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
  • C08G63/80—Solid-state polycondensation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/16—Auxiliary treatment of granules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B9/00—Making granules
  • B29B9/16—Auxiliary treatment of granules
  • B29B2009/165—Crystallizing granules

Definitions

• acetaldehyde occurs naturally in many foods, in the manufacture of polyesters, it is an undesirable product of degradation reactions. Because acetaldehyde is detectable at very low levels, even small amounts can adversely affect the taste and odor of food or beverages such as water. In the manufacture of polyester containers, therefore, it is desirable to reduce the amount of acetaldehyde in the container sidewall which in turn minimizes the amount of acetaldehyde that is absorbed into the contents of the container. We have discovered a process for producing polyester resins that yield satisfactorily reduced levels of acetaldehyde in container sidewalls with improved clarity.
• U.S. Patent No. 5,362,844 describes a process in which PET is polymerized to an intrinsic viscosity of at least 0.60 dl/g (preferably at least 0.65 dl/g) in a melt polycondensation reactor. Between the exit of the reactor and the exit of the pelletizer, the temperature of the PET is not increased and the residence time is sufficiently low so that the free acetaldehyde in the polymer is not increased by more than 30 ppm. The pellets are then hardened (a key step in the process), crystallized, and subjected to a drying (dealdehydization) step. Slight solid-state polycondensation of the PET occurs simultaneously with the dealdehydization.
• U.S. Patent No. 4,340,721 describes a process to prepare low acetaldehyde PET in which the polymer is polycondensed in melt phase to an intrinsic viscosity of 0.55 to 0.70 dl/g.
• An essential feature of the process is the intrinsic viscosity achieved in melt phase is between 75 and 90% of the maximum intrinsic viscosity obtainable; this maximum is defined as a threshold beyond which viscosity can no longer be increased at given operating conditions because degradation reactions dominate the polycondensation reaction.
• a process comprising the steps of: polycondensing in the melt phase, a polyester monomer/oligomer mixture under conditions sufficient to form a precursor having an intrinsic viscosity less than 75% of a possible maximum intrinsic viscosity; and solid stating said precursor under conditions sufficient to increase said intrinsic viscosity at least about 0.05 dl/g.
• the process of the present invention provides polyesters having improved properties for packaging, particularly reduced levels of acetaldehyde and improved clarity.
• the process of the present invention further comprises a) esterification (or transesterification) of one or more dicarboxylic acids (or their dialkyl esters) to form a mixture of polyester monomer and oligomers; b) polycondensation to produce a low molecular weight precursor polymer having an intrinsic viscosity of less than 75% of a maximum attainable intrinsic viscosity; and c) crystallization and solid-state polycondensation to produce the desired product.
• the polyesters are any crystallizable polyester homopolymer or copolymer that are suitable for use in packaging, and particularly food packaging.
• polyesters are generally known in the art and may be formed from aromatic dicarboxylic acids, esters of dicarboxylic acids, anhydrides of dicarboxylic esters, glycols, and mixtures thereof. More preferably the polyesters are formed from terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl-2,6-naphthalenedicarboxylate, 2,6-naphthalenedicarboxylic acid, ethylene glycol, diethylene glycol, 1 ,4-cyclohexane-dimethanol, 1 ,4-butanediol, and mixtures thereof.
• the dicarboxylic acid component of the polyester may optionally be modified with up to about 15 mole percent of one or more different dicarboxylic acids.
• additional dicarboxylic acids include aromatic dicarboxylic acids preferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having 8 to 12 carbon atoms.
• dicarboxylic acids to be included with terephthalic acid are: phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'- dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like.
• the glycol component may optionally be modified with up to about 15 mole percent, of one or more different diols other than ethylene glycol.
• Such additional diols include cycloaliphatic diols preferably having 6 to 20 carbon atoms, aliphatic diols preferably having 3 to 20 carbon atoms and aromatic diols having 6 to 14 carbon atoms.
