Methods of post-polymerisation extruder injection in condensation polymer production

ES 2 223 958 T3

DESCRIPTION

Procedures for post-polymerization injection with an extruder in the production of condensation polymers.

Referral to a related request

This application is a continuation, in part, of the US patent application. serial number 09 / 932,150 for Post-Polymerization Injection Procedures with Extruder in Polyethylene Terephthalate Production, filed August 17, 2001, which is itself a continuation, in part, of the US patent application. ., co-pending and currently assigned, with serial number 09 / 738,150, for Post-polymerization Injection Procedures in Continuous Production of Polyethylene Terephthalate, filed December 15, 2000. This application is also related to the copending and commonly assigned application, serial number 10 / 017,612, for Post-Polymerization Injection Procedures in Condensation Polymer Production. Each of these pending applications is currently assigned with this application and is incorporated in its entirety herein by reference.

Field of the invention

The present invention relates to the processing of condensation polymers and, more particularly, the present invention relates to the late introduction of additives into condensation polymers via reactive carriers.

Background of the invention

Polyester fibers and films, due to their resistance to heat and resistance to chemicals, are an integral part of many consumer products manufactured around the world. The most commonly used commercial polyester for polyester fibers and films is polyethylene terephthalate polyester (PET). Since polyethylene terephthalate forms a lightweight, unbreakable product, another popular use for polyethylene terephthalate is as a resin for containers, especially beverage bottles.

Before 1965 the only feasible process for producing polyethylene terephthalate polyester was the use of dimethyl terephthalate (DMT). In this technique, dimethyl terephthalate and ethylene glycol are reacted within a catalyzed ester exchange reaction to form monomers and oligomers of bis (2-hydroxyethyl) terephthalate, as well as a by-product of methanol that is continuously removed. These bis (2-hydroxyethyl) terephthalate monomers and oligomers are then polymerized by polycondensation to produce polyethylene terephthalate polymers.

Increasingly pure forms of terephthalic acid (TA) are now available, therefore terephthalic acid has become an acceptable, if not preferred, alternative to dimethyl terephthalate as a starting material for the production of polyethylene terephthalate. In this alternative technique, terephthalic acid and ethylene glycol react within a generally uncatalyzed esterification reaction to produce low molecular weight monomers and oligomers, as well as an aqueous by-product that is continuously removed. As in the dimethyl terephthalate technique, the monomers and oligomers are then polymerized by polycondensation to form a polyethylene terephthalate polyester. The resulting polyethylene terephthalate polymer is nearly identical to the polyethylene terephthalate polymer that results from dimethyl terephthalate, albeit with some differences in the end group.

Polyethylene terephthalate polyester can be produced in a batch process, where the product of the ester exchange, or esterification reaction, is formed in one vessel and then transferred to a second vessel for polymerization. In general, the second vessel is agitated and the polymerization reaction is continued until the energy used by the agitator reaches a level that indicates that the polyester melt has achieved the desired intrinsic viscosity. However, it is more commercially practical to carry out the esterification or ester exchange reactions, and then the polymerization reaction as a continuous process. Continuous production of polyethylene terephthalate results in higher productivity and is therefore more typical in large-scale manufacturing facilities.

Typically, when the polymerization process is complete, the resulting polymer melt is extruded and pelleted for convenient storage and transportation before it is transformed into specific polyester articles (eg, filaments, films, or bottles). These latter classes of steps are referred to herein as "polyester processing."

Often, in both batch and continuous processes, a high activity catalyst is employed to increase the rate of polymerization, thereby increasing the overall yield of the resulting polyethylene terephthalate polyester. High activity catalysts used in the polymerization of polyethylene terephthalate polyester can be basic, acidic or neutral, and often metallic catalysts.

Mainly the traditional polymerization catalysts that are used in the formation of polyethylene terephthalate starting from both terephthalic acid and dimethyl terephthalate contain antimony, more usually antimony trioxide (Sb₂OR₃). Although polymerization catalysts, such as antimony trioxide, increase the rate of production, over time they will begin to catalyze or stimulate degradation of the polyethylene terephthalate polymer. Such polymeric degradation results in acetaldehyde formation, discoloration (eg, yellowing) of the polyethylene terephthalate polyester, and reduction in the molecular weight of the polymer.

Furthermore, the recent availability of "hotter" catalysts, which can significantly increase overall yield, has created a corresponding need for better stabilization in the resulting polyester. US Patent No. 5,008,230 for a Catalyst for preparing colorless polyethylene terephthalate with high clarity is an example of such an improved catalyst. To reduce degradation and discoloration of the polyethylene terephthalate polyester, stabilizer compounds are employed to sequester ("cool") the catalyst thereby reducing its effectiveness. The most commonly used catalysts contain phosphorus, typically in the form of phosphates and phosphites. The stabilizers that contain

ES 2 223 958 T3 phosphorus were first employed in batch processes to prevent degradation and discoloration of the polyethylene terephthalate polyester.

