A PROCESS AND APPARATUS FOR FORMING CRYSTALLINE POLYMERIC MICROSPHERESFIELD OF THE INVENTIONThe present invention relates to a process and apparatus for forming a particulate polymer. More particularly, this invention relates to a process and apparatus for forming uniform, crystalline microspheres, from an amorphous polyester melt material.
BACKGROUND OF THE INVENTIONThe formation of the particles from viscous materials is well known. Conventional methods and apparatuses frequently involve the formation of liquid or droplet portions which are subsequently collected and solidified. For example, Froeschke, in U.S. Pat. No. 4,279,579, describes an apparatus for the extrusion of a mass that can flow on a conveyor device. The device has internal and external cylindrical coaxial containers. The inner container, placed inside the inner container, has a passage for the distribution of the mass that can flow. The external container has several holes and rotates around the REF: 25175 internal container. When the outer container rotates, the holes on the outer container align cyclically with the passageway on the inner container. With each alignment, the mass that can flow flows from the inner container, through the aligned orifices, and is distributed and deposited on a conveyor device, for example a conveyor belt, to form what is frequently referred to as pellets. Chang et al, in U.S. Pat. No. 5,340,509, discloses a pelletizing or pelletizing process for converting ultra-high melt flow crystalline polymers into microspheres, ie, a crystalline polymer which is a polyolefin homopolymer, a polyolefin copolymer, or mixtures thereof. Initially, the molten polymer is transferred to a droplet forming medium. The droplet forming means is generally an external container, with orifices, which rotates around an internal container to allow a uniform amount of the polymer to melt to exit as droplets. The droplets are collected on a conveyor device, which cools the droplets for a period of time sufficient to solidify the droplets.
The formation of uniform, robust microspheres of a polyester material has been difficult or problematic. For example, low molecular weight polyesters, characterized as oligomers or prepolymers, may have such low viscosity that the formation of the initial particle may be difficult. The oligomer may be too liquid to form particles or microspheres of uniform size and shape. This is because the oligomers, which have a relatively short chain length, can have a relatively low amount of entanglements of the chain, in addition to forces or a limited intermolecular junction. Known processes for forming polyester particles can lead to particles which lack structural integrity. The weakness of such particles can make them difficult to handle and susceptible to abrasion during transport or during other mechanical manipulations. Abrasion can generate undesirable amounts of fine materials. The polymer particles are useful as a raw material for a process, to produce a higher molecular weight polymer, including solid phase polymerization ("solid state") processes. For such processes, it is desirable that the particles have certain characteristics. For example, particles having a relatively uniform size and shape, for uniform polymerization within each particle, may be desirable. For solid state polymerization, it is desirable that the particles be sufficiently robust to withstand the elevated temperatures of the solid state polymerization without agglomeration. Conventionally, the robust polyester particles can be obtained by subjecting the particles to a prolonged and expensive thermal treatment or to an annealing step. Such annealing increases the crystallinity and robustness of the particles. Such annealing, however, typically adds time and cost to a total process to produce a high molecular weight product. It may be desirable to reduce or eliminate such annealing. In view of the foregoing, there is a need for an improved process and apparatus for the formation of polyester particles. There is a need for a more economical and efficient production of quality polyester particles, which, for example, are useful under stringent circumstances and with limited pretreatment prior to use as a raw material for further polymerization. In addition, there is a need for an improved process for shaping a low molecular weight polyester oligomer into crystalline particles. In addition, there could be an additional advantage if the resulting particles exhibited improved crystalline morphology or related properties compared to conventional processes.