• diols include: diethylene glycol, triethylene glycol, 1 ,4-cyclohexanedimethanol, propane- 1,3 -diol, butane- 1,4-diol, pentane-l,5-diol, hexane-l,6-diol, 3-methylpentanediol-(2,4), 2-methylpentanediol- (1,4), 2,2,4-trimethylpentane-diol-(l,3), 2-ethylhexanediol-(l,3), 2,2- diethylpropane-diol-(l,3), hexanediol-(l,3), 1 ,
• the resin may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride, pentaerythritol, and other polyester forming polyacids or polyols generally known in the art.
• trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride, pentaerythritol, and other polyester forming polyacids or polyols generally known in the art.
• the polyesters of the present invention contain an amount of ethylene glycol from about 1 to 100 mole% relative to the total glycols in the polyester and more preferably from about 85 to about 100 mole%.
• polyester monomer diglycol esters of dicarboxylic acids
• oligomers Prior to the polycondensation portion of the melt-phase process, a mixture of polyester monomer (diglycol esters of dicarboxylic acids) and oligomers are produced by conventional, well-known processes.
• One such process is the esterification of one or more dicarboxylic acids with one or more glycols; in another process, one or more dialkyl esters of dicarboxylic acids undergo transesterification with one or more glycols in the presence of a catalyst such as a salt of manganese, zinc, cobalt, titanium, calcium, magnesium or lithium.
• the monomer and oligomer mixture is typically produced continuously in a series of one or more reactors operating at elevated temperature and pressures at one atmosphere or greater.
• the monomer and oligomer mixture could be produced in one or more batch reactors.
• Suitable conditions for esterification and transesterification include temperatures between about 220°C to about 250°C and pressures of about 0 to about 20 psig.
• the mixture of polyester monomer and oligomers undergoes melt- phase polycondensation to produce a low molecular weight precursor polymer.
• the precursor is produced in a series of one or more reactors operating at elevated temperatures.
• the polycondensation reactors are run under a vacuum or purged with an inert gas.
• Inert gas is any gas which does not cause unwanted reaction. Suitable gases include, but are not limited to partially or fully dehumidified air, CO 2 , argon, helium and nitrogen.
• Catalysts for the polycondensation reaction include salts of antimony, germanium, tin, lead, or gallium, preferably antimony or germanium.
• Reactions conditions for polycondensation include a temperature less than about 290°C, and preferably between about 240°C and 290°C at a pressure sufficient to aid in removing undesirable reaction products such as ethylene glycol.
• the monomer and oligomer mixture is typically produced continuously in a series of one or more reactors operating at elevated temperature and pressures at one atmosphere or greater. Alternately, the monomer and oligomer mixture could be produced in one or more batch reactors.
• a key feature of the invention is maintaining the intrinsic viscosity of the precursor produced by melt-phase polycondensation at a level significantly lower than that which could be obtained at the final reactor operating conditions.
• High intrinsic viscosities greater than about 75% of the maximum attainable intrinsic viscosity at the reactor conditions, require relatively long residence times in the reactor since the degree of polymerization increases more slowly as the intrinsic viscosity approaches its maximum attainable value.
• long residence times at this stage of processing generate much of the acetaldehyde and acetaldehyde precursors found in the polyester.
• the intrinsic viscosity of the precursor produced in melt- phase polycondensation should be limited to less than 75% of the maximum intrinsic viscosity that could be attained at the operating conditions, preferably to less than 65% of the maximum attainable intrinsic viscosity, and more preferably to less than 55% of the maximum attainable intrinsic viscosity.
• the maximum intrinsic viscosity limitation was surprising as U.S. 4,340,721 states that if the precursor intrinsic viscosity is less than 75% of that attainable, the process is not a high-performance process. We find, however, that when producing precursor with lower intrinsic viscosities, higher production rates can be achieved, giving improved process performance, an advantage of the present invention.
• intrinsic viscosity of the polyester precursor should be less than 0.70 dl/g, preferably less than 0.65 dl/g, more preferably less than 0.60 dl/g. Intrinsic viscosity is measured using 0.25 g polyester in 50 ml of 60:40 phenol/tetrachloroethane at 25°C.
