MXPA00012792A - Process for crystallising polyethylene naphthalate copolymers in the absence of a devolatilization step - Google Patents

Abstract

The present invention provides a process for crystallising polyethylene naphthalate copolymer in the absence of a devolatilization step comprising:a) copolymerising carboxylic acids made up of at least 60 mole%of 2,6-naphthalene dicarboxylic acid;withpolyols comprising at least 80 mole%ethylene glycol and from 2 to 20 mole%of a polyol having three or more carbon atoms, based on the total moles of polyols, to form PEN copolymer solids;and b) subsequently crystallising said solids comprising heating said solids to at least their sticking temperature at an average rate of at least 10°C/min, to form agglomerate-free crystallised solids. In another embodiment of the invention, there is provided a process wherein said crystallising solids are subsequently solid state polymerised.

Description

PROCESS TO CRYSTALLIZE POLYETHYLENNAFTALATE COPOLYMERS IN THE ABSENCE OF A STAGE OF DEVELOPMENT FIELD OF THE INVENTION The invention relates to a process for crystallizing copolymers of polye ti lennaft alato in the absence of a devolatilization step.

BACKGROUND OF THE INVENTION High molecular weight polyesters are commonly produced from low molecular weight polyesters of the same composition, by solid state polymerization. The low molecular weight polyesters that are used in those solid state polymerizations are generally prepared by conventional melt polymerizations. Solid state polymerization is generally considered advantageous because the handling of high molecular weight molten polymers and REF .: 126080 ultra high viscosity, during the polymerization phase. The thermal degradation is also essentially avoided during the solid state portion of the polymerization. The low molecular weight polyesters used in the solid state polymerizations are generally in the form of pellets or chips. These pellets can vary greatly in size; however, as a general rule, the smaller the size of the polyester pellets, the faster the solid state polymerization will be carried out. Very fast solid state polymerization rates can be achieved using polyesters which are in the form of porous pills. Most thermoplastic polyesters, including polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), produced by melt phase polymerization, are almost completely amorphous in nature. Those amorphous polyesters which are prepared by polymerization in the molten state are normally converted from the amorphous state to the crystalline state, before the polymerization in the solid state to raise their adhesion temperature. This is done to prevent the pellets or polyester chips from adhering to each other as a solid mass, during the polymerization in the solid state. When an amorphous polyester is heated from room temperature to approximately its vitreous transition temperature (Tg), it will soften and become sticky before it begins to crystallize. The adhesion temperature of an amorphous polyester is usually about 20 ° C above its Tg. The crystallization rate of the polyester will not be fast enough to be practical until its temperature is further raised to about 30 ° C above its adhesion temperature. To achieve the maximum crystallization rate, the temperature of the polyester must rise even more. For example, PET has a Tg of 74 ° C and an adhesion temperature of about 95 ° C. The crystallization rate of PET is quite low until the temperature rises above 125 C, and in practice, PET usually crystallizes at temperatures between 150 ° C and 190 ° C. PEN has prong properties for fiber and packaging applications. The PEN has a Tg of about 118 ° C and a crystalline melting point Tm of 268 ° C. It exhibits a peak of crystallization between 180 ° C and 220 ° C. Its adhesion temperature is about 140 ° C when it is in the amorphous state. According to conventional knowledge, the best crystallization temperature range for the PEN polymer would be between 180 ° C and 220 ° C. During the crystallization process, the PEN polyester undergoes an adhesion step. This takes place within the period of time in which the temperature of the polyester exceeds the adhesion temperature (softening) and the time in which the polyester becomes well crystallized. To mitigate the agglomeration and the clumping effect when the PEN polyester pellets raise their temperature from the adhesion temperature to their crystallization temperature, the commercial scale crystallizers, for the continuous crystallization of the polyester, can be equipped with means for providing vigorous stirring. In a batch process, a rotating container of variable speed and variable temperature can be used. With respect to PET polyester polymers, two types of continuous crystallizers have been widely used, especially stirred vessels and fluidized beds. Hitherto, in the continuous crystallization process of the particulate polyesters, the PET in particular, the polyester pellets are loaded at room temperature directly into the crystallizer, without any pretreatment. The heat transfer medium in a crystallizer used in a continuous process, is generally hot air, hot nitrogen, or hot oil, to subject the polyester pellets to a rapid rate of temperature increase and maintain a constant temperature of crystallization. . Under appropriate operating conditions, the PET polyester pellets can crystallize without forming lumps or ^^^ ¡^ agglomeration. However, unlike PET pellets, when PEN pellets are exposed to crystallization conditions where the rate of temperature increase towards the crystallization temperature rises rapidly, the pellets will "jump like popcorn" to the pellets. suffer a rapid and sudden expansion when heated near the crystallization temperature. The swollen films of the pellets are very adhesive and, in a few seconds, the pellets agglomerate compactly into large lumps, regardless of whether there is vigorous agitation. The phenomena of behavior similar to that of popcorn, indicate that these conventional PET crystallization processes, in which the speed of the temperature increase in a crystallizer is high, are not convenient when it is desired to crystallize polyesters of PEN in a production large-scale commercial The sudden expansion of the PEN pellets during the increase of the heating in the crystallization can be due to the total internal vapor pressure of the volatile material (such as water) that is inside the pellet, which exceeds the atmospheric pressure when the pellet temperature reaches the softening point of the PEN pellet. Once the pellet softens, the pressurized volatile materials within the pellet can escape and diffuse from the PEN pellet. Since the softening point of the PEN is above of the boiling point of the moisture trapped within the pellet, the increase in vapor pressure of the volatile components inside the pellet exceeds the atmospheric pressure, while the morphology, structure, and / or barrier properties, of the pellet, remain intact. Without an escape route, such as through diffusion through a softened pellet, the volatilized materials swell the pellet when the point at which the pellet is soft enough to deform is reached. The behavior effect similar to that of popcorn, is not observed in the PET pellets because the Tg and the «Atfea» atefa.

