Title of Invention

FILAMENT-FORMING CHAIN-BRANCHED POLYESTERS AND COPOLYESTERS

Abstract

FILAMENT-FORMING CHAIN-BRANCHED POLYESTERS AND COPOLYESTERS Filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of >10000 are provided, obtained by condensing into the polyester-forming starting components 50-500 ppm of one or more chain-branching agents added during the polyester manufacture and having the general formula where n=2-54. They are excellently suited for high-speed spinning of textile and industrial yarns with w3inding speeds of 2500-10000 m/min, followed by conventional drawing or texturizing processes.

Full Text

The invention relates to filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of >10000, containing very small amounts of chain-branching agents, and a process for their manufacture. The invention further relates to the use of these polyesters and copolyesters in high¬speed spinning of textile and industrial yarns. Filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of >10000, containing very small amounts of pentaerythritol or other polyfunctional compounds such as glycerin, trimethylol propane, or mellitic acid (benzenehexacarboxylic acid) as chain-branching agents and suited to high-speed spinning of POY (pre-oriented yarn) yarns, are known from DE-OS 2 72 8 095. These chain-branched polyesters and copolyesters differ from the older chain-branched polyesters and copolyesters, which met the requirements of providing, in particular, improved dye affinity or reduced pilling tendency of the polyester fibers (= US-A-2 895 946, US-A-2 905 657, US-A-3 033 824, US-A-3 669 935, US-A-3 669 933, US-A-3 671 494, US-A-3 668 187, US-A-3 668 188, US-A 3 669 925, and US-A-3 576 773) by often requiring that they contain small amounts of polyfunctional compounds. If, for example, pentaerythritol is used as a chain-branching agent, anti-pilling fibers or polyester fibers with improved dye affinity require addition of 0.1 to 1 mole percent, corresponding to 708 to 7080 ppm. POY yarns, on the other hand, require an added amount of 100 to 625 ppm pentaerythritoT. Of all polyfunctional compounds studied, pentaerythritol is, according to DE-OS 27 28 095, the best suited chain-branching agent. This tetrafunctional branching agent provides not only improved results in high-speed spinning of polyesters and copolyesters compared to all trifunctional branching agents, but also better results than with the hexafunctional mellitic acid. This, of course, helped to support the view that the best branching agent for the stated purpose had been found in pentaerythritol. Even at that time, however, such branched polyesters and copolyesters were in need of improvement. High residual elongation and consequent productivity gains can be obtained only by adding relatively large amounts of this chain-branching agent in the range of 500 to 625 ppm, while with small added quantities of 100 to 200 ppm the residual elongation and hence the resulting productivity gains decline significantly (see Table 1 in DE-OS 27 28 095). For large added amounts of pentaerythritol, however, the characteristics of the further-processed POY yarns are, due to the higher degree of branching of the corresponding polyesters, too different from the conventional polyester yarns, whose valued and proven characteristics one naturally seeks to retain in large part, and, especially at spinning speeds of 4023 m/min and up, unacceptable fluctuation of the yarn characteristics occurs (see Table III of DE-OS 27 28 095). For this reason, only 110 - Therefore, another process principle was developed to spin polyesters and copolyesters to POY yarns with high residual elongation at high winding speeds. EP-0 047 464 proposes for this purpose the homogeneous incorporation, prior to spinning, of 0.2 to 10 percent by weight, preferably 0.5 to 6 percent by weight, of defined thermoplastic polymers, preferably poly(4-methyl-l- pentene) and polymethacrylic acid alkyl esters whose alkyl group consists of 1 to 5 C atoms. The residual elongation and resulting productivity gains are higher than those attainable on the basis of the branched polyesters. It must be noted, however, that an objective comparison is not possible, not only due to the comparatively large amounts of polymers added but also to the fact that typical polymer blends are spun at least in the middle and upper weight percentages of the added polymers, where by nature the higher increases in elongation occur. To eliminate the