|Title of Invention||
METHOD FOR THE DIRECT AND CONTINUOUS PRODUCTION OF HOLLOW BODIES FROM A POLYESTER MELT
|Abstract||The invention relates to a method and a device for producing moulded bodies from a highly condensed polyester melt. The invention is characterised in that the melt never solidifies between the polycondensation reactor and the moulding units and that there is no degassing device between the end reactor and said moulding units.|
METHOD FOR DIRECT AND CONTINUOUS MANUFACTURING OF HOLLOW
BODIES FROM POLYESTER MELTS
The present invention relates to a continuous method for the direct manufacturing of molded bodies from a highly condensed polyester melt.
In the following, hollow bodies are referred to instead of molded bodies. However, the present invention is also similarly applicable to the manufacturing of films which must fulfill comparable requirements as the cited hollow bodies.
The known aromatic polyesters or copolyesters, particularly polyethylene terephthalate and its copolymers having small components of, for example, isophthalic acid or cyclohexane dimethanol, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, and their copolyesters, which are used as a starting material for manufacturing hollow bodies, are processed into hollow bodies in injection molding machines after a melt polycondensation at a specific intrinsic viscosity (IV) , which is in the range between 0.65 - 0.90 dl/g for polyethylene terephthalate and its corresponding low modified copolyesters, for example.
The current standard method for manufacturing PET for use as food packaging, particularly bottles, is as follows:
Terephthalic acid and/or its esters are esterified or transesterified with ethylene glycol in an esterification stage, which may comprise one or more reactors connected one after another.
These esters are polycondensed with further temperature increase and pressure reduction in the melt into a PET of moderate viscosity having IV = 0.55 - 0.65 dl/g and the product is cooled and granulated. The polycondensation is typically performed in at least two stages in a pre-condensation reactor and a following final reactor, both of which are also referred to in general in the following as condensation reactors. A higher number of condensation reactors positioned one after another is also possible depending on the facility capacity and other conditions.
The melt coming out of the final reactor is granulated and this PET granulate is subsequently brought to a mean viscosity of 0.75 - 0.85 dl/g in a reactor for solid-state polycondensation (SSP) under inert gas at temperatures from 180 - 230°C. The granulate is typically referred to as the final product and sold. Processors of this granulate are above all manufacturers of hollow bodies who have molding units available. Various types of molding units are known to those skilled in the art, such as injection molding and blow molding machines. Frequently, preforms are manufactured in preform machines operating according to the injection molding method, from which polyester bottles are produced in a blow molding method in a further step at a further processor, and typically also at a different location. Other types of molding for polyester granulate, for example, in machines for film manufacturing, are also possible in using the method according to the present invention presented here.
SSP is primarily employed for two reasons: in order to obtain adequate mechanical stability of the finished bottle, the viscosity must be raised above the level typical in polyester for textile applications. In addition, the acetaldehyde content in the polymer melt coming out of the final reactor must be reduced from approximately 3 0 -70 ppm to
polycondensation in order to impair the taste of the decanted product in the finished PET bottle as little as possible.
Acetaldehyde (AA) arises as a typical and unavoidable byproduct in PET manufacturing. For reasons of taste above all, the AA content in the finished bottle must be kept correspondingly low. This component is controllable up to a certain degree through the technological conditions of the polycondensation and the subsequent solid-state polycondensation. Acetaldehyde is again formed during the melting phase of the granulate as a function of the pretreatment of the polymer melt ("previous thermal history"), the conditions in the solid-state polycondensation, and the operation of the preform machine. The acetaldehyde concentration only changes marginally during the bottle manufacturing in the blow molding machine.
In the finished bottle to be filled with sweetened beverages, the AA value is not to exceed 8 ppm, and it is not to exceed 4 parts per million if the bottle is filled with water.
Performing SSP requires a significant outlay for apparatus: before SSP may be performed, the amorphous chips must be crystallized in a complex crystallization stage in order to avoid sticking in the subsequent solid-state polycondensation. Significant quantities of inert gas are required in both stages, which must additionally be purified after its use so it may be reintroduced into the process.
Since the demand for polyester bottles has increased strongly in the meantime, the facilities for manufacturing preforms have now reached sizes which make the use of a separate polyester synthesis facility exclusively for
supplying preform manufacturing economically advisable. Therefore, the possibility has arisen of conducting the finished polyester melts directly into the preform machines.
Therefore, there has not been a lack of experiments in bypassing the very time-consuming and costly steps in SSP directly from the polycondensation melt, analogously to fiber manufacturing.
