Stock material or miscellaneous articles – Web or sheet containing structurally defined element or...
Reexamination Certificate
2002-06-14
2003-12-02
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
C528S190000, C528S194000, C528S195000, C528S198000, C528S275000, C528S298000, C528S300000, C528S302000, C528S308000, C528S308600, C524S081000, C524S779000, C264S176100, C264S177170, C264S211120, C264S280000, C264S291000, C264S299000, C428S357000, C428S480000
Reexamination Certificate
active
06656577
ABSTRACT:
FIELD OF THE INVENTION
The present invention is a process for making poly(ethylene-co-isosorbide) terephthalate polymer that has low color and low diethylene glycol (DEG) content.
TECHNICAL BACKGROUND OF THE INVENTION
The diol 1,4:3,6-dianhydro-D-sorbitol, referred to herein as isosorbide, is readily made from renewable resources, such as sugars and starches. For example, isosorbide can be made from D-glucose by hydrogenation followed by acid-catalyzed dehydration.
Poly(ethylene-co-isosorbide) terephthalate polymer (PEIT) is a polymer with a higher glass transition temperature (Tg) than polyethylene terephthalate (PET). This positions it for use in products such as bottles, hot-fill containers, film, thick sheet, fibers, strand and optical articles. In many of these markets, aesthetics are important, and having a very low color resin is highly desirable. To maximize the Tg-enhancing effects of isosorbide, it may also be desirable to minimize the presence of Tg-reducing impurities, such as diethylene glycol (DEG).
U.S. Pat. No. 5,912,307 discloses the use of tetramethylammonium hydroxide (TMAH) to suppress DEG formation in the melt polymerization of ethylene glycol with mixtures of the aromatic diacids, terephthalic acid, isophthalic acid and 2,6-naphthalenedicarboxylic acid.
U.S. Pat. No. 5,959,066 discloses polyesters that include isosorbide as a co-monomer and methods for making them (Charbonneau et al.). This patent discloses process steps to obtain isosorbide-containing polymers from esterification to solid-state polymerization. No mention is made concerning the need to obtain polymer with low color. Example 2 describes the preparation of isosorbide-containing polyesters with 1% DEG content without the use of TMAH.
U.S. Pat. No. 6,063,465 discloses the range of isosorbide content in PEIT resins suitable for making polyester containers, processes for making such resin, and a method for making containers from that resin. Melt polymerization processes are described using either dimethyl terephthalate or terephthalic acid as the acid component. This patent is hereby incorporated by reference (Charbonneau, Johnson).
U.S. Pat. No. 6,063,464 describes isosorbide-containing polyesters and methods for making same (Charbonneau et al.). The patent claims the composition of isosorbide containing polyesters and a process for their solid-state polymerization. The possible applications include beverage bottle, film or sheet, fibers, optical materials, and compact disc or digital versatile disc. The patent does not make mention of any process conditions aimed at the minimization of color or DEG content.
U.S. Pat. No. 5,958,581 describes polyester film and methods for making the same (Khanarian et al.). Film comprised of isosorbide-containing polyester is claimed. Several compositions are claimed. No mention is made concerning color or DEG content.
U.S. Pat. No. 6,063,495 describes PEIT fiber and methods for making the same. It is noted that DEG may be produced as a by-product of the polymerization process. It is noted that polymer without DEG is obtainable in a solution polymerization process. However, there is no disclosure concerning minimizing DEG formation in a melt polymerization process. There is also no mention of color formation.