BRIEF DESCRIPTION OF THE INVENTIONThis invention provides an apparatus for producing microspheres of a polymer from its polymer melt material, comprising: (a) a microsphere former comprising a rotating container having a plurality of outlets, defining corresponding openings of 0.5 to 5 mm of diameter, for dosing a polymer melt material on the surface of a conveyor device. (b) a conveyor apparatus comprising a surface, which is adapted for relative movement to the outputs of the microsphere former, to receive the polymer melt material, from the microsphere former, in the form of a plurality of droplets or microspheres crystalline, the conveyor apparatus is adapter for transporting the microspheres through a crystallization section; and (c) a crystallization section extending from the point at which the microspheres are received on the surface of the conveyor apparatus, which extends along at least a portion of the conveyor apparatus to a point downstream; the crystallization section further comprises means for controlling the surface temperature of the conveyor apparatus within a predetermined temperature range above 50 ° C when the surface passes through the crystallization section. In omercial practice, the crystallization section may further comprise a temperature controller for controlling the temperature of the surface within the crystallization section, such that the microspheres are subjected to a surface within a predetermined temperature range for a period of time. predetermined time period. The apparatus described above can have a variety of uses, including the production of microspheres of a polyester polymer having a glass transition temperature (Tg) greater than about 25 ° C. One such process comprises: (a) dosing a polymeric molten material of the polyester polymer through a multitude of outlets in a rotating container, each outlet defining an orifice of 0.5 to 5 mm in diameter, whereby forming a plurality of molten droplets; (b) collecting the molten droplets, immediately after they are formed, on a solid, moving surface, the solid moving surface is maintained within a predetermined temperature range within a heating zone, whereby the microspheres are held in contact with the moving, solid surface, within the heating zone, for a predetermined period of time.
BRIEF DESCRIPTION OF THE DRAWINGSFigure 1 is a schematic view of the preferred process and apparatus for producing polymeric microspheres. Figure 2 is a cross-sectional view of the crystallization section of the apparatus of Figure 1.
DETAILED DESCRIPTION OF THE INVENTIONThis invention provides an apparatus and process for producing low molecular weight polymer particles or microspheres. The polymeric microspheres are produced in a pellet former commonly referred to as a pastillator or pelletizer, and are collected on a hot surface. The hot surface controls the rate at which the microspheres are relatively cooled (from the molten material) and the temperature at which the microspheres are relatively cooled. The microspheres thus formed can have a relatively uniform size and shape. By the term "relatively uniform" is meant that at least 90 percent, by weight, of the microspheres are within 30 percent more / less of the average diameter. Preferably, at least 95 percent, by weight of the particles, are within 10 percent more / less of the average diameter. The present process is capable of producing microspheres that are stronger and more resistant to abrasion than microspheres formed by various other conventional methods and apparatuses. The microspheres are suitable for transport or subsequent treatment by solid state polymerization, with or without additional annealing. One embodiment of the present invention, which includes an apparatus for producing microspheres, is shown schematically in Figures 1 and 2. For the purposes of this invention, the term "microsphere" means any discrete unit or portion of a given material, which has any form or configuration, whether regular or irregular. Accordingly, the term "microsphere" can encompass particles, droplets, pieces, portions, or pellets of a given material. By the term "polymer" is meant a compound or mixture of compounds consisting essentially of repeating structural units called monomers, and is meant to include a prepolymer or an oligomer, i.e., a polymer having a low molecular weight or a polymer proposed as a raw material for a higher molecular weight polymer. By the term "molten polymer" is meant a polymer at a temperature at or above its melting temperature. Similarly, by the term "molten droplet" or "droplet" is meant a portion of a polymer at least partially at a temperature at or above the melting point of the polymer. Accordingly, temperature gradients may exist in the droplet, which may begin crystallization immediately after they are formed. The melting point (Tm) of a polymer is preferably determined as the maximum of the endotherm of the main melt during the first heating, as measured by Differential Scanning Calorimetry (DSC). The size of the microsphere is the largest cross-sectional dimension of a given microsphere. As part of an integrated process, the droplet former may be in communication, by means of a conduit or other means of transferring the material, with a means for producing a polymer in the molten form. A means for producing a polymer melt