Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/78—Preparation processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/17—Component parts, details or accessories; Auxiliary operations
  • B29C45/18—Feeding the material into the injection moulding apparatus, i.e. feeding the non-plastified material into the injection unit
  • B29C2045/1883—Feeding the material into the injection moulding apparatus, i.e. feeding the non-plastified material into the injection unit directly injecting moulding material from the chemical production plant into the mould without granulating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/0002—Condition, form or state of moulded material or of the material to be shaped monomers or prepolymers

Definitions

• Polyesters are widely used in the manufacture of fibers, molded objects, films, sheeting, food trays, as well as food and beverage containers. These polymers are generally made by batch or continuous melt phase polycondensation reactions well known in the art. The polymers are then pelletized and used in various extrusion or molding operations. In certain applications where high molecular weight polymers are required, the pellets are subjected to "solid state" polycondensation conditions in which the inherent viscosity (IhV) value is significantly increased. Such solid state polycondensation reactions are required since the melt viscosity of polyester polymers is quite high for polymers having IhV values greater than 0.6.
• IhV inherent viscosity
• acetaldehyde During the preparation or processing of polyesters in the melt phase, certain byproducts are formed.
• One such byproduct is acetaldehyde, and its presence in molded objects such as food containers, beverage bottles, water bottles, and the like is quite deleterious from a taste standpoint.
• Particularly for sensitive beverages such as cola and water it is highly desirable to produce preforms having less than 10 ppm and preferably less than 5 ppm of acetaldehyde. Achieving this low level of acetaldehyde is difficult, however, because, as is well known to practitioners of the art, acetaldehyde is continually formed as a byproduct during the polymerization and subsequent melt processing of PET and similar polymers.
• a three-stage process has been universally used to provide polyester polymers suitable for uses in which it is important to minimize the presence of acetaldehyde.
• Such a process typically involves the preparation of a relatively low molecular weight precursor polymer, having an IhV value of 0.6, by melt- phase polymerization techniques that are well known in the art.
• the acetaldehyde content of such a precursor may range from 30 ppm to over 150 ppm, depending on the reaction conditions chosen. This precursor is then cooled, shaped into pellets, crystallized, and subjected to solid-state polymerization.
• an inert gas is used to strip glycols, acetaldehyde, and other reaction byproducts from the pellets so that at the end of the solid-state process, the IhV value has been increased to 0.70 or more, and the acetaldehyde content has been reduced to below 1 ppm or less.
• the product so prepared must still be heated and melted in a third step in order to be formed into a useful shape, such as a beverage bottle preform, and this process typically causes an increase in acetaldehyde content of from less than 1 ppm in the pellets, to up to 8 or 10 ppm or more in the shaped article.
• polyesters such as PET and similar polymers may be prepared in the melt, purified of excess acetaldehyde and other byproducts, and molded directly from the melt into useful shaped articles, such as for example beverage bottle preforms, said shaped articles having surprisingly low acetaldehyde content.
• U.S. Serial No. 08/498,404 describes an apparatus and method for distributing molten polymer to multiple molding machines.
• U.S. Serial No. 08/501,114 describes an improved process for lowering the acetaldehyde content of molten PET to levels suitable for direct use in providing articles for food packaging by using an inert gas purge to contact the molten polyester.
• Japan Patent Application 53-71162 (1978) describes remelting polyester chips and holding the molten polymer under vacuum to reduce the concentration of acetaldehyde.
• U.S. 4,263,425 describes the solid stating of PET pellets to provide polymer having a low concentration of acetaldehyde.
• the reference discloses partial acetaldehyde elimination via treatment of the stirred melt at higher temperatures under vacuum.
• U.S. 4,064,112 describes a method for overcoming sticking problems during the solid stating process. It discloses that melt phase processes without solid stating yield elevated concentrations of acetaldehyde in the melt polyester.
• U.S. 4,372,910 describes a method and apparatus for molding hollow plastic articles. It describes remelting pellets in an extruder and extruding hot plasticized resin to sequentially mold preforms from a continuous molten stream and then to directly transfer preforms to a blowing process.
• U.S. 4,836,767 describes a method to reduce acetaldehyde during molding. It states that acetaldehyde increases linearly with time and exponentially with temperature.
• Japan Patent Application 57-191320 (1982) describes the removal of acetaldehyde from PET polymer to a concentration of less than 300 ppm just prior to melt spinning of fibers.
• Japan Patent Application 55-069618 (1980) states that PET with acetaldehyde content less than 20 ppm is obtained by melt polymerization followed by extrusion into fiber or film and subsequently passing the fiber or film through a fluid or vacuum. Fluids used included air, nitrogen, water, and steam.
