DE3523242A1 - Process for recycling thermoplastic film waste, direct feeding device for extruders and system for carrying out the process - Google Patents

Abstract

The process serves for recycling thermoplastic film waste into the thermoplastic processing and is carried out by introducing the non-regenerated film wastes into an extruder supplied continuously with thermoplastic granules by forming, from particulate, comminuted film waste of relatively low bulk density and thermoplastic granules of relatively high bulk density, a mechanically stabilized, virtually homogeneous feed stream of film waste comminuted preferably in the form of flakes and thermoplastic granules and feeding it into the extruder. By this means a separate regeneration of the wastes is unnecessary and thermal degradation of the thermoplastic material as a result of regeneration is eliminated. Further advantages of the process consist in the fact that the economic efficiency of the recycling of thermoplastic film waste can be increased and the danger of dust accumulation on the waste can be reduced or eliminated. The process may be carried out with a simple and reliably operating device (10) which possesses a drop shaft (11) with two mixing zones (M<1>, M<2>) disposed one above the other; a falling stream comprising a premixture with a portion of the granules is initially generated in said mixing zone (M<1>, M<2>) and is then combined with the remainder of the granules. <IMAGE>

Description

Process for recycling thermoplastic film

waste, direct feed device for extruder and installation for implementation of the procedure Process for recycling thermoplastic film waste, Direct feed device for extruder and system for carrying out the process The invention relates to a method for recycling or recovering waste made of thermoplastic films, such as those used in the manufacture of polyolefin films continuously accrues under cutting or trimming in the form of edge strips. the The invention also relates to a device for producing a device for direct feeding in an extruder suitable stream of thermoplastic granulate and flakes and a thermoplastic processing plant to carry out the recycling process.

The term "recycling" of thermoplastic film waste is used here as Recycling understood material utilization; uhter recovery of thermoplastic film waste one understands the recovery of the thermoplastic material contained in the waste in the form of finished products or semi-finished products, e.g. B.

Foils or other thermoplastic extrudates, and generally with addition of fresh and / or regenerated thermoplastic granulate, optionally with the usual additives, pigments and the like.

Foil waste is taking for the recovery of thermoplastic mass especially problematic because of the heating of foil waste for the production of granular Regenerated because of the proportionate large specific surface areas to an increased oxidative degradation or to a leads to a considerable reduction in the quality of the thermoplastic material.

The usual recovery of thermoplastic material from film waste is based ensure that the film waste - if necessary after shredding - to the formation granulate or granular extrudate is heated to sufficiently high temperatures, to bring it to at least a plastic state; that from foil waste available, thermally granulated regrind therefore not only has the cost disadvantage the warming, but also that of an increased quality degradation, the z. B. continuous measurements of the melt index are cumbersome or uncertain and the risk of irregularities in viscosity or melt flow increased in the extrusion of thermoplastic material with such regenerate.

The separate thermal granulation of the Avoid thermoplastic film waste by having the sufficiently shredded ("Foil shred") waste from thermoplastic film material directly as a feed to a Production extruder used; for production operations, however, is normally more thermoplastic is required than in the form of sufficiently homogeneous film waste material is available.

Therefore, the film waste must be mixed with the usual feed material be used that have the usual bulk densities for granulate or regrind of typically 0.4 to 0.6 kg / dm3 or more; Foil shreds with their typical about three to ten times lower bulk density of typically less than 0.1 kg / dm3 tend accordingly in addition to floating up when mixed with granules, which was not a uniform feed mixture for the extruder supplies.

Especially in thermoplastic film production plants where Cutting or trimming of extruded film web material a continuous The waste stream from edge trim material is the processing of the film waste a problem that has not yet been satisfactorily solved, which can either be achieved through centralization recovery (i.e. off-site regeneration) or by installing special Facilities (i.e.

in-house regeneration). In the former case are because of the need for baling presses or storage rooms, additional investments and special operational or

Personnel expenses cannot be completely eliminated, apart from the usual depreciation of about 50%.

In the second case, i. H. in the case of film waste regeneration through in-house processing, either the problem of material uniformity, e.g. B. by sorting by Color and / or material differences, solved or dispensed with homogeneity and a mixed regenerate can be accepted, which is only suitable for products of the lowest Price ranges, such as garbage bags or construction foils, are suitable. There is also the problem of Build-up of electrostatic charges on the film waste and the resultant Accumulation of dust in the waste.

