Title of Invention	"Method of Manufacturing High Molecular-Weight Polyethylene Terephthalate (PET) or Mixed Polyesters Thereof"
Abstract	The invention relates to a method of manufacturing polyesters, particularly high molecular-weight polyethylene terephthalate (PET), using titanium-containing catalyst-inhibitor combinations.

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The present invention relates to a method of manufacturing high molecular-weight polyethylene terephthalate (PET) or mixed polyesters thereof. The industrial production of polyethylene terephthalate and its mixed polyesters is normally carried out in two stages. In the first stage the polybasic carboxylic acids, e.g. terephthalic acid or its alkyl esters, are converted with ethylene glycol or a mixture of various multifunctional alcohols into a low molecular-weight precondensate, which is polycondensed in a second stage to form high molecular-weight polyethylene terephthalate of a corresponding copolyester. In order to achieve industrially practicable conversion times, and polyesters with a high molecular weight and good product quality, both stages of the polyester manufacture require catalytic acceleration. Esterification of terephthalic acid with ethylene glycol is already catalysed by the protons released from the erephthalic acid, and can be accelerated by specific compounds, or its progress can be influenced, e.g. with respect to the formation of by-products such as diethylene glycol. In order to accelerate the ester interchange and polycondensation, special catalysts must be added. Numerous compounds are proposed as ester interchange and polyester manufacture require catalytic acceleration. Esterification of terephthalic acid with ethylene glycol is already catalysed by the protons released from the terephthalic acid, and can be accelerated by specific compounds, or its progress can be influenced, e.g. with respect to the formation of by-products such as diethylene glycol. In order to accelerate the ester interchange and polycondensation, special catalysts must be added. Numerous compounds are proposed as ester interchange and polycondensation catalysts. Metallic compounds are preferred, such for example as are described in H. Ludewig "Polyesterfasern" (Polyester Fibres) (Akademie-Verlag Berlin 1975). However, catalysts For polyester production not only catalyse the generative reaction, but to varying degrees accelerate degradative reactions, heat-resistance, the formation of by-products, the colour and the processing behaviour of the end-product. In order to improve the production procedure and the product properties, therefore, catalysts and catalyst combinations co-ordinated with the respective proposed use, and catalyst inhibitors and stabilisers are used. Salts of organic acids with bivalent metals (e.g. manganese, zinc, cobalt or calcium acetate) are preferably used as ester interchange catalysts, which per se also catalyse the polycondensation reaction. Due to their catalytic action on degradative reactions of PET, the metallic catalysts must be rendered ineffective before the start of polycondensation by conversion with specific catalyst inhibitors. Phosphorus-containing compounds, such as phosphorous acids or respective proposed use, and catalyst inhibitors and stabilisers are used. Salts of organic acids with bivalent metals (e.g. manganese, zinc, cobalt or calcium acetate) are preferably used as ester interchange catalysts, which per se also catalyse the polycondensation reaction. Due to their catalytic action on degradative reactions of PET, the metallic catalysts must be rendered ineffective before the start of polycondensation by conversion with specific catalyst inhibitors. Phosphorus-containing compounds, such as phosphorous acids or phosphoric acid and their esters are principally used as inhibitors. Antimony, germanium and titanium compounds are preferred as polycondensation catalysts. Antimony compounds have become widely used in the manufacture of PET for various fields of application because they catalyse the polycondensation reaction relatively well, and do little to advance degradative reactions and the formation of by-products. Disadvantages in the use of antimony compounds reside in their toxicity, and a continually-observed grey cast in the polycondensates due to elementary antimony. The toxicity of antimony compounds and