METHOD FOR PRODUCING A PET STARTING MATERIAL THAT IS SUITABLE FOR USE IN AN EXTRUSION BLOW MOLDING METHOD, AND HOLLOW ARTICLE PRODUCED IN THE EXTRUSION BLOW MOLDING METHOD

Abstract

The invention relates to a method for producing an EBM bottle with 0.90 to 1.5 dL/g from a bottle-grade PET post-consumer recycling flake, i.e., a recycled, post-consumer PET with a viscosity of 0.65 to 0.84 dL/g, using extrusion processes, solid state polycondensation processes, and a blowing process.

Claims

1. A method for producing a PET starting material suitable for use in an extrusion blow molding method, for producing a hollow article made of plastic, comprising: a) sorting by type, washing and comminuting post-consumer PET articles, b) removing contaminants, such as metal or paper, arc removed before, simultaneously to, or after method step a), c) drying the comminuted PET material, d) melting the comminuted PET material, admixing a chain extender or chain brancher, and extruding reactively the melt of comminuted PET material and chain extender or chain brancher, wherein the admixing of the chain extender or the chain brancher can take place before or during melting, and e) producing granules from the extruded PET material, and f) increasing an intrinsic viscosity of the granules is further increased by a subsequent heat treatment in solid state polycondensation.

2. The method according to claim 1, wherein the intrinsic viscosity increase is higher than that in method step d).

3. The method according to claim 1 or 2, characterized in that the solid state polycondensation is carried out at temperatures of ≤225° C.

4. The method according to claim 1, wherein a dwell time of the granules in an SSP reactor is less than 20 h.

5. The method according to claim 1, wherein the post-consumer PET material uscd in mcthod step a) has a viscosity between 0.65 and 0.84 dL/g.

6. The method according to claim 1, wherein the reactive extrusion increases the viscosity of the PET material used by 0.05 to 0.2 dL/g.

7. The method according to one of claim 1, wherein the intrinsic viscosity is increased by a further 0.1 to 0.6 dL/g using solid state polycondensation.

8. The method according to claim 1, wherein a temperature during extrusion and a quantity of chain extender or chain brancher are selected such that the extruded PET material has an IV greater than 0.75 dL/g.

9. The method according to claim 1, wherein a polyfunctional anhydride is used as the chain extender.

10. The method according to claim 1, wherein tetracarboxylic dianhydrides are used as chain extenders.

11. The method according to claim 1, wherein pyromellitic dianhydride is used as chain extender.

12. The method Mcthod according to claim 1, wherein the chain extender consists of one of: bisoxazolines, bisepoxides, diisocyanates, polyepoxides, compounds carrying several glycidyl groups, maleic anhydride, phthalic anhydride, triphenyl phosphates, lactamyl phosphites, ciclo phosphazene, polyacyl lactam, and also bis-2-oxazolines, bis-5,6-dihydro-4h-1,3-oxazines, diisocyanates, trimethyl 1,2,4-benzene tricarboxylate (trimethyl trimellitate, TMT), or carbonyl bis (1-caprolactam).

13. The method according to claim 1, wherein polyols are used as chain branchers.

14. The method according to claim 1, wherein compounds with more than two hydroxyl groups are used as chain branchers.

15. The method according to claim 1, wherein glycerol, pentaerythritol, or a combination thereof are used as polyols.

16. The method according to claim 1, wherein between 0.05 wt % and 1.0 wt % of chain extender or chain brancher are admixed to the PET material.

17. The method according to claim 1, wherein the extruded PET material is filtered before granulation.

18. The method according to claim 1, wherein the extruded PET material is pressed through a perforated filter with a hole size between 30 μm and 300 μm.

19. The method according to claim 1, further comprising admixing an acid scavenger to the PET material before the extrusion.

20. The method according to claim 19, wherein the acid scavenger is calcium stearate, zinc stearate, zinc oxide, or hydrotalcite, or a combination thereof.