Thus, for example, in DE 195 03 053, a method is described in which the melt coming out of the polycondensation reactor is admixed in a line provided with static mixing elements with an inert gas and an AA-reducing low-volatility amide compound and the melt is fed to a molding device for manufacturing preforms in the shortest possible time and with the least possible shearing under vacuum degassing.
In DE 195 05 680, the polycondensation melt having an IV = 0.5 - 0.75 dl/g is admixed with an inert gas, polycondensed in a post condensation reactor under vacuum to a viscosity of 0.75 - 0.95 dl/g, and the melt is then immediately conducted into an injection mold.
EP 0 842 210 cites another possibility for bypassing SSP. The melt polycondensation is performed therein to a viscosity of 0.65 - 0.85 dl/g, the polyester is cooled and granulated, melted again and then freed of volatile substances such as AA through flushing with a suitable flushing agent in a suitable device while forming a large surface.
EP 0 842 211 suggests a method in which the polycondensation melt is transferred into a degassing extruder having a polymer compression zone, a suitable flushing agent is simultaneously supplied and removed
again, and the melt thus treated is transferred directly into a molding device.
EP 0 836 54 8 is concerned with the operative design of conveying a polycondensation melt via a mixing line and a distributor into an injection molding device, without citing further details of the method.
US 6,099,778 discloses a method in which a polycondensation melt is transferred directly into a molding device. The method is linked to the conditions that the catalyst for the polycondensation is free of cobalt, an acetaldehyde-reducing compound is added, and the melt is degassed at a pressure above 25 mm Hg to almost normal pressure before being fed into the molding device, the degassing device also able to comprise a degassing extruder or another suitable conventional apparatus, for example. Polyamides, polyester amides, and polyethylene isophthalate are primarily cited as AA-reducing substances.
WO 98/4131 describes an apparatus and a continuous method for manufacturing molded polyester articles having low AA content from the polycondensation melt without intermediate solidification of the polyester. In this case, the polycondensation melt is mixed with an inert gas under pressure in an extruder, the melt is degassed under vacuum and reacted in a mixing zone with an AA-reducing compound, in order to then be fed immediately into the injection molding unit. In principle, the compounds cited in the above-mentioned US application are listed as AA-reducing compounds.
A similar process is described in EP 0 968 243. The polycondensation melt is fed into a mixing device therein, which may comprise a static mixer, a gearwheel pump, or an extruder. A stripping agent such as nitrogen or carbon dioxide and AA-reducing agents such as polyamides or
polyester amides are fed into it. The melt is transferred from this mixing device via one or more nozzles into a rapid evaporator. It is degassed therein under vacuum of 5-50 mm Hg and fed into a molding device, where AA-reducing agents may be added again.
In a presentat ion on February 2 5 and 26, 2003, Inventa-Fischer presented a further process for manufacturing preforms directly from the polycondensation melt. According to this process, a high-viscosity reactor is installed in a line which provides PET prepolymer, and the viscosity is raised to 0.85 dl/g. AA-reducing agent and possibly other additives are then fed into the melt and the mixture is transferred via a mixer into the injection molding machine.
DE 100 45 719 suggests a method in which a part of the polycondensation melt branches off after the final reactor and this partial stream has AA-reducing agents such as amides made of polycarboxylic acids and multivalent amines, as well as polyester stabilizers, such as triethyl phosphate, admixed in a double screw extruder. In the same extruder, gaseous reaction products are removed through a degassing connecting piece. The partial stream is subsequently combined with the main stream again. This method has the advantage that the complex degassing extruder must only be designed for a partial stream of the polycondensation melt and is correspondingly less expensive. However, the basic requirement of degassing remains.
In US 6,274,212, compounds which have at least two hydrogen-substituted heteroatoms bonded to carbon and form organic compounds, which contain at least two heteroatoms in an unabridged 5-member or 6-member ring, upon reaction with AA in the polyester, are suggested as further possible AA-reducing agents, upon whose use SSP is no longer necessary. Anthranilamide is cited as a possible compound
of this group. These additives may be sprayed on polyester granulate as a suspension, admixed with the polyester granulate in the form of masterbatch granulate, or admixed with the melt after melting the granulate, for example.
The methods described therefore have the disadvantage that the use of costly carrier gas for melt degassing and an additional degassing unit are necessary, and therefore a larger and thus more costly apparatus must be operated and finally, as a function of the point of time of the acetaldehyde scavenger addition, renewed AA formation is not prevented in any case.