particularly of antimony trioxide, which is preferably used as a polycondensation catalyst, has a disadvantageous effect on the one hand in the manufacturing process during application and handling of the catalyst solutions, and on the other hand, during processing, use and disposal of the end-products, leads to environmental pollution, because the antimony is partly washed out by water, and passes into sewage, or pollutes the air when the polyesters are burned. used as a polycondensation catalyst, has a disadvantageous effect on the one hand in the manufacturing process during application and handling of the catalyst solutions, and on the other hand, during processing, use and disposal of the end-products, leads to environmental pollution, because the antimony is partly washed out by water, and passes into sewage, or pollutes the air when the polyesters are burned. In electrical and electronic components made of PET, which remain at high temperatures for long periods, antimony tends to migrate and forms surface coatings which can lead to contact problems. The colour cast of germanium-containing polyesters is indeed brighter than that of products containing antimony; germanium however advances the formation of by-products, particularly diethylene glycol, and catalyses thermooxidative degradation. Titanium compounds, in the first stage of polyester manufacture, catalyse both the ester interchange and esterification and lead to a pronounced increase in polycondensation speed; the polycondensates however have a considerable yellow colouring. It is known from GB PS 588 833 and 769 220 that trivalent and pentavalent phosphorus compounds can be used to inhibit the discoloration of polyesters. In DE PA 26 26 827, metallic phosphoric acid is proposed for stabilising titanium-containing polyesters. DE esterification and lead to a pronounced increase in polycondensation speed; the polycondensates however have a considerable yellow colouring. It is known from GB PS 588 833 and 769 220 that trivalent and pentavalent phosphorus compounds can be used to inhibit the discoloration of polyesters. In DE PA 26 26 827, metallic phosphoric acid is proposed for stabilising titanium-containing polyesters. DE OAS 24 34 213 shows that the discoloration of titanium-containing polyesters can be successfully restrained by the addition of phosphoric acid or phosphate esters. On the other hand, the addition of phosphoric acid and phosphate esters also leads to inhibition of the catalytic action of the titanium during polycondensation of the polyester. Therefore DE OS 24 34 213 proposes to carry out esterification of terephthalic acid with ethylene glycol in the presence of a titanium compound soluble in the reaction mixture, to deactivate the titanium compound after completion of the esterification by conversion with phosphoric acid or a phosphate ester, and to accelerate the following polycondensation by adding a soluble antimony or germanium compound. This again however leads to the known disadvantages in the use of antimony and germanium compounds. The object underlying the present invention is therefore to eliminate environmental pollution through the release of antimony, by replacing antimony trioxide as a polycondensation catalyst in soluble antimony or germanium compound. This again however leads to the known disadvantages in the use of antimony and germanium c ompounds. The ob]ect underlying the present invention is therefore to eliminate environmental pollution through the release of antimony, by replacing antimony trioxide as a polycondensation catalyst in polyester synthesis by the use of non-toxic catalysts, and to produce bright-coloured polyesters with a low proportion of byproducts and acetaldehyde, and with high thermal and thermooxidative asistance. At the same time the polyesters should contain a particularly low content of metallic compounds. This object is achieved in process terms by the characterising teatures of claim 1, and with reference to polyesters, by the features of claim 6. The sub-claims reveal advantageous further developments. Accordingly the present invention relates to method of manufacturing high molecular-weight polyethylene terephthalate (PET) or mixed polyesters thereof, in which, in a first stage, a low molecular-weight precondensate is produced from a polybasic carboxylic acid selected from terephthalic acid, or its alkyl