METHOD FOR PRODUCING A PLASTIC GRANULATE, AND USE OF THE GRANULATE

Abstract

A method for the production of granulate suitable for the production of extrusion-blow-molded hollow bodies, comprising: sorting by type, washing, and comminuting PET articles originating from a post-consumer collection of plastic packaging, removing contaminants from the PET articles, premixing PET material from various types of the sorted PET articles so that a Trouton ratio of mixed PET material at a shear rate of 50 to 200 s.sup.?1 is less than 4, drying the PET material, melting the dried PET material, pressing the PET material through a filter, dividing the PET material into individual melt streams, cooling and solidifying the melt streams in a water bath and separating the solidified melt flows into pellets, wherein the pellets have an intrinsic viscosity of 0.5 to 0.75 dl/g, crystallizing the pellets, and drying and condensing the crystallized pellets in a solid-phase polycondensation reactor until they reach an intrinsic viscosity of 1.0 to 1.7 dl/g.

Claims

1. Method of producing a plastic granulate suitable for the production of extrusion-blow-molded hollow bodies, comprising: sorting by type, washing, and comminuting PET articles originating from a post-consumer collection of plastic packaging to form a PET material, removing contaminants, before, at the same time or after the sorting, premixing the PET material from various types of the sorted PET articles so that a Trouton ratio of PET material at a shear rate of 50 to 200 s.sup.?1 is less than 4, drying the premixed PET material, melting the dried PET material, pressing the melted PET material through a melt filter, dividing the filtered PET material into a plurality of individual melt streams, cooling and solidifying the plurality of melt streams in a water bath, separating the solidified melt flows into pellets, wherein the pellets thus obtained have an intrinsic viscosity of 0.5 to 0.75 dl/g, crystallizing the pellets, and drying and condensing the crystallized pellets in a solid-phase polycondensation reactor until they reach an intrinsic viscosity of 1.0 to 1.7 dl/g.

2. Method according to claim 1, wherein the Trouton ratio of the crystallized pellets at a shear rate of 50 to 200 s.sup.?1 is less than 4.

3. Method according to claim 2, wherein during the melting any substances added that do not cause the Trouton ratio of the crystallized pellets at a shear rate of 50 to 200 s.sup.?1 to rise above 4.

4. Method according to claim 1, further comprising passing the plurality of melt streams through a water bath for the cooling and solidification, to form to form a plurality of continuous, and cutting the plurality of continuous strands into pellets.

5. Method according to claim 1 further comprising, pressing the plurality of melt streams into a water bath and cutting the plurality of melt streams with a blade directly at an outlet of an aperture plate to form melt droplets, which melt droplets solidify in the water bath to form the crystalline pellets that are flushed away by flowing water in the water bath and are subsequently separated from the water.

6. Method according to claim 1 further comprising, crystallizing the pellets by introduction into a hot-air crystallizer, where the pellets are treated with continuous agitation by a continuous application of heat by introducing hot air at a temperature between 100 and 200? C. with a typical dwell time of 5 to 120 minutes or by being crystallized in a crystallizer operating with infrared radiation, wherein the pellets are introduced into a rotating drum, wherein infrared radiators are placed above the bulk material and wherein an energy input/heat input into the pellets is affected by a released infrared radiation.

7. Method according to claim 1, wherein the pellets are dried to less than 50 ppm residual moisture content.

8. A method of using a PET granulate for production of an extrusion-blow-molded hollow body, comprising: sorting by type, washing, and comminuting PET articles originating from a post-consumer collection of plastic packaging to form a PET material, removing contaminants, before, at the same time or after sorting, premixing the PET material from various types of the sorted PET articles so that a Trouton ratio of mixed PET material at a shear rate of 50 to 200 s.sup.?1 is less than 4, drying the premixed PET material, melting the dried PET material, pressing the melted PET material through a melt filter, dividing the filtered PET material into a plurality of melt streams, cooling and solidifying the plurality of melt streams in a water bath, separating the solidified melt flows into pellets, wherein the pellets have an intrinsic viscosity of 0.5 to 0.75 dl/g, crystallizing the pellets, and drying and condensing the crystallized pellets in a solid-phase polycondensation reactor until they reach an intrinsic viscosity of 1.0 to 1.7 dl/g, and forming an extrusion-blow-molded hollow body from the dried and condensed crystallized pellets, wherein the hollow body passes a drop test (Bruceton staircase drop test according to procedure B from ASTM D2463) from at least a same height as an identically constructed hollow body made of a linear vPET having an intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603).

9. to the method of claim 8, wherein the hollow body passes the drop test from the height that corresponds to at least 80% of the same height that the identically constructed hollow body made of a linear vPET having the same intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603) reaches in the drop test.

