METHOD FOR PRODUCING AN RPET PLASTIC MATERIAL FOR USE IN A THIN WALL INJECTION MOLDING PROCESS AND HOLLOW BODY PRODUCED IN THE THIN WALL INJECTION MOLDING PROCESS

Abstract

The invention relates to a method in which a starting material for injection-molding, having a viscosity of between 0.50 and 0.7 dL/g, is produced with the aid of a chain breaker from a recycled post-consumer PET having a viscosity of between 0.72 and 0.86 dL/g according to ASTM D4603 and a copolymer fraction of at most approximately 3%. In the method, the comminuted and dried PET material is melted and decontaminated to such a degree that it is suitable for applications in the food sector and the consumer goods sector. A chain breaker is added to the rPET material in the melt of the recycling extruder and/or preferably the melt of the injection unit in order to lower the viscosity and to enrich the PET with copolymers.

Claims

1. A method for producing an rPET plastic material for use in a thin-wall injection-molding process, with a ratio of wall thickness (L) to flow path (D) of 1 to 100 to 1 to 350, or to 1 to 500 for thin-wall injection-molding, the method comprising: sorting, washing and comminuting post-consumer PET articles comprised mostly of PET bottles produced by an ISBM process, PET material of which has an intrinsic viscosity between 0.72 and 0.86 dL/g according to ASTM D4603, removing impurities such as metal or paper before, simultaneously with, or after the sorting, washing and comminuting, drying the comminuted PET material, melting and optionally decontaminating the PET material in a degassing and/or recycling extruder, and then granulating the PET material, and producing a thin-walled injection-molded article from the PET material in an injection-molding process, and adding a chain breaker to the granulated PET material, and reactively extruding and directly injecting a melt of the PET material into an injection mold, wherein an intrinsic viscosity of a thin-walled injection-molded article formed from the PET material is lowered to 0.5 to 0.7 dL/g during extrusion and has a ratio of wall thickness (L) of the resulting thin-walled injection-molded article to a flow path (D) of 1 to 100 to 1 to 350.

2. The method according to claim 1, wherein a temperature during extrusion, a residence time of the material in the extruder, and an amount of the chain breaker are selected such that the extruded PET material has an intrinsic viscosity (IV) greater than 0.5 dL/g.

3. The method according to claim 1, wherein an amount of monoethylene glycol or an amount of water is used as the chain breaker.

4. The method according to claim 1, wherein the PET material used for the extruding contains 100 to 1,000 ppm water.

5. The method according to claim 1, further comprising adding between 50 and 1,000 ppm of monoethylene glycol to the granulated PET material.

6. The method according to claim 1, further comprising compounds which can be incorporated into PET polymer molecules and thus lead to a higher copolymer fraction are used as chain breakers.

7. The method according to claim 6, wherein the copolymer fraction is raised by at least 1% compared to the starting PET material.

8. The method according to claim 6, wherein diols are used as the chain breaker.

9. The method according to claim 8, wherein diethylene glycol, propylene glycol, butylene glycol, and/or cyclic polyalcohols are used as diols.

10. The method according to claim 6, wherein dicarboxylic acids are used as the chain breaker.

11. The method according to claim 10, wherein isophthalic acid, 2,5-furandicarboxylic acid, and/or naphthalene dicarboxylic acid is used as the dicarboxylic acid.

12. The method according to claim 6, wherein diesters are used as the chain breaker.

13. The method according to claim 12, wherein dimethylisophthalate and/or bis(hydroxyethyl)isophthalate are used as the diester.

14. The method according to claim 6, wherein PET copolymer chains with 2 to 20 monomers, with an isophthalic acid (IPA), furandicarboxylic acid (FDCA), naphthalene dicarboxylic acid, or diethylene glycol fraction, are used as the chain breakers.

15. The method according to claim 14, wherein a fraction of isophthalic acid (IPA), furandicarboxylic acid (FDCA), naphthalene dicarboxylic acid, or diethylene glycol is between 3 and 10 wt %.