Although adding a stabilizer to a polymer melt within a batch reactor is a relatively straightforward process, many problems arise if stabilizers are added within continuous production of polyethylene terephthalate. For example, although the early addition of the stabilizer prevents discoloration and degradation of the polyester it also causes a lower overall production yield (ie, slows down the polycondensation reaction). Furthermore, it is typical for such a stabilizer to dissolve in ethylene glycol, the addition of which further retards the polymerization process. Accordingly, the early addition of the stabilizer within the polymerization process demands the undesirable choice between the total yield of the production and the thermal stability of the polymer. As used herein, "thermal stability" refers to a low rate of acetaldehyde generation, low discoloration, and retention of molecular weight following heat treatment or other process.

Late addition of the stabilizer (for example, after the polymerization process during polymer treatment) may provide insufficient opportunity for the stabilizer to fully mix with the polymer. Therefore the stabilizer may not prevent discoloration and degradation of the polymer. Furthermore, the addition of the stabilizer during the treatment of the polymer is inconvenient and does not provide economies of scale.

In US Patent No. 5,376,702 for a Process and Apparatus for Continuous and Direct Modification of Polymeric Melts, the division of a polymer melt stream into an unmodified stream and a bypass current receiving additives. In particular, a side stream carries a part of the bypass stream into an extruder, where the additives are introduced. However such techniques are not only complicated but also expensive, requiring a screw extruder and melt pipes to process the additives, so such arrangements are inconvenient and even impractical when the total additive concentrations are low (eg, less than one percent by weight).

There are certain problems associated with late addition of stabilizer that are discussed in US Patent No. 5,898,058, for a High Activity Catalyst Post-Polymerization Stabilization Process in Continuous Production of Polyethylene Terephthalate, in which A process for stabilizing highly active polymerization catalysts in the continuous production of polyethylene terephthalate is disclosed. This patent, which is commonly assigned with this application, is hereby incorporated in its entirety herein by reference.

In particular, US Patent No. 5,898,058 discloses the addition of a stabilizer, which is preferably phosphorous-containing, at or after the end of the polymerization reaction and before treatment of the polymer. This deactivates the polymerization catalyst and increases the overall yield of the polyester without adversely influencing the thermal stability of the polyethylene terephthalate polyester. Although it is a noteworthy improvement, US Patent No. 5,898,058 shows the addition of the stabilizer without a carrier. Consequently, the addition of solids into the polymer requires the expensive use of an extruder.

A process for the production of high quality polyethylene terephthalate polyester is disclosed in US Patent Application Serial No. 09 / 738,150, for Post Polymerization Injection Procedures in Continuous Production of Polyethylene Terephthalate improvement after stabilizer addition techniques disclosed in commonly assigned U.S. Patent No. 5,898,058.

More specifically, US application number 09 / 738,150 discloses a process for late introduction of additives into the process for making polyethylene terephthalate. The additives are introduced during, and preferably after, the polycondensation of polyethylene terephthalate polymers. In particular, this method uses a reactive carrier that not only functions as a delivery vehicle for one or more additives but also reacts with polyethylene terephthalate, thereby binding the carrier within the polyethylene terephthalate resin. . Furthermore, in US application number 09 / 738,150 it is disclosed that this can be achieved by employing a simplified additive discharge system that does not require the use of an extruder.

The technology in US Patent Application No. 09 / 738,150 is effectively employed in US Application No. 09 / 738,619, co-pending and commonly assigned, for Polyester Resins for Bottles with Friction Properties. and methods for making the same, which was also filed on December 15, 2000, and is incorporated herein by reference in its entirety. Likewise, in certain preferred embodiments, in US application serial number 09 / 738,619, a simplified system is employed for the discharge of the additive that does not require the use of an extruder.

Despite the preference to exclude an extruder from additive discharge systems, there are certain circumstances where the use of an extruder is advantageous, for example, the introduction of additives into an extruder facilitates rapid formulation changes. Also, while introducing additives into an extruder can hamper productivity in larger scale operations, it may be appropriate for smaller scale operations.

