Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-10-18
2004-03-16
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C528S275000, C528S277000, C528S279000, C528S281000, C528S283000, C528S284000, C528S285000, C528S296000, C528S298000, C528S302000, C528S308000, C528S308600, C528S503000, C524S779000, C524S780000, C524S783000, C524S784000, C524S788000, C524S791000, C525S437000, C525S444000
Reexamination Certificate
active
06706396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing very low inherent viscosity (IV) polyester resin. More specifically but not by way of limitation, the present invention relates to production of pelletized polyethylene terephthalate, polybutylene terephthalate and corresponding polyester naphthalates having an inherent viscosity within the range of about 0.20 dL/g to about 0.45 dL/g.
2. Description of the Related Art
Emerging technologies, such as melt blown fibers and the nonwoven textiles produced therefrom, require very low melt viscosity polymeric materials. In a melt-blowing process, a non-woven web is formed by extruding a molten polymer through a die and then attenuating and breaking the resulting filaments with a hot, high-velocity gas stream. This process generates short, very fine fibers that can be collected on a moving belt where they bond with each other during cooling. Melt-blown webs can be made that exhibit very good barrier properties.
For poly(ethylene terephthalate) materials, this has been translated to polyesters which have inherent viscosities in the range of 0.25 to 0.45 dL/g, as disclosed by Rudisill, in WO 01/86044 A1. The production of discrete, particulate poly(ethylene terephthalate) materials with inherent viscosities within this range have proven to be difficult. For example, according to the Rudisill disclosure, poly(ethylene terephthalate) materials with inherent viscosities of 0.63 dL/g were used in the examples and then subsequently hydrolytically or thermally cracked down to poly(ethylene terephthalate) materials with inherent viscosities of 0.34 dL/g. One shortcoming of disclosed procedure is that the added cracking processes provides further complications to the overall processes, which would be desirable to avoid.
Typical poly(ethylene terephthalate) production processes are not able to directly produce materials with inherent viscosities below about 0.45 dL/g. In a typical poly(ethylene terephthalate) production process, the polyester exits the polymerizer through a die plate and falls through an air gap of typically 1 to 24 inches, more commonly 6 to 12 inches, to a water trough. The polyester strand hardens in the water trough and is then pelletized. Poly(ethylene terephthalate) materials with inherent viscosities below about 0.45 dL/g do not have the melt strength to be self supporting. This is evident in the above mentioned typical process in the form of the strands breaking or dropping in the air gap because they do not have the melt strength to support their own weight. As one skilled in the art would understand, this would preclude the production of such low inherent viscosity polyesters by typical processes.
Particulate poly(ethylene terephthalate) materials with inherent viscosities within the range of 0.20 to 0.45 dL/g are available. However, they are provided through crushing or pulverization processes that produce irregularly shaped particles having a wide range of sizes. For example, polymers may be formed into solidified strands, ribbons, or sheets, which may then be broken into particles. Fracturing or granulation of a sheet, for example, into particles may be accomplished by various processes including ball milling. Such processes of particle formation, however, may result in particles that are not uniform in size and/or shape. Furthermore, such processes may generate an undesirable amount of fines, i.e. particles of sizes substantially smaller than the average size or a target size, which further complicates particle handling and processing. Such irregular, non-uniform, particles provide difficulties within further process steps, such as crystallization, drying and feeding to extruders. It is desirable to provide poly(ethylene terephthalate) materials having inherent viscosities within the range of 0.20 to 0.45 dL/g, in a uniform particulate form convenient for use in subsequent processes.
Attempts have been made to overcome these deficiencies by producing prepolymers having intrinsic viscosities within the range of 0.10 to 0.35 dL/g in the form of spherical beads, for example, as disclosed in U.S. Pat. No. 4,165,420. Spherical prepolymer beads are disclosed having diameters in the range of 100 to 250 microns, and are produced either by spray congealing or atomization. U.S. Pat. No. 4,755,587 and U.S. Pat. No. 4,876,326 disclose the production of polyester prepolymers in the form of porous pills. However, the disclosed processes require complex processes to produce powders or porous pills, and the disclosures do not include the production of conventional pellets having desirable intrinsic viscosities and uniformity.
Other processes have been developed to fill the need for a uniform, discrete particulate form of very low inherent viscosity poly(ethylene terephthalate) materials. For example, it has been suggested that pastillation solves this need. Pastillation is a process wherein one forms polymer droplets from the polymer melt and subsequently solidifies the polymer droplets into polymer particles or pellets. An example of the use of pastillation processes for the production of uniform, discrete particles of low inherent viscosity polyesters is taught by Stouffer, et al., in U.S. Pat. No. 5,540,868. Further disclosures of the use of pastillation processes can be found in, for example; U.S. Pat. No. 5,510,454, U.S. Pat. No. 5,532,333, U.S. Pat. No. 5,633,018, U.S. Pat. No. 5,714,262, U.S. Pat. No. 5,744,074, and U.S. Pat. No. 5,830,982. A shortcoming of such pastillation processes is the need for complex equipment, such as rotoformers and heated belts, and complicated manufacturing schemes required.
Schiavone, in U.S. Pat. No. 6,335,422, discloses a process for producing certain copolyesters, including copolyesters comprising terephthalic acid, 84 to 94 mole percent ethylene glycol, 2 to 6 mole percent diethylene glycol and 4 to 10 mole percent cyclohexane dimethanol to an intrinsic viscosity of between 0.25 and 0.40 dL/g, forming the prepolymer into chips and in turn, solid state polymerizing the chips to a higher intrinsic viscosity. With regard to how the materials are formed into particles, the disclosure states that prior to the solid state polymerization step, the copolyester prepolymer composition is formed into discrete particles by “conventional techniques (e.g., strand pelletization and hot-cut pelletization-drops from a vibrating plate die, or drops or pastillates from a rotating die or plate will not work within the intrinsic viscosity range of the invention)”. The use of homopoly(ethylene terephthalate) in forming polyesters having low viscosities is not included in the disclosure.
BRIEF SUMMARY OF THE INVENTION
One aspect of the present invention provides processes for producing very low inherent viscosity polyesters in a certain discrete particulate form. The processes described herein are preferably used to form polyesters selected from the group consisting of poly(ethylene terephthalate), poly(1,4-butylene terephthalate), poly(ethylene 2,6-naphthalenedicarboxylate), and poly(1,4-butylene 2,6-naphthlalenedicarboxylate). The polyesters may be optionally branched. The polyesters have inherent viscosities in the range of about 0.20 to about 0.45 dL/g. The polyesters are formed by providing one aromatic compound selected from the group consisting of terephthalic acid, 2,6-naphthalene dicarboxylic acid, and acid chlorides and lower esters thereof; and contacting, under polymerization conditions, the aromatic dicarboxylic acid with one aliphatic diol selected from the group consisting of ethylene glycol and 1,4-butanediol, to copolymerize the aromatic dicarboxylic acid with said aliphatic diol and form the polymer. The term “lower esters” is known to those skilled in the art. Preferably, for use in the processes disclosed herein, lower esters have 5 or fewer carbon atoms, more preferably 4 or fewer carbon atoms.
In preferred embodiments, the polyesters are formed by providing one aromatic compound selected from the group consisting of terephthalic ac
Hayes Richard Allen
Hoffmann Gregory W.
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