PET softening point are generally below the boiling point of water. Accordingly, the vapor pressure of the internal moisture within the pellet does not undergo a change to increase and exceed the atmospheric pressure. Since the PET pellet softens before the vapor pressure of the moisture inside the pellet exceeds the atmospheric pressure, moisture can escape (diffuse) from the softened pellet, when the temperature reaches the boiling point of the water. The sudden expansion of PEN pellets during the increase of heating to crystallization is discussed in US Pat. No. 4,963,644. According to this patent, the cause of the sudden expansion of PEN pellets, during crystallization, was investigated by subjecting a pellet of PEN to a DTA scan. His DTA thermogram showed an endother near the beginning of the crystallization exotherm. It was believed that the endotherm arose from the sudden vaporization and / or sudden release of the volatile components, whose total internal vapor pressure exceeded atmospheric pressure, trapped inside the pellet when the PEN softens close to its crystallization temperature. This phenomenon explained the sudden expansion of PEN pellets when exposed to standard crystallization temperatures, from 180 ° C to 220 ° C. The volatile material entrapped within the PEN pellets arose from a number of different sources, such as from contaminants that entered the process during the melt polymerization, or the formation of by-products generated during the melt polymerization. Due to the higher temperature at which the melt of the PEN polymer is maintained during the polymerization in the molten state, compared to the temperature at which the PET is maintained during the polymerization in the molten state, the number and amount of by-products generated in the molten state. the polymerization in the molten state of the PEN is greater than in the polymerization in the molten state of the PET. The degradation of PEN could generate water, ethylene glycol, acetaldehyde and the like. to "--.

