NL1009599C2 - Recycling polyethylene film by extrusion and granulation, including a quality analysis step to check the gas content in the granules and reject them if necessary - Google Patents

Abstract

A main or partial flow (8,9) of granules formed by extrusion is subjected to a detection step where the granules are analyzed for their gas content, and rejected if the gas content is too high. A process for producing granules from used plastic material such as polyethylene film, optionally containing ink, moisture and/or other contaminants, for use in e.g. extrusion processes and containing an acceptably low level of contaminants, comprises the following steps: (a) extrusion of the crude plastic material; (b) granulating and cooling the extrudate to form solid granules; (c) supplying the granules to a first storage vessel (10), optionally via an intermediate storage vessel; (d) optionally removing a partial flow of granules from the main flow; (e) subjecting the main or partial flow to a detection step in order to determine how many granules have an acceptable gas content; and (f) diverting the flow of granules to a second storage vessel (20) if the amount of granules with a gas content is below a given limit, so that rejected granules are transported to the second vessel and useable granules are returned to the first storage vessel. Independent claims are also included for (a) a similar process using a flow of liquid medium, preferably alcohol, in step (d) to see whether the granules sink or float, depending on their gas content, and (b) the apparatus for carrying out either of these automated processes.

Description

METHOD FOR MANUFACTURING RE-USEFUL PLASTIC GRANULES FROM CONTAMINATED PLASTIC

To make plastic material suitable for reuse, for example polyethylene film, such as contaminated and optionally printed agricultural plastic, the film material is comminuted, washed and dried.

Subsequently, the thus cleaned and dry material is heated as much as possible, so that it is melted by means of an extrusion process using filtering means, for example a mesh filter, after which the extrusion process is comminuted into granules by a granulator and then cooled. These granules, also referred to as a plastic batch, can be used as a new raw material for the production of plastic products. It is of the utmost importance that the quality of the said granules meets certain minimum requirements. Particularly problematic is the presence on the raw material of printing ink or the like and moisture. During said extrusion at a temperature of the order of 230-250 ° C, evaporation of the printing ink and possibly moisture takes place, as a result of which gas inclusions can occur in some granules. Sometimes these gas inclusions are recognizable because the grain is relatively large in size and has bubbles. Sometimes a gas inclusions on the outside of the grain cannot be detected.

Since there is a tendency to use ever thinner foil material for agricultural plastic, plastic bags and the like, the relative amount of printing ink gradually increases.

Another cause for the increase in the relative amount of printing ink per unit weight of material lies in modern printing techniques, which, although they enable better quality printing, often use more ink for this.

It is an object of the invention to enable such a detection of the granules with gas inclusions that a distinction can be made between masses of granules of acceptable quality, ie a quality that meets a set standard, and masses of granules which are below this standard and should therefore be rejected, at least represent a lower quality 10, and therefore cannot or only be used for products of lower quality.

A quality measurement is known in which a sample of granular material 15 is occasionally taken from a main stream of granules, which is formed into a plastic plastic material in the form of a balloon by means of a small extruder. When inflating the balloon under controlled conditions, it must have a specific diameter to be determined by measuring instruments. In the case of deviations, i.e. an impermissibly large amount of trapped gas, for example water vapor, in the mass of granules, the diameter of the balloon will be outside a set value. This is an indication that the batch of granules concerned must be rejected.

In this context, another object of the invention is to provide a method and an apparatus which enable a continuous measurement of the grain quality, for instance such that a main stream of grains in case of good quality is fed to a first storage vessel and in case of impermissible quality to a second storage vessel; lined.

In connection with the above objects, the invention generally provides a method for the manufacture of recycled plastic from used, possibly contaminated with ink, moisture and / or other foreign substances, such as PE (polyethylene) foil. r λ o 3 granules usable for extrusion or other production techniques, in which the relative amount of foreign substances is limited to an acceptable value, the method comprising the following steps: a) extruding the contaminated plastic material into an extrudate; b) granulating and cooling the extrudate to form solid granules? c) feeding a stream of granules, possibly through an intermediate storage vessel, to a first storage vessel? d) optionally branching from the flow of a partial flow of granules; e) subjecting the stream or, optionally, the substream to a detection, in order to determine whether the stream or, if appropriate, the substream and thus also the stream, comprises a relative quantity of granules with a gas inclusion above a selected detection value; F) in the case of positive detection, at least temporarily rejecting the grains of the stream and, on the basis of that decision, changing the stream so that it leads to a second storage vessel, such that the first storage vessel is thus only an amount statistically receive approved reusable plastic beads, and the second storage vessel receives only a quantity of statistically rejected plastic beads.