16. The method according to claim 6 or 7, characterized in that compounds which have an alcohol group and a dicarboxylic acid or an ester group, such as, for example, hydroxyethanoic acid, hydroxypropanoic acid, hydroxybutanoic acid, and the like, are used as the chain breakers. 15).

17. The method according to claim 6, wherein caffeine is used as the chain breaker.

18. The method according to claim 1, wherein an admixture of the chain breaker is added to the PET material before or during the melting.

19. The method according to claim 1, wherein the post-consumer PET material used, before the drying and recycling, has a copolymer fraction of not more than about 3%.

20. The method according to claim 1, the adding the chain breaker is carried out in such a manner that the copolymer fraction in the rPET, in total, is raised to 2.5 to 8%.

21. The method according to one of claim 1, further comprising decontaminating the post-consumer input goods by degassing volatile contaminants at elevated temperature between 70 and 330? C. before the recycling extruder and/or in the recycling extruder and/or after the recycling extruder, with a vacuum of less than 0.2 bar absolute, and/or with nitrogen flushing between 0.1 sec and 20 hours.

22. The method according to claim 1, wherein the PET material is decontaminated to such an extent before the injection-molding so that it is suitable for applications in the food and/or utensils sector.

23. The method of claim 1, further comprising producing a master batch using the granulated PET material and a chain breaker, and metering the master batch directly into an inlet of an injection-molding machine.

24. The method according to claim 1, wherein the comminuted and dried PET material is dried at temperatures between 60 and 180? C. for 1 to 8 hours.

25. The method according to claim 1, wherein a reactive extrusion reduces a viscosity of the PET material by 0.05 to 0.3 dL/g.

26. The method according to claim 1, wherein a crystallization fraction of a treated rPET injection-molded part is reduced by at least 10% compared to an untreated material without an increased copolymer fraction.

27. The method according to claim 1, wherein a temperature during extrusion and a quantity of chain breaker are selected such that an extruded PET material and/or the PET material of an injection-molded article produced has an IV greater than 0.5 dL/g.

28. The method according to claim 6, wherein between 0.05 wt % and 2.8 wt % of chain breaker is added to the granulated PET material.

29. The method according to claim 1, wherein the melt of the PET material is filtered before being granulated.

30. The method according to claim 29, wherein the melt of the PET material is pressed through a hole filter having a hole size between 30 ?m and 300 ?m.

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

32. The method according to claim 1, the melt of the PET material is divided into thin layers or strands during extrusion.

33. The method according to of claim 1, wherein the extruding is carried out in a vacuum or in a protective gas atmosphere.

34. The method according to claim 1, wherein a certain amount of chain breaker is added to the PET material prior to melting.

35. The method according to claim 1, wherein a residence time of the PET material in an injection-molding unit or recycling extruder is in each case between 20 and 400 sec.

36. The method according to claim 1, wherein the post-consumer PET material has a viscosity between about 0.7 and about 0.86 dL/g.

37. The method according to claim 1, wherein the PET material is subjected to an alternative form of injection-molding and/or a mixed form of injection-molding comprising compression molding or injection foaming.

38. A hollow body formed an rPET plastic material for use in a thin-wall injection-molding process, with a ratio of wall thickness (L) to flow path (D) of 1 to 100 to 1 to 350, or to 1 to 500 for thin-wall injection-molding, the rPET plastic material formed by a method, comprising: sorting, washing and comminuting post-consumer PET articles comprised mostly of PET bottles produced by an ISBM process, PET material of which has an intrinsic viscosity between 0.72 and 0.86 dL/g according to ASTM D4603, removing impurities such as metal or paper before, simultaneously with, or after the sorting, washing and comminuting, drying the comminuted PET material, melting and optionally decontaminating the PET material in a degassing and/or recycling extruder, and then granulating the PET material, and producing a thin-walled injection-molded article from the PET material in an injection-molding process, and adding a chain breaker to the granulated PET material, and reactively extruding and directly injecting a melt of the PET material into an injection mold, wherein an intrinsic viscosity of a thin-walled injection-molded article formed from the PET material is lowered to 0.5 to 0.7 dL/g during extrusion and has a ratio of wall thickness (L) of the resulting thin-walled injection-molded article to a flow path (D) of 1 to 100 to 1 to 350.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0075] For the method, post-consumer PET material having a viscosity between about 0.7 and about 0.86 dL/g is used. A PET bottle stream may be used which contains particularly few impurities of polymers other than PET (for example, PA blends). In the context of the present invention, particularly few is understood to mean that the proportion of PA blends, radical scavengers, and other additives such as, for example, oxygen scavengers, acetaldehyde scavengers, UV absorbers, slip additives, infrared absorbers, etc., is less than 10 wt %, less than 5 wt %, or more advantageously less than 3 wt %.