• U.S. 5,270,444 and U.S. 5,241,046 describe the treatment of PET with water to reduce the amount of acetaldehyde and cyclic oligomer in the polymer.
• U.S. 5,262,513 states that the oligomer content is 1-2% in melt phase polymer and 0.5-1.0% in solid stated PET polymer.
• U.S. 5,169,582 describes a process in which vacuum is applied to linked, vented extruders to remove monomer from nylon-6 (caprolactam) polymers.
• U.S. 3,183,366 and 3,578,640 disclose the direct spinning of nylon-6.
• U.S. 3,657,195 discloses the production of high molecular weight nylon-6,6 by continuous condensation of low molecular weight nylon-6,6 in a vented screw extruder in the presence of steam.
• the following patents disclose various aspects of solid stating: U.S. 4,963,644, 4,223,128, 4,591,629, 4,395,222, 4,374,97 and 5,119,170 and U.S. 5,090,134, which disclose the necessity of solid stating PET polymers to obtain low acetaldehyde concentrations.
• U.S. 4,820,795 states that a vessel is prepared by melting the polyester and injecting the melt into a mold. Acetaldehyde concentration is reduced by a combination of catalyst selection and crystallization of the polymer.
• U.S. 5,246,992 provides background on the mechanism for acetaldehyde formation from PET and states that thermal decomposition of the PET is influenced by the level of the reaction temperature, the residence time, and possibly by the nature of the polycondensation catalyst.
• U.S. 4,237,261 describes the direct spinning process for PET fibers. Such polymers have to have an IhV of only 0.6 and no mention is made of molding articles, minimization of degradation products, or acetaldehyde formation.
• U.S. 4,230,819 describes the removal of acetaldehyde from crystalline PET with a dry inert gas (air or nitrogen at 170-250°C) . It states that acetaldehyde can not be completely removed from PET by heating it under reduced pressure.
• U.S. 5,102,594 (supplying a thermoplastic condensation polymer in powder form to a vented extruder for devolatilization and melting), U.S. 4,980,105 (devolatilization of polycarbonates in an extruder to remove volatiles (especially cyclic di er) and forcing the melt through a die) , U.S. 4,362,852 (devolatilization of molten polymers such as nylon and PET with a rotary disk processor), U.S. 3,486,864 (polymerization reactor in which a solid prepolymer is melted and then a vacuum is used to remove volatile glycol products as fast as possible) ; U.S.
• FIGURE 1 is a flow diagram of the present invention.
• FIGURE 2 is a flow diagram of the prior art process .
• the present invention provides a process for producing molded articles comprising the steps of: a) melt reacting at least one glycol and at least one dicarboxylic acid to form a polyester having an IhV of at least 0.5 dl/g, wherein said at least one glycol is selected from the group consisting of glycols having up to 10 carbon atoms and mixtures thereof and said dicarboxylic is selected from the group consisting of alkyl dicarboxylic acids having 2 to 16 carbon atoms, aryl dicarboxylic acids having 8 to 16 carbon atoms and mixtures thereof; and b) forming said polyester into shaped articles directly from step a.
• IhV refers to the Inherent Viscosity of the polymer, as determined by standard methods on a solution of 0.5 g of polymer dissolved in 100 ml of a mixture of phenol (60% by volume) and tetrachloroethane (40% by volume) .
• the process of the present invention provides a "melt-to-mold" process in which polyester polymers or copolymers are prepared in the melt phase to an IhV value of greater than 0.5 dl/g and then the melt is fed directly from the polycondensation reactor, 1, to at least one molding or shaping machine, 6.
• Any conventional melt polymerization process capable of producing the required IhV may be used for the polycondensation and the reactor may comprise one or more reaction vessels or zones which are capable of producing polyester having the required IhV.
• the molten polyester is directed from 1 to 6 by means of a viscous fluid pump, such as an extruder, gear pump or diskpac pump. It should be understood that although only one molding machine is shown in Figure 1, a plurality of molding machines may be used.
• the polymer is devolatilized to remove acetaldehyde and other undesirable volatiles.
• the devolatilization step may be conducted in a separate devolatilization unit (not shown) , concurrently in the polycondensation reactor l, or concurrently in molding machine, 6.
• Figure 2 depicts the process practiced prior to the present invention. Common units are numbered as in Figure 1.
• the conventional process begins by forming polymer in a melt polymerization reactor, 1.
• the molted polymer is directed to a pelletizer (2) where the polymer is extruded into solid pellets. After pelletization the pellets may be stored or fed directly to a crystallization unit, 3.
