Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-08-10
2002-11-19
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C528S298000, C528S300000, C528S301000, C528S302000, C528S307000, C528S308000, C528S308600, C525S440030, C525S443000, C525S445000, C525S540000, C525S437000, C428S397000, C524S195000, C264S176100
Reexamination Certificate
active
06482513
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to monofilaments. More specifically, the invention relates to monofilaments produced from branched poly(ethylene terephthalate)s.
Polymeric monofilaments have found use as reinforcements for rubbers, fishing lines, toothbrush bristles, paint brush bristles and the like. In addition, woven fabrics produced from monofilaments have found use as industrial belts and paper machine clothing.
Polyesters have generally been taught to be useful as monofilaments. Polyester monofilaments are used due to their high strength and good dimensional stability. For example, U.S. Pat. Nos. 3,051,212 and 3,869,427 teach the use of polyester monofilaments as reinforcements for rubber articles. The use of polyester monofilaments to make fabric for processing and drying wet pulp to make paper is described in U.S. Pat. Nos. 3,858,623, 4,071,050, 4,374,960, 5,169,499, 5,169,711, 5,283,110, 5,297,590, 5,635,298, 5,692,938, and 5,885,709, and Kirk-Othmer Encyclopedia of Chemical Technology (2
nd
Ed.) (Interscience) 1967, Vol. 14, pp. 503-508 and the references cited therein.
Linear poly(ethylene terephthalate)s having inherent viscosities between 0.60 and 1.0 dL/g have typically been taught within the background art as useful in the production of monofilaments. Generally, it has been taught the inherent viscosity is greater than 0.70 dL/g. U.S. Pat. Nos. 3,051,212, 3,627,867, 3,657,191, 3,869,427, 3,959,215, 3,959,228, 3,975,329, 4,016,142, 4,017,463, 4,139,521, 4,374,960, 5,472,780, 5,635,298, 5,763,538, and 5,885,709 teach the use of high molecular weight, linear polyesters for use in the manufacture of monofilaments. To achieve poly(ethylene terephthalate) inherent viscosities of 0.70 or greater, additional processes must be undertaken. One process to achieve said inherent viscosity of 0.70 or greater is to increase the melt finishing time, typically through the use of two finishers. An example of this is taught within U.S. Pat. No. 4,139,521. However, the increased time in the melt allows the resultant polyester to degrade and discolor. Another process taught within the art to achieve the desired inherent viscosity of 0.70 or greater which avoids this polyester discoloration is solid phase polymerization (SSP). Generally this process involves heating poly(ethylene terephthalate) pellets to temperatures in excess of about 225° C. either under an inert gas purge or under vacuum for extended lengths of time. U.S. Pat. Nos. 3,051,212, 3,657,191, and 5,635,298 teach the use of solid state polymerization to increase the inherent viscosity of polyesters for use in the production of monofilaments.
Occasionally, general reference has suggested the use of branched polyesters for use as monofilaments. For example, U.S. Pat. No. 5,378,537 discloses a polyester monofilament comprising 0.005 to 1.5 weight percent of a carbodiimide and 0.01 to 30 weight percent of a random copolymer having tetrafluoroethylene and ethylene as main components. At column 2, lines 54-58, this references states that, “It is permissible to use an addition of a small amount of a chain-branching agent such as pentaerythritol, trimethylol propane, trimellitic acid, trimesic acid, or boric acid.” However, U.S. Pat. No. 5,378,537 only exemplifies the use of a linear poly(ethylene terephthalate) with an inherent viscosity of 0.93 dL/g.
As a further example, U.S. Pat. No. 5,686,552 discloses a polyester composition consisting of 99.8 to 60 weight percent of a polyester, 0.2 to 40 weight percent of a thermoplastic polymer which is not a reaction product of a dicarboxylic acid and a glycol and which contains no fluorine atoms, and 0.005 to 1.5 weight percent of an unreacted carbodiimide compound. This reference further teaches that said polyester “may also be combined with a small amount of a chain-branching agent such as pentaerythritol, trimethylol propane, trimellitic acid, or boric acid” (column 3, lines 49-51) and that “The limiting viscosity of the polyester is normally at least 0.6, and it is preferably at least 0.7 for particularly superior strength.” (column 3, line 66, through column 4, line 1). However, in the 230 examples disclosed therein, U.S. Pat. No. 5,686,552 consistently utilizes a linear poly(ethylene terephthalate) with an inherent viscosity of 0.94 dl/g.