The present invention is therefore based on the object of providing a method for the continuous direct manufacturing of hollow bodies from aromatic polyesters and their copolymers which has a simplified apparatus, causes the least possible costs for additional chemicals, and with which the especially high-quality demands on polyesters for hollow bodies, particularly for containers for the decanting of food and particularly for beverage bottles, such as viscosity, color, and acetaldehyde, may simultaneously be maintained or even improved.
Surprisingly, it has been found that this object may be achieved by a method for manufacturing molded bodies from a highly condensed polyester melt, in which the melt never solidifies between the polycondensation reactor (s) and the molding units and there are no degassing devices between the final reactor and the molding units.
Such a method has the advantage that neither an additional SSP stage having associated granulation device, crystallization and gas preparation unit, and high gas costs, nor a degassing extruder, whose construction, manufacture, and maintenance are costly, are necessary. Such a method is not known in the related art.
The method according to the present invention is suitable for manufacturing molded bodies from high viscosity melts made of aromatic polyesters or copolyesters, which may be obtained from one or more dicarboxylic acids and/or their methyl esters, such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and/or 4,4-bisphenyl dicarboxylic acid, and one or more diols, such as ethylene glycol, propylene glycol, 1,4-butane diol, 1,4-cyclohexane dimethylol, neopentyl glycol, and/or diethylene glycol.
These starting compounds may be processed into a high viscosity polyester melt in a way known per se according to the continuous methods of esterification or transesterification using known catalysts with a subsequent melt polycondensation in modified polycondensation reactors under vacuum. Polyethylene terephthalate homopolymers or their copolymers having a comonomer content of less than 10 mass-percent are preferably used.
The polymer melt is conducted from the final reactor via a defined pipeline system to its distribution directly into the molding units. The melt preferably has an intrinsic viscosity (IV) between 0.74 and 0.85 dl/g when it leaves the final reactor. Since the production output of the final reactor may not be adapted immediately to the changed removal quantity in the event of a brief shutdown of one or more molding units because of maintenance or defect, in a preferred embodiment of the method according to the present invention, up to 50%, preferably up to 20%, and especially preferably at most 10% of the melt stream is returned via a product regulation valve into the esterification stage. This part of the melt is preferably transferred outward by the product pump which conveys the melt out of the final reactor. On the way to the esterif ication stage, the high viscosity melt is possibly glycolized by adding at most 10% ethylene glycol and the low viscosity melt is returned to the esterification stage.
Alternately, a part of the main melt stream may be fed to a granulation device. The polyester granulate thus produced may, for example, be processed in a preform machine by the manufacturer himself to produce preforms or may be sold. Before the processing of the granulate thus obtained into preforms for manufacturing bottles, only modified drying, which prevents sticking of the only slightly crystallized chips, must be performed.
The outward transfer of a part of the melt just described also allows setting the feed pressure for the molding units independently of the current production output of the final reactor. In this way, variations in the melt removal by the molding machines may be compensated for above all.
The pressure in the melt line is controlled directly before the molding units and the pressure is set between 1-20 bar, preferably 10±1 bar by regulating the melt stream outward transfer.
As defined in the present invention, the main melt stream refers to the melt stream on the path between final reactor and molding units. The melt streams which are fed to the esterification and/or the granulation device after the outward transfer are not included in the main melt stream.
For example, a polycondensation reactor for producing high intrinsic viscosities may be used as a final reactor, as is described in EP 0320586. A double drive reactor (manufacturer: Zimmer AG), which is described in US 3,617,225, is particularly also suitable as a final reactor. This contains a divided shaft, on which the stirring elements are seated, instead of a continuous shaft. The two half shafts are each driven by their own drives. Adaptation of the speed to the reaction conditions, particularly to the viscosity of the polymer melt, is thus possible unrestrictedly.
In order to increase the flexibility of a facility, the intermediate product may be fed from the precondensation reactor to at least two final reactors connected in parallel, which supply different molding units. This is advisable, for example, if products which differ significantly in their final viscosity are to be produced. Both final reactors may then be operated at different process conditions and the economic advantages of a facility of larger capacity may nonetheless be maintained as much as possible. The embodiments described in the following relate to the section after a final reactor, independently of whether only one or multiple final reactors are supplied by a precondensation reactor.
The melts are preferably fed from a final reactor to at least two molding units. Before the first division of the melt stream, a further pressure elevation device is possibly provided in addition to the delivery pump of the final reactor as a function of the pressure loss of the overall melt transfer system, in order to ensure the continuous melt stream to the molding units.