Due to the very high melt viscosity of the PEN, these byproducts are difficult to remove during the formation of the pellets. In addition, PEN pellets are often formed under nitrogen pressure. In this case, nitrogen could also be trapped inside the pellets. PET, on the other hand, generates fewer byproducts, is more stable in its molten state, and its viscosity in the molten state is lower than that of PEN. The amount of by-products generated in the PET is relatively smaller and these are removed more easily during the formation of the pellets. Therefore, very little volatile material is trapped inside the PET pellets to cause lumping and adhesion problems during crystallization. The solution proposed in US Pat. No. 4,963,644 for the problem of clumping and adhesion, of PEN pellets, during crystallization, was to slowly remove the volatile components trapped inside the pellets, at temperatures below their temperature of adhesion, before the crystallization stage. This process incorporated a devolatilization step before the crystallization step. This patent requires a devolatilization step that involves (1) heating the amorphous polyethylenenaphthalate to a temperature that is within the range of 80 ° C to 140 ° C, in the presence of an inert gas stream or under vacuum, to desvolat i i the amorphous polynephthalate; Y (2) Subsequently heating the devolatilized polyethylenenaphthalate to a temperature in the range of 150 ° C to 260 ° C while stirring to produce the crystallized polyethylenenaphthalate. It would be desirable, in order to improve the process speed, to find a way to avoid the need to subject PEN pellets to the slow devolatilization stage, without sacrificing the advantage of reducing the tendency of the pellets to lump together and produce a large mass. It would be desirable to rapidly heat the PEN pellets during the heat increase phase, in a crystallization stage comparable to the rapid heating of the PET pellets in crystallizers, such as in fluidized or stirred bed crystallizers, without experiencing the effect similar to that of production of corn popcorn.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a process for crystallizing polyethylene terephthalate copolymer, in the absence of a devolatilization step, comprising: (a) copolymerizing the carboxylic acids composed of at least 60% mole of acid 2,6-naphthalenedicarboxylic acid; with polyols comprising at least 80% mol of ethylene glycol and 2 to 20% mol of a polyol having three or more carbon atoms, based on the total moles of the polyols, to form copolymer solids of PEN; and (b) subsequently crystallizing the solids, which comprises heating said solids to at least their adhesion temperature, at an average velocity of at least 10 ° C / minute, to form crystallized solids free of agglomerates. In another embodiment of the invention, a process is provided wherein the solids that crystallize subsequently polish in the solid state. The process of the present invention avoids the need to carry out the devolatilization step, as described in US Patent No. 4,963,644, wherein a stream of inert gas must be passed through the pellets, for a period of time effective to remove volatile compounds at a temperature below the adhesion point of the pellets, or the pellets are subjected to vacuum.