resulting disadvantages, EP-0 631 638 proposed incorporating into polyesters and copolyesters preferably only 0.3 to 1.0 percent by weight of 50 to 90% iraidized polymethacrylic acid alkyl esters whose ester group contains an alcohol with 1 to 6 C atoms, the alkyl esters being only partially soluble in the cited polyesters and present therein mainly in interstitial form. Using this process approach, it was possible to obtain POY yarns with residual elongation that occasionally also exceeds that of the yarns made from polyesters branched with 100 to 200 ppm pentaerythritol. The present invention addresses the objective of providing new filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of > 10000. They should exhibit, with minimum ppm amounts of the chain-branching agent,- higher residual elongation in high-speed spinning of textile and industrial yarns compared to the known polyesters and copolyesters that are chain-branched with pentaerythritol. Surprisingly, it was discovered that the objective of the invention is met by adding, during polyester manufacture, 50-500 ppm of one or more chain-branching agents of the general formula: where n = 2-4, to the polyester-forming starting components. Since the hexafunctional mellitic acid must be condensed into polyethylene terephthalate in higher ppm amounts than the tetrafunctional pentaerythritol, to preserve the same residual elongation (see Table IV on page 33 of DE-OS 27 28 095), it could not be anticipated that the chain-branching agents of the invention, despite their 6, 8, and 10 reactable groups per molecule, would in fact exhibit the opposite effect (see Tables 1-14 of the experimental part of this invention), something which predestines the agents for use in the desired and preferred lower ranges of ppm amounts. Moreover, as an advantageous technical side effect, with increasing amounts of the chain-branching agents of the invention there is constantly greater abbreviation of the polycondensation time in the synthesis of the polyesters, amounting to about 10 to 30% in the Eange of 50 to 500 ppm of chain-branching agents of the invention, for example in the synthesis of the polyethylene terephthalate modified 'in accordance with the invention. Dipentaerythritol, tripentaerythritol, and tetrapentaerythritol can thus be condensed into the polyester-forming starting components simultaneously if necessary, or only one of the possible subsets of this three-material combination, which in particular also include the condensing of only one of the three cited chain-branching agents. The amount employed of chain-branching agents of the invention can generally vary from 50 to 500 ppm, whereby the amount contemplated for a specific application can be subjected to considerable variation in this range, depending in particular on the selected specific chain-branching agent or agents and their molar relationships. Since tripentaerythritol and tetrapentaerythritol require smaller molar amounts than dipentaerythritol, however, one skilled in the art can readily determine in each case the appropriate amount on the basis of simple trials, depending on the desired qualitative chemical composition of the chain-branching agents, the type of polyester to be modified, the desired level of productivity increase resulting from improved residual elongation, and the desired yarn characteristics. Preferred polyesters and copolyesters can be obtained by condensing into the polyester-forming starting components 80-350 ppm and preferably 100-250 ppm dipentaerythritol or 50-200 ppm tripentaerythritol or tetrapentaerythritol as a chain branching agent, whereby these agents can in principle be added to the polyester-forming starting components during polyester manufacture. Preferred polyester-forming starting components include diols and dicarboxylic acids, or dicarboxylic acid derivatives such as dicarboxylic acid diester, that lead to the formation of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, poly(ethylene-2,6-naphthalene dicarboxylate) , poly (butylene-2, 6-naphthalene dicarbo'xylate) , poly(1,4-dimethylenecyclohexane terephthalate) or their polyester blends on the basis of high homopolyester fractions of at least 90 mole percent. The remaining dicarboxylic acid and diol components of the just cited polyester blends can be the conventional co-components in the manufacture of drawn polyester objects, in amounts up to 10 mole percent, such as isophthalic acid, p,p'-diphenyl dicarboxylic acid, any