Accordingly, in US Patent Application Serial No. 09 / 932,150 for extruder post-polymerization injection processes in the production of polyethylene terephthalate, which is a continuation, in part, of US Lead Application Serial No. 09 / 738,150 discloses a process for late introduction of additive, into an extruder, during the process for making polyethylene terephthalate. In this process, in particular, a reactive carrier is employed which not only functions as a delivery vehicle for one or more additives but also reacts with the polyethylene terephthalate to bind the carrier within the polyethylene terephthalate resin. This not only prevents the wearer from leaving the

ES 2 223 958 T3 polyethylene terephthalate during post-treatment (e.g. solid state polymerization, drying operations, injection molding operations), but also increases the dispersion of the additive within the polymer and reduces the tendency of the additive to emerge and deposit in the equipment for the treatment of the polymer during the polymerization in solid state.

The process of US application serial number 09 / 932,150 generally has application in the production of condensation polymers. Indeed, there is a need for a post-polymerization injection technique that ensures that late addition of additives during polymer treatment processes produces condensation polymers whose additives and carriers are an integral part of the polymeric condensation resin, while retaining the advantages associated with the addition of an extruder.

Summary of the invention

Therefore, an object of the present invention is to provide a process for adding additives to condensation polymers, in an extruder, by means of a reactive carrier.

Another object of the present invention is to provide a process for adding additives to condensation polymers, by means of a reactive carrier, in a manner that allows rapid changes in the formulation.

Yet another object of the present invention is to provide a process for adding additives to condensation polymers through a reactive carrier in order to reduce polymeric transition times and eliminate inconveniences in processes, resulting from changes in formulations of polymers.

Yet another object of the present invention is to provide a method of introducing additives into condensation polymers in a way that reduces degradation or volatilization of such additives.

The foregoing objectives, as well as other objectives and advantages of this invention and the manner in which they are achieved, are specified below within the following detailed description and its accompanying drawings.

Brief description of the drawings

Figure 1 illustrates the theoretical loss in molecular weight (measured by the number expressing the average degree of polymerization) for condensation polymers with an initial degree of polymerization of approximately 100 as a function of the concentration of the reactive carrier at various molecular weights.

Figure 2 illustrates the theoretical loss of molecular weight (measured by means of the number expressing the average degree of polymerization) for condensation polymers with an initial degree of polymerization of about 70 as a function of the concentration of the reactive carrier at various molecular weights.

Figure 3 illustrates the theoretical intrinsic viscosity loss of polyethylene terephthalate with an intrinsic viscosity of 0.63 dl / g as a function of the reactive carrier concentration at various molecular weights.

Figure 4 illustrates the theoretical loss of intrinsic viscosity of polyethylene terephthalate with an intrinsic viscosity of 0.45 dl / g as a function of the reactive carrier concentration at various molecular weights.

Detailed description

This invention is a novel process for the late introduction of additives into an extruder during the processing of condensation polymers (ie, one or more additives are introduced into condensation polymers by means of a reactive carrier). As noted above, a reactive carrier is employed in this process that not only functions as a delivery vehicle for one or more additives, but also reacts with the condensation polymers to bind the reactive carrier within the polymeric resin. This prevents the carrier from leaking out of the condensation polymers during post-processing, such as solid state polymerization, drying, spinning, film extrusion, and injection molding operations. This also improves the dispersion of the additive in the condensation polymers and reduces the tendency for the carrier to deposit on the polymerization process equipment during solid state polymerization.

The present invention includes combining, in an extruder, condensation polymers having carbonyl functionality and a reactive carrier having a molecular weight of less than about 10,000 g / mol and being the delivery vehicle for one or more additives.

The present invention includes, in a related aspect, the first polymerization of oligomeric precursors by means of liquefied phase polycondensation to form condensation polymers having carbonyl functionality. After this, one or more additives are introduced into the condensation polymers, in an extruder, by means of a reactive carrier having a molecular weight of less than about 10,000 g / mol.

As used herein, the concept of combining (or introducing, adding, etc.) the condensation polymers and the reactive carrier, in an extruder, encompasses (1) the introduction of both the condensation polymers and the reactive carrier within the extruder, (2) introducing the reactive carrier into the condensation polymers before the extruder, and mixing the condensation polymers and the reactive carrier within the extruder, and (3) introduction of the reactive carrier into the condensation polymers after the extruder.

As used herein, the term "carbonyl functionality" refers to a carbon-oxygen double binder that is available at the reaction site. Carbonyl-functional condensation polymers are typically characterized by the presence of a carbonyl functional group (i.e., C = O) with at least one adjacent heteroatom (for example, an oxygen atom, a nitrogen atom, or a sulfur) functioning as a connector within the polymer chain. Thus "carbonyl functionality" means that it encompasses various functional groups including, without limitation, esters, amides, imides, carbonates, and urethanes.

Suitable polycondensation polymers according to the present invention include, without limitation, polyesters, polyurethanes, polycarbonates, polyamides, and polyimides. Polyesters, such as te

ES 2 223 958 T3 polyethylene refthalate, polymethylene terephthalate and polybutylene terephthalate are preferred.

