High molecular weight polyester polymers with reduced acetaldehyde
View Patent ↗Polyester compositions, especially polyethylene terephthalate homopolymer and copolymers, are disclosed containing titanium catalysts and catalyst deactivator added late in the manufacturing processing having reduced acetaldehyde generation rates. The polyester compositions are low in free acetaldehyde, making them suitable for fabrication into beverage containers for relatively tasteless beverages such as bottle water. Furthermore, the polyesters are polymerized to a high inherent viscosity in reduced processing time, without the necessity of further polymerization in the solid state, and in the absence of acetaldehyde scavengers leading to polyester polymers having reduced color.
1. A method for the production of solid polyester polymer particles comprising:
a) polycondensing a molten polyester polymer composition in the presence of a polycondensation catalyst composition comprising titanium species;
b) adding a catalyst deactivator compound to the molten polyester polymer composition;
c) after reaching an It.V. of about 0.69 dL/g or more, solidifying the molten polyester polymer composition into solid polyester polymer particles which do not contain added acetaldehyde scavengers; and
d) reducing the amount of residual acetaldehyde in the solid particles to a level of about 10 ppm or less in the solid state without increasing the It.V. of the particles by more than about 0.03 dL/g in the solid state to form solid polyester polymer particles comprising from 5 to 10 ppm titanium and from 12 to 25 ppm phosphorus;
wherein the catalyst deactivator compound is added to the molten polyester polymer composition in step b) at one or more of the following points:
(i) within a final reactor for polycondensing the molten polyester polymer or between said final reactor and before a cutter for cutting the molten polyester polymer composition into said solid particles; or
(ii) after the It.V. of the molten polyester polymer composition has risen to at least 0.5 dL/g; or
(iii) vacuum applied to the molten polyester polymer melt, if any, is at least partially released; or
(iv) following at least 75% of the polycondensation time; or (v) within ±0.10 dL/g, of the It.V. obtained upon solidification; or
(vi) within 30 minutes before solidifying the melt, wherein the polycondensing is carried out in the absence of antimony.
2. The method of claim 1 , wherein the catalyst deactivator and polycondensation catalyst are present in a P:Ti ratio of at least 1.2:1.
3. The method of claim 2 , wherein the catalyst deactivator is at least one member selected from the group consisting of a phosphoric acid, a phosphorous acid, a pyrophosphoric acid and a polyphosphoric acid.
4. The method of claim 2 , wherein solid polyester polymer particles comprising from 12 to 18 ppm phosphorus.