Looking for an effective and economical solution to the in-house regeneration of film waste, which has the problems set out above Approved to solve justifiable equipment and operational expenditure, were allowed in the Course of the investigations leading to the invention by the applicant various systems examined. It was first noticed that the problems of sorting and dust accumulation practically only with "in-line" systems (in the production flow) can be solved, d. H. by making the one with a given production line Film waste stream continuously and preferably without intermediate storage in the material feed this or a parallel production line that works with the same or compatible material returns.

Both compression / cutting methods, which are a tablet-like Delivering material or working with forced feed, as well as secondary extrusion methods investigated in which the waste plasticized in a smaller auxiliary extruder and from this is introduced into the main extruder.

In the first case, the results were mainly due to lack of results Security of an even material feed and in the second case because of a lot too high investment costs not satisfactory.

The object of the invention is to provide a for recycling thermoplastic film waste to specify a process suitable for thermoplastic processing, the "in-house" as well as "in-line" is feasible and with comparatively little installation and operation # Expenditure of trouble-free and value-preserving reprocessing of thermoplastic film waste enables.

The object of the invention is also to provide one for carrying out such a Process suitable device or thermoplastic processing plant to specify.

Surprisingly, it was found that these goals go against the Expectation without a special thermal or compressive regeneration step can be achieved by a simple blending method in which one can see the differences the bulk densities of granulate and film waste not by compression or Seeks to diminish fusion but, on the contrary, maintains or even strengthens it.

The inventive method for recycling thermoplastic film waste in thermoplastic processing is characterized by the fact that the thermally non-regenerated film waste in a continuous with thermoplastic granulate Introduced fed extruder by making out particulate and preferably flaky shredded film waste. relatively lower bulk density and the thermoplastic granulate relatively higher bulk density a mechanically stabilized, practically uniform one Feed stream from the shredded film waste and the thermoplastic granulate forms and introduces this feed stream into the extruder.

As particulate shredded film waste with a relatively lower bulk density " is understood to be one whose bulk density, z. B. expressed in units of kg / dm3, a maximum of a third (33%), preferably less than a quarter (25th %) and typically about a fifth (20%) or less of that expressed in equal units The bulk density of the thermoplastic granulate is, accordingly, a relative has a higher "bulk density and is obtained from conventional fresh and / or regeneratively obtained granulated material can exist.

The bulk density of the particulate comminuted is typical Foil waste about 0.1 kg / dm3 or less, while the bulk density of the granules is about 0.5 or more in equal units.

Also preferably the largest particle dimensions are the scrap film particles on average (e.g. determined by sieving) not more than three times as large and preferably no more than twice as large as the largest average particle dimensions of the granulate (e.g. also determined by sieving).

According to the invention, the feed current is mechanically stabilized; this in connection with the invention denotes a distribution state that occurs during the continuous feeding into the extruder practically no segregation effects shows.

In general, according to the invention, this distribution state is thereby achieved achieved that the mechanically, z. B. in a mill, for the formation of film flakes processed waste, e.g. B.

Edge strips, in falling stream, e.g. B. in a chute, with combined with a first partial stream of granules to form a premix, which is then mostly in the form of a bed with a second granulate substream to the stabilized feed stream is united. The granulate particles cause a hail-like effect in the falling stream Precipitation effect on the flakes and fix them in the resulting premix bed, which collects near the lower end of the chute and continuously together is drawn into the extruder with the granulate of the second substream.

Those formed, for example, in a knife mill and by a conveyor fan Foil flakes passed through a sieve into a cyclone separator can be used in a falling air stream combined with the first granulate substream for premixing will; the air flow can then through corresponding slots in the lower end of the Chute through a bed of thermoplastic granulate, which the The lower end of the chute surrounds any remains of film flakes in the filter-like manner to retain effective granulate bedding.

Since the inventive method in operational and apparatus Is extraordinarily easy to implement, it can also be done in the case of relatively low rates of film waste formation can be carried out in-line, e.g. B.

by the feed stream formed according to the invention again the one Extruder is fed, which also produces the film delivering the waste.