SUMMARY OF THE INVENTION
This invention provides a melt polymerization process for the preparation of poly(ethylene-co-isosorbide) terephthalate (PEIT), comprising:
a) providing a mixture comprising terephthalic acid or its alkyl ester, ethylene glycol and isosorbide, wherein the molar ratio of diols to terephthalic acid or its alkyl ester is from about 1.05:1 to about 1.3:1 and the molar ratio of ethylene glycol to isosorbide is from about 1.2:1 to about 24:1;
b) reacting the mixture in an inert atmosphere at a temperature in the range 180-255° C. and a pressure in the range of 0-60 psig, with concurrent removal of a distillate comprising water or volatile alkanol products derived from the reaction of terephthalic acid or its ester with ethylene glycol and isosorbide, wherein the distillate contains less than about 5 wt % ethylene glycol and less than about 1 wt % isosorbide; and
c) continuing the reaction in the presence of a polycondensation catalyst at a pressure of about 0.25 to about 2 mm and a temperature of 260 to 275° C. to form a PEIT having a Hunter b* color value between about −2.0 and about +2.0.
The present invention also relates to the low color PEIT polymers made by this process.
The present invention also relates to bottles, hot-fill containers, films, thick sheet, optical articles, fibers, strand and polymer blends and alloys made from the PEIT polymer of the process described herein.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a process to make PEIT polymer that has low color for use in hot-fill container, bottle, thick sheet, film, fiber, strand, optical articles and other applications. Color is commonly expressed in terms of Hunter numbers which correspond to the lightness or darkness (“L”) of a sample, the color value (“a*”) on a red-green scale, and the color value (“b*”) on a yellow-blue scale. It is usually desired to produce polymers with “L” between 80 and 100, preferably 90 to 100. Similarly, for low color polymers, “a*” and “b*” are preferably between about −2.0 and about +2.0, more preferably between about −1.0 and about +1.0, as measured by the process described herein. It has been found that these objectives can be met for PEIT without the use of color-correcting additives by controlling critical process parameters at each stage of the process, especially temperature and pressure.
For low color PEIT, it is also important to eliminate, or at least minimize, the color-forming impurities present in the monomer diols. Preferably, the UV absorbance of ethylene glycol and isosorbide are less than 0.20 at 220 nm, more preferably less than 0.10.
The choice of polycondensation catalyst also influences the color of the final polymer. Suitable catalysts include Sb(III) or Ti(IV) salts; acetate and other alkanoate salts of Co(II), and Sb(III); oxides of Sb(III); oxides of Sb(III) and Ge(IV); and Ti(OR)
4
, where R is an alkyl group having 2 to 12 carbon atoms. Glycol solubilized oxides of these metal salts may also be used. Oxides of Ge such as GeO
2
are preferred. The preferred amount of polycondensation catalyst is generally from about 10 to about 300 ppm by weight. More specifically, the molar ratio of catalyst to terephthalic acid or its ester is about 1:1000 to about 1:7300, preferably about 1:2200 to about 1:4400.
Inclusion of the isosorbide monomer raises the Tg of the final PEIT polymer (relative to PET), while DEG incorporation into the polymer tends to lower the Tg. DEG can be formed, and subsequently incorporated into the polymer, when terephthalic acid is used in the polymerization process. For applications in which low DEG is desired and the polymerization process uses terephthalic acid, one can add a suitable base and also minimize the ratio of ethylene glycol to diacid in the initial esterification reaction. It has been found that adding suitable bases with the monomers charged to the reactor suppresses DEG formation in PEIT polymers. Suitable bases include sodium acetate, sodium hydroxide, and tetramethylammonium hydroxide (TMAH). An effective amount of base is about 10 to about 300 ppm, based on terephthalic acid. In examples herein, the combination of germanium oxide (GeO
2
) and TMAH give especially low color and low DEG content polymer when terephthalic acid is used in the process. For applications needing high Tg values, the DEG content is preferably less than about 1.5 mol %, more preferably less than about 1.0 mol %.
The polymerization process of this invention is a condensation polymerization of ethylene glycol, isosorbide, and terephthalic acid or its alkyl ester. Suitable terephthalic acid esters for the process of this invention include mono- and di-alkyl esters of terephthalic acid, wherein the alkyl group is chosen from the group of C
1
to C
6
alkyls.
Adelman Douglas J.
Charbonneau Larry F.
Ung Sophie
Acquah Samuel A.
E. I. du Pont de Nemours & Company
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