A specific embodiment further comprises (g) subjecting the granules from the second storage vessel to the process again. In this embodiment, the mass of grains of statistically rejected quality is again subjected to the process, so that, possibly through iteration, ultimately only negligible rejects, ie grains of inadmissibly poor quality, can be minimized.

1009599 4

A further embodiment comprises (h) performing the detection by passing the stream or optionally the partial stream through a liquid medium, for example alcohol, in which granules sink without appreciable gas inclusion and on which granules float with a substantial gas inclusion. In this embodiment, detection takes place on the basis of the difference in specific mass between high-quality and high-quality granules to be rejected.

Alternatively, use can be made of step (i) to perform the detection based on an absorption measurement of electromagnetic radiation in the near infrared region.

In this embodiment, the source of the infrared radiation and the detector of this radiation will be placed on the same side of the current. The IR absorption is measured relative to the high-quality reference granules, the quality of which has been determined otherwise.

Alternatively, use can be made of step (j) to perform the detection based on an absorption measurement of gamma radiation. In principle, this technique is analogous to that according to step (i), with the proviso that the source of the gamma radiation and the detector must be placed on mutually opposite sides of the grain stream. It is to be understood that granules with gas inclusions absorb less gamma radiation than substantially solid granules.

..... j The above described versions according to the; j steps (g), (h), (i) and (j) are based on statistical i methods.

As an alternative, the detection and also the separation between qualitatively admissible and qualitatively impermissible granules can take place in a non-statistical manner, such that a strict separation arises between qualitatively compliant granules and - 1009599 5 qualitatively non-conforming granules. In connection with this, the invention further provides a method for manufacturing plastics material, such as PE (polyethylene) film, which is contaminated with ink, moisture and / or other foreign substances, in which the granules can be used again for extrusion or other production techniques, in which the relative amount of foreign matter is limited to an acceptable value, the method comprising the following steps: (k) extruding the contaminated plastic material into an extrudate; (l) forming solid granules from the extrudate by granulation and cooling; (M) forming a stream of grains, optionally through an intermediate storage vessel, to a first storage vessel; (n) subjecting the stream to detection to determine whether the stream comprises a relative amount of grains with a gas inclusion above a selected detection value; (o) performing the detection by passing the flow through a liquid medium, for example alcohol, in which granules sink without significant gas inclusion and on which granules float with a substantial gas inclusion, the sinking granules being led to a first storage vessel and the floating granules are passed to a second storage vessel such that the first storage vessel thus receives only approved reusable plastic granules and the second storage vessel receives only an amount of rejected plastic granules such that the detection also separates said two types of granules triggers.

Finally, the invention provides an apparatus for performing the method according to the above specifications. This apparatus includes 10095996 automated operating stations for performing the specified process steps.

The invention will now be elucidated with reference to the annexed drawings. In the drawings show: FIG. 1 is a highly schematic representation of a first exemplary embodiment of a device for performing the method according to the invention;

Fig. 2 is a view corresponding with FIG. 1 of a second exemplary embodiment; and FIG. 3 is a view corresponding with FIGS. 1 and 2 of a second exemplary embodiment.

In the figures, as far as possible and applicable, corresponding elements are indicated with the same reference numbers.

The contaminated, but pre-washed and dried raw material, which has possibly been comminuted in advance, is stored in a storage vessel 1 and from there is fed to an extruder 2, at the outlet of which a granulator 3 is connected, which is fed into the still warm, plastic extrudate. the shape of spaghetti-like strands, using a chopping operation, is reduced to granules, which are fed to a funnel 4. During these described operations, the material cools down, transferring from the plastic to the solid phase. The granulate is then fed to a collection storage vessel 5, to which, in the embodiment according to Fig. 1 and that according to Fig. 2, further grain flows can be supplied.