10. that the method of claim 8, wherein the hollow body has a gloss similar to the identically constructed hollow body made of a linear vPET having the same intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603).

11. that the The method of claim 10, wherein the hollow body has at least 70% of the gloss as an identically constructed hollow body made of a linear vPET having the same intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603).

12. that the The method of claim 8, wherein the dried and condensed pellets are melted on an extrusion blow-molding line by a single-screw extruder with admixture of 0 to 60% of crystallized and dried ground material comprised of production waste that accrues during extrusion blow-molding and 0 to 10% admixture of a concentrate, which contains colorants and/or technically customary functional auxiliaries, in order to form a melt.

13. that the The method of claim 12, wherein the melt obtained is fed to a melt distributor for forming the plurality of melt strands into parisons, in order to divide them into a corresponding number of parisons corresponding to a number of mold cavities present in a blowing mold.

14. that the The method of claim 13, wherein the parisons obtained are formed in a suitable blowing mold into hollow bodies with or without a handle, which have a volume of 25 ml to 25 l.

15. The method of claim 8, further comprising removing protrusions formed on the hollow body during the blowing process by machine.

16. Method for the production of granulate suitable for the production of parisons by injection-molding for stretch blow-molding, comprising: admixing a post consumer collection of hollow bodies formed from PET pellets having an intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603), plastic packaging, and stretch-blow-molded PET bottles in a proportion of a maximum of 50%, wherein the mixing is carried out according to the following method steps: sorting by type, washing, and comminuting of PET articles originating from the post-consumer collection of plastic packaging to form a PET material, removing contaminants, before, at the same time or after the sorting, drying the PET material, melting the dried PET material, pressing the melted PET material through a melt filter, dividing the filtered PET material into individual melt streams, cooling and solidifying the melt streams in a water bath; and separating the solidified melt streams into pellets, wherein the pellets thus obtained have an intrinsic viscosity of 0.75 to 0.9 dl/g.

17. A hollow body produced from a PET granulate formed by a method, comprising: sorting by type, washing, and comminuting PET articles originating from a post-consumer collection of plastic packaging to form a PET material, removing contaminants, before, at the same time or after sorting, premixing the PET material from various types of the sorted PET articles so that a Trouton ratio of mixed PET material at a shear rate of 50 to 200 s.sup.?1 is less than 4, drying the premixed PET material, melting the dried PET material, pressing the melted PET material through a melt filter, dividing the filtered PET material into a plurality of melt streams, cooling and solidifying the plurality of melt streams in a water bath, separating the solidified melt flows into pellets, wherein the pellets have an intrinsic viscosity of 0.5 to 0.75 dl/g, crystallizing the pellets, and drying and condensing the crystallized pellets in a solid-phase polycondensation reactor until they reach an intrinsic viscosity of 1.0 to 1.7 dl/g, and forming a hollow body from the dried and condensed crystallized pellets, wherein the hollow body passes a drop test (Bruceton staircase drop test according to procedure B from ASTM D2463) from at least a same height as an identically constructed hollow body made of a linear vPET having an intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603).

Description

[0043] Further advantages and features of the invention are apparent from the following description of several experimental examples:

