pressure-intrusion mold with the plasticized molding composition,

Aftertreatment of the filled Druckintrusionsform including cooling and demolding of the three-dimensional objects, characterized in that

recycled plastic waste is used to produce the first recycled plastic pulp whose main components are polyethylene, polypropylene and polystyrene in varying proportions depending on the amount of recycled plastic waste

the polyethylene content of the first recycled plastic mass is determined, recycled plastic waste is used to produce a second recycled plastic mass whose main constituents are polyethylene, polypropylene and polystyrene, the polyethylene content being increased compared with the first recycled plastic mass,

a determination of the required content of polyethylene and of the proportion of the second recycled plastic mass to be mixed to the first recycled plastic mass takes place,

the proportion of the second recycled plastic mixture is supplied

and mixing the proportion of the supplied second recycled plastic mass with the first recycled plastic mass.

2. Method according to claim 1, characterized in that

the selection criterion for the mixing ratio of the first and second recycled plastic mass is the flowability of the plasticized molding compound.

3. The method according to claim 1,

characterized in that

the selection criterion for the mixing ratio of first and second recycled plastic mass is the number and / or the size and / or the distribution of vacuoles in the shaped three-dimensional article.

4. The method according to claim 1,

characterized in that

the second recycled plastic material in particular low density polyethylene (LDPE) and / or linear low density polyethylene (LLDPE) contains.

5. The method according to claim 1,

characterized in that

first and second recycled plastics material are prepared by comminuting and / or freeing admixtures and / or agglomerating and / or pelleting from recycled and / or technical plastic waste.

6. The method according to claim 5,

characterized in that

first and / or second recycled plastic material can be prepared by adding plastic materials of a different composition.

7. Method according to claim 1,

characterized in that

the mixing of the first and the second recycled plastic mass takes place in a mixer, a conveyor, an agglomerator, a hot pelletizer or an extruder.

8. The method according to claim 1, characterized in that

a work is included, according to which prior to the production of the plasticized molding compound dehumidification (drying) at least a heating of the recycled plastic compositions over a temperature of 373 ° K takes place.

9. The method according to claim 1,

characterized in that

after a possible process step for dehumidifying (drying) the recycled plastic masses a period is provided in which a relaxation of any resulting vapor and / or gas bubbles and their escape from the recycled plastic mass can take place.

10. The method according to claim 1,

characterized in that

the period of relaxation is performed after an agglomeration, hot pelletizing or intermediate step within an extruder cascade.

1 1 .Method according to claim 1,

characterized in that

the filling pressure of the extrusion mold filling extruder is at least 20 bar.

12. The method according to claim 1,

characterized in that

at the conclusion of the filling of the mold, an increase in pressure takes place to an approximately 5 times the value of the filling pressure of the extruder.

13. Use of a produced by the method according to claim 1 to 12 three-dimensional object made of recycled plastic materials as sheet pile board, profile board, peg, pole, sharpened pole, railway sleeper, mold, tubular part, antenna or lamppost.