Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-05-11
2001-10-02
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C528S499000
Reexamination Certificate
active
06297315
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the preparation of 1,3-propanediol based polyesters such as polytrimethylene terephthalate. In one aspect, the invention relates to a process for reducing the tendency of polytrimethylene terephthalate pellets to stick together during storage or transportation, particularly at elevated temperatures such as encountered in warm climates. In a further aspect, the invention relates to the reduction of fines in the manufacture of polytrimethylene terephthalate.
Polytrimethylene terephthalate is a polyester useful in fiber applications in the carpet and textile industries. The manufacture of polytrimethylene terephthalate involves the condensation polymerization of 1,3-propanediol and terephthalic acid to a polymer having an intrinsic viscosity (IV) of about 0.5 to 1.0 dl/g. The polymer melt is discharged from the bottom of the melt reactor and extruded through an extrusion die into strands. The strands are quenched in cold water and cut into pellets for storage or transportation.
It has been found that polytrimethylene terephthalate pellets tend to stick together, or “block,” during storage or shipping at temperatures above the polymer Tg (about 45°C.), which can be reached during the summer in a silo or rail car. Agglomeration of the pellets can also occur during drying using a hopper-type dryer.
It is therefore an object of the invention to produce polytrimethylene terephthalate pellets which are resistant to blocking during storage or shipping. It is a further object to produce polytrimethylene terephthalate pellets which can be dried in a hopper without agglomeration. It is a further object of one aspect of the invention to reduce fines production in the manufacture of polytrimethylene terephthalate.
BRIEF SUMMARY OF THE INVENTION
According to the invention, the polyester product of condensation polymerization of 1,3-propanediol and terephthalic acid is stabilized against blocking by immersing pellets of the polyester in an aqueous liquid such as water at a temperature within the range of 60 to about 100 ° C. for a time sufficient to achieve a crystallinity of at least about 35% and a pellet density of at least about 1.33 g/cm
3
.
The process is preferably carried out in a continuous liquid moving bed. The desired pellet properties are generally reached in an immersion time within the range of about 3 seconds to about 3 minutes.
REFERENCES:
patent: 2829771 (1958-08-01), Dahlstrom
patent: 3014011 (1961-12-01), Zoetbrood
patent: 5532335 (1996-07-01), Kimball et al.
patent: 5540868 (1996-07-01), Stouffer et al.
patent: 5763104 (1998-06-01), Stouffer et al.
patent: 5782935 (1998-07-01), Hirt et al.
patent: 1294019 (1957-02-01), None
patent: 0631007 (1994-12-01), None
patent: WO 97/23543 (1997-07-01), None
Chen Ye-Mon
Corey Ann Marie
Duh Ben
Shell Oil Company
Woodward Ana
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