In the embodiment according to Fig. 1, the main stream 6 branches from a funnel 7 into a measuring substream 8 and a secondary main stream 9, which is fed to a storage vessel 10, which receives only approved masses of grains in the manner described below, and is arranged such that it can deposit these granules in, for example, a means of transport such as a tanker 11.

In the embodiment according to Fig. 1, the measuring stream 8, the composition of which is statistically: 10095 ¢ 9 7 identical to that according to the primary main stream 6, is poured into a vessel 12, in which alcohol 13, in particular methanol, is present in this embodiment. , with a density of 920 kg / m3. Alcohol is chosen in this embodiment because the plastic granules, which are substantially solid, for example PE granules, sink into the alcohol and the granules containing gas inclusions float on the liquid. The sinking granules are taken up by an endless conveyor belt 14 with 10 bulkheads 15. The direction of transport is indicated by an arrow 16. The conveyor belt is arranged in the manner clearly shown in Fig. 1 near the bottom of the tray 12. At the end of the active part of the conveyor belt, which extends above and outside the liquid 13, a collection tray 17 is placed.

The granules with gas inclusions above a certain volume will show a relatively low specific mass and float. These grains can pass through a flow generated by means (not shown) in accordance with the direction of arrow 16 a detector 18 which, when exceeding a certain number of grains per time unit or a number of grains in relation to the total number of grains in the flow 8, which can be determined by a counter 19, for example, determine whether the number of floating, that is to say to be rejected, granules is above a set standard. Alternatively, use can also be made of a comparison between the number of detected floating granules in relation to the total flow rate of the partial flow 8. In the affirmative case, so 30 when a value is found which exceeds the set standard, the detector 18, possibly control a three-way valve 30 via signal processing means such as a PLC, in connection with the counting signal supplied by counter 19, whereby the secondary main flow 9 is diverted from storage vessel 10 and passed to another storage vessel 20. It is thus ensured that storage vessel 10 only contains granules of statistically acceptable quality, while storage vessel 20 can only contain a statistically rejected mass of granules.

Fig. 2 shows another embodiment in which the detection is based on the use of a source 21 for gamma radiation. A gamma source 21 has been added to the storage vessel 5, with which gamma radiation source a sensor 22 arranged on the other side of vessel 5 cooperates. By means of means not shown, the sensor 22 can determine whether the mass 23 of plastic granules at the level of the source 21 and the sensor 22 exhibits an impermissibly large gamma radiation transmission. In this context, the term "impermissible" is understood to mean a transmission above a selected standard value, which indicates the presence of an amount of gas inclusions in the plastic granules 23 above a selected value. On this basis valve 30 can be controlled for diverting main flow 9 such that it is no longer supplied to supply vessel 10 to supply vessel 20.

The transport of the granules takes place by means of a fan 24. A number of level detectors 25 are added to storage vessel 5.

In the embodiment according to Figure 3, the partial flow 8 is divided into two partial flows, 25 'and 8' and 8 "respectively. The current 8 'is supplied to a detection device 28 to be described below. The partial flow 8" is supplied by means of a fan 27 is supplied to a detection device 28, and to a test extruder 26 placed for the sake of completeness. This extruder is included in the installation for the sake of completeness and simulates the operating conditions of the company extruder placed with a customer of the material ultimately obtained.

The detection device 28 comprises a vertical tube 32, through which the partial flow 8 is passed. At the closed end a source 33 for infrared radiation from the near infrared region j is added to the tube, which emits radiation in the axial direction 33]. 1009599 9 through a semipermeable mirror 35. The reflected radiation is reflected by the semipermeable mirror 35, which is arranged below 45 °, in the direction of a sensor 36 which determines the intensity of the reflected radiation. On this basis, a control signal can be supplied to valve 30 when sensor certain value is taken into account, taking into account a corresponding reference value, so that flow 9 is no longer supplied to supply vessel 10, but to supply vessel 20.