As will be understood by those of ordinary skill in the art, oligomeric precursors of condensation polymers can be formed by the reaction of a first polyfunctional component and a second polyfunctional component. For example, oligomeric polycarbonate precursors can be formed by reacting diols and carbonic acid derivatives, oligomeric polyurethane precursors can be formed by reacting diisocyanates and diols, oligomeric polyamide precursors can be formed by means of diacids and diamines, and precursors can be formed. oligomeric polyimides reacting dianhydrides and diamines. See, for example, Odian, Principles of Polymerization (second edition, 1981). These classes of reactions are well understood by those of ordinary skill in the polymer arts and will not be discussed further herein.

Also those of ordinary skill in the art will understand that certain monomers possessing multifunctionality can self-polymerize to produce condensation polymers. For example, amino acids and nylon salts are each capable of self-polymerizing to polyamides and hydroxy acids (eg, lactic acid) can self-polymerize to polyesters (eg, polylactic acid).

Polyesters are the preferred polycondensation polymers and therefore the present invention is described herein with particular reference to the introduction of additives into the process for the manufacture of polyethylene terephthalate. In this regard, oligomeric polyester precursors can be formed by reacting diacids and diols or by reacting diesters and diols. Diols can be aliphatic or aromatic.

It will be apparent to those of ordinary skill in the polymer art that the description of the present invention is directed not only to the introduction of additives into polyethylene terephthalate, but also to the introduction of additives into any condensation polymer possessing carbonyl functionality. along its polymer chain. It is hoped that an exemplary description of this invention with the use of a preferred condensation polymer (i.e., polyethylene terephthalate) will allow those skilled in the polymer art to practice, without undue experimentation, this invention for any condensation polymer. having carbonyl functionality. In this regard, those of ordinary skill in the polymer art will recognize that there are numerous classes of condensation polymers and copolymers that can be synthesized without departing from the scope and spirit of the present invention.

It is preferable that this invention includes the reaction of a terephthalate component and a diol component to form polyethylene terephthalate precursors, eg, bis (2-hydroxyethyl) terephthalate. These oligomeric precursors are then polymerized by means of liquefied phase polycondensation to form polyethylene terephthalate polymers. During polycondensation, which is usually enhanced by catalysts, ethylene glycol is continuously removed to create favorable reaction kinetics. One or more additives are then introduced by means of a reactive carrier into the polyethylene terephthalate polymers (ie, the reactive carrier functions as an additive delivery vehicle).

In a particular embodiment of this invention, the polyethylene terephthalate polymers can be pelletized, and then the polyethylene terephthalate polymers and the reactive carrier are preferably introduced into an extruder. The reactive carrier, which has a molecular weight of less than about 10,000 g / mol, not only facilitates the mixing of the additives within the polymer melt, but also reacts with the polyethylene terephthalate polymers to ensure that they the carrier does not emerge during subsequent processes.

The term "intrinsic viscosity", as used herein, is the ratio between the specific viscosity of a polymer solution of known concentration and the concentration of the dissolved substance, extrapolated to the zero concentration. Intrinsic viscosity, which is widely recognized for standard measurements of polymer characteristics, is directly proportional to the average molecular weight of the polymer. See, for example, Dictionary of Fiber and Fabric Technology, Hoechst Celanese Corporation (1990); Tortora & Merkel, Fairchild's Dictionary of Tissues (7^toedition, 1996).

Those of ordinary skill in the art can measure and determine intrinsic viscosity without undue experimentation. For the intrinsic viscosity values ​​described herein, the intrinsic speed is determined by dissolving the copolyester in orthochlorophenol (OCP), measuring the relative viscosity of the solution using a Schott autoviscometer (Viscosystem AVS Schott and AVS 500), and then calculating the intrinsic viscosity based on the relative viscosity. See, for example, Dictionary of Fiber and Fabric Technology ("Intrinsic Viscosity").

In particular, a 0.6 gram (± 0.005 g) sample of dry polymer sample is dissolved in about 50 ml (61.0 to 63.5 grams) of orthochlorophenol at a temperature of about 105 ° C. It is typical to cut fiber and yarn samples into small pieces, while wafer-shaped samples are ground. The solution, after cooling to room temperature, is placed into the viscometer at a constant regulated temperature (eg, between about 20 and 25 ° C) and the relative viscosity is measured. As mentioned, the intrinsic viscosity is calculated starting from the relative viscosity.

The term "diol component" refers primarily herein to ethylene glycol, although other diols (eg, low molecular weight polyethylene glycol) may also be used. Those of ordinary skill in the art will understand that it is common for the diol component to form most of the end ends of the polymer chains and is therefore present in the composition in slightly larger fractions. For example, the molar ratio of the terephthalate component to the diol component is typically between about 1.0: 1.0 and 1.0: 1.6.