The device according to the invention can accordingly be used as an additional device be designed into a conventional extruder and is characterized by a Chute, e.g. B. an approximately vertical downpipe with a rectangular, circular or polygonal cross-section; the top of the shaft is with a source for film flakes, e.g. B. a mill connected; the lower end of the chute leads to the feed opening of the extruder and through the machine hopper, which surrounds the lower end of the chute; a first upper one opens into the chute Granulate feed and a second lower granulate feed; the chute forms between the two granulate feeds an upper mixing zone to produce a falling stream from a premix of granules and flakes; on the second Granulate feed creates a lower mixing zone to create a bed of particles, in which the premix continues with granules from the lower granule feed is combined and can then be introduced as a feed stream into the extruder.

If the device according to the invention according to a preferred embodiment as part of a thermoplastic processing plant for carrying out the inventive Process is used and connected directly to an extruder as a feed system is, the feed stream can be a material cover lying on the screw of the extruder form that before being drawn into the extrusion cylinder and possibly also additionally mixed during the drawing-in of the screw or the screw thread before the drawn-in material is compressed and plasticized in the extruder.

The device according to the invention preferably also has a generally designed as a funnel upper granulate storage container, one of which The first granulate line leads to the chute and there the beginning of the first mixing zone Are defined; this first granulate line generally has a slide valve or one similarly acting device with which the per time unit in the first mixing zone arriving amount of granulate can be controlled or regulated. A second granulate line leads from the upper granulate storage container to the machine hopper in such a way that their mouth determines the height of the granulate bed in the machine hopper, which one surrounds the chute. This allows refilling of granules on the top Granulate containers are limited and automatically monitored there if required, because the granulate bed in the machine hopper is automatic through the second granulate line is kept at the level defined by the position of their mouth.

The invention is further explained with reference to the drawings. Show it: 1 shows the schematic partial view of a for carrying out the inventive Process suitable thermoplastic processing plant with the inventive Device, FIG. 2A shows the semi-schematic, broken-away sectional view of an inventive device Device, and FIG. 2B shows the device from FIG. 2A in section along A-A.

The schematic representation shown in Fig. 1 shows the partially broken off, greatly simplified section through a thermoplastic processing plant 1 for implementation of the method according to the invention. The system 1 comprises the device according to the invention 10, which mainly depends on the generally hollow prismatic, z. B. with a rectangular cross-section or hollow cylindrical, formed chute 11 and the machine hopper 14 is formed.

The upper end 110 of the chute 11 is with the output end of a source 12 for thermoplastic film flakes 129 connected from a device 120, e.g. B. a knife mill, to form the flakes 129 from the foil strips 131, a conveyor fan 121 and a cyclone 122, which the upper end 110 of the chute 11 is supplied with a falling stream of film flakes 129. While the main part of the air flow generated by the conveyor fan 121 upwards in the cyclone flows off through the line 123, a part of the air flow with the flakes 129 enter down into the chute 11 and influence its speed of fall.

An upper or first granulate feed 151 opens into the chute 11, z. B. as the mouth of the first granule line 161, which from the upper granule storage container, z. B. the granulate funnel 16, is branched off and, for example, under the effect gravity feeds a partial flow of granules into the chute 11. The from this granulate partial flow per unit of time in the chute 11 fed amount of granules is z. B. with a slide 163 or the like manually or preferably automatically controllable or adjustable.

The upper granulate feed 151 defines the upper end of a first Mixing zone M1, in which the granulate particles 169 with the flakes 129 in the chute 11 form a premix; the mixing zone M1 is a comparatively dynamic one Mixing zone in which the parts to be mixed move relatively quickly (order of magnitude 10 1 to 100 m / sec).

As a result, the relatively higher bulk density of the granulate particles 169 (which debris density is, in turn, also a consequence of the shape of the particles, such as in the case of the film flakes 129), the granulate particles 169 exert an impact on the film flakes Kind of "hailstorm effect" in the sense that the granulate particles 169 when falling through the mixing zone M1 pull the flakes of film with them and with them at the lower end the mixing zone M form a bed from the premix produced in this way; in this The flakes are fixed between the granulate particles in the premix bed Meaning that the granules 169 with their per particle in relation to the Flakes 129 of a larger mass form a mobile granulate matrix in the spaces between them the flakes or flake groups are "trapped" and move with the matrix but can no longer separate from the matrix; the premix is now in the second mixing zone M2, which is relatively static and has a typical speed of movement in the order of 10 to 10 ## 4 m / sec.