• Maximum attainable intrinsic viscosity for a particular catalyst system and finisher conditions may be determined experimentally. About 25 g of polyester oligomer containing the desired catalyst system are melt polymerized at the temperature and pressure of interest in a flask. Several experiments were run at various polymerization times to find the maximum attainable intrinsic viscosity.
• the precursor is crystallized and undergoes further polycondensation in the solid state by conventional, well-known processes, such as those disclosed in 4,064,112.
• Solid-state polycondensation can be conducted in the presence of an inert gas as defined above, or under vacuum conditions, and in a batch or continuous process.
• the polyester can be in the form of pellets, granules, chips, or powder.
• Temperature during the solid-state polycondensation process should be maintained less than 240°C, preferably less than 230°C.
• the increase in intrinsic viscosity during solid-state polycondensation is at least about 0.05 dl/g, preferably at least about 0.10 dl/g. No hardening step is necessary prior to crystallization.
• Additives which are known to reduce AA may also be added.
• Such additives include polyamides selected from the group consisting of low molecular weight partially aromatic polyamides having a number average molecular weight of less than 15,000, low molecular weight aliphatic polyamides having a number average molecular weight of less than 7,000 and wholly aromatic polyamides and polyesteramides as disclosed in U.S. Ser. No. 595,460. Suitable polyamides are disclosed in U.S. Ser. No. 548,162.
• Other ingredients may be added to the compositions of this invention as desired to enhance the performance properties of the polyesters.
• surface lubricants denesting agents, stabilizers, antioxidants, ultraviolet light absorbing agents, mold release agents, metal deactivators, colorants, nucleating agents, phosphorus-containing stabilizers, reheat rate enhancers, zeolites, fillers and the like may be added.
• Poly(ethylene terephthalate) modified with 1.5 wt% diethylene glycol, 1.1 wt% 1 ,4-cyclohexanedimethanol, and an antimony-phosphorus catalyst system was produced as follows. Terephthalic acid was continuously esterified with ethylene glycol in a series of two reactors. The mixture of monomer and oligomer thus produced was then polycondensed in melt-phase to an intrinsic viscosity of 0.57 dl/g (which represents at most 53% of the maximum attainable intrinsic viscosity, which at the temperature, pressure, and catalyst levels employed was at least 1.08 dl/g).
• the precursor underwent crystallization, followed by solid-state polycondensation at a temperature of about 215°C, reaching an intrinsic viscosity of 0.72 dl/g, making the increase in intrinsic viscosity during solid-state polycondensation 0.15 dl/g.
• Water bottle parisons were injected molded from this polyester resin.
• Acetaldehyde content of the parisons was 3.0 ppm (by weight) maximum, well within the specification of 4.0 ppm.
• Comparative Example Poly(ethylene terephthalate) modified with 1.5 wt% diethylene glycol, 1.1 wt% 1 ,4-cyclohexanedimethanol, and an antimony-phosphorus catalyst system was produced as follows. Terephthalic acid was continuously esterified with ethylene glycol in a series of two reactors. The mixture of monomer and oligomer thus produced was then polycondensed in melt-phase to an intrinsic viscosity of 0.66 dl/g under conditions where the maximum attainable intrinsic viscosity was about 0.854 dl/g, or 77% of the maximum achievable intrinsic viscosity.
• the precursor underwent crystallization, followed by solid-state polycondensation at a temperature of about 215 °C, reaching an intrinsic viscosity of 0.80 dl/g, making the increase in intrinsic viscosity during solid-state polycondensation 0.14 dl/g.
• Water bottle parisons were injected molded from this polyester resin.
• Acetaldehyde content of the parisons was 4.5 ppm (by weight) maximum, above the specification of 4.0 ppm.

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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)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Polyesters Or Polycarbonates (AREA)

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• 1998
  • 1998-04-24 US US09/065,990 patent/US6048957A/en not_active Expired - Lifetime
  • 1998-05-01 ES ES98920151T patent/ES2231983T3/es not_active Expired - Lifetime
  • 1998-05-01 BR BR9809781-4A patent/BR9809781A/pt not_active IP Right Cessation
  • 1998-05-01 DE DE69828391T patent/DE69828391T2/de not_active Expired - Fee Related
  • 1998-05-01 JP JP54745498A patent/JP2001522400A/ja active Pending
  • 1998-05-01 CN CN98804602A patent/CN1253571A/zh active Pending
  • 1998-05-01 EP EP98920151A patent/EP0977793B1/en not_active Expired - Lifetime
  • 1998-05-01 WO PCT/US1998/008948 patent/WO1998049217A1/en not_active Ceased

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