DETAILED DESCRIPTION OF THE INVENTION In the International Publication WO90 / 03993 a composition of PEN copolymerized with 2,7-naphthalenedicarboxylic acid, diethylene glycol has been described., 1,4-cyclohexanedimethanol, isophthalic acid or terephthalic acid. This publication describes the modification of PEN with one of these monomers to reduce the melting point of PEN and allow it to be processed more easily by injection molding and stretch blow molding, by blow molding with stretch and reheat or by molding by blowing and extrusion. This publication does not mention anything regarding the processing techniques used to crystallize the PEN polymer, and nothing further states that conventional polymer processing techniques can be used to make the described polyester. This publication found that all the comonomers described worked well in their process, which was related to the reduction of the melting point of PEN. With respect to the crystallization of PEN pellets, the known and / or patented techniques, used to crystallize the PEN, involve the removal of the moisture trapped inside the pellet, by slowly heating the pellets to their adhesion temperature, to sufficiently dry the pellets and to avoid a significant amount of swelling under agitation, or to subject the pellets to a vacuum or an inert gas stream, in a discrete devolatilization stage, for a period of time below their point of adhesion. Each of these processes are inadequate because they reduce the speed of processing. However, a process comprising rapidly heating to the point of adhesion, of the PEN copolyester, was unexpectedly discovered by subjecting a copolymerized PEN with an alkylene glycol different from ethylene glycol, such as diethylene glycol, upon rapid heating, without suffering the disadvantage of formation of lumps or agglomeration. Other comonomers, such as terephthalic acid, described in WO90 / 3993, equally useful to diethylene glycol to reduce the melting point of PEN, failed to provide the PEN copolymer, useful, in a present process for rapid heating without experience the formation of lumps and agglomeration, including low agitation. The polyethylenenaphthalate copolymer (PEN copolymer) used in accordance with the present invention is typically prepared by standard melt polymerization techniques, either in a continuous or batch process. These polymerizations in the molten state result in the formation of a PEN copolymer which is essentially amorphous in nature. This is intended to imply that the PEN copolymer is virtually completely amorphous, although it may contain small regions where there is no origin. The PEN copolymer is generally produced by melt-stirring carboxylic acids composed of at least 60 mol%, preferably at least 80 mol%, and more preferably from 85 to 100 mol%, most preferably from 90 to 100% mol, of naphthalenedicarboxylic acid; with polyols comprising at least 80% by mol of ethylene glycol, preferably 90% by mol to 96% by mol, and 2% by mol to 20% by mol of a polyol having three or more carbon atoms, each based on the total moles of polyols. By "acid" or "dicarboxylic acid", when used with reference to a polyester monomer, it is meant that it is the free acid monomer, its lower alkyl esters, and other derivatives thereof that can be made reacting with a glycol, to produce repeated units of naphthalic ester bonds, such as the anhydrides or acid halides of these acids. However, many conventional melt polymerization processes employ the free acids, thereby avoiding the need to remove the lower alcohol by-products from the reaction mixture. In preferred embodiments, the naphthalenedicarboxylic acid comprises a 2,6-naphthalenedicarboxylic acid. Generally, the amount of 2,6-naphthalenedicarboxylic acid will vary from 85% mol to 95% mol, based on the moles of the acid. The naphthalate units are beneficial in improving the gas barrier properties of polyesters. Other types of dicarboxylic or polycarboxylic acids can be copolymerized with the naphthalenedicarboxylic acid. An example of this additional acid is terephthalic acid, which can be added in an amount of about 4 mol% to 40 mol%, based on the weight of all the polymerizable carboxylic acids. Since it is preferred to keep the number of naphthalate units high, the preferred amount of the additional dicarboxylic or polycarboxylic acid, preferably the dicarboxylic acid, ranges from 4 to 15 mol% based on the total moles of polymerizing acids, more preferably preferably from 5 to 10% by mol of terephthalic acid. Other examples of carboxylic acids include isophthalic-dicarboxylic, succinic-dicarboxylic, adipic-dicarboxylic, 1/4-cyclohexanedicarboxylic and 1,3-cyclohexanedicarboxylic, suberic-dicarboxylic, glutaric-dicarboxylic acids, sebacic-dicarboxylic, 1, 12 -dodecane-di carboxy 1 i co. The combination of the polyol having 3 or more carbon atoms during the copolymerization of the PEN is necessary to avoid the devolatilization step and produce crystalline solids without agglomerates. The amount of the polyol having 3 or more carbon atoms, preferably ranges from 2% by mol, more preferably 3% by mol to 20% by mol, more preferably 10% by mol, most preferably up to 7% by mol , based on the total moles of polyols. Suitable types of polyols having 3 or more carbon atoms are the aliphatic, cycloaliphatic and aromatic diols, and the higher polyols with hydroxyl functionality, which include the glycol ethers. The polyol having 3 or more carbon atoms may or may not contain a heteroatom (s) such as oxygen or nitrogen, in the main chain of the molecule. Examples of polyols having 3 or more carbon atoms are diethylene glycol, dipropylene glycol, 1,4-dihydroxyethoxybenzene, trimethylene glycol, tetramethylene glycol, neopentyl glycol, propylene glycol, 1,3-propanediol, triethylene glycol, 2,4-dimethyl-2-. ethylhexan-1, 3-diol, 2-ethyl-2-butyl-l, 3-propanediol, 2-ethyl-2-isobutyl-1, 3-propanediol, 1,3-butylamino, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-, 1,3- and 1,4-cyclohexanedimethylene, 2,2,4,4-tetramethyl-1,3-cyclobutyl andiol, 1,4 -xi 1 i lendiol, trimetheiloletane, 1, 2, 6-hexantriol, alpha-methyl glucoside, glycerin, sucrose, trimethylolpropane, sorbitol, pent erythritol, and the higher molecular weight polyoxyalkylene polyether adducts, manufactured react these polyols with alkylene oxides. Preferably the polyol having three or more carbon atoms will have from 3 to 12 carbon atoms, and more preferably from 3 to 8 carbon atoms, and is a diol or triol. Examples of the most preferred diols and triols having from 3 to 8 carbon atoms are trimethylene glycol, or tetramethyl ene, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,3-propanediol, triethylene glycol, 2,4-dimethyl-2-. ethylhexan-l, 3-diol, 1,3-butanediol, 1,4-butanediol, 1/5-pentanediol, 1,6-hexanediol, 1,2-trimethylolethane, 1, 2, 6-hexantol, glycerin, and trimethylolpropane. The intrinsic viscosity (IV) of the PEN copolymer is not limited. The PEN copolymer will generally have an initial, intrinsic starting viscosity of at least about 0.2 dl / g measured in a phenol: tetrachloroethane solvent system, 60:40 at a temperature of 30 ° C and at a concentration of 0.4 g / dl. The amorphous PEN copolymer will preferably have an initial intrinsic viscosity or starting viscosity, from 0.3 to 0.7 dl / g. The amorphous PEN copolymer will, more preferably, have an initial intrinsic viscosity of 0.4 to 0.5 dl /? F. The glass transition temperature (Tg) of the PEN copolymer is also not limited. In general, the Tg of the copolymer is above 100 ° C and will often vary from 105 ° C to 130 ° C. Preferably the Tg of the copolymer varies from 115 ° C to 125 ° C. In the process described in the Patent No. 4,963,644, the devolatilization step comprising heating the PEN prepolymer to a temperature below the adhesion temperature of the PEN prepolymer (from 80 ° C to 140 ° C) in the presence of an inert gas stream or under a vacuum to devolate the copolymer of PEN amorphous, for a period of time (typically one to four hours) sufficient to remove most volatile materials, such as water, ethylene glycol, acetaldehyde, etc., from the PEN copolymer. This step is now eliminated in the process of this invention. The PEN copolymer can be added directly to a crystallizer, heated to a temperature through the range of 150 to 260 ° C, where the temperature rise of the PEN copolymer grows at a fast average speed of at least 10 ° C. / minute at least up to the point of adhesion of the PEN copolymer. The average temperature increase of the pellets, of at least 10 ° C / minute, is measured through the heating cycle, from the temperature at which the pellets are introduced to the crystallizer, to the adhesion temperature of the PEN copolymer . To take full advantage of the processing speeds, the average temperature rise of at least 10 ° C occurs up to 150 ° C, and more preferably up to the crystallization temperature of the PEN copolymer. In another embodiment, the average rate of temperature increase to the point of