In the mixing zone M2 that is formed at the lower end of the mixing zone M1 Premix bed of flakes 129 and the first partial flow of granulate particles 169 combined with the second substream of granulate particles 169; this second Partial flow is fed from the granulate bed 149 which is contained in the machine hopper 14 and surrounds in the lower part of the chute 11 at least up to the height, in which the lower granulate feed 152 is arranged.

In general, the chute 11 has several air outlet openings 114, which by appropriate covers, slats, slot widths, grids or the like are designed so that air from the mixing zone M through the granulate bed 149 to the outside but practically no granulate particles 169 from bedding 149 in the mixing zone M1 can get; the bedding works as easily understandable 149 thereby as a filter for the down through the chute 11 flowing air and holds any film flakes 129 that may be carried along in the bedding 149 back.

At least one lower granulate feed opens into the lower mixing zone M2 152, e.g. B. in the form of at least one formed in the wall of the chute 11 Granulate passage opening 118 through which granulate particles from the bedding 149 enter the mixing zone M2 and there with the premix formed in M1 to a mechanically stabilized, practically even supply current Combine shredded film waste and thermoplastic granulate for the extruder 100. This mechanical stabilization of the mixture is likely due in part to that the film flakes 129 are already running continuously at the end of the mixing zone M1 forming premix bed of the granulate particles 169 or that formed by these movable matrix are fixed at least so far that segregation phenomena practically no longer occur.

As a result, the film flakes contained in the premix have 129 already lost their free mobility when entering the mixed zone M2, as a result of the "hail effect" of the granulate particles 169 in each case suddenly and to the extent that they get into the premix bed. It goes without saying that for this purpose the amount of granulate particles fed into the mixing zone M1 per unit of time 169 be sufficiently large, i.e. H. an excess of film flakes 129 in the resulting Premix bedding should be avoided.

A defined boundary between the lower end of the upper mixing zone M1 and the upper end of the lower mixing zone M2 cannot normally be seen; the transition is rather a function of the respective working conditions or feed-in rates depends and it is of no practical importance whether one is the ongoing #ntsttchencIc Bed linen from premixed as the lower end of the upper mixed inch M1 or as the upper one Considered the end of the lower mixing zone M2.

The mixing process essential for the mixing zone M2 is the continuous one Combination of the premix with the second granulate sub-stream, which the remaining Supplies granules of the feed stream; preferably forms the bedding Premixing an upper cover of the mixing zone M2 or an overlying layer, their thickness with the help of the respective feed rates (first granulate flow, flake flow, second granulate flow) can be controlled.

In many normal working conditions (usual rate of attack of film waste in continuous production of typically less than 10% by weight, e.g. 13. About 5% by weight) it is sufficient to control the granulate feed into the lower mixing zone M2 only via the control of the granulate feed in the upper one To carry out mixing zone M1, d. H. that although the rate of injection of granules variable at the upper granulate feed 151 or the process management is ongoing but the rate of granulate feed through the lower granulate feeder is designed to be adaptable 152 is kept practically constant.

For a corresponding regulation in a system according to FIG therefore mostly the actuation of the slide 163 for a more or less large one Proportion of the granulate proportion flowing in at 151 in the total mixture is sufficient and control of the lower granulate feed 152 is not required.

As a control parameter for the slide 163, for. B. the optically measured The density of the stream of film flakes 129 entering the chute 11 is used. Alternatively or complementarily, the height of the bedding can also be monitored forms in the second, relatively static mixing zone M2, as an excessive An increase in this height could lead to the first mixing zone M1 by the second mixing zone M2 displaced, d. H. filled and thereby the formation of a mechanical stabilized mixture would be difficult or impossible.

So as far as there is the possibility under given operating conditions, that the dynamic mixing zone M1 by an upwardly rising bed of the mixing zone M2 is filled out, a corresponding sensor in the mixing zone M1 can determine the feed rates throttle accordingly, z. B. via the slide 163.