naphthalene dicarboxylic acid, hexahydroterephthalic acid, adipic acid, sebacic acid, and glycols such as trimethylene, tetramethylene, hexamethylene, and decamethylene glycol. Since the chain-branched polyesters and copolyesters of the invention can in particular also be regarded as modified homopolyesters and copolyesters of the aforementioned types or those cited in Claim 10, it is not even necessary for their manufacture to alter the mode of manufacture of the applicable homopolyesters and copolyesters or the transesterification or polycondensation conditions. The only difference is that the chain-branching agents are added in the required ppm amounts to the corresponding polyester-forming starting components during the otherwise conventional polyester manufacturing process. This is illustrated on the basis of the especially preferred chain-branched polyester of the invention, which is obtained by adding the chain-branching agent or agents of the invention to those polyester-forming starting components that result in formation of polyethylene terephthalate. The manufacture of polyethylene terephthalate can proceed in a known manner in two reaction stages. The first reaction stage, which can be conducted continuously or discontinuously, consists in the transesterification of dimethyl terephthalate with ethylene glycol to form bis-(2-hydroxyethyl) terephthalate using transesterification catalysts at 150-200°C, for example, or in the direct esterification of terephthalic acid with ethylene glycol at about 260°C under pressure, which generally requires no catalyst and from which bis-(2-hydroxyethyl)terephthalate is also formed. Through oligocondensation reactions, which already take place under the transesterification and direct esterification conditions, lesser or greater amounts of linear oligomers of bis-(2-hydroxyethyl) terephthalate are formed. A preferred embodiment of the invention consists in adding the chain-branching agent or agents of the invention before or during the transesterification reaction, or the direct esterification, to the polyester-forming starting components, in the present case to the dimethyl terephthalate and ethylene glycol or to the terephthalic acid and ethylene glycol, such that a uniformly reacting mixture can develop. After the transesterification has ended, it is advantageous to block, in a manner known per se, any transesterification catalysts present, by adding one or more phosphorus compounds. Blocking agents include in particular carbethoxymethyl diethyl phosphonate, di (polyoxyethylene)hydroxymethyl phosphonate, tetraisopropyl methylene diphosphonate, phosphonoacetic acid ethyl ester and/or H3PO4, whereby a concentration of added P of 30-50 ppm is;' generally sufficient. If the manufacture of bis-(2-hydroxyethyl) terephthalate and its oligomers is conducted by addition of ethylene oxide to terephthalic acid, terephthalic acid and ethylene oxide by nature represent the polyester-forming starting components. The term polyester-forming starting components fundamentally includes all dicarboxylic acid and diol derivatives, for example also dicarboxylic acid chlorides or diol diacetates, that are suited to forming the polyesters and copolyesters known per se, which for their part are subjected during the polyester and copolyester synthesis to a modification by the chain-branching agents of the invention. The second reaction stage, which can be conducted continuously or discontinuously, consists in the polycondensation of the bis-(2-hydroxyethyl) terephthalate and its oligomers to .form polyethylene terephthalate at 280-290°C, for example,' in a vacuum using known polycondensation catalysts. A further preferred embodiment of the invention consists in adding the chain-branching agent or agents to the polyester-forming starting components, in the present case to the bis-(2-hydroxyethyl) terephthalate and its oligomers, even before this melt polycondensation. While addition of the chain-branching agents of the invention in the initial part of the polycondensation stage is also possible in principle, it is less recommended, since it has been shown that if they are added in the late polycondensation stage, with smooth transitions that are difficult to predict, fluctuations in the yarn characteristics can occasionally occur. The chain-branched polyethylene terephthalate manufactured according to the invention has an intrinsic viscosity of 0.70 to 0.75, corresponding to a relative solution viscosity