[0044] Extrusion-blow-molded bottles were produced on a pilot line in a blowing mold with a mold cavity. The ejection of the parison was continuous. This pilot line is representative of a production line with a plurality of mold cavities connected in parallel, which allow the parisons extruded in parallel to be formed simultaneously into a number of bottles equal to the number of parisons. Pilot molds were available for bottles with 1 l, 2.7 l and 5 l nominal volume. The vPET types 1 to 3 are commercially available EBM PET types from various manufacturers. The reference material vPET 1 is a commercially available vPET that is marketed for use in the extrusion blow-molding of bottles with a handle in the range of 1 l or larger. The vPET 4 material used for comparison purposes was obtained by solid-phase polycondensation of an injection-molded PET with IV 0.8 dl/g. The vPET 5 is a commercially available PET type for the injection-molding of parisons with IV 0.81 dl/g. The rPET types 1, 2 and 4 were produced analogously to the method in the Swiss patent request with the application number 00304/20. The rPET type 1 contained 0.083% PMDA and was solid-phase polycondensed for 10 h, the rPET type 2 contained 0.099% PMDA, and was solid-phase polycondensed for 11 h. The rPET type 4 contained 0.105% PMDA and was solid-phase polycondensed for 10 h. The rPET type 3 was prepared according to steps (a) to (j), with no substances being admixed in method step (e). The method steps (a) to (j) for the production of rPET type 3 are as follows: [0045] (a) the PET articles originating from the post-consumer collection of plastic packaging, in particular PET bottles separated by source (region of origin and product category of the filling material) and color are sorted by type, washed and comminuted, [0046] (b) contaminants such as metal or paper are removed before, at the same time or after method step (a), [0047] (c) the comminuted PET material from various sources is premixed in such a way that its Trouton ratio and that of the material obtained thereby in step (j) at a shear rate of between 50 and 200 s.sup.?1 is less than 4 (this means that batches whose Trouton ratio in the specified range of shear rate is 4 or greater cannot be used for these purposes), [0048] (d) the comminuted, premixed PET material is then dried, [0049] (e) the comminuted, premixed PET material is then melted, and in this step only those substances are added which do not cause the Trouton ratio of the material resulting in step (j) to rise above 4 (at a shear rate of between 50 and 200 s.sup.?1), [0050] (f) the comminuted, premixed, melted PET material is then pressed through a melt filter, [0051] (g) the filtered melt is passed via an aperture plate with many outlet openings, in order to divide it into individual melt streams; and [0052] (h) these melt streams are passed through a water bath for solidification and cooling, forming a quasi-endless strand, and are then separated into pellets by a cutting device. Alternatively, these melt streams are pressed into a water bath and separated into melt droplets by a blade directly at the outlet from the aperture plate. The melt droplets are solidified into pellets in the water bath, flushed away by the flowing water and separated from the water by a suitable method (for example, hydrocyclone, screen).

[0053] The pellets obtained in this way have an intrinsic viscosity of 0.5 to 0.75 dl/g.

[0054] In method steps (i) to (j), the pellets obtained are further processed: [0055] (i) the pellets thus obtained are crystallized and [0056] (j) the crystallized pellets are dried and condensed in a solid-phase polycondensation reactor until they reach an intrinsic viscosity of 1.0 to 1.7 dl/g.

[0057] By means of the following method steps (k) to (o), a hollow body is extrusion-blow-molded from the pellets: [0058] (k) the pellets thus obtained are dried to less than 50 ppm residual moisture content, or more advantageously less than 30 ppm. [0059] (l) the dried pellets are melted on an extrusion blow-molding line by means of a single-screw extruder with admixture of 0 to 60% crystallized and dried ground material of production waste, that usually accrues during extrusion blow-molding as a result of the process (so-called flash, which is ground by means of a mill), and 0 to 10% admixture of a concentrate, which contains colorants (dyes and/or pigments) and/or technically customary functional auxiliaries (additives such as UV absorbers, lubricants, antistatic agents, etc.), in order to form a melt [0060] (m) the melt thus obtained is fed to a melt distributor followed by an apparatus for forming the melt strands into parisons, in order to divide them into the number of parisons corresponding to the number of mold cavities present in the blowing mold, [0061] (n) the parisons thus obtained are formed in a suitable blowing mold into hollow bodies with or without a handle, having a volume of 25 ml to 25 l, [0062] (o) the protrusions on the bottle shoulder, base and, if necessary, in the region of the handle, which are not part of the hollow body, are removed by machine.

[0063] This production method, which maintains the Trouton ratio in steps (c) and (e), can produce a hollow body with the following properties: [0064] The hollow body has a relative drop height similar to that of the same hollow body when made made (at comparable weight) from a linear vPET having the same intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603), wherein the relative drop height of the linear vPET is set at 100% and is hereinafter referred to as reference dimension 1 [0065] The hollow body exhibits, at comparable weight, a relative gloss such as that exhibited by the same hollow body when made of a linear vPET having intrinsic viscosity of 1.0 to 1.7 dl/g (measured according to ASTM D4603), wherein the relative gloss of the linear vPET is set to be 100% and is hereinafter referred to as reference dimension 2 [0066] The hollow body can after use be fed to the post-consumer collection of plastic packaging and can be admixed in a quantity of up to 50% to stretch-blow-molded PET bottles, which also come from post-consumer collection. The mixture can be prepared again into pellets by the usual technical processing methods according to method steps (a) to (j). However, with the deviating target of an IV in step (j) of 0.75 to 0.9 dl/g, making the pellets suitable for the production of parisons by means of injection-molding for stretch blow-molding.