esters, with one or more multifunctional alcohols selected from ethylene glycol, using a titanium catalyst, and that in the second stage a conversion to high molecular-weight PET or a corresponding copolyester is effected, an inhibitor in the form of a phosphorus containing compound being added, characterised in that in the first stage a titanium compound is added as a catalyst in a concentration of 0.005 - 0.05 mmol per mol of polycarboxylic acid, and the conversion is continued until a conversion of at least 95%, measured from the degree of water separation, is achieved, and in that the second stage of the polycondensation takes place in the presence of the titanium compound present from the first stage, with the addition of cobalt-containing compounds at a concentration of 0.02 - 0.2 mmol cobalt per mol polycarboxylic acid, the phosphorus containing inhibitor being added at a concentration of 0.004 - 0.4 mmol phosphorus per mol polycarboxylic acid, before or simultaneously with the addition of the cobalt catalyst to obtain the desired product. According to the invention, the method of manufacturing polyesters and mixed polyesters comprises the conversion of at least one dicarboxylic acid, e.g. terephthalic acid, which can be partly replaced by other dicarboxylic acids or higher-valency polycarboxylic acids, with at least one alkane diol. e.g. ethylene glycol, which can also contain other bivalent and polyvalent alkane polyhydric alcohols, in the presence of a titanium-containing catalyst such as titanium tetrabutylate in a quantity of 0.005 to at least one dicarboxylic acid, e.g. terephthalic acid, which can be partly replaced by other dicarboxylic acids or higher-valency polycarboxylic acids, with at least one alkane diol, e.g. ethylene glycol, which can also contain other bivalent and polyvalent alkane polyhydric alcohols, in the presence of a titanium-containing catalyst such as titanium tetrabutylate in a quantity of 0.005 to 0.05 mmol/mol dicarboxylic acid, and following addition of a phosphorus-containing inhibitor in a quantity of 0.004 to 0.4 mmol phosphorus/raol polycarboxylic acid. By means of adding the phosphorus compound, according to the invention especially phosphoric acid, phosphorous acid, phosphonic acid and its esters, the catalytic activity of the titanium is partly inhibited, as indicated in DE OS 24 34 213. It has however been discovered, surprisingly, that the catalytic activity of titanium as a polycondensation catalyst is retained or re-established if a cobalt salt such as cobalt acetate is added in a quantity of 0.5 to 5 mol cobalt/mol phosphorus, preferably 0.7 to 2 mol/mol, simultaneously with or after the addition of the phosphorus-containing inhibitor, and that in this way brightly-coloured polyesters with a low byproduct content and a low new formation rate of acetaldehyde are obtained. Catalyst inhibitor combinations on a basis of cobalt, titanium and phosphorus compounds belong to prior art to the extent that cobalt compounds are used as a catalyst for the ester interchange of terephthalic acid dimethyl ester with ethylene glycol, are then with a low by-product content and a low new formation rate of acetaldehyde are obtained. Catalyst inhibitor combinations on a basis of cobalt, titanium and phosphorus compounds belong to prior art to the extent that cobalt compounds are used as a catalyst for the ester interchange of terephthalic acid dimethyl ester with ethylene glycol, are then inhibited by the addition of phosphorus compounds, and the polycondensation is carried out in the presence of known polycondensation catalysts such as antimony, titanium or germanium. Such combinations are described, for example, in US PS 3, 907, 754. The present case however involves the production of a polyester precondensate by esterification of terephthalic acid or a mixture of terephthalic acid and other di- and polycarboxylic acids, and ethylene glycol, which can also contain other alkane diols or higher-valency polyhydric alcohols, in which cobalt compounds are catalytically inactive, and are converted into poorly-soluble cobalt terephthalate by conversion with the excess terephthalic acid present. Another surprising factor in this respect is that titanium concentrations of e.g. 0.02 mmol titanium/mol have a catalytic activity which is comparable with that of approximately 0.3 mmol antimony/mol dicarboxylic