material can encompass many variations. For example, the medium can be an extruder which uses a polymer in the form of flakes, microspheres or tablets, as a raw material. An extruder can heat the raw material to the melting temperature or at a higher temperature and extrude the extruded polymer in various ways, for subsequent transfer to the droplet former. The means for producing the polymer can also include a reactor for polymerization. Such a reactor is well known in the art. Polymerization is often carried out in the molten material, and therefore melt polymerizers are also suitable as a means to produce the polymer in the form of molten material by this invention. An example of a preferred reactor for producing the polymer melt is described in the application N.S. commonly assigned, co-pending, (record No. CR-9524), incorporated herein for reference in its entirety. Of course, for its use as raw material for the present apparatus and process it is also possible to commercially buy the polymer or store the polymer hech <; ~ previously for subsequent introduction into a medium to produce a molten polymer material. A preferred embodiment of the present apparatus is shown schematically in Figure 1. A microsphere former 10 receives a polymer melt material from a reactor or polymerizer of the molten material (not shown). A conventional molten material polymerizer, if employed, usually has an inlet for receiving the reagent and an outlet connected to a conduit for transporting the polymer melt material to the microsphere former 10. The polymer leaving the outlet is typically at or above its melting temperature. The polymer can be transferred to a microsphere former by any pressure-displacing device such as a variable speed displacement pump or a gear pump for molten material. The microsphere former 10 is commonly referred to as an apparatus for manufacturing pellets or pastillator, in the broadest sense of the word. Various types of apparatus for forming pills are known in the art for various uses. The apparatus for making pills, in one embodiment, can typically comprise internal and external coaxial cylindrical containers. Accordingly, polymeric molten material transferred from the reactor could be received in the inner container or cylinder. The outer container has a plurality of holes spaced circumferentially on the periphery of the outer container. The plurality of the holes are positioned in such a way that they align with a dosing bar or channel on the inner container when the outer cylinder is rotated. The holes on the outer container can vary in size typically from about 0.5mm to 5mm. The inner cylinder containing the polymeric melt materials is under pressure and distributes the molten material in uniform amounts when each of the plurality of the holes on the outer cylinder is aligned with the mud or dosage channel on the inner cylinder. Tabletting apparatuses, as described, are commercially available, for example, ROTOFORMERR manufactured by Sandvik Process Systems (Totawa, NJ). In commercial use, for economic efficiencies of the maximum production, at scale, there may be many holes on the outer cylinder of the apparatus for manufacturing the pellets, typically at least 100, for example, between 100 and 50,000, depending on the scale of the operations. The microspheres can be properly produced on the 1 kg scale. to 10 metric tons per hour, preferably 1 to 10 metric tons per hour. For such an operation, the apparatus for manufacturing the pellets could be adapted to rotate at a speed which is sufficient to supply the microspheres to the conveyor surface at the desired production speed. The droplets or crystallization microspheres18, formed by the tabletting apparatus, are received directly on a moving surface 12 of a conveyor belt, which is substantially level. By "substantially level" it is understood that it does not vary by more than 10 ° from the horizontal. By "moving surface" is meant any surface which can support and transport the microspheres. The moving surface 12 generally moves relative to the tablet making apparatus, in a direction tangential to the direction of rotation of the outer container of the apparatus for manufacturing the tablets. The moving surface 12 has a lower surface 16 and an upper surface 14, the latter comprising a substantially level moving surface which supports the microspheres. The moving surface 12 transports the microspheres through the crystallization section, which can also be referred to as a heating section. The moving surface is generally maintained at a constant speed to pass the microspheres through the crystallization section, although the chosen speed may vary to vary the time that the microspheres are within the crystallization section. A key feature or component of the present apparatus is the crystallization section. The crystallization section begins at or very close to the point at which the microspheres are received from the apparatus 10 to manufacture the pellets on the moving surface and extends along at least a portion of the moving conveying surface. An important feature of the crystallization section of the apparatus is that it includes means for controlling the temperature of the moving surface, when it passes through the crystallization section, at an elevated temperature. Furnaces that contain a heating coil can be used. In the