[0067] Crystallization according to method step (i) can be carried out as follows: Crystallization is carried out according to standard industrial procedures by either inserting such pellets into a hot-air crystallizer of typical industrial design (such as Eisb?r crystallizer, Piovan CR series, SP Protec SOMOS crystallizers, SB plastics vertical crystallizer CR series, Viscotec Cry20, etc.) and treated there under continuous stirring by continuous application of heat by introducing hot air at a temperature between 100 and 200? C. with a typical dwell time of 5 to 120 minutes, or crystallized in a crystallizer customary in the industry operating with infrared radiation, wherein the granulate is introduced into a rotating drum, where infrared radiators are placed above the bulk material (such as, for example, SB Plastics ITD, Kreyenborg IRD, Kreyenborg IR Batch) and the energy input/heat input into the granulate is effected via the released infrared radiation. Here, the rotating drum serves for the movement of the bulk material (on the one hand for the circulation of the bulk material, such that a uniform heat input into the granulate takes place, along with the conveying of the bulk material in the axial direction of the drum) and analogously to the agitator in the aforementioned container, in order to prevent the pellets sticking together during the crystallization process. Crystallization of the pellets prevents sticking or agglomeration of the granulate in the subsequent method steps. In technically common production lines, the crystallizer can be part of a common recycling line (for example, Viscotec recoSTAR).

[0068] Other possible pelletization methods in addition to the pelletization methods according to step (h) are: [0069] Pelletization in a water ring granulator:
The melt exiting through the holes of the heated pelletizing aperture plate (1) is knocked off by rotating knives (2). The pellets are thrown outward into a rotating water ring (3) by centrifugal force. This cools the pellets and transports them via a flexible discharge channel to the granulate dewatering screen, where the pellets are separated from the cooling water (4). After oversize separation, the granulate passes to the drying centrifuge. By means of air flow, it is conveyed onward to the silo or to the bagging station via a transport line. The cooling water is recirculated to the pelletizing head via a cooling water filtration device and a heat exchanger by means of a water pump. [0070] Hot-cut pelletizing systems with air technology:
Functioning as with underwater pelletization (h), except that air is used as the heat transfer medium or fluid.

[0071] The melt is pressed through an aperture plate, [0072] the hot-cut is effected by knives, [0073] the pellets are washed away by the air, [0074] and separation of the pellets from the air is carried out. [0075] Partial underwater strand pelletizing system:
Functioning as with the cold-cut pelletizing method, except that a water spray is used for cooling instead of a water bath.

[0076] The melt is discharged from the aperture plate (a plurality of holes) into a strand cooling trough.

[0077] The strand cooling trough is covered with a flowing film of water; there are also spray heads (shower heads) that apply water. This is followed by pelletization in the strand pelletizer. Dewatering (for example, a screen) and post-drying (for example, a centrifuge) then takes place or the pellets go straight to a centrifuge for dewatering and drying.

[0078] In the case of drying after underwater pelletization, the drying centrifuge should generally be mentioned, in addition to the hydrocyclone. With methods in which water is used, a screen is usually inserted after the pelletizer for coarse dewatering or separation. After this, post-drying (for example, by means of a centrifuge) is common.

[0079] Of the materials produced, the intrinsic viscosity of the granulate was determined. Table 1 summarizes the results of a sampling with a 5 l bottle with a handle. It can be seen that vPET types 1 to 3 have an IV of 1.30 to 1.41 dl/g and a Trouton ratio of approximately 3, and gave comparable relative drop heights in the drop test, and that the measured gloss was approximately the same. The vPET 4, also with a Trouton ratio of 3, showed a parison strength that was too low to enable the same bottle be formed. Surprisingly, the type rPET1 showed high parison stiffness at an IV of only 0.96 dl/g, but only 53% of relative drop height and only 86% of gloss compared to vPET1. The Trouton ratio of clearly above 3 observed for rPET 1 suggests that this type has greater elasticity than types vPET 1 to 4, and therefore must exhibit branching and hence affects the high parison stiffness. Apart from the fact that the rPET 1 does not achieve the same results in the drop test and in gloss as types vPET 1 to 3, bottles made of rPET 1 should not be further processed after use into material for injection-molding parisons. This is because an atypical material input stream for this application during recycling inevitably leads to atypical processing behavior in the stretch blow-molding process. The vPET5 with IV 0.81 dl/g had a parison stiffness that was much too low. Table 2 shows results of tests with a 2.7 l bottle with a handle. The linear PET types (vPET 1 and rPET 3) exhibit higher relative drop test and gloss than the two branched types (rPET 1 and rPET 2). It was further shown that there are also limits to the modification of PET by means of branching. The bottles made of branched rPET 1 and branched rPET 2 from the example in Table 2 showed a less clear appearance when viewed by an individual; in general, the surface appeared less glossy compared to the linear vPET 1 and linear rPET 3. This can be verified on the basis of the measured gloss. This observation is made analogously by H?rth and D?rnh?fer 2020.sup.13 for a blown film, where the use of a branching additive causes a strong turbidity of the blown film.