adhesion of the PEN copolymer is at least 15 ° C / minute, and more preferably at least 18 ° C. Since the PEN copolymer is not devolatilized in accordance with the process described in US Patent No. 4,963,644, its content of volatile components when introduced to the crystallization stage, can advantageously be at least substantially the same or greater than the content of volatile components in the solidification, upon completion of the melt polymerization step. In other words, the PEN copolymer solid does not need to be treated, such as by drying or devolatilization, to reduce the content of volatile components between its solidification, at the end of the melt polymerization stage, and the crystallization step. The volatile components are defined as any agent that is within the PEN copolymer, which vaporizes at temperatures below the adhesion temperature of the PEN copolymer under atmospheric pressure. Typical volatile components include water, ethylene glycol, acetyl aldehyde, and nitrogen. In general, the volatile component content of the PEN copolymer solids is within the range of 0.1% to 0.7%. The exact content of the volatile components will vary depending on the purity of the knitting monomers and the stability of the conditions of polymerization in the molten state, as well as the environmental conditions of pellet formation, to which the pellets are exposed, which also vary from station to station. The process of the invention is particularly useful for the crystallization of pellets having high contents of volatile components, such as 0.2% in weight or more. The PEN homopolymer pellets, which have not undergone devolatilization or which have not been dried for significant periods of time, suffer a expansion and swelling, significant, which is visible to the naked eye at the end of crystallization, resulting in an agglomerate that is not broken to produce the individual pellets, in many cases, even when subjected to agitation. However, during and at the end of the crystallization step, pellets of the PEN copolymer, as described herein, will not agglomerate, and in most cases, do not there is expansion or swelling of pellets at a glance. It is usually preferred to carry out the crystallization at a temperature which is within the range of 160 ° C to 220 ° C. Typically it is more preferred that the crystallization temperature is within the range of 170 ° C to 200 ° C. Although agitation is not necessary to prevent agglomeration of the PEN pellets into an inseparable mass, it is preferred to stir the PEN solids during the crystallization step, to reduce their potential to form lumps. The preferred form of agitation can be provided using a crystallizer having a fluidized bed. In those fluidized bed crystallizers, air or an inert gas is typically allowed to flow through the crystallizer at a sufficient rate to keep the chips or pellets in the fluidized state. Of course, it is also possible to carry out the crystallization step in a stirred vessel. The crystallization step can be carried out as a continuous operation or in batches. The optimal period of time, ... t i * ¿* £ *. required for crystallization, is dependent on the equipment used, the type of PEN copolymer, and the size and shape of the pellets or chips. The time required for the crystallization will typically be within the range of 1 minute to 4 hours. In a continuous process, the crystallization step will usually take from 2 minutes to 30 minutes, preferably from 2 minutes to 10 minutes. He The PEN copolymer will usually be subjected to crystallization conditions until the solids achieve a degree of crystallinity of 15% or more, more preferably 20% or more. Regardless of the residence time in the crystallizer, whether in a continuous or batch process, the average rate of increase of heating, will be as described herein, until the temperature reaches at least the pellet adhesion temperature of PEN copolymer, after which any heating increase profile can be employed. After the PEN copolymer has crystallized, it can be polymerized in solid state in a batch process or .- L a - 'l StÉ? Tt YES * \ continuous. Appropriate solid state polymerization temperatures may vary from a temperature just above the threshold temperature of the polymerization reaction to a temperature within a few degrees of the adhesion temperature of the PEN copolymer, which may be very high. below its melting point. The solid state polymerization temperature, used, will typically be 1 ° C to 50 ° C below the melting point of the crystallized PEN copolymer. The optimum reaction temperature in solid state will differ somewhat for polymers of different composition or degree of polymerization. As a general rule, the optimum solid state polymerization temperature, for the PEN copolymer, will be 5 ° C to 20 ° C below its melting point. For example, in the solid state polymerization, of the crystalline PEN copolymer, the temperature employed will normally vary from 210 ° C to 265 ° C. Generally, the crystalline PEN copolymer will be polymerized in the solid state at a temperature of 230 ° C to 265 ° C. In most cases, the PEN copolymer is ¿Fe-si- é will polymerize in a solid state at a temperature of 240 ° C to 260 ° C. As the solid state polymerization of the PEN copolymer continues, its adhesion temperature can be increased. In this way, the polymerization temperature in the solid state can increase increasingly during the course of the polymerization. For example, U.S. Patent No. 3,718,621 describes such a technique in the solid state polymerization of PET. The polymerization in the solid state is carried out under vacuum in the presence of a stream of an inert gas. Normally, those solid state polymerizations are carried out in the presence of an inert gas stream. It is highly desirable that the inert gas flows uniformly through the solid state polymerization zone, which is filled with the polyester being polymerized. In order to assist in ensuring that the inert gas flows homogeneously or uniformly through the solid state polymerization zone, without being bypassed by certain areas therein, a device is generally used to disperse the inert gas. In this way, a good polymerization reactor will be designed in such a way that the inert gas flows homogeneously through the polyester found therein. It will be noted that the inert gas actually flows around the polyester pellets or chips as it flows through the polymerization zone in the solid state. Some inert gases suitable for use in the solid state polymerization process of this invention include nitrogen, carbon dioxide, helium, argon, neon, krypton, zenon, and certain industrial waste gases. Various combinations or mixtures of different inert gases can also be used. In most cases, nitrogen will be used as the inert gas. In a continuous process the mass flow ratio of the PEN copolymer to the nitrogen gas will be in the range of 1: 0.25 to 1: 1. The solid state polymerization reactor employed may have a fixed bed, a static bed, a fluidized bed, or a moving bed. In most cases it is preferred to use a cylindrical polymerization reactor in which the PEN copolymer flows through the reactor for the desired residence time. These cylindrical reactors have a substantially uniform cross section and a sufficient height to allow the PEN copolymer to flow by gravity, from the top to the bottom of the reactor, at the desired residence time. In other words, the PEN copolymer moves from the top to the bottom of that cylindrical polymerization reactor in a partially dammed state. The flow velocity through that reactor can be controlled by regulating the discharge at the bottom of the reactor. It is generally preferred to allow an inert gas to flow countercurrently (upstream) through the reactor at a gas velocity well below the point of turbulence, such that the pellets or chips of the PEN copolymer do not fluidize (which always stay in contact with each other). The pellets or chips of the PEN copolymer remain substantially in the same physical form through the solder polymerization process. The PEN copolymer will polymerize in the solid state for a sufficient time to increase its molecular weight or intrinsic viscosity to that of the desired high molecular weight PEN copolymer resin. It will be desirable that the high molecular weight PEN copolymer resin be prepared to have an intrinsic viscosity of at least 0.5 dl / g. In most cases the high molecular weight resin will have an intrinsic viscosity of at least 0.65 dl / g and for some applications it will preferably have an intrinsic viscosity of at least 0.8 dl / g. The necessary polymerization time will normally vary from 1 to 36 hours and in most cases it will vary from 6 to 24 hours. This invention is illustrated by the following examples which are solely for the purpose of illustration and are not to be construed as limiting the scope of the invention or the manner in which it may be practiced. Unless otherwise specified or indicated, all parts and percentages are given by weight.