preferred apparatus of the present invention, the temperature of the upper surface 14 within the crystallization section is maintained above 50 ° C, depending on the surface material of the conveyor apparatus. If the surface material is metallic, then a conventional heater should be layer, in practice, to raise the temperature to at least 50 ° C, preferably at least 100 ° C, more preferably between 100 ° C and 225 ° C, which It may depend on the heat transfer coefficient of the surface. In the broad process of the invention, however, the temperature may vary below 50 ° C, if the surface of the conveyor apparatus has a lower heat transfer coefficient than metals such as steel. The crystallization must be able to maintain a relatively stable or permanent temperature, although some gradient along the crystallization section is permissible. Preferably, the temperature of the surface in the crystallization section is carefully controlled, as further described below. Preferably, a portion of the lower surface of the moving surface 12 is heated within the crystallization section. It is also possible to have a heater prior to the point at which the microspheres are received on the conveyor surface, in which case the crystallization section only requires insulation and / or light heating. The crystallization section may further comprise means for adjusting the temperature and / or flow of a heat exchange fluid and supplying a flow of the heat exchange fluid to the lower surface 16, as shown within the crystallization section. 20 in Figure 1. In the embodiment shown in Figure 1, an air heater 26 supplies the hot air to a lower plenum chamber 24, which encloses a portion of the lower surface 16 of the moving surface 12. The plenum chamber lower 24 generally contains an inlet and outlet for the heat exchange fluid, so that the heat exchange fluid can circulate continuously through the lower plenum chamber 24. The lower plenum chamber 24 extends along the portion of the moving surface 12, which comprises the crystallization section. In this way, the microspheres 18 are subjected to appropriate heating immediately after they are formed and collected on the moving surface 12. To obtain a rapid heat transfer from the moving conveyor surface to the newly formed polymer microspheres, it is preferred that the material for the moving conveyor surface 12 has a relatively high heat transfer coefficient. Metals are particularly useful for this purpose, especially metals, such as steel, with high heat transfer coefficients. Therefore metals are the preferred materials for the moving conveyor surface, although other materials, for example, plastic or plastic coatings are possible. The temperature of the upper surface 14 of the moving surface 12 within the crystallization section can be controlled automatically or manually with the use of a temperature sensor 28 located within the crystallization section. Preferably, however, a temperature controller can automatically control the temperature of the upper surface 14 of the moving conveyor surface 12 in the crystallization section within a predetermined temperature range. Temperature control, in combination with controlling the speed of the moving conveyor surface supporting the microspheres, will lead to the microspheres 18 being subjected to the predetermined temperature range for a minimum amount of time which may be predetermined. This occurs when the microspheres 18 pass through the crystallization section. In general, the temperature controller comprises a sensor 28 for determining the temperature of the upper surface 14 within the crystallization section, a comparator (not shown) for comparing the temperature determined by the sensor with a set point within the range of the predetermined temperature, and a temperature adjuster (not shown) for adjusting the temperature of the heat exchange fluid supplied to the lower surface 16 of the moving surface 12. Conventional temperature controllers are well known in the art. , as will be appreciated by those skilled in the art, and are commercially available from a wide variety of sources. The control of the temperature of the metal surface of the strip may sometimes require the removal of heat from the heat exchange fluid or from the lower surface 16, ie a relative cooling, although the crystallization section may be heated in relation to the environment. Typically, when a heat exchange fluid is supplied in a continuous flow to the lower surface 16, and the set point temperature is exceeded, a controller will typically send a signal of no additional heat input. This, however, does not contravene the spirit of the invention, since the general result is the heating of the lower surface 16, and consequently the upper surface 14. In FIG. 1, a heater for the lower surface 16 of the surface in FIG. movement 12 is inside the crystallization section. The primary function of the heater is to heat the moving surface 12 in such a way that the upper surface 14 is within a predetermined temperature range. The heating of the moving surface 12 so that it is maintained at a temperature within the predetermined temperature range can be effected by a variety of means known to those skilled in the art. Various embodiments and apparatus for heating are encompassed within the scope of this invention. In the preferred embodiment of figure 