Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-10-19
2002-02-26
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S437000, C525S439000, C525S450000, C525S466000
Reexamination Certificate
active
06350822
ABSTRACT:
The present invention relates to polyesters, in particular the present invention relates to modified polyesters having improved melt rheology (as can be measured by a number of means eg melt strength, melt viscosity, swell ratio, extensibility etc) and/or improved physical properties (eg reduced gas permeability, increased heat resistance, higher impact strength etc). The present invention further relates to a method of modifying a polyester to provide improved melt rheology and/or physical properties.
Thermoplastic polyesters resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) have good mechanical characteristics, heat resistance, chemical resistance and dimensional stability (although there is scope for improvements in these and many other properties). These polyesters are widely used in the fields of extrusion, injection moulding and stretch blow moulding to produce products such as fibres containers and film.
While polyesters may be used in fields such as film blowing, tentering, thermoforming and foam extrusion, their use in these fields is often limited due to difficulties resulting from a narrow processing window and the need for specialized processing equipment. This is generally a result of deficiencies in the melt rheology of polyesters for these and other applications. Polyesters typically have low melt viscosity, low melt strength and low melt elasticity. While in some cases the deficiencies in the melt rheology a polyester resin may be partially overcome by the use of relatively expensive and sophisticated processing equipment, generally these deficiencies restrict such uses of polyester resins.
The use of various polyfunctional coupling agents including pyromellitic dianhydride (PDMA) to introduce branching into polyesters in order to improve melt viscosity or melt strength is discussed in, for example, Leslie et al. U.S. Pat. No. 4,145,466 and Ghatta et al. U.S. Pat. No. 5,362,763 and U.S. Pat. No. 5,422,381. Such reagents are incorporated during polyester synthesis by a solid state polycondensation process or require such a process following melt mixing to give a product of sufficient intrinsic viscosity. Dijkstra U.S. Pat. No. 3,553,157, Hayashi U.S. Pat. No. 5,134,028 and Rotter and Melquist U.S. Pat. No. 5,288,764 disclose the use of PDMA either alone or as a masterbatch in PET to improve the properties of PET in a melt processing method.
Muschiatti U.S. Pat. No. 5,229,432 describes the use of various branching agents including diacids, dianhydrides, and polyhydroxy compounds in an extruder to provide high melt strength PET for foaming applications. Similarly, Smith and Trevitt CH 688184 A5 disclose that a polycarboxylic acid anhydride (including PMDA) together with a polyhydric alcohol may be combined with PET in a melt mixing process to improve melt viscosity. These publications are however silent about the need of careful control over the ratio of components required to achieve the substantial improvements in rheological properties which we have found.
In addition to the melt rheology limitations of polyesters, they also generally have poor melt stability. Melt stability may be described as resistance toward polymer degradation during processing in the molten state (as evidenced by decreased molecular weight or decreased intrinsic viscosity and/or an increase in the amount of degradation products). Hydrolysis is one route via which polyesters degrade to produce lower molecular weight (lower intrinsic viscosity) materials. Hydrolysis is also evidenced by a reduction in polymer physical properties such as tear and tensile strengths, impact strength as well as flex life.
The lack of melt stability of polyesters is also evidenced in the inability to efficiently recycle PET scrap, in particular for food contact applications. For example, when PET is used to make carbonated beverage containers (by injection moulding into preforms and then subsequent stretch-blow moulding) a significant decrease in the molecular weight and corresponding decrease in the intrinsic viscosity of the PET occurs. This results in a decrease in the melt viscosity and melt strength of the PET relative to the virgin resin, making the processed material unsuitable for reprocessing into carbonated beverage bottles. One approach being employed to make use of recycled PET scrap is to incorporate it as an intermediate layer between virgin PET during the production of the bottle preforms by injection moulding. This approach requires very sophisticated injection moulding equipment and the method is not entirely satisfactory as the sandwiched preforms are more difficult to stretch-blow mould into bottles than the preform made of virgin PET only.
Other processes aimed at increasing the molecular weight of recycled PET, such as solid-stating, are costly and often render the use of recycled PET economically unattractive.
We have now found that the melt phase reaction of a polyester resin with a polyhydric alcohol and a polyfunctional acid anhydride in combination may be controlled to produce significant improvements in the melt rheology (eg melt viscosity, melt strength), intrinsic viscosity and molecular weight (Mw, Mz) of the polyester.
According to a first aspect, there is provided a polymer blend comprising a polyester, a polyfunctional acid anhydride wherein said polyfunctional acid anhydride has a functionality as described herein of three or more, and a polyhydric alcohol or precursor thereto wherein said polyhydric alcohol has a functionality of three or more, and wherein said molar ratio of said polyfunctional acid anhydride to the polyhydric alcohol or precursor thereto is in the range of 0.5:1 to (10×C):1, where C is the number of moles of alcohol or equivalent in the polyhydric alcohol or precursor thereto.
According to a second aspect of the present invention, there is provided a method for modifying a polyester comprising reacting said polyester with a polyfunctional acid anhydride and a polyhydric alcohol or precursor thereto wherein said polyfunctional acid anhydride has a functionality as described herein of three or more and wherein said polyhydric alcohol has a functionality of three or more and wherein the molar ratio of said polyfunctional acid or anhydride to the polyhydric alcohol or precursor thereto is present in the range of 0.5:1 to (10×C):1, where C is the number of moles of alcohol or equivalent in the polyhydric alcohol or precursor thereto.
According to a third aspect of the present invention, there is provided a method for coupling polyesters to at least one reactive polymer comprising reacting said polyester and said at least one reactive polymer with a polyfunctional acid anhydride and a polyhydric alcohol or precursor thereto wherein said polyfunctional acid anhydride has a functionality as described herein of three or more and wherein said polyhydric alcohol or precursor thereto has a functionality of three or more and wherein the molar ratio of said polyfunctional acid anhydride to the polyhydric alcohol or derivative thereof is present in the range of 0.5:1 to (10×C):1, where C is the number of moles of alcohol or equivalent in the polyhydric alcohol or precursor thereto.
According to a fourth aspect of the present invention there is provided a branched or chain extended polyester or a polyester blend formed by the melt phase reaction of a polyester resin with a polyhydric alcohol or precursor thereto and a polyfunctional acid anhydride in combination wherein said polyfunctional acid anhydride has a functionality as described herein of three or more and wherein said polyhydric alcohol has a functionality of three or more and wherein the molar ratio of said polyfunctional acid or anhydride to the polyhydric alcohol or precursor thereto is present in the range of 0.5:1 to (10×C):1, where C is the number of moles of alcohol or equivalent in the polyhydric alcohol or precursor thereto.
The present invention also provides polymers and polymer blends produced by the processes described herein.
Polyesters suitab
Moad Graeme
O'Shea Michael Shane
Van Diepen Gary Joseph
Polymers Australia Pty Limited
Seed Intellectual Property Law Group PLLC
Short Patricia A.
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