The path which the melt is to cover between the first pressure elevation device and the molding units is to be designed in such a way that the design of the pipeline systems and the distances to the molding units are each identical and therefore the entire melt is subjected to thermal treatment which is as identical as possible. This is preferably achieved in that the melt lines are each divided symmetrically if needed. The temperature gradient in the melt, which is set from the outside to the inside, is preferably equalized via static mixing elements once again within each pipeline and before each division. The mixing elements are ideally to be as close as possible in front of the particular branching points in this case. The length of these static mixers is at most one to six times,
preferably at most one to three times the internal diameter of the pipeline.
In order to design the symmetry of the melt lines optimally, the main melt stream from a final reactor is expediently guided to an even number of molding units. Arranging the molding units in packs of four is especially preferred. This means that the main melt stream is finally distributed to four pipelines, each of which then leads directly to a molding unit. For reasons of symmetry, the preceding melt distributions are each performed to two pipelines. It results from this that four or eight or 16, etc., molding units must be provided for each final reactor. The number of divisions of the melt depends on the overall output of the facility and the individual output of the molding units used. The number of sequential divisions may advantageously be between one and four.
In order to keep the acetaldehyde content of the preform low, a substance causing AA reduction or a substance mixture causing AA reduction is dosed once or at most twice into the main melt stream before the entry into the molding units. This substance and/or the substance mixture is to be referred to in the following in short as an additive for reasons of clarity. The additive is distributed homogeneously in the polymer melt with the aid of static, possibly cooled mixing assemblies, which are installed alternately in the pipeline, and the reaction with the vinyl ester end groups of the polyester and/or with the acetaldehyde present is subsequently initiated. The additive is supplied to the melt stream as a solid, solid mixture, or in the form of an additive slurry, i.e., as a slurry in a dispersant.
The additive may contain individual compounds or a mixture of compounds which reduce the AA content of the polymer
melt alone or as a whole. Such compounds are known from the related art described.
The additive may also contain compounds which prevent the chain termination reaction of the polyester as much as possible and reduce the formation of AA beforehand in this way. Compounds of this type are also known in the related art. Compounds containing phosphorus are preferably used. The use of carboxy phosphonic acid compounds is possible, for example, as are described in DE 196 31 068, the content of whose disclosure is expressly included in the present application, among other places. Further suitable phosphoric stabilizer compounds are cited in the application DE 103 37 522. It has now been found that the simultaneous addition of substances from both classes results in especially low AA content in the preform.
If the additive is introduced into the process as a slurry, a compound which also participates in the polycondensation reaction, such as ethylene glycol in the case of a polyethylene terephthalate process, is preferably also to be used as a dispersant. The additive slurry may contain further desired substances, such as colors, UV absorbers, and oxygen and carbon dioxide scavengers. The additive is introduced into the polyester melt using additive feed units known in the related art. Suitable devices are described, for example, in DE 198 41 376, 198 51 948, and DE 100 4 9 617, but other devices suitable for this purpose are also usable. In any case, a brief dwell time of the melt between the final reactor and the molding units and uniform distribution of the additive in the melt, dead spaces having to be avoided, among other things, are important for successful application of the present invention in any case.
It is expedient to position a first additive feed unit in the melt lines after the product delivery pump of the final reactor before the first melt distribution.
With the addition of the additive at this point, the acet aldehyde content is lowered to at most 25 ppm, preferably 8 parts per million and especially preferably less than 4 parts per million in the preform. If necessary, these concentrations may be achieved through a further additive addition directly before the molding machine. A preferred embodiment of the present invention therefore contains an additional additive feed unit after the last melt distributor and before the particular molding unit. Therefore, an additive may be added at two points lying one after another in the main melt stream. The quantities of additive dosed may thus be adapted to the requirements, for example, the quantity of acetaldehyde newly formed during the melt transportation. In addition, for example, inks, UV stabilizers, accessory agents for improving the barrier properties or to increase the thermal stability, and similar things may be dosed in here, for example. Incorporation and uniform distribution of these substances is performed both via static mixing elements and also via the mixing line in the molding machine. This system allows, for example, the manufacturing of preforms for bottles of greatly varying requirements.
In a further preferred embodiment of the method according to the present invention, an additive, which may contain both a stabilizer and also an AA-reducing substance, is added using the first additive feed unit. By adding a stabilizer, the discolorations of the polyester which may possibly occur if AA-reducing substances containing nitrogen are used are kept low. The stabilizer is especially preferably selected from the group of carboxy phosphonic acids in this case.