1, the heating is mainly by means of the heating of the lower surface 16 of the moving surface 12. The total system can also include auxiliary, additional heating means. For example, a second temperature controlled (ie, generally heated) heat exchange fluid, preferably an inert gas to prevent degradation of the microspheres 18, may be provided to heat the portion of the upper surface 14 that supports the microspheres. that are inside the crystallization section. Preferably the gas is inert. Suitable gases include nitrogen, noble gases such as argon and helium, oxygen, air, and the like. In this preferred embodiment, the microspheres18 are subjected to a temperature control, at an elevated temperature, by means of both the hot moving surface 12 and the flow of the hot inert gas. The inert gas is preferably at a temperature which is lower than that of the upper surface 14. For example, for PET, the temperature of the inert gas, for example, nitrogen, typically varies from 25 ° C to 100 ° C, although higher temperatures are feasible. A flow of inert gas heated over the microspheres can be provided to control the temperature gradient that will exist through the thickness of each microsphere, thus serving to achieve a more uniform crystallization through each microsphere. The more uniform the temperature across the microsphere during the minimum predetermined amount of time, the more uniform the crystallization will be within each microsphere, although the temperature gradients within the microspheres will, to some degree, probably occur while they are within the microsphere. the crystallization section. An important goal of the crystallization section is to bring the temperature of the polymeric microspheres to the desired crystallization temperature as quickly as possible and to maintain it at a predetermined temperature for a minimum period of time. As indicated above, although the temperature of a continuous flow of the inert gas is controlled, there may be temporary periods of time when the gas is not hot, so that the temperature of the set point is obtained. The total effect, however, will be the control of the temperature, by means of gas, of the environment surrounding the newly formed microspheres. A second means for heating and supplying a continuous flow of a second heat exchange fluid is shown in Figure 1 as a heater 22 for heating a flow of nitrogen supplied to an upper plenum chamber 20. The upper plenum chamber 20 can enclose the upper surface 14 within the crystallization section, and generally contains an inlet and an outlet for continuously circulating the nitrogen through the upper plenum 20. Figure 2 is a cross-sectional view of an upper and lower plenum chamber wraps the crystallization section. As shown in Figure 2, a conveyor belt 12 covers the upper opening of the lower plenum 24. The roller or cylinder for the belt is shown by the dotted line. The conveyor belt 12 also serves to cover the lower opening of the upper plenum chamber 20. Resting or relying on the belt, the seals 42, typically made of TEFLON® (DuPont, Wilmington, DE), can be employed to prevent excess loss. of the heat exchange fluid which is circulated through the upper plenum 20. As an example of auxiliary heating to help maintain the temperature of the upper surface 14 within a predetermined range, a third heat exchange fluid it can be supplied to an internal chamber 34 located in the roller or cylinder upstream of the conveyor apparatus. The internal chamber 34 may include an inlet and an outlet which are connected by conduits to a means for heating and circulating the third heat exchange fluid. Figure 1 also shows a heated pump 38, inside a hot oil bath 43, for supplying the third heat exchange fluid, for example, a hot oil, through a duct 36 to the internal chamber 34 of the running roller top 30. The roller is preferably constructed of a material capable of conducting heat to ensure that the heat from the hot oil is efficiently conducted from the inner chamber 34, through the roller 30 to the lower surface 16 of the conveyor belt. Heating the upstream roller 30 as described, provides supplemental heating which counteracts normal heat loss and reduces the load on the primary heater 26. It may also be possible, however, to provide primary heating upstream of the microspheres, in combination with insulation and / or heating supplementary after the point at which the microspheres are received on the band. After the crystallization section, the low molecular weight microspheres 18, now crystallized, can be collected and transported for further treatment. The present apparatus can be used to manufacture relatively robust and uniform microspheres of a polyester polymer. One such process, which is particularly advantageous, will now be described. In the preferred process, a polyester polymer in the form of molten material having a desired intrinsic viscosity, IV is processed in an apparatus in accordance with the present invention. In general, the polymer having an IV ranging from about 0.05 to about 0.40 dl / g is adequate. An IV that ranges from about 0.09 to about 0.36 dl / g is preferred. The IV is determined as follows. A solvent is made by mixing one volume of trifluoroacetic acid and three volumes of methylene chloride. The PET, in the amount of 0.050 g, is then weighed in a clean dry ampule, and 