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
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.
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, wherein the post-consumer PET material has an intrinsic viscosity between 0.65 and 0.84 dL/g,
b) removing contaminants before, simultaneously to, or after step a),
c) drying the comminuted PET material,
d) melting the comminuted PET material, admixing a pyromellitic dianhydride as 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 wherein a temperature during extrusion and a quantity of chain extender or chain brancher are selected such that the reactive extrusion increases the intrinsic viscosity by 0.05 to 0.2 dL/g and the extruded material has an IV greater than 0.75 dL/g,
e) producing granules from the extruded PET material, and
f) increasing an intrinsic viscosity of the granules further by a subsequent heat treatment in solid state polycondensation, wherein the solid state polycondensation is carried out at temperatures of ≤225° C. increasing the intrinsic viscosity by a further 0.1 to 0.6 dL/g to above 0.9 dL/g.
2 . The method according to claim 1 , wherein the intrinsic viscosity increase of the granules in step f) 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 a temperatures of ≤200° C.
4 . The method according to claim 1 , wherein a dwell time of the granules in an SSP reactor is less than 12 h.
5 . The method according to one of claim 1 , wherein the intrinsic viscosity is increased by a further 0.15 to 0.55 dL/g using solid state polycondensation.
6 . 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 intrinsic viscosity between 0.8 and 0.9 dL/g.
7 . 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.
8 . The method according to claim 1 , wherein the extruded PET material is filtered before granulation.
9 . 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.
10 . The method according to claim 1 , further comprising admixing an acid scavenger to the PET material before the extrusion.
11 . The method according to claim 10 , wherein the acid scavenger is calcium stearate, zinc stearate, zinc oxide, or hydrotalcite, or a combination thereof.
12 . The method according to claim 1 , wherein the PET material is degassed during the extrusion.
13 . 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 chain brancher is added once again in the EBM system.
14 . The method according to claim 1 , wherein the PET melt is split into thin layers or strands in the extrusion.
15 . The method according to claim 1 , wherein the extrusion takes place in vacuo or in a protective gas atmosphere.
16 . The method according to claim 1 , wherein the PET material is extruded into a tube, blown into a hollow article, and then cut off.
17 . The method according to claim 16 , wherein a strength of the tube is increased by active cooling by 5 to 50° C.
18 . The method according to claim 17 , wherein a hose is cooled by expansion of the tube, contact with another medium, by blowing nozzles, aerosols, heat pipes or heat dissipation.
19 . The method according to claim 1 , further comprising admixing untreated PET comprising new PET or rPET with an intrinsic viscosity 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.
20 . 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, wherein the post-consumer PET material has an intrinsic viscosity between 0.65 and 0.84 dL/g,
b) removing contaminants before, simultaneously to, or after step a),
c) drying the comminuted PET material,
d) melting the comminuted PET material, admixing 0.105 wt % of pyromellitic dianhydride as 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 wherein a temperature during extrusion is selected such that the reactive extrusion increases the intrinsic viscosity by 0.05 to 0.2 dL/g and the extruded material has an intrinsic viscosity between 0.8 and 0.9 dL/g,
e) producing granules from the extruded PET material, and
f) increasing an intrinsic viscosity of the granules further by a subsequent heat treatment in solid state polycondensation, wherein the solid state polycondensation is carried out at a temperature of 200° C. increasing the intrinsic viscosity by a further 0.1 to 0.6 dL/g to an intrinsic viscosity above 0.9 dL/g.