In order to be able to effectively control the AA content in the molded body, the dwell time of the melt between the last additive addition point and the entry into the molding units must be as brief as possible. It has been shown to be advantageous in this case to design this section in such a way that the mean dwell time is shorter than six minutes, preferably shorter than two minutes.
The quantity of additive to be dosed is a function of the AA base load from the polycondensation, the dwell time and temperature in the melt line, and the desired final concentration in the molded body. The longer the dwell time of the melt in the melt line, the higher the required additive quantity.
The mean dwell time of the melt between final reactor and entry into the molding unit may not be arbitrarily large in this case. However, it automatically becomes larger as the capacity of the final reactor increases, since the melt is then distributed to a larger number of molding units, which requires a larger number of branching stages as well as longer melt lines overall.
In any case, it is advantageous if the mean dwell time of the melt between final reactor and entry into the molding unit is at most 3 0 minutes, preferably at most 15 minutes, especially preferably at most 12 minutes.
To avoid the formation of a temperature gradient and increased punctual degradation of the melt, static mixers are used in an alternating arrangement, which counteract the anti-cyclic mixing of the boundary polymer melt with the core melt.
In order to achieve the shortest possible dwell time of the melt between final reactor and molding unit, the static mixers are implemented as short as possible. Their length
is preferably at most six times, especially preferably at most three times the internal diameter of the piece of pipe in which they are installed.
The preform machines currently typical are constructed in such a way that the machine part in which the melt enters must be moved frequently, for example, at least one time daily from its operating position to a maintenance position for cleaning and maintenance. This is possible without any problems if the preform machine is supplied with polymer granulate and contains a melting extruder. However, in the method according to the present invention, high-viscosity polymer melt is fed into a rigid double mantle pipe of the molding unit. In order to produce a suitable connection between the last additive feed unit and the movable machine, according to the present invention, a flexible pipeline, e.g., a flexible pipe swivel joint is used as a permanent connection between the rigid melt line and the movable machine. A horizontal movement of at most 10 0 cm, preferably at most 50 cm, and especially preferably at most 30 cm is compensated for by the flexible pipe swivel joint. In this case, the pipe swivel joint system may be designed lying horizontally having vertical axes of rotation or position vertically having horizontal axes of rotation.
A constant pressure is to be provided at the transition to the preform machine. In order to ensure a constant melt supplied to the machine, a pressure between 1 and 2 0 bar, preferably 10±1 bar is to be set. This pressure is set according to the present invention by the regulation of the removal of excess melt back to the esterif ication stage and/or to the granulation device. The pressure is measured directly before the preform machines. The preferred melt temperature is between 280 and 285°C.
The figure shows an exemplary embodiment of the method according to the present invention in the device according
to the present invention without restricting the present invention to this embodiment.
The prepolymer from a precondensation reactor is highly condensed in the final reactor 1 of the type HVSR or double-drive, for example, to the desired viscosity and delivered using the delivery pump 2. After passing through a static 3 x 3D mixing element, the desired quantity of additive and possibly further substances is added to the melt stream via a first additive feed unit and distributed uniformly therein by a subsequent static 15D mixing element. As a function of the pressure loss in the melt distribution up to the preform machines, a booster pump 5 may be used for increasing pressure. The feed pressure is regulated before the preform machines by measuring using pressure sensor PC and outward transfer of a part of the main melt stream via the regulated outward transfer pump 6 to a granulator 7. In a similar way, using a second outward transfer pump (not shown) , a part of the melt transferred outward may be returned to the esterification stage (also not shown) . The main melt stream is conducted through multiple melt divisions to the preform machines, a static mixer 8 being located before each division. After the last division, additive and possibly further substances are again dosed into the polymer melt using a second additive feed unit A2, the melt is homogenized in a downstream mixing line 8 and conducted via a flexible pipe swivel joint (not shown) into the preform machine.
The present invention will now be described in greater detail on the basis of several exemplary embodiments, which are not restrictive in any way. The characteristic values specified were determined as follows for this purpose:
The intrinsic viscosity (IV) was measured at 25°C in a solution of 500 mg polyester and 100 ml of a mixture made of phenol and 1, 2-dichlorobenzene (3:2 weight parts).