acid, a concentration which is usual in the large-scale industrial manufacture of PET. Thus the catalyst Another surprising factor in this respect is that titanium concentrations of e.g. 0.02 mmol titanium/mol have a catalytic activity which is comparable with that of approximately 0.3 mmol antimony/mol dicarboxylic acid, a concentration which is usual in the large-scale industrial manufacture of PET. Thus the catalyst dosage can be reduced to approximately a fortieth part (with respect to the mass of the metals). The invention renders accessible polyesters with a particularly low content of heavy metals. Apart from the fact that a low consumption of catalysts in the manufacture of polyesters has financial benefits, low concentrations of metallicions are also of importance for the properties of electrical and electronic components manufactured from these polyesters. Low concentrations of metalions reduce the relative permittivity, increase the electrical dielectric strength and the volume resistance, and thus extend the range of application for polyesters in the fields of electrotechnology and electronics. The low heavy metal content leads to a higher oxidation stability of the polymer in comparison to polymers manufactured with approximately 0.3 mmol antimony/mol dicarboxylic acid. This especially relates to the manufacture of rapidly-crystallising polyethylene terephthalate, where the crystallisation accelerators added advance the oxidative damage. Such rapidly-crystallismg The low heavy metal content leads to a higher oxidation stability of the polymer in comparison to polymers manufactured with approximately 0.3 mmol antimony/mol dicarboxylic acid. This especially relates to the manufacture of rapidly-crystallising polyethylene terephthalate, where the crystallisation accelerators added advance the oxidative damage. Such rapidly-crystallising products can for example also be produced from dimethyl terephthalate (DMT), if the ester interchange is catalysed by the addition of e.g. 0.02 mmol titanium tetrabutylate/mol DMT in combination with 6 to 10 mmol sodium acetate/mol DMT and 0.01 to 0.02 mmol cobalt acetate/mol DMT, and the subsequent polycondensation is likewise carried out in the presence of these additives. Esterification is carried out according to the invention in the presence of a titanium compound, up to a conversion of over 95%, preferably over 98%, measured by the degree of water separation, at temperatures of up to 270 °C at a slight excess pressure of up to about 3 bars absolute, or at normal pressure. The phosphorus-containing inhibitor is added in the form of a glycolic solution or suspension, or an another appropriate form, before, during or after esterification, and is homogeneously mixed. After termination of esterification and after addition of the inhibitor, a cobalt compound, e.g. cobalt acetate, dissolved in ethylene glycol, is mixed into the melt, and polycondensation is carried out in a known pressure. The phosphorus-containing inhibitor is added in the form of a glycolic solution or suspension, or an another appropriate form, before, during or after esterification, and is homogeneously mixed. After termination of esterification and after addition of the inhibitor, a cobalt compound, e.g. cobalt acetate, dissolved in ethylene glycol, is mixed into the melt, and polycondensation is carried out in a known way at a pressure gradually reducing to about 1 mbar, until an intrinsic viscosity of 0.6 dl/g is reached. The cobalt compound may also be added after a further completion of esterification, after the removal of glycol or after the start of pre-polycondensation. In order further to increase the intrinsic viscosity, the polyester produced according to the invention can be subjected in a known way to a solid-phase post-condensation. The invention will be explained in more detail in the following with reference to examples: Example l 690 g of terephthalic acid (TPA) are esterised with 3190 g of ethylene glycol with the addition of 0.02 mmol titanium tetrabutylate/mol TPA at temperatures rising from 250 up to 270°C, and at a pressure of 1 bar. The resultant water is distilled off until the theoretical quantity is achieved. Example l 690 g of terephthalic acid (TPA) are esterised with 3190 g of ethylene glycol with the addition of 0.02 mmol titanium tetrabutylate/mol TPA at temperatures rising from 250 up to 