21. The method according to claim 1, wherein the PET material is degassed during the extrusion.

22. The method according to claim 1, wherein the PET material obtained in method step f) is supplied to an EBM system, and another chain extender or a-chain brancher is added once again in the EBM system.

23. The method according to claim 1, wherein the PET melt is split into thin layers or strands in the extrusion.

24. The method according to claim 1, wherein the extrusion takes place in vacuo or in a protective gas atmosphere.

25. The method according to claim 1, wherein the PET material is extruded into a tube, blown into a hollow article, and then cut off.

26. The method according to claim 25, wherein a strength of the tube is increased by active cooling by 5 to 50° C.

27. The method according to claim 26, wherein a hose is cooled by expansion of the tube, contact with another medium, by blowing nozzles, aerosols, hea pipes or heat dissipation.

28. The method according to claim 1, further comprising admixing untreated PET comprising new PET or rPET with an IV of 0.6 to 0.95 dL/g in a mass fraction of 0 to 50% to the PET in order to adjust a melt strength in an article-specific manner.

29. A hollow article comprised at least partially of recycled PET, wherein: a PET starting material for producing the hollow article contains between 30 wt % and 100 wt % rPET with an intrinsic viscosity of between 0.90 and 1.5 dL/g and an extensional viscosity of more than 5,500 Pa*s and between 70 wt % and zero wt % vPET.

30. The hollow article according to claim 29, formed by: a) sorting by type, washing and comminuting post-consumer PET articles, b) removing contaminants before, simultaneously to, or after step a), c) drying the comminuted PET material, d) melting the comminuted PET material, admixing a chain extender or chain brancher, and extruding reactively the melt of comminuted PET material and chain extender or chain brancher, wherein the admixing of the chain extender or the chain brancher can take place before or during melting, and e) producing granules from the extruded PET material, and f) increasing an intrinsic viscosity of the granules is further increased by a subsequent heat treatment in solid state polycondensation.

31. The hollow article according to claim 29, wherein the recycled PET is produced from recycled, post-consumer PET with a viscosity between 0.65 and 0.84 dL/g by condensing.

32. The hollow article according to claim 29, wherein the PET starting material for producing the hollow article has a shear viscosity at 275° C. and 50s.sup.−1 of less than 3,000 Pa*s

33. The hollow article according to claim 29, wherein the PET starting material for producing the hollow article has an extensional viscosity of at least 5,500 Pa*s at 275° C. (50 s.sup.-1) in the production of small hollow articles and of more than 6,500 Pa*s, and in particular of between 7,000 Pa*s and 14,000 Pa*s, for hollow articles with a volume of more than 500 mL.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0064] FIG. 1 shows a subjective EBM rating relative to extensional viscosity according to Cogswell (EtaCo) at 275° C. and 50 s.sup.−1

DETAILED DESCRIPTION

EXAMPLES

Methods:

[0065] The melt-rheological characterization was carried out according to ISO 11443:2014. Samples are dried in vacuo at 120° C. for 12 h. A Gaffed Rheograph 75 with 2×15 mm test channel was used for the test. The capillaries 10/1 and 0/1 mm were used. The test temperature was 275° C. A Bagley correction and Rabinowitsch-Weissenberg correction was carried out. Both the shear viscosity and the extensional viscosity were determined. Using the method according to Cogswell (first description by Cogswell in 1972), the extensional viscosity was determined from the inlet pressure losses by means of WinRheo II software (Gattfert WerkstoffprUfmaschinen GmbH, Buchen, Germany).

Example 1

[0066] A commercially available new PET article for injection molding (IV 0.8 dL/g) was left in an SSP reactor at 215° C. for a period of 17 h. During the test in an EBM system, the material had a relatively poor melt stiffness. A cosmetic bottle of approx. 20 cm height and approx. 400 mL volume could only be formed with difficulty.

Examples 2-4

[0067] Commercially available types of new EBM PET goods were procured. A cosmetic bottle of approx. 20 cm height and approx. 400 mL volume could only be formed with difficulty from the material of Example 2. In contrast, the material of Example 3 was well-suited for this purpose. From the material of Example 4, bottles with handles and a volume of 1 L or greater could be formed.