Comparative Example 1 In each example, the crystallizer used was a stirred fluidized bed of a glass tube with a diameter of 3.18 centimeters (1.25 inches) and a length of 50.8 centimeters (20 inches). The crystallizer has a cone-shaped bottom to which a supply pipe for purge gas (air or heated nitrogen) has been adapted. During the crystallization test, two thirds of the length of the crystallizer was immersed in a bath of hot, transparent oil, whose temperature was controlled at 180 ° C and a stream of nitrogen was passed, preheated to 180 ° C, to through the crystallizer, at an expense of 0.45 m3 per hour (16 standard cubic feet per hour). A metal rod was used to stir the pellets that were to crystallize. The residence time of the crystallization, in each case, was 15 minutes. The average speed of the temperature increase, from the temperature of the pellets introduced to the crystallizer (environment) to the time in which the pellets reached their addition temperature, was at least 10 ° C / minute. Although the crystallizer used was a fluidized, batch, simple bed, it is capable of projecting the difficulty or ease with which the polyester pellets crystallize into continuous crystallizers on a commercial scale. Five grams of polymerized PEN homopolymer pellets were charged in the molten state, which had an intrinsic viscosity of 0.47 dl / g, a Tg of 120 ° C, a melting point of 270 ° C, and a moisture content of 0.54% , to the crystallizer whose temperature was maintained at 180 ° C. In a short time, when the temperature of the PEN pellets reached the softening temperature, they visibly swelled and agglomerated into a compact lump that could not be separated, even under agitation.