The COOH end group concentrations were determined using photometric titration with 0.05 m ethanolic potassium hydroxide solution against bromothymol blue of a solution of polyester in a mixture made of o-cresol and chloroform (70:30 weight parts).
The color values L and b were measured according to HUNTER. The polyester chips were first dried for an hour in the drying cabinet at 135± 5°C. The color values were then determined by measuring the color tone of the polyester sample in a three-range color measurement device using three photo cells, before each of which a red, green, and blue filter was connected (X, Y, and Z values) : the evaluation was performed according to the formula of HUNTER, in which
b = (7.0)/(VY(Y - 0.8467 Z) .
The acetaldehyde was driven out by heating in a closed vessel made of polyester and the acetaldehyde was determined in the gas chamber of the vessel using gas chromatography with the head space injection system H54 0, Perkin-Elmer; carrier gas: nitrogen; column: 1.5 m stainless steel; filling: Poropack Q, 80 -100 mesh; sample quantity: 2 g; heating temperature: 150°C; heating duration: 90 minutes.
The product was weighed and heated from a starting temperature around 3 5°C at a heating rate of 10 K/minute to
300°C and subsequently the melting point and the melting energy required for the melting procedure were determined.
The high viscosity polyethylene terephthalate melt for the experiments described in the examples was manufactured in a continuously operating polycondensation reactor of the type HVSR (high viscosity self-cleaning reactor), as is described in EP 0 32 0 586, for example. This reactor has an internal shaft having specially shaped heatable paddles and installed stators, which regularly return the high viscosity melt adhering to the shaft and the wall surfaces to the process. The starting assumption was for a commercially typical granulate for manufacturing bottles, to be filled with fruit juices having carbon dioxide, having an IV of 0.62 dl/g. The granulate was dried and melted in a single screw extruder from Hussmann, continuously supplied to the HVSR, and condensed there carefully at a throughput of approximately 2 0 kg/h at a pressure of 0.1 - 0.5 millibar and temperatures of 275°C -280°C to a viscosity of 0.80 - 0.84 dl/g, and acetaldehyde values of approximately 3 0 ppm and b values of -3 to -4. This product was continuously supplied using a gearwheel pump via the melt line, which was equipped with static mixing elements of the type SMX from Sulzer, directly to the modified preform machine XL 160 having a modified mixing line having a 2-cavity mold, using which two preforms may be molded simultaneously, and processed into preforms.
To fulfill the different requirements, the number of the mixing elements was varied in the experiments, the length of a mixing element always corresponding to the pipeline diameter (= ID) . To equalize the temperature gradient between boundary and core melt, 3 x 3D mixing elements were used alternately over the pipeline length and for uniform distribution of the additives, 15D mixing elements were used after the first additive addition in the melt line.
During a second additive addition in the melt line directly before the movable flexible swivel joint, in which the pipe joint arrangement was provided lying horizontally having vertical axes of rotation, the additives were only premixed using 3D mixing elements. The random distribution of the additives was first achieved in the modified mixing line in the preform machine.
During the experiments, the melt quantities for the preform machine were varied between 90% and 72% of the quantity coming from the final reactor by adapting the travel regime of the preform machine. In this case, the supply of the preform machine with melt was ensured by setting the pressure before the machine. The pressure was controlled by regulating the melt outward transfer from the main stream after the first additive addition using a gearwheel pump. The part of the melt transferred outward was processed into chips in a granulator. These chips were subsequently dried under nitrogen as a carrier gas in a crystallizer, crystallized, and processed further into preforms.
To determine the product quality, the granulate and the preforms (ground under nitrogen atmosphere) were assayed for the most important quality criteria in the laboratory according to the methods described.
The additives, stabilizers, and pigments used were dosed via lateral flow extruders from Hussmann in combination with a gearwheel pump. Commercially available additives were tested both in liquid and also in solid form during the experiments.
The essential process parameters and qualities are described in the following tables 1 through 3. In this case, D identifies the diameter of the melt line, L identifies the length of the melt line, L/D identifies the ratio of the length and the diameter of the melt line, t1
identifies the dwell time in the melt line up to the second additive system, t2 identifies the dwell time of the melt between the second additive system and entry into the preform machine, p identifies the process pressure of the melt at the end of the melt line, and T identifies the melt temperature upon leaving the flexible pipe swivel j oint. Addition 1 and addition 2 refer to the dose quantities of additive and other substances at the additive dosing units 1 and 2, respectively. In this case, AA identifies an acetaldehyde scavenger from Coca-Cola®, P identifies the stabilizer H-MOD from Rhodia, and D identifies the pigment Estofil Blue from Clariant.