With reference to Figure 1, attention is drawn to the fact that the method implemented therein can also be applied for effectively separating grains of sufficient quality to the standard and granules of insufficient quality to the standard. In the drawn embodiment, sunken and the floating granules are reunited by the ascending part of the working part of conveyor belt 14, so that the effected separation between the two categories of granules is thus undone. This separation can be maintained and, through an additional endless conveyor belt or other provisions, the floating granules can be removed from tray 12 via a different path from the sunken granules. In this way, the possibly required effective physical separation is practically effected.

In this case it could practically be considered to supply to the container with accessories serving as separating device not the measuring sub-flow 8 but the main flow 6, with adapted dimensioning of the through-flow capacity. This allows the measuring device to act as a separating device. Under these circumstances, the use of valve 30 can also be dispensed with. The flow of sunken grains can under all circumstances be supplied directly, possibly after drying, to storage vessel 10, while the flow of floating grains, which therefore do not meet the set standard under all circumstances is fed directly to 1009599 storage vessel 20. The active part 37 of the conveyor belt extends at its end 37, as already noted, above and outside of the liquid 13 and transports only approved, i.e. 5, granules conforming to the standard set. The other stream of granules, namely the granules that have floated on the surface of the alcohol 13, are all supplied directly to the storage vessel 20. The use of detector 18 can be completely dispensed with in this embodiment.

As will be apparent from the foregoing, the invention provides a non-random but continuously feasible measurement of the quality of the granules. As a result, reliability of the measurement is substantially improved and a complete physical separation itself can be brought about between acceptable and unacceptable grains.

j: 1009599

Claims (7)

1. A method for manufacturing plastic granules, possibly contaminated with ink, moisture and / or other foreign substances, such as PE (polyethylene) film, of making granules which can be used again for extrusion or other production techniques, in which the relative quantity of foreign substances is acceptable value is limited, the method comprising the following steps: a) extruding the contaminated plastic material into an extrudate; b) forming granules from the extrudate by granulation and cooling; c) feeding a stream of granules, optionally through an intermediate storage vessel, to a first storage vessel; d) optionally branching from the flow of a partial flow of granules; e) subjecting the stream or, optionally, the partial stream to a detection, in order to determine whether the stream or, if appropriate, the partial stream and thereby also the stream, comprises a relative quantity of granules with a gas inclusion above a selected detection value; f) in the case of positive detection, at least temporarily rejecting the grains of the stream and, on the basis of that decision, changing the stream so that it leads to a second storage vessel, such that the first storage vessel thus only contains an amount of statistically approved reusable plastic granules and the second storage vessel receives only a quantity of statistically rejected plastic granules. The method of claim 1, comprising step 1009599 (g) re-subjecting the granules from the second storage vessel to the method. A method according to claim 1, comprising the step 5 (h) of performing the detection by passing the stream or optionally the partial stream through a liquid medium, for example alcohol, in which granules sink without appreciable gas inclusion and on which granules with a substantial gas inclusion float. The method of claim 1, comprising the step (i) of performing the detection based on an absorption measurement of electromagnetic radiation in the near infrared region. The method of claim 1, comprising the step (j) of performing the detection based on an absorption measurement of gamma radiation. 6. A method for manufacturing plastic granules, possibly contaminated with ink, moisture and / or other foreign substances, such as PE (polyethylene) film, of making granules which can be used again for extrusion or other production techniques, in which the relative quantity of foreign substances is acceptable value is limited, the method comprising the following steps: (k) extruding the contaminated plastic material and forming an extrudate; (l) granulating solid! 30 granules from the extrudate; (m) forming a stream of grains, optionally through an intermediate storage vessel, to a first storage vessel; (n) subjecting the stream to detection to determine whether the stream comprises a relative amount of grains with a gas inclusion above a selected detection value; ™ 1 η η o ς qq% (o) conducting the detection by passing the current through a liquid medium, such as alcohol, in which granules sink without significant gas inclusion and on which granules float with a substantial gas inclusion, the sinking granules floating are conducted to a first storage vessel and the floating granules are passed to a second storage vessel such that the first storage vessel thus receives only approved reusable plastic granules and the second storage vessel receives only an amount of rejected plastic granules such that the detection is also causes a separation of the said two types of granules. 7. Device for performing the method according to any one of the preceding claims, which device comprises stations for automating the specified process steps. ΐηηαςοο