Example 5

[0068] Commercially available rPET granules consisting of post-consumer waste were procured and left in the SSP reactor at 210° C. for 15 h. The material is suitable for the production of the above-described cosmetic bottle.

Example 6

[0069] Commercially available rPET granules consisting of post-consumer waste were procured and left in the SSP reactor at 215° C. for 22 h. The material is suitable for the production of the above-described cosmetic bottle.

Examples 7 and 8

[0070] Ground stock of post-consumer PET waste (IV 0.792 dL/g), e.g., in the form of flakes or snippets, was admixed in an extruder with 0.105% PMDA (Example 7: PMDA in solid carrier; Example 8: PMDA in liquid carrier) and supplied to granulation. The IV of the resulting sem icrystalline granules was 0.847 dL/g (Example 7) or 0.867 dL/g (Example 8). The granules with a crystallinity of between 40 and 60% were left in the SSP reactor at 200° C. for 10 h. To the surprise of the inventors, the treated granules had a very high extensional viscosity, which also manifested in these materials exhibiting a very high or high tube stability in the EBM system. At the same time, a low melt pressure occurred in these materials due to the low shear viscosity in relation to the extensional viscosity.

TABLE-US-00001 TABLE 1 Material examples (shear and extensional viscosity measuring methods; see above) Shear IV viscosity Extensional Tube (ASTM 275° C. viscosity stability Starting Chain D4603) at 50 S.sup.−1 275° C. 50 in EBM No: material extender SSP [dL/g] [Pa*s] .sup.a) S.sup.−1 [Pa*s] .sup.b) system 1 New PET — 215° C., 1.193 1,669 5,331 Poor goods, 17 h condensed 2 New EBM — 1.161 1,891 5,151 Poor PET goods 3 New EBM — 1.292 2,186 5,677 Moderate PET goods 4 New EBM — 1.400 3,274 9,088 Good PET goods 5 rPET, — 210° C., 1.198 2,294 6,826 Good condensed 15 h 6 rPET, — 215° C., 1.239 1,899 6,610 Good condensed 22 h 7 rPET 0.105% 200° C., 1.194 1,657 13,192 Very admixed PMDA, 10 h good with PMDA solid carrier and condensed 8 rPET 0.105% 200° C., 1.074 1,452 7,641 Good admixed PMDA, 10 h with PMDA liquid and carrier condensed .sup.a) The values for 50 s.sup.−1 were derived from the measurement data via Carreau approximation, since the shear rates typically cannot be determined as precisely. The measurement range was typically in the range of 10 to 3,000 s.sup.−1. The determination was carried out as described under “Methods” .sup.b) Method according to Cogswell, determination by means of Gttfert WinRheo II software (Gttfert Werkstoff-Prfmaschinen GmbH, Buchen, Germany). Caution: Measuring points were interpolated from measurement data. The determination was carried out as described under “Methods.”

[0071] Examples 7 and 8 show that, by using PMDA in “mild” reaction conditions (lower process temperature, significantly shorter dwell time), work can be done in the SSP, and even higher extensional viscosities can be achieved than without using PMDA and with the significantly longer dwell times and process temperatures in Examples 5 and 6. The comparison of Examples 1 and 5 or 6 shows that rPET can basically have faster reaction kinetics than vPET (new goods). However, the behavior of rPET can definitely also fluctuate, depending upon the composition of the incoming goods flow.

[0072] The examples also show that the intrinsic viscosity is in general not a suitable measure of the suitability of PET types for EBM. For example, Examples 1 and 7 show an almost identical IV of 1.193 dL/g or 1.194 dL/g. The same is true for the shear viscosities of 1,669 Pa*s and 1,657 Pa*s at 275° C. and 50 s.sup.−1. At the same time, however, the two materials show massive differences in the extensional viscosity of 5,331 Pa*s or 13,192 Pa*s at 275° C. and 50 s.sup.-1. One weakness of the IV is in fact also that relatively small sample quantities in relation to the melt-rheological properties are used in the determination. In the case of materials that are quite prone to inhomogeneities (which recyclates can definitely be), this can lead to strongly scattering IV measured values or, in general, to a low accuracy of the determination.