Comparative Example 2 Crystallized in the same manner as in Example 1, 5 grams of pellets of PEN / T, 95/5 copolymer, polymerized in molten state (95% by mol of reacted naphthalenedicarboxylic acid and 5% by mol of terephthalic acid reacted, each based on the moles of all the polymeric acid monomers). These PEN / T copolymer pellets had an intrinsic viscosity of 0.45 dl / g, a Tg of 119 ° C, a melting point of 262 ° C, and a moisture content of 0.47%. Again, visibly, the pellets swelled and agglomerated into a compact lump that could not be separated after crystallization.

Comparative Example 3 Crystallized in the same manner as in Example 1, 5 grams of pellets of PEN / T, 95/10 copolymer, polymerized in the molten state, having an intrinsic viscosity of 0.46 dl / g, a Tg of 118 ° C , a melting point of 255 ° C and a moisture content of 0.28%. During crystallization, the pellets expanded substantially and tended to form lumps, but agglomeration was prevented, albeit with difficulty, by agitation. After 15 minutes of crystallization, pellets were obtained in the form of a bead.

E j us 4 Approximately 5 grams of melt polymerized PEN copolymer pellets, prepared by the addition of 5 mol% of diethylene glycol to the ethylene glycol precursor, based on the moles of all the hydroxyl-functionalized, polyester-containing compounds, were cut into the shape of cylindrical pellets. The PEN / DEG copolymer had an intrinsic viscosity of 0.446 dl / g, a Tg of 120 ° C, and a DSC melting point of 260 ° C. The pellets prepared had a moisture content of 0.13%. Approximately 5 grams of these pellets, without some previous treatment for the desvolat. The reaction was crystallized in the same manner as in Example 1. During and after the crystallization, the swelling or expansion of the pellets was not visibly observed, and the agglomeration of the pellets was prevented with to . l t í ¿-a ^ aa-áS: .. agitation. Well-crystallized pellets, with normal appearance, were obtained in 15 minutes of the crystallization cycle.