• the pellets After crystallization, the pellets are directed to a solid stating unit, 4, where the Ih.V. and molecular weight of the pellets are increased to the desired level and acetaldehyde is removed. In some processes the crystallization and solid stating units are combined. After solid stating the pellets are stored (either in silos or railcars, 5) , shipped to a molder (via railcar) , optionally stored again (railcars or silos) and dried. Finally the molder introduces the pellets into an extruder or other molding/shaping device, 6 and makes the final product. Pelletizers, crystallization units, solid stating units, dryers, extruders and molding/shaping devices are all generally known in the art.
• the process of the present invention eliminates the need for pelletization, crystallization, solid stating, drying, and remelting of the polymer before the molding/shaping device.
• the elimination of these steps not only results in enormous cost savings (because of the reduced equipment and energy requirements) but also produces polymer which is lower in undesirable contaminants such as acetaldehyde and other volatiles.
• the molding shaping device 6 may be any of those generally known in the art. For example, injection molds may be used to form preforms used to blow bottles, food/beverage containers, trays, or other desirable shapes. Also the polymer melts may be used in extrusion blow molding operations to provide bottles, food containers, and the like.
• the polymer melt may similarly be fed to an extruder to produce films, sheet, profiles, pipe and the like.
• acetaldehyde can be readily removed from the molten polymer using a viscous fluid processor such as an extruder, thin film evaporator, or discpack purged with an inert gas or by subjecting the melt to conditions of vacuum (U.S. Serial No. 08/501,114).
• Any viscous fluid processor capable of generating a large amount of surface area per unit volume and/or for rapidly regenerating the exposed melt surface can be used for this step.
• acetaldehyde levels can be readily reduced to less than 10 ppm.
• Typical acetaldehyde levels in polymer coming from the final reactor before this treatment are generally in the range of 30 to over 150 ppm.
• the rate at which this additional acetaldehyde accumulates is extremely rapid.
• the free acetaldehyde content of the polymer may increase from less than 1 ppm in the pellets to over 8 to 10 ppm in the bottle preform, during the less than 1 or 2 minute processing time of a typical molding machine.
• Such a rapid rate of acetaldehyde buildup would seem to preclude any practical means of distributing and molding continuously-produced molten polymer, no matter how well acetaldehyde could be removed.
• the preferred practice of this invention includes: 1) melt phase polymerization; 2) melt phase devolatilization and 3) forming the polyester into shaped articles directly from the melt phase.
• melt phase polymerization includes: 1) melt phase polymerization; 2) melt phase devolatilization and 3) forming the polyester into shaped articles directly from the melt phase.
• the polymerization is preferably carried out in combination with a polymer filtration step.
• This filtration should be completed as early in the process as is feasible to take advantage of the lower viscosity while keeping black specks in the polymer at an acceptable level.
• devolatilization & molding functions are: a) devolatilizing the entire polymer stream in one device followed by distributing the polymer to multiple multi-cavity molding machines.
• the devolatilization device can be any apparatus known in the art for generating a large amount of surface area per unit volume and ⁇ or for rapidly regenerating the exposed melt surface.
• the devolatilization device should subject the liquid surface to a low partial pressure of acetaldehyde either by inert gas purging or applied vacuum.
• the devolatilization apparatus may be a vented single-screw extruder (U.S. 4,107,787), a vented twin-screw extruder (U.S. 3,619,145), a rotating disk processor (U.S. 4,362,852) , or device which generates thin strands of polymer (U.S. 3,044,993), all of which are incorporated herein by reference.
• a combination of equipment design, production rates, and operating conditions can facilitate increasing the molecular weight of the polyester and devolatilizing acetaldehyde in the same piece of equipment.
• the polymer is rapidly distributed to a plurality of multi-cavity molding machines via a gear pump linked directly to the exit of the reactor.
• Suitable melt processing temperatures for poly(ethylene terephthalate) polymers will generally be in the range of 260 to 310°C. Of course, processing temperatures may be adjusted for other types of polyesters depending on the melting point, IhV value and the like.
• Modifying dibasic acids may contain from 2 to 40 carbon atoms and include isophthalic, adipic, glutaric, azelaic, sebacic, fumaric, dimer, cis- or trans-1,4- cyclohexanedicarboxylic, the various isomers of naphthalenedicarboxylic acids and the like. More preferably the polyesters of the present invention contain at least 80 mole% terephthalic acid, naphthalenedicarboxylic acid or a mixture thereof.