10 ml of the solvent is added to it using a volumetric pipette. The ampoule is closed (to prevent evaporation of the solvent) and stirred for 30 minutes or until the PET dissolves. The solution is poured into the large tube of a # 50 Cannon-FenskeR viscometer, which is placed in a 25 ° C water bath and allowed to equilibrate at this temperature. The times of fall or descent between the upper and lower marks are then measured in triplicate, and settle well in the course of 0.4 seconds. A similar measurement is made in the viscometer for the solvent alone. The IV is then calculated by the equation:IV = Ln (solution time / solvent time) 0.5The present process can be integrated with a method of producing a polymer in a molten material form. The production of the polymer in a molten form can be effected in several ways, described above, and includes extruding the polymer initially in the form of flakes, microspheres or tablets. Additionally, a complete process may include the polymerization of the reagents in a reactor for polymerization, for example, by polymerization of the molten material, as described above. In the preferred process, the polyester is initially at a first temperature which is at or above its melting temperature. For polyesters of interest, this initial temperature could be above 200 ° C. For PET, this initial temperature could be equal to or greater than about 250 ° C. It is preferred that the polymer melt material be essentially amorphous, that is, less than about 5%, preferably less than 1% crystalline. If the polymeric molten material is not amorphous initially, and instead is semicrystalline, it is desirable for the polymer to be fully and uniformly heated above its melting temperature to ensure that the semi-crystalline areas are furled in a sufficient amount. . The polyester polymers, at the first temperature mentioned above, are formed into microspheres in a droplet or microsphere former, described above. The microspheres are collected, when they are formed, on a substantially smooth or level surface which is maintained at a second temperature within a crystallization zone. (Substantially level means no greater than 10 ° from horizontal). The microspheres may be subjected to heating in the crystallization zone, as described with respect to the apparatus of this invention, particularly if the band is metallic. The key characteristic of the crystallization zone is that it allows the control of the temperature of the newly formed microspheres, such as the microspheres subjected to their desired crystallization temperature immediately after they are formed. Consequently, the microspheres can be produced, which are robust and uniform, even when it involves a low molecular weight polymer. Such microspheres are suitable for further transport and polymerization, for example, a solid state polymerization. To form polyester microspheres suitable for transport and further processing, the microspheres must be subjected to contact with a conveying surface at a temperature within a predetermined temperature range as quickly as possible after formation. This predetermined temperature range for the polyesters preferably ranges from about 80 ° C to about 23 ° C, preferably about 110 ° C to about 190 ° C. The preferred, additional process modes are also described in the N.S. (Proxy Registry No. CR-9638), N.S. (Proxy Registry No. CR-9607) and N.S. (Proxy Registry No. CR-9524) commonly assigned, filed concurrently, all of these three applications are incorporated herein for reference in their entirety. Submitting the polymer microsphere thus formed to a surface temperature within the predetermined temperature range will lead to an immediate temperature gradient between the polymeric microsphere, initially or close to its melting temperature, and its environment. This should be done as quickly as possible to obtain the desired, shaped crystal morphology. The crystalline morphology is related to the robustness and resistance to abrasion of the microspheres, especially the robustness during the subsequent polymerization. The microspheres are kept in contact with the hot surface for a predetermined amount of time, which for polyesters should be not less than about 3 seconds, preferably about 10 to 60 seconds. In general, the time necessary to produce crystalline, low molecular weight polyester microspheres having the desired crystallinity will not exceed approximately several minutes, although it would not be detrimental to keep the microspheres at the desired temperature for longer periods of time, example, 30 minutes or more. The term "crystalline" as defined herein means a crystallinity content greater than about 15%, preferably greater than 20%, and more preferably greater than 30%, corresponding, respectively, to PET, for example, at a higher density that about 1.36 g / cc, preferably greater than about 1.37 g / cc, more preferably greater than 1.39 g / ml. Accordingly, the term essentially crystalline or crystalline, as used herein, will include what is commonly referred to as "semi-crystalline", as are most polyesters of interest. The amount of crystallinity can be determined by DSC (calorimetry with differential scanning). For example, essentially crystalline PET is characterized by a total heat of fusion, expressed in J / g, of at least about 20, more preferably in approximate form 