Process for upgrading plastic material

• US 6,852,256 B2
• Filed: 06/12/2001
• Issued: 02/08/2005
• Est. Priority Date: 02/04/1999
• Status: Expired due to Fees

• Current Assignee: Bühler Thermal Processes AG
• Original Assignee: Buhler AG (Buhler Holding AG)
• Inventors: Culbert, Brent Allen, Borer, Camille
• Primary Examiner(s): Eashoo, Mark
• Application Number:
  US09/878,345
• Publication Number:
  US 20020036361A1
• Time in Patent Office: 1,337 Days
• Field of Search: 264/40.6, 264/85, 264/37.14, 264/37.17, 264/143, 264/211.2, 264/235, 264/236, 264/918, 264/920, 264/346, 264/347, 521/48
• US Class Current: 264/40.6
• CPC Class Codes: B29B 13/021 Heat treatment of powders
• CPC Class Codes: B29B 17/00 Recovery of plastics or other constituents of waste material containing plastics; volume reduction of waste plastics, e.g. by mechanical compacting or melting disposal of solid waste B09B; chemical recovery C08J11/00
• CPC Class Codes: B29B 9/06 in the form of filamentary material, e.g. combined with extrusion
• CPC Class Codes: B29C 48/04 Particle-shaped making granules B29B9/00
• CPC Class Codes: B29C 71/0063 for changing crystallisation
• CPC Class Codes: B29K 2067/00 Use of polyesters or derivatives thereof, as moulding material
• CPC Class Codes: B29K 2105/26 Scrap or recycled material
• CPC Class Codes: C08G 63/80 Solid-state polycondensation
• CPC Class Codes: C08G 63/88 Post-polymerisation treatment
• CPC Class Codes: Y02W 30/62 Plastics recycling; Rubber recycling
• CPC Class Codes: Y10S 264/92 by extruding material recycled from consumer used article or product

Abstract

In a process for upgrading cleaned used plastic material to be reclaimed, all steps are performed in a continuous way so as to extrude continuously the plastic material to provide elongated strands thereof, cutting the strands continuously as they are supplied by extrusion to convert them into pellets. Then, the pellets are fed without any intermediate storage to a continuous crystallizer in a stream of hot gas to heat the pellets to crystallizing temperature.

Claims

1. A process for upgrading non-virgin plastic material to be reclaimed comprising the steps of

continuously extruding said plastic material to provide elongated strands thereof;

continuously cutting said elongated strands as they are supplied by said extrusion step to convert them into pellets;

immediately feeding said pellets without intermediate storage;

continuously crystallizing said pellets, as they are fed in said feeding step from said cutting step, in a stream of hot gas of a desired temperature to heat the pellets to crystallizing temperature; and

immediately feeding said pellets from a crystallizer following the continuous crystallizing, without intermediate storage, for solid state condensing said pellets under heat in a continuous flow after said crystallization step to reach a desired intrinsic viscosity.

2. The process as claimed in claim 1, wherein said crystallizing step is carried out in a continuous fluidized bed of predetermined characteristic of flow of said pellets, said predetermined characteristic being a plunger characteristic.

3. The process as claimed in claim 1, wherein at least one of the following characteristics is provided:

a) said crystallizing step is a one-step process;

b) the step of solid state condensing said pellets is effected without substantial change in intrinsic viscosity of said pellets in comparison with that of the material before extrusion;

c) said condensing step is carried out at a temperature lower than that of said hot gas;

d) said condensing step is carried out under a stream of gas, preferably in counter-direction to said continuous flow;

e) at least one of said steps of heating said pellets is carried out in an atmosphere of nitrogen;

f) both steps of heating said pellets are carried out in a gas atmosphere, said gas being fed from said condensing step to said crystallizing step;

g) said non-virgin plastic material comprises polyethylene terephthalate.

4. The process as claimed in claim 1, further comprising the step of decontaminating the material to be reclaimed from migrated or adhering substances, said step comprising sucking material off which is selected from volatiles and fines, wherein preferably the gas of at least one of said steps of heating said pellets is separated from any solid matter and is recycled.

5. The process as claimed in claim 1, further comprising the step of monitoring the quality of the material to be reclaimed to obtain a grading value and controlling said desired temperature of said gas or of said heat using said grading value to obtain a substantially uniform desired quality, said grading value comprising the intrinsic viscosity.

6. The process as claimed in claim 1, further comprising at least one of the following steps:

a) cooling said pellets after said condensing step;

b) admixing pellets of fresh plastic material not previously used to said non-virgin plastic material, comprising

the step of solid state condensing said pellets in a continuous flow after said crystallization step; and

the step of cooling said pellets after said condensing step;

said admixing step being carried out after said cooling step.

7. The process as claimed in claim 1, wherein, after continuously extruding said plastic material, the rheological properties of the plastic melt are measured and converted to an intrinsic viscosity.

8. The process as claimed in claim 7, wherein the conditions in the solid state condensing step are controlled according to the difference between the measured and the desired intrinsic viscosity.

9. The process as claimed in claim 1, wherein the temperature in the solid state condensing step is controlled and the residence time is held substantially constant.

10. The process as claimed in claim 1, wherein, during the extrusion step for continuously extruding said plastic material, a gas barrier enhancing additive is added.

11. The process as claimed in claim 10, wherein said gas barrier enhancing additive is at least one of a scavenging type additive and a gas permeation restricting type additive.

12. The process as claimed in claim 1, wherein the crystallization in said crystallizing step is carried out to a degree of crystallization of less than 50%.

13. The process as claimed in claim 1, wherein the crystallization in said crystallizing step is carried out to a degree of crystallization of less than 45%.