As yet a further example, Pat. Abstracts of Japan publication number 59-094616 discloses monofilaments spun from a butylene terephthalate copolymer containing 3 to 30 weight percent branched alkylene terephthalate units or blends containing butylene terephthalate homopolymer and a branched alkylene terephthalate polymer and having an intrinsic viscosity greater than 1.1 dl/g.
For many end uses, the monofilaments require hydrolysis resistance. It has been taught within the art that lowered levels of carboxyl endgroups enhance the hydrolysis resistance of the as formed polyester monofilaments. For example, see the discussions in U.S. Pat. Nos. 3,051,212, 3,657,191, 4,139,521, 4,374,961, 5,246,992, 5,378,537 and the references cited therein.
Hydrolysis stabilization additives have been taught within the art. Generally, said hydrolysis stabilization additives have been taught to function by reacting with free polymeric carboxyl endgroups. U.S. Pat. Nos. 3,051,212 and 4,374,960 teach the use of diazomethane to “cap” the polyester carboxyl endgroups to enhance the hydrolysis resistance.
Carbodiimides are taught as polyester hydrolysis stabilization additives in U.S. Pat. Nos. 3,193,522, 3,193,523, 3,975,329, 5,169,499, 5,169,711, 5,246,992, 5,378,537, 5,464,890, 5,686,552, 5,763,538, 5,885,709 and 5,886,088. Epoxides are taught as polyester hydrolysis stabilization additives in U.S. Pat. Nos. 3,627,867, 3,657,191, 3,869,427, 4,016,142, 4,071,504, 4,139,521, 4,144,285, 4,374,960, 4,520,174, 4,520,175, and 5,763,538. Cyclic carbonates, such as ethylene carbonate, are disclosed as hydrolysis stabilization additives in U.S. Pat. Nos. 3,657,191, 4,374,960, and 4,374,961. U.S. Pat. No. 3,959,215 teaches the use of phenylene bisoxazolines for the stabilization of polyesters. Aziridine compounds have been disclosed in the production of low carboxyl polyesters in U.S. Pat. Nos. 3,959,228 and 5,763,538. U.S. Pat. No. 5,763,538 teaches the use of keteneimines and isocyanates as polyester monofilament hydrolysis stabilization additives.
A shortcoming found in the background art is the need for additional polymerization processes to achieve high molecular weight polyesters with inherent viscosities of 0.70 dL/g or greater to provide the desired high strength monofilaments. The present invention avoids said additional polymerization processes while providing adequate monofilament strengths.
BRIEF SUMMARY OF THE INVENTION
The present invention provides monofilaments comprising branched poly(ethylene terephthalate)s having an inherent viscosity of at least 0.5 dL/g. In one embodiment, the branched poly(ethylene terephthalate)s incorporate 0.01 to 1.0 mole percent of a polyfunctional branching agent and may optionally incorporate up to 5 mole percent of other diols and up to 5 mole percent of other dicarboxylic acids. In another embodiment, the branched poly(ethylene terephthalate)s have an inherent viscosity in the range of about 0.50 to 0.70 dL/g, preferably in the range of about 0.60 to 0.70 dL/g.
A further aspect of the present invention is branched poly(ethylene terephthalate)s stabilized with an effective amount of hydrolysis stabilization additive shaped in the form of monofilaments. Said hydrolysis stabilization additive chemically reacts with the carboxylic acid endgroups and is preferably carbodiimides.
A further aspect of the present invention is blends of branched poly(ethylene terephthalate)s with a polymer shaped in the form of monofilaments. The present invention is also provides blends of branched poly(ethylene terephthalate)s with other linear polyesters shaped in the form of monofilaments. Said other linear polyesters may be produced from dicarboxylic acids and diols. Further, the present invention provides blends of bra
Acquah Samuel A.
E. I. du Pont de Nemours and Company
Evans Craig
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