TABLE-US-00001 TABLE 1 Results of the tests with a 5 l bottle with a handle (Example 1) Drop test Gloss (relative) (relative) IV Trouton Parison to linear to linear [dl/g] ratio[?] stiffness vPET 1 vPET 1 vPET 1 1.32 2.9 (73 s.sup.?1) High 100% 100% 3.3 (157 s.sup.?1) (reference) (reference) vPET 2 1.30 3.0 (71 s.sup.?1) High 96% 99% 3.3 (157 s.sup.?1) vPET 3 1.41 2.9 (72 s.sup.?1) High 105% 100% 3.4 (153 s.sup.?1) vPET 4 1.16 3.0 (75 s.sup.?1) Low 3.0 (174 s.sup.?1) rPET 1 0.96 4.3 (58 s.sup.?1) High 53% 86% 5.5 (123 s.sup.?1) vPET 5 0.81 2.7 (84 s.sup.?1) Very low 2.5 (208 s.sup.?1) .sup.13 H?rth, M., D?rnh?fer, A.: Film blowing of linear and long-chain branched poly(ethylene terephthalate), Polymers 2020, 12, 1605.

TABLE-US-00002 TABLE 2 Results of tests with a 2.7 l bottle with a handle (Example 2) Drop test Gloss (relative) (relative) IV Trouton Parison to linear to linear [dl/g] ratio[?] stiffness vPET 1 vPET 1 vPET 1 1.32 2.9 (73 s.sup.?1) High 100% 100% 3.3 (157 s.sup.?1) (reference) (reference) rPET 1 0.96 4.3 (58 s.sup.?1) High 57% 81% 5.5 (123 s.sup.?1) rPET 2 1.02 5.1 (51 s.sup.?1) Very high 56% 66% 7.0 (103 s.sup.?1) rPET 3 1.17 3.3 (68 s.sup.?1) High 120% * 92% 3.7 (152 s.sup.?1) * In retrospect, this turned out to be an outlier.

[0080] Table 3 shows supplementary test results for the 2.7 l bottle with a handle, for which results have already been presented in Table 2. It now appears that the relative drop test of rPET 3 compared to vPET 1 is somewhat where it should be on the basis of the intrinsic viscosity.

TABLE-US-00003 TABLE 3 Results of tests with a 2.7 l bottle with a handle (Example 3) Drop test IV Parison (relative) to [dl/g] stiffness linear vPET 1 vPET 1 1.32 High 100% reference rPET 3 1.15 High 82%

[0081] Following this, a 1 l bottle with a handle was taken as a sample. Its results are shown in Table 4. The relative drop height of rPET 1 and rPET 4 relative to rPET 3 is approximately where one would expect on the basis of the intrinsic viscosity. For this reason, for illustrative purposes, the relative drop height was calculated in relation to vPET 1 by referencing the relative drop height reached by each material in Table 4 with the result for rPET 3 from Table 3.

TABLE-US-00004 TABLE 4 Results of tests with a 1 I bottle with a handle (Example 4) Drop test Drop test (relative) to Gloss IV Trouton Parison (relative) vPET 1 (relative) [dl/g] ratio[?] stiffness to rPET 3 (calculated) to rPET 3 rPET 3 1.15 3.3 (68 s.sup.?1) High 100% 82% 100% 3.7 (152 s.sup.?1) rPET 1 0.96 4.3 (58 s.sup.?1) High 77% 63% 87% 5.5 (123 s.sup.?1) rPET 4 0.96 4.2 (58 s.sup.?1) High 76% 63% 83% 5.4 (125 s.sup.?1)

[0082] It can thus be seen that rPET types 1, 2 and 4 did not meet the requirements placed on them. Although they show a high parison stiffness, which makes them suitable for molding the bottles with a handle described earlier, the obtained performance characteristics with respect to the relative drop test and relative gloss are much worse in relation to rPET 3 and relevant vPET types. Moreover, only the rPET 3 is not expected to affect the PET recycling stream in a negative way, since its Trouton ratio is below 4 between 50 and 200 s-1. Negative influence is expected for rPET 1, 2 and 4 due to their Trouton ratios above 4.

[0083] The tests show that the hollow bodies made of rPET 3 achieve a relative drop height of at least 80%, of at least 90% or of at least 95% of the relative drop height of the vPET (in particular vPET 1; reference dimension 1). The tests also show that the hollow bodies made of rPET 3 achieve a relative gloss of at least 70%, of at least 80% or of at least 90% of the relative gloss of the linear vPET (in particular vPET 1; reference dimension 2).