• naphthalene dicarboxylic acids include the 2,6-, 1,4-, 1,5-, or 2,7- isomers but the 1,2-, 1,3-, 1,6-, 1,7-, 1,8-, 2,3-, 2,4-, 2,5-, and/or 2,8- isomers may also be used.
• the dibasic acids may be used in acid form or as their esters such as the dimethyl esters for example.
• Typical modifying glycols may contain from 3 to 10 carbon atoms and include propylene glycol, 1,3- propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and the like.
• the 1,4-cyclohexanedimethanol may be in the cis or the trans form or as cis/tran ⁇ mixtures.
• polyesters of the present invention comprise at least 80 mole % ethylene glycol.
• polyesters comprise terepthalic acid and a mixture of 60 to 99 mole % ethylene glycol and 40 to 1 mole % cyclohexanedimethanol.
• the polyesters produced in the first step of the present invention have IhV's which are at least 0.5 dl/g, more preferably at least 0.65 dl/g and most preferably between 0.65 and 0.85 dl/g.
• the polyesters of this invention are readily prepared using polycondensation reaction conditions well known in the art.
• Typical polye ⁇ terification catalysts which may be used include titanium alkoxides, dibutyl tin dilaurate, and antimony oxide or antimony triacetate, used separately or in combination, optionally with zinc, manganese, or magnesium acetates or benzoates and/or other such catalyst materials as are well known to those skilled in the art.
• Phosphorus and cobalt compounds may also optionally be present.
• batch reactors operated in series may also be used.
• polyesters in this process in an unmodified form, other components such as nucleating agents, branching agents, colorants, pigments, fillers, antioxidants, ultraviolet light and heat stabilizers, impact modifiers and the like may be used if desired.
• Residual acetaldehyde refers to the acetaldehyde trapped within the PET polymer matrix after some previous melt history. Residual acetaldehyde was measured by storing the sample in a freezer at -40°C until ready to analyze. At that time the sample was removed from the freezer and placed in liquid nitrogen and cryogenically ground with a small laboratory scale Wiley mill to less than 20 mesh particles. Approximately 50 grams of ground sample was loaded into a metal GC desorption tube for AA analysis. Duplicates were run on each sample and results averaged. The sample tubes were stored in a freezer at -40°C until GC analysis.
• the GC desorption condition for the analysis was 10 minutes at 150°C during which time the AA is desorbed and swept into a trap and collected at liquid nitrogen temperatures by the aid of an inert carrier gas .
• the AA was subsequently desorbed from the trap onto a GC column and quantified by heating the cold trap to 300°C.
• Comparison of the present results with those of 24 hour acetaldehyde desorption into a bottle headspace indicate that 1 microgram per liter of headspace AA in a 2-liter bottle is comparable to ⁇ 3 ppm of residual AA as measured in the above test.
• the polymer entering the devolatilizing extruders contains 210 ppm residual acetaldehyde.
• the devolatilizers are purged with nitrogen. While in the devolatilizer for a mean residence time of 15 min, the polymer is cooled to 280°C.
• the polymer exiting the devolatilizer has 5 ppm residual acetaldehyde, and is ejected directly to a multi-cavity molding machine.
• the acetaldehyde regeneration rate during the transport of the polymer out of the devolatilizer & through the molding machine to the molds is measured to be 1 ppm per minute.
• the molten polymer with 20 ppm acetaldehyde is then pumped through a multi- hole die to generate thin threads which fall through an open vessel purged with inert gas.
• the molten polymer is then collected at the bottom of the vessel and distributed to four molding machines.
• the polymer containing 100 ppm residual acetaldehyde is fed to two devolatilizing reactors.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polyesters Or Polycarbonates (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)

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• 1997
  • 1997-02-26 ID IDP970576A patent/ID16094A/id unknown
  • 1997-02-27 JP JP9531102A patent/JP2000506199A/ja active Pending
  • 1997-02-27 PL PL97328606A patent/PL328606A1/xx unknown
  • 1997-02-27 CN CN97194115A patent/CN1217002A/zh active Pending
  • 1997-02-27 EP EP97907893A patent/EP0883643A1/de not_active Withdrawn
  • 1997-02-27 ZA ZA9701744A patent/ZA971744B/xx unknown
  • 1997-02-27 WO PCT/US1997/003037 patent/WO1997031968A1/en not_active Ceased
  • 1997-02-27 CA CA002248268A patent/CA2248268A1/en not_active Abandoned
  • 1997-02-27 AU AU19777/97A patent/AU1977797A/en not_active Abandoned
  • 1997-02-27 AR ARP970100787A patent/AR006022A1/es unknown
  • 1997-02-28 CO CO97010919A patent/CO4560470A1/es unknown

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