[0073] New and absolutely unexpected is the high swelling (diameter swelling) in comparison to all previously processed EBM PET types (new and rPET-based PET goods). This is an indication of a high melt elasticity. This is not typical for PET, since PET typically has a narrow molar mass distribution for production-related reasons or as a result of cross-esterification, and the polymer chains can thus relax very quickly, and the PET melt typically has a low melt elasticity as a result. Typically to be expected for PET is the following: [0074] low melt stiffness [0075] low or no swelling tendency at the nozzle outlet [0076] no or hardly any extensional strain hardening in the melt

[0077] Contrary to expectations, the rPET treated according to the invention showed an atypical behavior characterized by a high melt elasticity or extensional viscosity, as described with reference to the above examples, and a high swelling tendency. The high extensional viscosity in relation to the low shear viscosity is an indication of a rather elastic nature of the rPET treated according to the invention. As a result of the resulting high elastic restoring forces, these materials show a much lower tendency to adhere to metal surfaces in contrast to the materials of Examples 1 through 5 (materials with rather plastic behavior). Without these elastic restoring forces, the melt behavior with respect to metallic surfaces would be controlled by the wetting behavior (surface tension).

Description of FIG. 1:

[0078] FIG. 1 shows the subjective EBM rating relative to extensional viscosity according to Cogswell (EtaCo) at 275° C. and 50 s.sup.−1. The EBM rating results as follows: Materials that were difficult, even in the production of small bottles, as in Examples 1 and 2 above, were rated 0 (unsuitable) or 1 (difficulties with small bottle format). Materials that could be processed without problems for the aforementioned cosmetic bottle were rated 3. Materials that would be suitable for bottles with 1 L capacity or slightly larger (up to 5 L) were rated 4. In order to be able to take account of the observed, subjective melt strength that was even higher than class 4 in the EBM system, class 5 has also been introduced. It is apparent from FIG. 1 that the extensional viscosity defines a limit curve similar to a part of a parabola. It is not known whether this limit curve approaches an asymptote, since data in this respect are not available. This is currently also not relevant to the intended use according to the present invention of the materials. However, the limit curve clearly shows that an extensional viscosity of the PET of approx. at least 5,500 Pa*s at 275° C. and 50 s.sup.1 must be present so that it is suitable for extrusion blow molding of small hollow articles, i.e., of those with a volume between 100 mL and 500 mL, whereas, for larger hollow articles, i.e., for hollow articles with a volume greater than 500 mL, at least 6,500 Pa*s are required.

Description of the method:

[0079] In a first process step, post-consumer PET bottles are correctly sorted by type, washed, and cut, and contamination, such as metal, paper, and other contaminants, are removed.

[0080] In a second process step, the cut PET flakes are dried. Conditions in which the PET molecular weight increases can already be created during drying. (e.g., Vacurema method of the company EREMA Engineering Recycling Maschinen and Anlagen Ges.m.b.H., Ansfelden, Austria).

[0081] In a third process step, a chain extender and/or a chain brancher is admixed to the PET, and reactive extrusion of the flakes is carried out, which may be under vacuum. Under these conditions, the PET is rapidly condensed during the extrusion, i.e., the average molecular weight of the rPET increases. Instead of carrying out the extrusion under vacuum, it can also take place in a protective gas atmosphere.

[0082] Optionally, with the addition of the chain extender or the chain brancher, 0.01 to 1.0 wt %, and preferably 0.05 to 0.8 wt %, of an acid scavenger, such as calcium stearate, zinc stearate, zinc oxide, or hydrotalcite, or a combination of these acid scavengers, can additionally be admixed to the rPET, and the extrusion of the flakes can then be carried out. In this case, the acid scavenger can prevent or at least reduce the acid-catalyzed chain cleavage (hydrolysis) of PET in the melt.