270°C, and at a pressure of 1 bar. The resultant water is distilled off until the theoretical quantity is achieved. The esterification product is mixed with the stabilisers indicated in Table 1 and cobalt acetate, and polycondensed at a slowly-mcreasmg vacuum at 280°C for 150 minutes. The polyesters are characterised by determination of the intrinsic viscosity (IV) m phenol/1.2-dichlorobenzene (1:1) at 20°C, by the content of carboxylene groups and by the colour values of the CIE-L/a/b system, positive b-values indicating a yellow cast, negative b-values a blue cast. Table Polycondensation of the esterification product with a content of 0.02 mmol titanium tetrabutylate/mol terephthalic acid with various added stabilisers and cobalt acetate, polycondensation time 150 mm. at 280°C, final vacuum 0.1 mbar. (Table Removed) polycondensation time 150 mm. at 280°C, final vacuum 0.1 mbar. (Table Removed) TNPP: trisonylphenylphosphite HgP04: 85£ phosphoric acid BPDP: bis(2,4-di-tert-butylphenyl)-pentaerythnte-diphosphite Poly-PPS: polyphosphoric acid TPPat: triphenylphosphate 2. Comparative Examplesi 2.1 An esterification product is produced as in Example 1 in the presence of 0.2 mmol titanium butylate/mol TPA and polycondensed without further additives for 150 minutes as in Example 1. The polyester obtained has an IV of 0.69 dl/g, and with a b-value of 9.6, a definite yellow cast. 2.2 An esterification product as in Example 1 and 2.1, containing of 0.2 mmol titanium butylate/mol TPA, is mixed with 0.1 mmol trisonylphenylphosphite/mol TPA and polycondensed as in Example 1. in Example 1. The polyester obtained has an IV of 0.69 dl/g, and with a b-value of 9.6, a definite yellow cast. 2.2 An esterification product as in Example 1 and 2.1, containing of 0.2 mmol titanium butylate/mol TPA, is mixed with 0.1 mmol trisonylphenylphosphite/mol TPA and polycondensed as in Example 1. After a polycondensation time of 150 minutes an intrinsic viscosity of 0.55 dl/g is reached. 3. Example for a Continuous Process Terephthalic acid (TPA) and ethylene glycol (EG) are mixed in a paste mixer with a mol ratio of 1:1.18 with the addition of 0.02 mmol titanium tetrabutylate/mo1 TPA, fed continuously into a first esterising reactor and intensively mixed with the monomer melt already located there. At a pressure of 2.5 bar (absolute) and at a temperature of 260°C, the TPA is esterised with EG. The reaction water is drawn off via a distillation column, the EG which has partly evaporated with it is returned to the monomer melt. The melt passes into a second reactor which is subdivided into three stages, and the temperature is increased by stages to 260°C. In the first stage 0.07 mmol polyphosphoric acid/mol TPA (calculated on the phosphorus content) are mixed in, as a solution in EG. Excess EG evaporates and quits the reactor as vapour. At a polycondensation degree of the melt of 4 to 5, and a concentration of the carboxylene groups of less than 150 mmol/kg, a solution of cobalt acetate in EG is fed into the third stage of the reactor, and mixed. The solution is so metered that the melt contains 0.1 mmol cobalt per mol TPA. In the first stage 0.07 mmol polyphosphonc acid/mol TPA (calculated on the phosphorus content) are mixed in, as a solution in EG. Excess EG evaporates and quits the reactor as vapour. At a polycondensation degree of the melt of 4 to 5, and a concentration of the carfaoxylene groups of less than 150 mmol/kg, a solution of cobalt acetate in EG is fed into the third stage of the reactor, and mixed. The solution is so metered that the melt contains 0.1 mmol cobalt per mol TPA. After leaving the second reactor, the melt flows into a third reactor where further EG is extracted at 20 mbar and approx. 275°C, and the polycondensation is continued. In the following reactor, of the horizontal annular-disc type, the polycondensation is completed at 2 mbar and 280°C. The melt is continuously removed from the final reactor and granulated. The product has an intrinsic viscosity of 0.68 dl/g, a carboxylene group content of 16 mmol/kg and a colour value of b = -0.5. Example 4. 2. 