of 1.63 to 1.70, measured in 1% meta-cresol solution at 20°C. The polymer can be spun to textile POY yarns using conventional processes known per se and the yarns also further processed, likewise in a known manner, after winding at potential speeds of 2500-10000 m/min, preferably 3000-6000 m/min, whether for example by subsequent drawing or a simultaneous draw texturizing process or by friction texturizing. Drawn yarns can likewise be manufactured in one-stage spin processes such as spin draw winding, hot tube spinning, or super high-speed spinning. If the chain-branched polyethylene terephthalate of the invention is to be used to manufacture industrial yarns, such as for use in tire cords, its molecular weight must be increased in a manner analogous to the case of polyethylene terephthalate. This can be achieved using processes known per se for polyethylene terephthalate, including its conversion with agents that increase the degree of polymerization, such as 2,2'-bis(2-oxazolin), in accordance with EP-A-0 169 415. The required increase in intrinsic viscosity to 0.95-1.05, for example, corresponding to a relative solution viscosity of 1.86 to 2.05, measured in 1% meta-cresol solution at 20°C, is preferably achieved using subsequent polycondensation in the solid phase, as is also the practice for polyethylene terephthalate. In this case, the granulated chain-branched polyethylene terephthalate is heated in a vacuum or an inert gas stream to temperatures below the melting point, such as to 230°C. For use in tire cords, manufacture of the corresponding POY yarns is conducted at winding speeds of 2500-10000 m/min, preferably 3000-6000 m/min, followed by the usual drawing and thermal treatment processes. Accordingly, the present invention provides a process for manufacturing filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of > 10000, containing very small amounts of chain-branching agents, characterized in that 50-500 ppm of one or more chain-branching agents with the general formula where n = 2-4, are added to the polyester-forming starting components during polyester manufacture. The invention will be explained in more detail in accordance with the following examples: A. Manufacture of the chain-branched polyesters The manufacture of the chain-branched polyesters, including those modified both with the branching agents of the invention and with pentaerythritol (= PE) as comparative examples, took place in accordance with the standardized polycondensation guideline described in the following. This also applies to the manufacture of polyethylene terephthalate (= PET), with the exception that addition of a branching agent is omitted. Polyethylene terephthalate is produced in a two-stage process. In the first stage, the transesterification, the conversion of ethylene glycol and the selected ppm amount of the branching agent of the invention (dipentaerythritol = DiPE, tripentaerythritol = TriPE, or tetrapentaerythritol = TetraPE) takes place with dimethyl terephthalate (= DMT), whereby the molar relationship of ethylene glycol to DMT was 2.15:1 and the transesterification was conducted in the presence of 100 ppm zinc acetate (ZnAc2 . 2H20) and 150 ppm MnAc2 " 4H20 (Ac = acetate) as transesterification catalysts, with respect to DMT, at temperatures in the range of 175 to 250°C. To avoid a sublimation of the DMT, the continuous temperature increase from 175 to 250°C is not performed too rapidly. In addition to the cited transesterification catalysts, 10 ppm M 10 defoaming agent was added. The methanol released during transesterification is distilled off via a column. When a reaction temperature of 240°C is reached, 50 ppm phosphorus, with respect to DMT, is added in the form of the phosphonoacetic acid ethyl ester to block the transesterification catalysts. When a reaction temperature of 245°C is reached, 5000 ppm Ti02 suspension in ethylene glycol was added as a delustering agent. When the reaction temperature reached 250°C, 400 ppm of Sb203/ as an approx. 