E xemployment 5 The same PEN / DEG copolymer, such as the one prepared in Example 4, was exposed to ambient atmospheric humidity so that it absorbed more water in the pellets. One week later, the moisture content in the pellets was increased up to 0.20%. These pellets with higher moisture content crystallized in the same manner as in Example 1. Again, no swelling or visible expansion was observed during crystallization and at the end of it. Well-crystallized pellets with normal appearance were obtained. 20 Example 6 The same PEN / DEG copolymer, as prepared in Example 4, was wetted in water at room temperature to maximize the content ^^^ ¡¡¡¡¡¡¡¡^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^ ^ ^^^^^^^^^^^^^^^ ¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡moisture. One week later, the moisture content increased to 0.52%. These pellets were then crystallized in the same manner as in Example 1. During the crystallization, there was slight expansion of certain pellets and the pellets were somewhat stickier, but the formation of lumps and agglomeration was prevented even with stirring. Again, well-crystallized pellets were obtained, although some of the crystallized pellets were slightly deformed. There are many advantages associated with the process of this invention. As previously mentioned, if conventional PEN pellets are used, they tend to expand and agglomerate resulting in stoppages in the process. If PEN pellets are devolatized first, this adds a process step that increases the cycle time, and in some cases, adds equipment. This invention eliminates those problems. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (9)

1. A process for crystallizing copolymers of polyethylene phthalate, in the absence of a devolatilization step, characterized in that it comprises: a) copolymerizing carboxylic acids composed of at least 60% by mol of 2,6-naphthalenedicarboxylic acid; with polyols comprising at least 80% by mol of ethylene glycol and from 2 to 20% by mol of a polyol having three or more carbon atoms, based on the moles of total polyols, to form copolymer solids of PEN; and b) subsequently crystallizing those solids by heating said solids at least at their adhesion temperature, at an average velocity of at least 10 ° C / minute, to form crystallized solids free of agglomerates.

2. The process according to claim 1, characterized in that the amount of 2,6-naphthalenedicarboxylic acid is at least 80% mol.

3. The process according to claim 2, characterized in that the amount of polyol having 3 or more carbon atoms, varies from 3 to 10 mol%.

4. The process according to claim 1 or 3, characterized in that the polyol having three or more carbon atoms comprises diethylene glycol, dipropylene glycol, triethylene glycol, triethylene glycol 1 or triethylene glycol.

5. The process according to claim 4, characterized in that the polyol having three or more carbon atoms comprises diethylene glycol.

6. The process according to claim 1, characterized in that the content of volatile components within the solids, immediately before step b) varies from 0.1 to 0.7%.

7. The process according to claim 1, characterized in that the solids are heated at an average speed of at least 15 ° C / minute.

8. The process according to claim 1, characterized in that the intrinsic viscosity of the copolymer varies from 0.3 to 0.7 dl / g before crystallization.

9. The process according to any of claims 1 to 8, characterized in that the solids that crystallize are subsequently polymerized in soldered state. a-ai i l t JÉÉ-Mia PROCESS FOR CRYSTALLIZING POLYETHYLENNAFTALATE COPOLYMERS IN THE ABSENCE OF AN E APA DEVELOPMENT SUMMARY OF THE INVENTION The present invention provides a process for crystallizing polyethylene-naphthalate copolymer in the absence of a devolatilization step, comprising: a) co-polymerizing carboxylic acids composed of at least 60 mol% of 2,6-naphthalenedicarboxylic acid; with polyols comprising at least 80% in mol of ethylene glycol and from 2 to 20% in mol of a polyol having three or more carbon atoms, based on the moles of total polyols, to form solids of PEN copolymers, and b ) subsequently crystallizing the solids, which comprises heating the solids to at least their adhesion temperature, at an average velocity of at least 10 ° C / minute, to form crystallized solids free of agglomerates. In another embodiment of the invention, a process is provided wherein the solids that crystallize are subsequently polymerized in the solid state.