[0083] Optionally, stabilizing phosphorus compounds in the form of an acid (e.g., H3PO4) or an acid ester on the order of 0 to 50 ppm can be added to the rPET.

[0084] In a subsequent process step, the melt is filtered (optionally) and granulated.

[0085] In a subsequent process step, the granules are placed into an SSP reactor, and their viscosity is increased to above 0.9 dL/g.

[0086] In a subsequent process step, the material can be dried in the extrusion blow molding machine, wherein the viscosity is increased once again at a corresponding temperature. Optionally, the material can be mixed again with a chain extender and can be raised to a viscosity useful for the EBM process. In this case, the chain extender can be added before or simultaneously to the extrusion.

[0087] The material may be transferred directly from the SSP reactor into the EBM system. If, on the other hand, the material is filled, e.g., into Bigbags or storage containers, after the SSP process because it cannot be further processed directly, the residual moisture may be adjusted to below 50 ppm, or below 30 ppm (typically, by drying immediately before processing in the EBM system).

[0088] Small bottles require a lower viscosity than larger ones, since the tube is smaller, and lower tensile forces due to gravity arise. The fine adjustment of the viscosity can therefore take place in the blow molding machine in a product-related manner.

[0089] In the extrusion blow molding process, so-called slugs arise, which are separated from the final bottle and are preferably again supplied to the process by comminuting them to form flakes, the ground PET stock, and subjecting them to polycondensation in the SSP reactor or dryer. As a result, the viscosity of the ground PET stock can again be increased. This is important, since the intrinsic viscosity is typically reduced from 0.03 to 0.3 dL/g during extrusion. Optionally, a chain extender can also be admixed to the ground PET stock in order to enhance condensation.

[0090] In an optional process step, “untreated” PET (new goods (vPET) or rPET) with an IV of 0.6 to 0.95 dL/g in a mass fraction of 0 to 50% can be admixed to the rPET treated as described above, in order to adjust the melt strength in an article-specific manner. Because a high melt strength of the treated rPET can be achieved with the method according to the invention, the admixture of non-treated rPET or of vPET is allowed. As a result, the costs of the method can be reduced.

[0091] In an optional process step, a degassing zone is present in the extruder (method step d) and increases the PET by 0.01 to 0.10 dL/g during extrusion.

[0092] In an optional process step, melt splitting into thin layers or strands takes place in the extruder, as a result of which the surface of the material is massively enlarged and made more accessible for melt polymerization (condensation). As a result, the intrinsic viscosity can be increased by 0.10 to 0.50 in the melt. This process step ideally takes place under vacuum or a protective gas atmosphere - for example, under nitrogen.

[0093] In a subsequent process step, a tube is extruded and blown into a hollow article and cut. The remaining slugs above and under the bottle are separated off.

[0094] In an optional process step, the strength of the extruded tube can be increased by cooling the tube by 5 to 50° C. The cooling is carried out either by expansion of the tube, by contact with another medium, by blowing nozzles, by aerosols, or other forms of heat dissipation—in particular, by means of heat pipes. Through the evaporation of a medium, heat pipes lead to very uniform cooling, with temperature differences of less than 1° C.

[0095] In summary, the subject matter of the invention is a method for producing an EBM bottle with 0.90 to 1.5 dL/g from a bottle-grade PET post-consumer recycling flake, i.e., a recycled, post-consumer PET with a viscosity of 0.65 to 0.84 dL/g, using extrusion processes, solid state polycondensation processes, and a blowing process.

Sources:

[0096] Awaja F., Pavel D. (2005), Review Recycling of PET, European Polymer Journal 41, pp. 1,453-1,477 [0097] Awaja et al. (2004), Recycled Poly(ethylene terephthalate) Chain Extension by Reactive Extrusion Process, Polymer Engineering and Science, 44 (8), pp. 1,579-1,587 [0098] Cogswell F. N. (1972), Converging flow of polymer melts in extrusion dies, Polym. Eng. Sci. 12, pp. 64-73