The term "terephthalate component" refers herein to diacids and diesters that can be used to prepare polyethyl terephthalate.

ES 2 223 958 T3 leno. In particular, the terephthalate component includes, for the most part, terephthalic acid and dimethyl terephthalate, but can also include diacid and ester comonomers. In this regard, those of ordinary skill in the art will know that there are two conventional processes for forming polyethylene terephthalate. These procedures are well known to those of skill in the art.

In one process, a direct esterification reaction is employed using terephthalic acid and an excess of ethylene glycol. Within this technique, in the aforementioned step of the reaction of the terephthalate component and the diol component, the reaction of terephthalic acid and ethylene glycol is included within a heated esterification reaction to form monomers and oligomers of terephthalic acid and ethylene glycol, as well as also an aqueous by-product. To allow the esterification reaction to go to essentially complete, the water has to be withdrawn constantly as it forms.

The other procedure involves a two-step ester exchange reaction and polymerization using dimethyl terephthalate and an excess of ethylene glycol. Within this technique, in the aforementioned stage of the reaction of the terephthalate component and the diol component, the reaction of dimethyl terephthalate and ethylene glycol is included within a heated ester exchange reaction to form monomers and oligomers of terephthalate and ethylene glycol, as well as methanol as a by-product. To allow the ester exchange reaction to go to essentially complete, the methanol has to be withdrawn constantly as it is formed.

Those of ordinary skill in the art will understand that the polyethylene terephthalate described herein may be a polyethylene terephthalate modified to such an extent that the diol component includes other glycols in addition to ethylene glycol, such as diethylene glycol, 1,3-propanediol, 1, 4-butanediol and 1,4-cyclohexanedimethanol, or that the terephthalate component includes modifiers such as isophthalic acid, 2,6-naphthalene dicarboxylic acid, succinic acid or one or more functional derivatives of terephthalic acid. In reality, most commercial polyethylene terephthalate polymers are modified polyethylene terephthalate polyesters.

In this invention, the direct esterification reaction is preferred to the older two-stage ester exchange reaction. As noted, in the direct esterification reaction technique, terephthalic acid and ethylene glycol are reacted to form low molecular weight monomers, oligomers, and water.

For example, in a typical process the continuous feed enters a direct esterification vessel that is operated at a temperature of between about 240 ° C and 290 ° C and at a pressure of between about 34.5 and 586 kPa, for between about one and five hours. The reaction, which is typically uncatalyzed, forms low molecular weight monomers, oligomers, and water. The water is removed as the esterification reaction proceeds and the remaining ethylene glycol is removed to provide favorable reaction kinetics.

The low molecular weight monomers and oligomers are then polymerized by means of polycondensation to form polyethylene terephthalate polyester. In this stage of polycondensation, a series of two or more vessels are generally used that are operated at a temperature of between about 250 ° C and 305 ° C for between about one and four hours. The polycondensation reaction often begins in a first vessel called the low polymerizer. This low polymerizer is operated in a pressure range of between about 0 and 9.33 kPa. The monomers and oligomers are polycondensed to form polyethylene terephthalate and ethylene glycol.

As noted above, ethylene glycol is removed from the polymer melt using applied vacuum to drive the reaction to completion. In this regard, the polymer melt is typically agitated to encourage the escape of ethylene glycol from the polymer melt and to help the highly viscous polymer melt move throughout the polymerization vessel.

As the polymer melt is introduced into successive vessels, the molecular weight and thus the intrinsic viscosity of the polymer melt increase. In general, the temperature of each container is increased, and the pressure is lowered, to allow greater polymerization in each successive container.

The final vessel, generally called a "raised polymerizer" is operated at a pressure of between about 0 and 5.33 kPa. Each of the polymerization vessels is, like the base polymerizer, connected to a separation vessel and, typically, each is agitated to facilitate removal of the ethylene glycol. The residence time within the polymerization vessels and the feed rate of ethylene glycol and terephthalic acid to the continuous process are determined based, in part, on the target molecular weight of the polyethylene terephthalate polyester. Since molecular weight can be easily determined based on the intrinsic viscosity of the polymer melt, the intrinsic viscosity of the polymer melt is generally used to establish polymerization conditions, such as temperature, pressure, feed rate of the reagents and the residence time within the polymerization vessels.

It should be noted that, in addition to the formation of polyethylene terephthalate polymers, secondary reactions occur that produce undesirable by-products. For example, the esterification of ethylene glycol forms diethylene glycol (DEG), which is incorporated into the polymer chain. As is known to those skilled in the art, diethylene glycol lowers the softening temperature of the polymer. Furthermore, cyclic oligomers (eg trimers and tetramers of terephthalic acid and ethylene glycol) can be produced in very small amounts. Continuous removal of the ethylene glycol, as it forms in the polycondensation reaction, will generally reduce the formation of these by-products.

