Molded or extruded articles comprising polyhydroxyalkanoate...

Details Molded or extruded articles comprising polyhydroxyalkanoate... Molded or extruded articles comprising polyhydroxyalkanoate...

2003-05-08

2004-03-16

Acquah, Samuel A. (Department: 1711)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S372000, C528S361000, C528S50200C, C528S503000, C525S444000, C264S176100, C264S209100, C264S211170, C524S081000, C524S220000, C524S284000, C524S297000, C524S312000, C524S314000, C524S442000, C524S445000, C524S451000

Reexamination Certificate

active

06706942

ABSTRACT:

FIELD OF INVENTION
The present invention relates to polyhydroxyalkanoate copolymer (PHA) compositions having short annealing cycle times for manufacturing molded or extruded articles such as, for example, disposable articles, in particular, tampon applicators. Such molded or extruded articles are readily environmentally degradable.
BACKGROUND OF THE INVENTION
Polyhydroxyalkanoates (PHAs) are thermoplastic polymers desirable for use in molded or extruded articles particularly due to their biodegradability. However, existing PHA copolymer compositions are slow to crystallize and producing molded or extruded articles therefrom remains nonviable commercially. It is necessary for compositions to solidify in a mold in as short a cycle time as possible to allow a manufacturing process to be economically feasible.
U.S. Pat. No. 5,498,692, issued Mar. 12, 1996 to Noda, and U.S. Pat. No. 5,502,116, issued Mar. 26, 1996 to Noda, relate to molded articles comprising PHAs. Molded articles from such PHAs remain substantially tacky after they are cooled down from the melt, and remain as such until sufficient crystallinity sets in, particularly with PHA copolymers levels above 10 wt %. Residual tack typically can lead to material sticking to itself or to the processing equipment, or both, and thereby can restrict the speed at which a polymeric product is produced or prevent the product from being collected in a form of suitable quality. A poly(3-hydroxybutyrate-co-3-hydroxyvalerate) product commercialized under the name BIOPOL® suffers from hardness, brittleness, and from having very slow crystallization kinetics. Similarly, U.S. Pat. No. 5,292,860 to Shiotani lacks teachings regarding compositions having short cycle times in the manufacturing process for molded or extruded articles.
Consequently, there is a need for melt processable compositions of PHAs having economically viable annealing cycle times for use in molded or extruded articles. Moreover, the compositions should be suitable for use in conventional processing equipment, be environmentally degradable, and meet consumer acceptability for their structural integrity and aesthetic characteristics of smoothness, flexibility, reduced stickiness, stability, and the like.
SUMMARY OF THE INVENTION
Molded or extruded articles of the present invention comprise a PHA copolymer having at least two randomly repeating monomer units (RRMUs)
wherein a first monomer unit has structure (I)
where R
1
is CH
3
, and n is 1; and
wherein a second monomer unit has structure (II)
where R
2
is CH
2
CH
2
CH
3
.
Such a PHA is referred to herein as a C4C6 PHA copolymer. For the present invention, between 2 and 8% of the randomly repeating monomer units has the structure of the second monomer unit, the C6 unit. Further, such compositions are demonstrated herein to provide an annealing cycle time that is at least ten seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit. In certain embodiments of the invention, such an annealing cycle time is at least 15, 20, 25, 30, 35, 40, 45, or 50 seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit. A process of forming a molded or extruded article comprises heating to a molten state a C4C6 PHA copolymer as described herein, allowing the melted blend to anneal; and molding or extruding the article, the process having an annealing cycle time that is at least ten seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit.
The present invention also provides flushable tampon applicators comprising such PHA compositions wherein the applicator is greater than 50% disintegrated within 28 days under anaerobic conditions.
Filed on an even date herewith is U.S. Pat. Ser. No. 10/431,796, of the present inventors to PHA compositions in blends with an environmentally degradable polymer wherein molded or extruded articles made therefrom also provide annealing cycle times that are commercially feasible.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, a “molded or extruded article” is an object that is formed from a PHA copolymer as set forth herein using molding or extrusion techniques such as injection molding, blow molding, compression molding, or extrusion of pipes, tubes, profiles, cables, or films. Molded or extruded articles may be solid objects such as, for example, toys, or hollow objects such as, for example, bottles, containers, tampon applicators, applicators for insertion of medications into bodily orifices, medical equipment for single use, surgical equipment, or the like.
The annealing cycle time is defined herein as holding time plus cooling time. With process conditions substantially optimized for a particular mold, an annealing cycle time is a function of copolymer composition. Process conditions substantially optimized are the temperature settings of the zones, nozzle, and mold of the molding apparatus, the shot size, the injection pressure, and the hold pressure. Annealing cycle times provided herein are at least ten seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8%, or greater than 8%, of the randomly repeating monomer units have the structure of the second monomer unit. In certain embodiments of the invention, the annealing cycle time for a molded or extruded article is at least 15, 20, 25, 30, 35, 40, 45, or 50 seconds less than an annealing cycle time to form a molded or extruded article having the at least two randomly repeating monomer units wherein 8% or greater than 8% of the randomly repeating monomer units have the structure of the second monomer unit. A dogbone tensile bar having dimensions of ½ inch length (L) (12.7 mm)×⅛ inch width (W) (3.175 mm)×{fraction (1/16)} inch height (H) (1.5875 mm) made using an Engel Tiebarless ES 60 TL injection molding machine as provided herein provides a standard article as representative of a molded or extruded article for measuring annealing cycle times herein.
The holding time is the length of time that a part is held under a holding pressure after initial material injection. The result is that air bubbles and/or sink marks, preferably both, are not visually observable on the exterior surface, preferably both exterior and interior surfaces (if applicable), with the naked eye (of a person with 20—20 vision and no vision defects) from a distance of about 20 cm from the surface of the molded or extruded article. This is to ensure the accuracy and cosmetic quality of the part. Shrinkage is taken into account by the mold design, however, shrinkage of about 1.5% to 5%, from about 1.0% to 2.5%, or 1.2% to 2.0% may occur. A shorter holding time is determined by reducing the holding time until parts do not pass the visual test described supra, do not conform to the shape and texture of the mold, are not completely filled, or exhibit excessive shrinkage. The length of time prior to the time at which such events occur is then recorded as a shorter holding time.
The cooling time is defined as the time for the part to become solidified in the mold and to be ejected readily from the mold. The mold includes at least two parts, so that the molded article is readily removed. For removal, the mold is opened at the parting line of the two parts. The finished molded part can be removed manually from the opened mold, or it can be pushed out automatically without human intervention by an ejector system as the mold is being opened. Depending on the part geometry, such ejectors may cons

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