The polyester melt has the following properties at the outlet of the HVSR: IV = 0.83 dl/g, COOH content = 22 mmol/kg, AA content = 32 ppm, color b = -3 units.
The influence of different dwell times on the degradation is clearly recognizable from the results of experiments 1 -7 through reduced IV, carboxyl end groups, and the increase of the b color in the preforms. An additional degradation effect is also recognizable through the use of the acetaldehyde scavengers, which may be nearly compensated for again by the introduction of a stabilizing compound in the first additive system, however. The acetaldehyde content in the preform may be effectively reduced to the concentrations below 8 ppm which are acceptable in the marketplace. A very slight addition of blue pigment in a concentration of 0.5 ppm already contributed to improving a color.
It was determined in experiments 8 and 9 that the lengthening of the melt dwell time between the second additive system and the entry into the preform machine has a slight worsening effect on the preform equality in spite of adding a stabilizing compound together with the scavenger in the first additive system.
In experiments 10 through 12, further dwell time increases were investigated by enlarging the nominal widths of the melt-guiding pipelines, which were connected with an increase of temperature in the melt. This resulted in a further worsening in quality connected with an increase of the base acetaldehyde content (acetaldehyde values without adding scavengers). For compensation, the scavenger addition was increased in the first addition to 150% and the stabilizer concentration was increased by 10 ppm phosphorous component. The reduction in quality to be expected, in relation to the essential quality features of the polymer, could not be completely eliminated using these countermeasures. The acetaldehyde content in the preform rose to 8.5 ppm.
All preforms manufactured from the experiments 2-6, 8-9, and 13 were processed without problems on a laboratory bottle blowing machine into 0.5 1 contour bottles under standard settings using a mold from SIDEL LBO 01. The quality of the bottles corresponded to the market requirements.
The granulate produced in the experiments was crystallized in a fluid bed crystallizer from Vibra for 3 0 minutes at temperatures between 190 and 25°C under nitrogen as a carrier gas and further aldehyde was removed, the granulate was subsequently dried without sticking in a typical Challenger dryer for 4 hours at 170°C and processed in a laboratory preform machine having a 2-cavity mold from Husky into 28 g preforms having an AA content between 5-6 ppm.
1. A method for manufacturing molded bodies having an acetaldehyde content of at most 8 parts per million from a highly condensed polyester melt, a polycondensation reactor having a continuous or divided shaft being used as the final reactor, characterized in that the melt never solidifies between the polycondensation reactor and the molding units and no degassing device is provided between final reactor and molding units and an acetaldehyde-reducing substance or in the acetaldehyde-reducing substance mixture is dosed once or at most twice to the main melt stream before the entry into the molding units.
2. The method according to claim 1,
characterized in that 50 - 100% of the melt coming out of the final reactor enters the molding units.
3. The method according to one of claim 1 through 2, characterized in that the feed pressure for the molding units is set through outward transfer of a part of the melt.
4. The method according to one of claim 1 through 3, characterized in that the pressure in the melt line is controlled directly before the molding units and the pressure is set between 1-20 bar, preferably 10+1 bar, by regulating the melt stream outward transfer.
5. The method according to one of claims 1 through 4, characterized in that the part of the melt transferred outward is returned to the esterification stage and alternately also to a granulation device.
6. The method according to one of claims 1 through 5,
characterized in that between 0 and 50% of the melt coming out of the final reactor is returned to the esterification stage and to a granulation device.
7. The method according to one of claims 1 through 6, characterized in that at most 20%, preferably at most 10% of the melt coming out of the final reactor is returned to the esterification stage.
8. The method according to one of claims 1 through 7, characterized in that at most 10% ethylene glycol is fed to the high viscosity melt returned to the esterification stage.
9. The method according to one of claims 1 through 8, characterized in that a double-drive reactor is used as the final reactor.
10. The method according to one of claims 1 through 9, characterized in that at least two final reactors are used in parallel, which supply different molding units.
11. The method according to one of claims 1 through 10, characterized in that the melt from one final reactor is fed to at least two molding units.
12. The method according to one of claims 1 through 11, characterized in that at least one pressure elevation pump is used before the first melt division.
13. The method according to one of claims 1 through 12, characterized in that the main melt stream is conducted from a final reactor to an even number of molding units.
14. The method according to one of claims 1 through 13,
characterized in that a substance or a substance mixture is added as a solid or as a slurry to the melt stream before the entry into the molding unit.
