Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-06-12
2002-03-19
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C528S271000
Reexamination Certificate
active
06358578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a method for the production of polyester by transesterification of at least a dicarboxylic acid dialkyl ester or esterification of at least a dicarboxylic acid with at least a diol, and subsequent pre-condensation and polycondensation in the presence of the usual catalysts as well as an additional co-catalyst, and the use of this polyester to produce films, bottles, molded articles or fibers.
2. Description of the Related Art
The production of polyesters in general takes place by means of the conversion of a diol with a dicarboxylic acid or a dicarboxylic acid ester, e.g., dimethyl ester. Initially the diol diester of the dicarboxylic acid is formed, which is then polycondensed by a single- or multi-staged process at increasing temperatures under diminishing pressure, whereby diol and water are liberated. Compounds of Ti, Mn, Mg, Ca, Li, Co and/or Zn are used as catalysts for transesterification, compounds of Sb, Ti, Ge and/or Sn are used for the esterification, and compounds of Sb, Ti, Pb, Ge, Zn and/or Sn or a zeolite are used for the polycondensation, whereby the quantity of metal in the catalyst used for the polycondensation alone can amount to up to 500 ppm relative to polyester. Antimony compounds, as the most frequently used esterification and polycondensation catalysts in the production of polyester, are required in quantities of approximately 150-250 ppm antimony, but concentrations of more than 200 ppm antimony are undesirable, in particular for using polyester for foodstuffs packagings.
From the literature (Derwent-abstract No. 81-33905 D of SU 759541 B1) it is known that the transesterification of dimethyl terephthalate with ethylene glycol can be carried out in the presence of a mixture of titanium tetrabutylate and activated charcoal at a ratio by weight of approximately 0.017:1, whereby very high quantities of approximately 2 weight % activated charcoal (relative to dialkyl ester) are employed. The activated charcoal serves as an agent to influence the color.
In another method (Derwent abstract No. 76-88266X of SU 495333 A) to produce PVC plasticizers, mixtures of di- and tricarboxylic acid methyl esters are transesterified with neopentyl glycol in the presence of zinc acetate and activated charcoal. According to the patent, approximately 0.6 weight % zinc acetate and approximately 1.2 weight % activated charcoal (relative to methyl ester) are required. A further disclosure (Derwent abstract No. 88-297391 of JP 63 218750 A) specifies the production of low molecular weight plasticizers through co-polymerization of adipic acid and hydroxy stearic acid with butylene glycol and ethyl hexanol in the presence of approximately 0.045 weight % dibutyl tin oxide and approximately 0.9 weight % activated charcoal (relative to the sum of the acids). To date nothing is known, however, as far as a specific catalytic activity of activated charcoal and/or its use as a co-catalyst when polycondensing linear polyester is concerned.
We recognized that prior art methods of producing polyesters resulted in a product having an amount of catalytic metal compounds (and other harmful substances) that would be desirable to reduce to make a safer product for use, for example, in the packaging of foodstuffs. The present invention accomplishes this goal.
SUMMARY OF THE INVENTION
The present invention comprises a method of producing polyester for use, in particular, in bottles, films, and miscellaneous foodstuffs packaging as well as filaments and fibers, which polyester has a reduced content of catalytic metal compounds and possibly other substances that may be harmful to health as compared to polyesters produced by prior art methods.
The method of the present invention is characterized by the fact that polycondensation and, optionally, esterification take place in the presence of an additional carbon containing co-catalyst. The carbon containing co-catalyst is preferably activated charcoal with a specific surface area of more than 500 m
2
/g and an average grain size of less than 2 &mgr;m.
The foregoing merely summarizes certain aspects of the present invention and is not intended, nor should it be construed, as limiting the invention in any manner. The invention is described in more detail below.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Surprisingly, it was found that activated charcoal, in conjunction with the usual catalytic metal compounds, acts as a co-catalyst for the polycondensation and/or the esterification reaction. The catalytic effect can be attributed to the properties of the activated charcoal. The basis for the secondary structure of the activated charcoal lies in the given random arrangement of graphite crystalites and amorphous carbon. Gaps and pores are located between these individual particles (micropores<2 nm, mesopores 2-50 nm, macropores>50 nm), which form a very great cavity system and result in the large, specific surface area typical of activated charcoal. As a result of the special crystal structure of the activated charcoal, the carbon atoms positioned at the edge of the layer structure are chemically unsaturated and form so called active centers that are the basis for the reactivity of the activated charcoal. Activated charcoal having a specific surface area of more than 500 m
2
/g (preferably more than 900 m
2
/g) is suited to function as a co-catalyst.
An elemental analysis reveals that, in addition to hydrogen, oxygen and nitrogen, other inorganic components originating from the raw material of the activated charcoal, such as Ca, K, Na, Si, Fe, Mg, Mn, Zn and Cl, can be found in trace amounts in the activated charcoal. (Hartmut v. Kienle, Erich Baeder; Activated Charcoal and its Industrial Applications, Ferdinand Enke Verlag/Stuttgart, (1980)). The preferred activated charcoal has a quality such as is used commercially for treating drinking water, for the foodstuffs industry, or for medicinal purposes. Such activated charcoal provides the advantage of being free of polycyclic aromatic compounds that are harmful to health, such as benzopyrene, so that the polyester that is produced can be used without problems for foodstuffs packaging.
Since the catalytic activity of the activated charcoal and the coloration of polyester mixed with activated charcoal is to a great degree dependent on the size of the grain, the activated charcoal according to the invention is selected so as to have a grain size (arithmetic mean) d
50
of less than 2 &mgr;m, preferably less than 0.5 &mgr;m. Preferably, the selection of the grain size takes place by milling the powdered activated charcoal in a liquid medium (preferably the diol that is the basis of the polyester, e.g., for polyethylene terephthalate or -naphthalate in ethylene glycol).
The carbon containing co-catalyst is used in addition to the usual polycondensation catalysts, such as compounds of Sb, Ti, Pb, Ge, Zn and/or Sn or a Zeolite, and, optionally, in addition to the usual esterification catalysts, such as compounds of Sb, Ti, Ge and/or Sn, in quantities of 0.1 to 1000 ppm (preferably 0.1 to 500 ppm) co-catalyst relative to polyester at a ratio by weight of catalyst to co-catalyst of 1 to from 0.01 to 5 (preferably 1 to from 0.01 to 3).
As the concentration of co-catalyst increases, the concentration of the usual catalysts used for the polycondensation or esterification can be reduced, whereby preferably 1 to 3 parts by weight of activated charcoal replaces approximately 1 part by weight of the metal of the usual catalyst. The quantity of the usual catalyst that is used together with the co-catalyst should be at least approximately 50% of the quantity that would be required without the co-catalyst. The concentration of co-catalyst can be selected specifically for each application by routine experimentation. Experience has shown that for the production of transparent foodstuffs packaging such as beverage bottles, a concentration range of 0.1 to 50 ppm (preferably 0.5-15 ppm) of activated charcoal is favorable, whereas to produce
Otto Brigitta
Schiebisch Jens
Thiele Ulrich
Hon Sow-Fun
McDonnell & Boehnen Hulbert & Berghoff
Pyon Harold
Zimmer Aktiengesellschaft
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