With the preferred bulk density ratio granulate: film flakes from 4: 1 to 6: 1 is at a normal feed rate of film waste of up to The bulk volume ratio of granulate: film waste is always greater than 10% by weight 1, which is why it is generally not necessary to regulate the flow of film flakes is. If necessary, the hail effect of the granulate particles in the mixing zone can be avoided M1 by reinforcing the film flakes leading into the chute 11 Air flow supplements and thereby the capacity for increasing proportions of film flakes if necessary enlarged.

The one in £ Oj ~ J. 1 litetter-shaped upper granulate container In addition to the first granulate line 161, 1G has the mixing zone M with granulate supplied, a second granulate line 162, which the machine hopper 14 or the Granulate bedding 149 located therein, which acts like a filter and supplements the feed Granules supplied. The position of the mouth of the granulate line 162 in the machine funnel 14 is expediently chosen so that the desired height of the bedding 149 (in particular sufficiently high above the air passage openings 114) automatically adjusts when the granulate container 16 is filled. The monitoring of the granulate supply can then limited to the granulate container 16.

The comminuting device 120 can be a commercially available knife mill or a similarly acting punching or cutting system to break up the film waste and will be appropriate to the type of waste that arises (strips, ribbons, Tracks) adjusted; the appropriate shape of the particles from shredded film waste results from (a) the normal density of the usual thermoplastic masses (0.8-1), (b) the desired bulk density, which is generally preferably below 0.1 the flakes and (c) the desired size ratio of granulate to flake material. The largest dimensions (e.g. determined as the number of sieves) of the flakes should in general not be more than three times larger than the largest dimensions of the granulate particles; typically the largest surface dimensions are on average at most twice as large, as the largest granulate dimensions; the largest surface dimensions are expedient on average almost as large as the largest granulate dimensions; one Much greater crushing of the flakes, d. H. lower mean values of the Largest flake dimensions are possible, but generally have no advantages.

The device 10 or the system 100 shown in FIG. 1 enables trouble-free and economical recycling of thermoplastic film waste; Construction and operation are clearly simple and economical; typically can with one additional energy consumption of a maximum of about 10 KW / hour that of a film production plant Waste generated by edge trimming can be recovered with practically no loss, without problems of dust accumulation and thermal degradation.

The thermoplastic feed flow generated in accordance with FIG. 1 can preferably be a material cover lying directly on the extruder screw 102 form and in this by the action of the extruder screw 102 or the screw flight are additionally mixed, as shown in Fig. 1 by the screw mixing zone designated area 19 is indicated by arrows; the circumferential worm gear 104 can be a more or less strong agitation or additional homogenization of the feed stream by drawing part of it into the extruder, compressed in it and as with the plastification zone drawn with hatched lines 109 indicated in the plastic state and at the end of the extruder (not shown) squeezes out; Another part of the feed stream is from the worm gear 104 in the Screw mixer zone 19 circulated in the direction of the arrows.

Fig. 2A shows in a schematic broken sectional view the two mixing zones M11 M2 of a device 20 according to the invention, the beginning the mixing zone M1 (mouth of the upper granulate feed) omitted and in the Mitteilteil the falling granulate particles represented schematically by circles and squares 269 or flakes 229 are not shown; also the density of the particles and Flakes in the area of the escargot mixture 29 does not correspond to reality, there the screw thread 204 of the screw 202 increases the particles of the feed tube condensed The chute 21 consists of a manhole top 210, which is inserted into the shaft lower part 211. The lower part 211 has in each Side wall two air passage openings 213, 214; 215, 216, each from a lamella 223, 224; 225, 226 are covered so that the in the chute 21 air flowing downwards through the granulate bed (only partially shown) 249 can exit in the direction of the arrows, but the granules in turn do not get into the chute 21 through the air passage openings.

The premix formed in the mixing zone M1 collects as slowly downward flowing material bedding in the mixing zone M2 and is there with additional Granulate from the bedding 249 mixed, which is passed through a granulate passage 221, 222; 223, 224 in each wall of the lower part of the chute from the machine hopper 24 can enter the mixing zone M2. The opening 222 in the front wall is not shown.