1120 g (6.75 mol) of terephthalic acid are mixed with 523 g (8.4 mol) ethylene glycol to form a paste. After the addition of 66 mg of titanium tetrabutylate, dissolved in 11 g of ethylene glycol, the paste is added under normal pressure to a melt of 600 g of an esterising product from a previous run. The melt is located in an autoclave heated via a double jacket with a liquid heat-transfer medium. The paste is added so slowly that the heating system can maintain a constant temperature in the melt. addition of 66 mg of titanium tetrabutylate, dissolved in 11 g of ethylene glycol, the paste is added under normal pressure to a melt of 600 g of an esterising product from a previous run. The melt is located in an autoclave heated via a double jacket with a liquid heat-transfer medium. The paste is added so slowly that the heating system can maintain a constant temperature in the melt. The reaction water is distilled off by a separator column. After termination of the addition of paste, the temperature is gradually increased to 270°C. After 163 minutes the theoretical quantity of water, of 243 g, is distilled off. In a comparative run without the addition of titanium tetrabutylate, esterification is complete only after 220 minutes. After termination of the esterification, 288 g of trisonylphenylphosphite are added. Pre-condensation is begun with a slow application of vacuum. When a pressure of 20 mbar is reached, 156 mg of cobalt acetate-tetrahydrate, dissolved in 25 g of ethylene glycol, are added to the pre-condensate melt and mixed, and polycondensation is continued for 100 minutes until a final vacuum of 2.7 mbar is achieved. The bright-coloured polyester has an IV of 0.675 and a carboxylene group content of 17.9 mmol/kg. Example 5i An esterification product is produced as in Example 4, the previously-located esterification product being melted with the condensate melt and mixed, and polycondensation is continued for 100 minutes until a final vacuum of 2.7 mbar is achieved. The bright-coloured polyester has an IV of 0.675 and a carboxylene group content of 17.9 mmol/kg. WE CLAIM 1. Method of manufacturing high molecular-weight polyethylene terephthalate (PET) or mixed polyesters thereof, in which, in a first stage, a low molecular-weight precondensate is produced from a polybasic carboxylic acid selected from terephthalic acid, or its alkyl esters, with one or more multifunctional alcohols selected from ethylene glycol, using a titanium catalyst, and that in the second stage a conversion to high molecular-weight PET or a corresponding copolyester is effected, an inhibitor in the form of a phosphorus-containing compound being added, characterised in that in the first stage a titanium compound is added as a catalyst in a concentration of 0.005 - 0.05 mmol per mol of polycarboxylic acid, and the conversion is continued until a conversion of at least 95%, measured from the degree of water separation, is achieved, and in that the second stage of the polycondensation takes place in the presence of the titanium compound present from the first stage, with the addition of cobalt-containing compounds at a concentration of 0.02 - 0.2 mmol cobalt per mol polycarboxylic acid, the phosphorus-containing inhibitor being added at a concentration of 0.004 - 0.4 mmol phosphorus per mol polycarboxylic acid, before or simultaneously with the addition of the cobalt catalyst to obtain the desired product. 2. Method as claimed in claim 1, wherein the concentration of the titanium catalyst is 0.01 to 0.03 mmol per mol polycarboxylic acid. 3. Method as claimed claim 1, wherein the concentration of the phosphorus-containing Inhibitor is 0.01 to 0.3 mmol per mol polycarboxylic acid. 4. Method as claimed in claim 1, wherein conversion in the first stage is undertaken up to a conversion of 85%. 5. Method as claimed in claim 1, wherein the phosphorus-containing inhibitor is added together with the titanium compound in the first stage, and the cobalt compound is added in the second stage. 6. Method of manufacturing high molecular-weight polyethylene terephthalate (PET) or mixed polyesters thereof substantially as illustrated in foregoing examples.

Documents:

1278-del-1996-abstract.pdf

1278-del-1996-claims.pdf

1278-del-1996-complete specification (granted).pdf

1278-DEL-1996-Correspondence Others-(07-06-2011).pdf

1278-del-1996-correspondence-others.pdf

1278-del-1996-correspondence-po.pdf

1278-del-1996-description (complete).pdf

1278-del-1996-form-1.pdf

1278-del-1996-form-13.pdf

1278-del-1996-form-2.pdf

1278-del-1996-form-3.pdf

1278-del-1996-form-4.pdf

1278-del-1996-pa.pdf

1278-del-1996-petition-137.pdf

1278-del-1996-petition-138.pdf