15. The method according to one of claims 1 through 14, characterized in that an additive feed unit is provided after the first pressure elevation pump.
16. The method according to one of claims 1 through 15, characterized in that an additive feed unit is positioned in the melt line after the last melt distributor and before each molding unit.
17. The method according to one of claims 1 through 16, characterized in that different additives and/or different further substances are added to the melt before different preform machines using the additive feed units positioned after the last melt distributor.
18. The method according to one of claims 1 through 17, characterized in that the mean dwell time of the melt between the last additive feed unit in the entry into the molding unit is at most 6 minutes, preferably at most 2 minutes.
19. The method according to one of claims 1 through 18, characterized in that a static mixing element having a minimum length of 15D is inserted into the melt line after the first additive feed unit.
20. The method according to one of claims 1 through 19, characterized in that a static mixing element having a minimum length of 3D is inserted into the melt line after the second additive feed unit in the melt line directly before the movable flexible pipe swivel joint, in which the pipe joint system is provided horizontally having vertical axes of rotation.
21. The method according to one of claims 1 through 20, characterized in that the additive contains at least one compound containing phosphorus.
22. The method according to one of claims 1 through 22, characterized in that the additive contains at least one acetaldehyde-reducing substance.
23. The method according to one of claims 1 through 22, characterized in that the mean dwell time of the melt between final reactor and entry into the molding unit is at most 3 0 minutes, preferably at most 15 minutes, and especially preferably 12 minutes.
24. The method according to one of claims 1 through 23, characterized in that the melt line between the last additive feed unit and entry into the molding unit may perform a horizontal movement of the molding device of at least 100 cm, preferably at least 50 cm, especially preferably at most 30 centimeters.
25. The method according to one of claims 1 through 24, characterized in that the melt line is designed for an operating pressure of at most 2 00 bar and at most 320°C, preferably 280 - 285°C.
26. A method for manufacturing molded bodies from a highly condensed polyester melt, characterized in that
50 to 100% of the melt coming out of the final reactor enters the molding units,
the part of the melt transferred outward is returned to the esterification stage and alternately also to a granulation device,
the main melt stream is conducted to an even number of molding units,
an additive feed unit is positioned in the melt line after the last melt distributor and before each molding unit,
at least one acetaldehyde-reducing substance or at least one acetaldehyde-reducing substance mixture is added as a solid or dispersion to the main melt stream before the entry into the molding unit, and
the melt never solidifies between the polycondensation reactor(s) and the molding units and no degassing device is provided between final reactor and molding unit.
27. A device for manufacturing molded bodies from a highly
condensed polyester melt, the melt never solidifying
between the polycondensation reactor and the molding
units and no degassing device being provided between
final reactor and molding units,
characterized in that at least two additive feed units are positioned in the melt line between the polycondensation reactor and a molding unit.
28. The device according to claim 27,
characterized in that the pipelines positioned in parallel for conveying the main melt stream to the molding machines each have the same design.
29. The device according to one of claims 27 through 28,
characterized in that static mixers, whose length is
at most one to six times, preferably at most one to
three times the internal diameter of the pipelines,
are inserted alternately, but at least in front of each pipeline division, to homogenize the melt.
30. The device according to one of claims 27 through 29,
characterized in that the pipeline between the last
additive feed unit and the molding machine is so
flexible that it allows a horizontal movement of the
31. The device according to one of claims 2 7 through 30,
characterized in that the flexible pipeline contains a
flexible pipe swivel joint, whose joints have either
only vertical or only horizontal axes of rotation,
which is used for the permanent connection between the
rigid melt line and the molding machine.
32. The device according to one of claims 27 through 31,
characterized in that the melt line between the last
additive unit and the molding machine allows a
horizontal movement of the molding machine by at most
100 cm, preferably at most 50 cm, especially
preferably at most 3 0 cm.
33. The device according to claim 27,
characterized in that the pipeline between the last additive feed unit and the molding machine contains a flexible pipe swivel joint which allows a horizontal movement of the molding machine.
|Indian Patent Application Number||1868/CHENP/2006|
|PG Journal Number||03/2012|
|Date of Filing||26-May-2006|
|Name of Patentee||LURGI ZIMMER GMBH|
|Applicant Address||LURGIALLEE 5, 60295, FRANKFURT AM MAIN|
|PCT International Classification Number||C08G63/78|
|PCT International Application Number||PCT/EP2004/005769|
|PCT International Filing date||2004-05-28|