Although the foregoing discussion concentrates on the continuous production of polyester terephthalate polymers, it will be understood that this invention is not so limited. The techniques disclosed herein can be applied to other polycondensation polymers using continuous processes, semi-continuous processes, and batch processes.

For example, condensation polymers of

ES 2 223 958 T3 present invention are generally filtered and extruded in the molten phase to form polymeric sheets, filaments or nodules. It is preferable that the polymeric melt is extruded immediately after polycondensation. The polymers, after extrusion, are rapidly cooled, preferably by spraying with water or immersion in a bucket with water, to promote solidification. The solidified condensation polymers are cut into wafers or pellets for storage and handling. As used herein, the term "nodules" is generally used to refer to wafers, nodules, and the like.

As those of ordinary skill in the art will know, nodules that are formed from condensation polymers can, in some circumstances, undergo crystallization followed by solid state polymerization (SSP) to increase the molecular weight of the polymeric resin. . Solid state polymerization can be initiated either before or after introduction of the reactive carrier. It should be noted that the inclusion of the reactive carrier does not adversely affect the speed of the SSP and will often even increase the speed of the SSP. After this, the polymeric wafers are remelted and extruded again to form articles such as containers (eg, beverage bottles), filaments, films, or other applications. Those of ordinary skill in the art will recognize that some condensation polymers, such as amorphous polycarbonates, do not need to undergo SSP.

The present invention improves upon the prior art by employing a reactive carrier in place of an inert carrier or no carrier at all. The reactive carrier has to be introduced into the condensation polymers in amounts such that the properties of the bulk polymer are not significantly affected. It is preferable that the reactive carrier is capable of combining with the condensation polymers so that it is not extractable during subsequent process operations.

Therefore, in a preferred embodiment, the invention includes the introduction, into the extruder, of condensation polymers having carbonyl functionality and a reactive carrier that is the delivery vehicle for one or more additives. Furthermore, the reactive carrier, which has an average molecular weight of less than about 10,000 g / mol, is fed into the extruder in such amounts that the bulk polymer properties of the condensation polymers are not significantly affected.

As used herein, the concept of introduction into an extruder of condensation polymers and a reactive carrier encompasses (1) the introduction of both the condensation polymers and the reactive carrier into the extruder, and (2) introduction of the reactive carrier within the condensation polymers before the extruder, and then mixing of the condensation polymers and the reactive carrier within the extruder.

Preferably, the reactive carrier has a melting temperature that ensures it is a liquid or suspension at about 100 ° C, which can be achieved using low pressure steam. Most preferably, the reactive carrier has a melting temperature that ensures that it is a liquid or suspension close to room temperature. As used herein, the term "near ambient" includes temperatures between about 20 ° C and 60 ° C. The near ambient temperatures simplify the unit operations required to introduce the additives since no complicated heating systems are needed to introduce the reactive carrier into the condensation polymers.

Since an extruder is used in the present invention it is preferable that the condensation polymers are solid (ie polymeric wafers or pellets) when combined with the reactive carrier in the extruder (eg fed into the extruder).

Likewise, the reactive carrier can be a solid when combined with the condensation polymers in the extruder. In this regard, it is preferable to introduce a solid reactive carrier into the extruder towards the rear of the extruder as this promotes melting and mixing (and reaction) of the condensation polymers and the reactive carrier.

However, it is preferable that the reactive carrier is a liquid or a suspension when combined with the condensation polymers in the extruder. A liquid or suspension reactive carrier can be inserted at the rear or front of the extruder. As indicated, it is preferable that the reactive carrier is a liquid or a suspension at room temperature.

As a general rule, the reactive carrier should not make up more than about one percent of the polymeric resin (ie, 10,000 ppm). It is preferable that the reactive carrier is introduced into the condensation polymers in amounts such that its concentration within the polymeric resin is less than about 1,000 ppm (ie, 0.1 percent by weight). Reducing the reactive carrier to amounts such that its concentration within the polymeric resin is less than 500 ppm (i.e., 0.05 percent by weight) will further reduce potential adverse effects to most of the polymer's properties. .

Figures 1 and 2 illustrate the theoretical loss of molecular weight (measured by means of the number expressing the average degree of polymerization) as a function of the concentration of the reactive carrier at various molecular weights.