[0076] In a first process step, post-consumer PET bottles are sorted into a single type, washed, and cut, and impurities such as metal, paper, etc., are removed. During sorting, the collected PET material is initially sorted for color, and then foreign plastics may be sorted out.

[0077] In a second process step, the cut PET flakes are dried.

[0078] In a third process step, the rPET is decontaminated and granulated in a degassing or recycling extruder.

[0079] In a fourth process step, a chain breaker is added to the granulate, and a reactive extrusion of the granulate is then carried out. Under these conditions, the rPET rapidly decomposes during extrusion in the injection unit, i.e., the average molecular weight of the rPET and thus the intrinsic viscosity decreases.

[0080] The addition of the chain breaker is predominantly envisaged in the injection-molding unit, but can alternatively be added in rare cases or complementarily in the recycling extruder. As a result of the addition of chain breaker not only in the extruder of the injection-molding machine, but also in the extruder of the recycling machine, the recycling material can be deliberately decomposed and enriched with copolymers in the extrusion process.

EXEMPLARY EMBODIMENTS

Example 1

[0081] Ground material of post-consumer PET bottles with an average IV of 0.72 dL/g and an average copolymer fraction of 1% isophthalic acid and 1.3% diethylene glycol are admixed with 0.5% diethylene glycol in a recycling extruder and extruded at 290? C. on average. Surprisingly, the viscosity after the recycling extruder was reduced much more than usual to a value of only 0.58 dL/g. After a subsequent SSP (6 h at 220? C., to achieve food contact compliance), the granulate had built up only to 0.72 dL/g. This granulate is dried to below 50 ppm water content and added to an injection-molding machine together with a second quantity of diethylene glycol (0.2%). Surprisingly, the PET could again drop to a viscosity of only 0.55 dL/g, and a preform could be injection molded with only 1 mm wall thickness and a flow path of 120 mm.

Example 2

[0082] Material of post-consumer bottles is decomposed in a conventional recycling process to form granulate for an injection stretch blow molding process, with a viscosity in an SSP of 0.76 dL/g. However, the dried granulate (180? C.-6 h, dried air, 2 m.sup.2 air/kg PET, dew point ?35? C.) is fed to an injection-molding machine and admixed with 2% diethylene glycol. In the melt, the diethylene glycol brought the PET down to a viscosity of 0.61 dL/g, and, surprisingly, it was possible to mold a preform with only 1 mm wall thickness and 120 mm flow path.

[0083] The invention provides a method by which previously used polyester materials, including either production waste polyester materials and/or used polyester materials, can be recovered and purified conveniently and efficiently. In the process, the collected PET material is initially sorted for color, may then sorted again, cut into small pieces (milled), washed, dried, extruded, and may at the same time be decontaminated, granulated, and optionally polymerized and again decontaminated, and then extruded into a thin-walled article in the presence of chain breakers.

[0084] The invention relates to a method in which a recycled post-consumer PET having a viscosity of between 0.72 and 0.86 dL/g according to ASTM D4603 and a copolymer fraction of not more than about 3 wt % is used to produce, with the aid of a chain breaker, a starting material for injection-molding having a viscosity between 0.50 and 0.7 dL/g. In the method, the comminuted and dried PET material is melted and decontaminated sufficiently that it is suitable for applications in the food and utensils sector. A chain breaker is added to the rPET material in the melt of the recycling extruder and/or the melt of the injection unit in order to lower the viscosity and to enrich the PET with copolymers.