The mechanically stabilized mixture of flakes 229, the hail-like acting falling granulate particles 269 of the first granulate stream and the out the bedding 249 slipping granulate particles is, as explained above, by the Effect of the revolving screw flight 205 in the screw mixing zone 29 in the direction moves the arrows and thus additionally mixed.

Fig. 2B shows the device 20 in section A-A of Fig. 2A, where the flakes and granulate particles only in the area of the screw mixing zone 29 are shown schematically are indicated to the material circulation also taking place in axial weighting to clarify before moving into the extruder 200.

The invention is not directed to the recycling of film waste limited to the production of foils. Rather, according to the invention, thermoplastic Foil waste is processed that is generated during the processing of plastic foils, z. B.

in textile or packaging technology or in other processes attack. Preferred examples of typical thermoplastic film waste are those made from homo- or copolymeric polyolefins, such as polyethylenes of the various types Types and copolymers of ethylene and acrylic acid and other thermoplastic polymer compounds to be named with similar extrusion properties - L e r s e i t e

Claims (10)

Claims 1. A method for recycling thermoplastic film waste in thermoplastic processing, characterized in that the non-regenerated Foil waste in an extruder continuously supplied with thermoplastic granulate introduces by making relatively less from particulate shredded film waste Bulk density and the thermoplastic granulate relatively higher bulk density one mechanically stabilized, practically uniform feed stream from the shredded film waste as well as the thermoplastic granulate and introduces this feed stream into the extruder. 2. The method according to claim 1, characterized in that the mechanical, e.g. B. in a mill, processed waste to form film flakes combined in a falling stream with a first granulate substream to form a premix, which then with a second granulate substream to the stabilized feed stream is united. 3. The method according to claim 1 or 2, characterized in that the film flakes in a falling air stream with the first granulate substream combined for premixing and the air flow after or during the formation of the stabilized Feed flow through a bedding made of thermoplastic granulate leads to the air flow practically completely free of film flakes. 4. The method according to any one of claims 1 to 3, characterized in that that the feed stream in the feed opening (101) of the extruder (100) a Forms material cover lying on the extruder screw (102) before being drawn in is mixed in the extrusion cylinder (103) from the screw flight (104). 5. The method according to any one of claims 1 to 4, characterized in, that the bulk density of the granulate is at least three times greater than the bulk density of the crushed flake waste and that the largest particle dimensions of the the latter are on average at most twice as large as that of the former. 6. Device for producing a practically uniform and for direct feeding into an extruder (100) suitable stream of thermoplastic granulate and thermoplastic flakes, characterized by a chute (11), the upper one End (110) for connection to a source (12) for the flakes and its lower End (111) for connection to a feed opening (101) of the extruder (10) is determined, and by a machine funnel (14), which the chute (11) surrounds near its lower end (111), with an upper granulate feed in the chute (11) (151) and a lower granulate feed (152) opens out between the two granulate feeds (151, 152) an upper mixing zone (M1) for generating a falling stream to form a granulate / flake premix and to the lower granulate feed (152) to form a lower mixing zone (M2) for generating a bed of particles, in which the premix continues with granules from the lower granule feed (152) is combined and fed as a feed into the extruder (10). 7. Apparatus according to claim 6, characterized by the upper inside Granulate funnel (16), from which a first granulate line (161) to the upper one Granulate feed (151) and a second granulate line (162) to the machine hopper (14) is branched off. 8. Apparatus according to claim 6 or 7, characterized in that the machine hopper (14) surrounds the lower section of the chute (11), the at least one granule passage opening (118), which the lower granule feed (152) forms, and has at least one air outlet opening (114), the latter opens into the part of the machine funnel (14), which is used to accommodate one of the Outer granulate bed (149) surrounding the lower section of the chute (11) is determined, which feeds the lower mixing zone (M2) with granules and acts as a filter is used for thermoplastic flakes. 9. Device according to one of claims 6 to 8, characterized by a device (120) for shredding film waste with the formation of film flakes, which device (120), preferably via a fan (121) and a cyclone (122), is connected to the upper end (110) of the chute (11). 10. Thermoplastic processing plant for carrying out the method according to one of claims 1 to 5, characterized by an extruder (100), the is connected to a device according to one of claims 6 to 9.