Figure 1 depicts the impact of reactive carrier on condensation polymers having an initial degree of polymerization of approximately 100. Similarly, Figure 2 depicts the impact of reactive carrier on condensation polymers having an initial degree of polymerization of about 70. (For polyethylene terephthalate, a degree of polymerization of about 100 corresponds to an intrinsic viscosity of about 0.61 dl / g and a degree of polymerization of about 70 corresponds to an intrinsic viscosity of about 0.45 dl / g). Note that, at any concentration within a polymeric condensation resin, reactive carriers with higher molecular weights have less adverse effect on the average degree of polymerization of the polymeric resin.

Similarly, Figures 3 and 4 illustrate the theoretical loss of intrinsic viscosity as a function of the concentration of the reactive carrier at various molecular weights. Figure 3 represents the impact

ES 2 223 958 T3 of the reactive carrier on polyethylene terephthalate with an intrinsic viscosity of 0.63 dl / g. Similarly, figure 4 represents the impact of the reactive carrier on polyethylene terephthalate with an intrinsic viscosity of 0.45 dl / g.

As will be understood by those of ordinary skill in the art, macromolecules having a degree of polymerization of about 70 are considered high polymers. For polyethylene terephthalate this translates to approximately a molecular weight of at least approximately 13,000 g / mol. At this molecular weight, polyethylene terephthalate polymers possess sufficient molecular weight, mechanical properties, melt strength, and crystallinity to facilitate processing of the polymer.

In contrast, reactive carriers according to the present invention have molecular weights less than about 10,000 g / mol. It is typical that the molecular weight of the reactive carrier is less than 6,000 g / mol, it is preferable that it is less than 4,000 g / mol, and more preferably it is between about 300 and 2,000 g / mol, and most preferably it is between about 400 and 1,000 g / mol. As used herein, molecular weight refers to the number that expresses the average molecular weight rather than the weight that expresses the average molecular weight.

In general, reactive carriers having carboxy, hydroxyl, or amino functional groups are favored. Suitable reactive carriers include esters (even low polymers derived from caprolactone), amides (even low polymers derived from caprolactam), imides, amines, isocyanates, oxazolines, acids, and anhydrides that are capable of reacting with condensation polymers in such a manner. that decreases the loss of molecular weight of condensation polymers during subsequent thermoprocesses, such as injection molding and extrusion operations.

Also preferred are polyols, especially polyester polyols and polyether polyols having a molecular weight that is high enough such that the polyol almost does not reduce the average molecular weight of the condensation polymers, and a viscosity that facilitates the pumping of the polyol. Polyethylene glycol is the preferred polyol. Other examples of polyols include functional polyethers, such as propylene glycol that is prepared starting from propylene oxide, random and block polymers of ethylene oxide and propylene oxide, and polytetramethylene glycol that is derived from the polymerization of tetrahydrofuran.

Alternatively, the reactive carrier can also include dimeric and trimeric acids and anhydrides. In another embodiment, the reactive carrier may possess, in addition to or instead of terminal functional groups, internal functional groups (eg, esters, amides, and anhydrides) that react with the condensation polymers. In yet another embodiment, the reactive carrier may include esters without terminal functional groups, amides without terminal functional groups, or anhydrides without terminal functional groups that are capable of reacting within condensation polymers during solid state polymerization and that do not cause the polymers of condensation suffer loss of molecular weight during injection molding or extrusion processes. As noted, and as will be appreciated by those of ordinary skill in the art, reactive carriers derived from heterocycles (eg, caprolactone and caprolactam) are within the scope of this invention.

It should be recognized that additives are sometimes marketed with oligomers that constitute an acceptable reactive carrier. For example, TINUVIN® 213, which is available from Ciba Specialty Chemicals, includes a hydroxyphenylbenzotriazole ultraviolet light absorber within an unreacted polyethylene glycol solution having a molecular weight of 300 g / mol. As noted above, polyethylene glycol is the preferred reactive carrier. Accordingly, the present invention includes the use of such premixed reactive carrier and additive products.

An example of a process according to this invention includes the reaction of terephthalic acid and ethylene glycol within a heated esterification reaction to form monomers and oligomers via melt phase polycondensation to form polyethylene terephthalate polymers. The polyethylene terephthalate polymers are then shaped into wafers (or pellets with a polymer cutting blade) and solid state polymerized. After this, an additive is introduced into an extruder into the polyethylene terephthalate polymers using a reactive carrier, which facilitates mixing within the polymeric melt. It is preferable that the reactive carrier is a glycol (for example, polyethylene glycol) having a molecular weight that allows the polyol to be pumped at temperatures close to ambient (i.e. less than 60 ° C) and to be introduced into the polyethylene terephthalate polymers in amounts such that most of the properties of polyethylene terephthalate polymers are not significantly affected. It is important that the polyol reactive carrier is combined with the polyethylene terephthalate polymer in such a way that it is not extractable during subsequent processing operations (eg, the formation of polyester beverage bottles).

