Clarity, low haze polymer
View Patent ↗A method of manufacturing an improved clarity, low haze, low melt flow rate homopolymer polypropylene and thermoformed parts therefrom using an additive package such that the additive package alone provides the improved qualities, and process adjustments at the thermoforming stage are not required. The additive package does not contain a phosphite antioxidant, and the homopolymer polypropylene is either virgin material or virgin material mixed with at least 25 percent reground homopolymer polypropylene of the improved formulation described herein and combined with the improved clarity additive package.
1. A method of manufacturing high clarity thermoformed parts substantially free of phosphite antioxidants comprising
combining at least one additive selected from the group consisting of non-phosphite antioxidants, nucleating agents, antistatic agents, clarifying agents, and acid scavengers with virgin polypropylene homopolymer to form an improved clarity homopolymer,
combining said improved clarity homopolymer with reground thermoformed polypropylene homopolymer to create a homopolymer mixture,
extruding said homopolymer mixture into sheet form, and
thermoforming said homopolymer mixture.
2. The method of claim 1 wherein the content of said at least one additive in the improved clarity homopolymer is from about 100 to about 2000 ppm.
3. The method of claim 1 wherein the haze of said thermoformed parts is less than about 7% and the clarity is greater than about 80%.
4. The method of claim 1 wherein the haze of said thermoformed parts is between about 3 and 5%.
5. The method of claim 1 , wherein said thermoforming is carried out at a sheet temperature between about 146° C. and 155° C.
6. The method of claim 1 wherein said reground thermoformed polypropylene homopolymer comprises at least 25 percent of the homopolymer mixture.
7. The method of claim 6 wherein the haze of said thermoformed part is less than about 7% and clarity is greater than about 80%.
8. The method of claim 1 wherein the melt flow rate of the homopolymer mixture is between about 1 and about 4 g/10 mm, and wherein the homopolymer mixture contains about 2.5 to about 4.5 percent xylene solubles.
9. High clarity thermoformed parts substantially free of phosphite antioxidants, manufactured by a process comprising combining at least one additive selected from the group consisting of non-phosphite antioxidants, nucleating agents, antistatic agents, clarifying agents, and acid scavengers, with virgin polypropylene homopolymer to form an improved clarity homopolymer, combining said improved clarity homopolymer with reground thermoformed polypropylene homopolymer to create a homopolymer mixture, wherein said homopolymer mixture has a melt flow rate of between about 1 and about 4 g/10 min; a xylene solubles content of about 2.5 percent to about 4.5 percent; and wherein said homopolymer mixture is extruded and thermoformed at a temperature between about 146° C. and about 155° C.
10. The thermoformed parts of claim 9 wherein the content of said at least one additive in the improved clarity homopolymer is between about 100 and about 2000 ppm.
11. The thermoformed parts of claim 9 wherein the haze of said high clarity thermoformed parts is less than about 7% and the clarity is greater than about 80%.
12. High clarity thermoformed parts substantially free of phosphite antioxidants, said parts having a haze of between about 3 and 5%, wherein said parts are manufactured by a process comprising combining at least one additive selected from the group consisting of non-phosphite antioxidants, nucleating agents, antistatic agents, clarifying agents, and acid scavengers, with virgin polypropylene homopolymer to form an improved clarity homopolymer, combining said improved clarity homopolymer with reground thermoformed polypropylene homopolymer to create a homopolymer mixture, wherein said homopolymer mixture is extruded, and thermoformed at a temperature between about 146° C. and about 155° C.
13. The thermoformed parts of claim 9 wherein said reground thermoformed polypropylene homopolymer comprises at least 25 percent of the homopolymer mixture.
14. The thermoformed parts of claim 13 wherein the haze of said high clarity thermoformed parts is less than about 7% and the clarity is greater than about 80%.
15. The thermoformed parts of claim 13 wherein said reground thermoformed polypropylene homopolymer comprises polypropylene homopolymer manufactured with at least one additive selected from the group consisting of non-phosphite antioxidants, nucleating agents, antistatic agents, clarifying agents, and acid scavengers, wherein the content of said at least one additive in the reground thermoformed polypropylene homopolymer is between about 100 and about 2000 ppm, and wherein said reground thermoformed polypropylene homopolymer is substantially free of phosphite antioxidants, extruded, and thermoformed at a temperature between about 146° C. and about 155° C., then reground.
16. An improved clarity homopolymer, substantially free of phosphite antioxidants, comprising reground thermoformed polypropylene homopolymer, virgin polypropylene homopolymer, and an additive package, said additive package containing a non-phosphite antioxidant, and at least one additive selected from the group consisting of nucleating agents, antistatic agents, clarifying agents, and acid scavengers.
17. The homopolymer of claim 16 wherein the content of said non-phosphite antioxidant is between about 100 and about 2000 ppm.
18. The method of claim 1 wherein said reground thermoformed polypropylene homopolymer is manufactured by combining at least one additive selected from the group consisting of non-phosphite antioxidants, nucleating agents, antistatic agents, clarifying agents, and acid scavengers with virgin polypropylene homopolymer, wherein the content of said at least one additive in the polypropylene homopolymer is between about 100 and about 2000 ppm, and wherein said polypropylene homopolymer is substantially free of phosphite antioxidants, extruded, and thermoformed at a temperature between about 146° C. and about 155° C., then reground.
19. The method of claim 1 wherein said reground thermoformed material comprises between 30% and 70% of the total polypropylene homopolyiner content.
20. High clarity thermoformed parts substantially free of phosphite antioxidants having a haze of less than about 7% and clarity of greater than about 80%, wherein said parts are manufactured by a process comprising combining at least one additive selected from the group consisting of non-phosphite antioxidants, nucleating agents, antistatic agents, clarifying agents, and acid scavengers, with virgin polypropylene homopolymer to form an improved clarity homopolymer, and combining said improved clarity homopolymer with reground thermoformed polypropylene homopolymer to create a homopolymer mixture, wherein said homopolymer mixture is extruded, and thermoformed at a temperature between about 146° C. and about 155° C.