1% solution in ethylene glycol, was added to the reaction mixture. The polycondensation reaction was conducted at 290°C in a vacuum of 2.4 torr. When the melt reached a relative solution viscosity of about 1.64, measured in 1% meta-cresol solution at 20°C, the polycondensation was terminated. The modified and unmodified polyethylene terephthalates thus produced are listed in Tables 1 to 14. B. High-speed spinning of chain-branched polyesters The polyesters manufactured in accordance with A., after drying to a residual moisture content of Specifically, Tables 1-9 show the trials in which, at winding speeds of 3500 m/min, 4000 m/min, and 4500 m/min, both unmodified polyethylene terephthalate (= PET) and chain-branched polyethylene terephthalate that had been modified with 110 ppm and 200 ppm dipentaerythritol (= DiPE, Tables 1-3), with 110 ppm and 200 ppm tripentaerythritol (= TriPE, Tables 4-6), and with 110 ppm and 200 ppm tetrapentaerythritol (= TetraPE, Tables 7-9) were spun. The same trials are shown in Tables 10 to 12, with the only difference being that the polyethylene terephthalate had been modified with 110 ppm and 200 ppm pentaerythritol (= PE). By reading the respective elongation of the undrawn yarns, wound at the same speed, a comparison of Tables 1 to 9 with Tables 10 to 12 readily shows the pronounced increase in elongation of the polyethylene terephthalates modified using the branching agents of the invention compared to the polyethylene terephthalates modified with pentaerythritol. Elongation increases of over 20% can be attained as a rule. Tables 13 and 14 show trials in which, at winding speeds of 2500 m/min and 4000 m/min, a) unmodified polyethylene terephthalate, b) polyethylene terephthalate modified with 500 ppm dipentaerythritol, and c) polyethylene terephthalate modified with 500 ppm pentaerythritol, were spun. The elongation increases achieved with dipentaerythritol compared to pentaerythritol can be seen directly in Tables 13 and 14 and amount to 30.2 and 26.6%, respectively. WE CLAIM: 1. A process for manufacturing filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of > 10000, containing very small amounts of chain-branching agents, characterized in that 50-500 ppm of one or more chain-branching agents with the general formula where n = 2-4, are added to the polyester-forming starting components during polyester manufacture. 2. The process as claimed in claim 1, wherein 80-350 ppm dipentaerythritol is added to the polyester-forming starting components. 3. The process as claimed in claim 1,. wherein 100-250 ppm dipentaerythritol is added to the polyester-forming starting components. 4. The process as claimed in claim 1, wherein 50-200 ppm tripentaerythritol or tetrapentaerythritol is added to the polyester-forming starting components. 5. The process as claimed in one or more claims 1 to 4, wherein one or more chain-branching agents are added to those polyester-forming starting components that result in the formation of polyethylene terephthalate, polypropylene terephthalate, polybutylene teraphthalate, poly(ethylene-2, 6-naphthalene dicarboxylate), poly(butylenes-2,6-naphthalene dicarboxylate), poly(l,4-dimethylene-cyclohexane teraphthalate) or their polyester blends on the basis of high homopolyester fractions of at least 90 mole percent. 6. The process as claimed in claims 1 to 5, wherein chain-branching agent or agents is/are added to the polyester-forming starting components before their melt polycondensation. 7. The process as claimed in one or more claims 1 to 5, wherein chain-branching agent or agents is/are added to the polyester-forming starting components before or during the transesterification reaction or the direct esterification. 8. The process as claimed in one or more claims 1 to 7, wherein any existing transesterification catalysts from the first reactions stage are blocked by adding one or more phosphorus compounds. 9. The process as claimed in claim 8, wherein carbethoxymethyl diethyl phosphonate, di(polyoxyethylene)-hydroxymethyl phosphonate, tetraisopropyl methylene diphosphonate, phosphonoacetic acid ethyl ester and/or H3P04 are added as blocking agents. 10. A process for high-speed spinning of textile and industrial yarns with winding speeds of 2500-10000 m/min., preferably 3000-6000 m/min., followed by conventional drawing or texturizing processes comprising filament-forming chain-branched polyesters and copolyesters with a relative molecular weight of > 10000, containing very small amounts of chain-branching agents and obtained by condensing in 50-500 ppm of one or more chain-branching agents, added during the polyester manufacture and having the general formula where n = 2-4. 11. A process for manufacturing filament-forming chain-branched polyesters and copolyesters substantially as herein described.

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836-mas-1998 abstract-duplicate.pdf

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