As indicated, this invention includes the late addition of various classes of additives through the reactive carrier. Late addition is especially desirable when the additives are volatile or subject to heat degradation. Conventional injection of additives prior to polycondensation, such as during an esterification stage in polyester synthesis, or early during the polycondensation stage, subjects the additives to high temperature conditions (greater than 260 ° C) for several hours. and reduced pressure (less than 1.33 kPa). Consequently, additives that have a significant vapor pressure under these conditions will be lost from the process. It is advantageous that the process of the present invention significantly reduces the time that the additives are exposed to high polycondensation temperatures.

Preformed heating rate enhancers, friction reducing additives, stabilizers, inert particulate additives (eg clays or silica), colorants, antioxidants, branching substances, oxygen barrier substances may be included in the additives according to the present invention. , carbon dioxide barrier substances, oxygen scavengers, flame retardants, substances for regulating crystallisation, re

ES 2 223 958 T3 acetaldehyde ductors, impact modifiers, catalyst deactivators, melt strength enhancers, antistatic substances, lubricants, chain extenders, nucleating substances, solvents, fillers and plasticizers.

In a preferred embodiment, the additive is an ultraviolet (UV) absorber. As understood by those familiar with polyester packaging, UV absorbers protect polyethylene terephthalate polymers and package contents from UV degradation.

In another preferred embodiment the additive is an inert particulate additive, it being preferable that it be talc (i.e., natural hydrated magnesium silicate of the representative formula 3MgO 4SiO₂ H₂O) or precipitated calcium carbonate. The inert particulate additive is introduced in low concentrations (i.e., approximately 20 and 200 ppm based on the combined weight of the condensation polymers, reactive carrier, and particulate inert additive) to ensure that bottles formed with condensation polymers possess characteristics reduced friction. Furthermore, the inert particulate additive, which is preferably surface treated to minimize haze formation in the bottles, preferably has an average grain size of less than about ten microns, and more preferably less than two microns. As described in commonly assigned and co-pending US patent application. Serial number 09 / 38.619, bottles made from polyethylene terephthalate condensation polymers have better frictional characteristics that reduce, and can eliminate, the need to apply external lubricants to polyester bottles during filling operations .

In another preferred embodiment, the additive is an exfoliated clay nanocomposite, which enhances the gas barrier properties in films and containers.

It is preferable that the nanocomposites are in the form of lamellae with a thickness of between about 6 and 15 angstroms.

As those skilled in the art will know, polymerization catalysts increase polymerization rate and thus productivity. Unfortunately these same catalysts will degrade, over time, the thermostability of the polymeric resin. Thus, in yet another embodiment, the additive carried by the reactive carrier is a catalyst stabilizer and, more typically, an extra catalyst stabilizer. In this regard, while phosphorus-containing stabilizers are preferred, any stabilizer that can deactivate the polymerization catalyst can be introduced through a reactive carrier. In general, the stabilizer must not be reactive with the polymer and must have low residual moisture.

In US Patent Application Serial No. 09 / 738,150 it is explained that near completion of the polycondensation reaction of the polyethylene terephthalate, the catalyst begins to form acetaldehyde and causes discoloration or yellowing of the polyethylene terephthalate. Therefore, as explained herein, "thermally stable polyester" refers to polyester having a low acetaldehyde content, low discoloration, and high molecular weight retention despite exposure to high temperatures.

Acetaldehyde is an unacceptable by-product of the degradation of polyethylene terephthalate. This is a particular concern in the food and beverage industry because acetaldehyde, even in minute amounts, adversely affects the taste of the product. Furthermore, it is typical that polymer degradation will cause undesirable discoloration or yellowing. For this reason it is preferred to add a stabilizer containing phosphorus to the polymeric melt.

Advantageously, the late addition of the stabilizer to the polymer melt and then again to an extruder prevents the stabilizer from inhibiting ("cooling") the polymerization catalyst during the polycondensation reaction. This increases the production efficiency of continuous polyethylene terephthalate processes. Furthermore, since the stabilizer is added before processing the polymer, the stabilizer can adequately prevent discoloration and degradation of the polyethylene terephthalate polyester.

Finally, it should be noted that since the melting and extrusion stages in the formation of condensation polymers are carried out at elevated temperatures (for example, usually greater than 260 ° C for polyethylene terephthalate), it is important that the condensation polymers are thermostable. Therefore, the stabilizer additive has to be properly mixed with the polymer melt to deactivate the polymerization catalysts. The reactive carrier facilitates the incorporation of the stabilizer into the polymeric resin.

Typical embodiments of the invention have been described in the specification and drawings. The scope of the invention is set forth in the following claims.