35, when 140 J / g are used as the total melting heat of PET crystalline. Higher heats of melting indicate a more crystalline polymer. The percentage of crystallinity within a sample of a polyester material or microsphere can be determined by comparing the heat of fusion (J / g) of the crystallites present with the heat of fusion of the "pure" crystalline polyester. The polyester employed in the present invention or process comprises diester or diacid components, suitably including alkyl dicarboxylic acids which contain from 4 to 36 carbon atoms, diesters of alkyl dicarboxylic acids which contain from 6 to 38 carbon atoms, aryl dicarboxylic acids which contain from 8 to 20 carbon atoms, diesters of aryl dicarboxylic acids which contain from 10 to 22 carbon atoms, alkyl substituted aryl dicarboxylic acids which contain from 9 to 22 carbon atoms, or diesters of alkyl substituted aryl dicarboxylic acids which contain from 11 to 22 carbon atoms. Preferred alkyl dicarboxylic acids contain from 4 to 12 carbon atoms. Some representative examples of such alkyl dicarboxylic acids include glutaric acid, adipic acid, pimelic acid and the like. The diesters of preferred alkyl dicarboxylic acids contain from 6 to 12 carbon atoms. A representative sample of such a diester of an alkyl dicarboxylic acid is azelaic acid. Preferred aryl dicarboxylic acids contain from 8 to 16 carbon atoms. Some representative examples of aryl dicarboxylic acids are terephthalic acid, isophthalic acid and orthophthalic acid. The preferred diesters of the aryl dicarboxylic acids contain from 10 to 18 carbon atoms. Some of the representative examples of diesters of aryl dicarboxylic acids include diethyl terephthalate, diethyl isophthalate, diethyl or orthophosphate, dimethyl naphthalate, diethyl naphthalate and the like. Preferred alkyl substituted aryl dicarboxylic acids contain from 9 to 16 carbon atoms and the preferred diesters of the aryl-substituted aryl dicarboxylic acids contain from 11 to 15 carbon atoms. The diol components for the polyesters used in the invention here comprise suitably glycols containing from 2 to 12 carbon atoms, glycol ethers containing from 4 to 12 carbon atoms and polyether glycols having the structural formula HO- (AO) nH, wherein A is an alkylene group containing from 2 to 6 carbon atoms and wherein n is an integer from 2 to 400. In general, such polyether glycols will have a molecular weight of about 400 to 4000. Preferred glycols contain suitably from 2 to 8 carbon atoms, with the preferred glycol ethers containing from 4 to 8 carbon atoms. Some representative examples of the glycols, which can be employed as the diol component of the polyester, include ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 2,2-diethyl-1,3-propanediol, 2, 2 -dimethyl-l, 3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-l, 3-propanediol, 1,3-butanediol, 1,4-butanediol, 1 , 5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,3-cyclohexanedimethanol, 1,4-diclohexanedimethanol, 2,2,4,4-tetramethyl-1 , 3-cyclobutanediol, and the like. Some representative examples of polyether glycol (PolymegR) and polyethylene glycol (Carbowax®). Branched or unbranched polyesters can also be used. The present process is applicable to both polyester homopolymers and polyester copolymers thereof. In addition, the process of this invention is particularly useful for polyesters that do not crystallize easily, ie, which require heating, in accordance with the present process, to crystallize. These could include, for example, poly (ethylene terephthalate) (PET), poly (ethylene naphthalate) (PEN), poly (trimethylene terephthalate) (3G-T), and poly (trimethylene naphthalate) (3G-N) ). In general, such polyesters have a glass transition temperature, Tg, above about 25 ° C, and a melting temperature, Tm, which usually ranges from about 200 ° C to about 320 ° C. Particularly preferred are polyesters modified to 10% by weight of a comonomer. The comonomers include diethylene glycol (DEG), triethylene glycol, 1,4-dichlohexanedimethanol, isophthalic acid (IPA), 2,6-naphthalene dicarboxylic acid, adipic acid and mixtures thereof. Preferred comonomers for PET include 0.5% by weight of IPA and 0.3% by weight of DEG. As indicated above, the crystalline polymer microspheres produced according to the present invention can be introduced into a solid state polymerization reactor to increase the molecular weight of the polymer. Preferably, the IV (intrinsic viscosity) of the polyester in the microspheres is below 0.4, preferably below 0.36, more preferably below 0.3, and the IV of the polyester product of the solid state polymerization reactor is above 0.5, preferably 0.6. to 1.2. For example, for PET, the polymerization in solid state is suitably operated at a temperature of between 200 and 270 ° C, preferably 220 and 250 ° C, provided it is below the melting point of the polymer for a period of time that it is preferably less than 24 hours.
EXAMPLE 1This example illustrates a design for a demonstration unit. The PET with an IV of 0.21 dl / g and ends of COOH of 92.5 Eq / 106 g, which is produced by a polymerization process, is processed at 74 rpm through a 28 mm barrel extruder, with twin screws, with six heated zones. The temperatures in the zones are:IT T2 T3 T4 T5 T6130 ° C 274 ° C 285 ° C 262 ° C 284 ° C 281 ° CThe discharge of the extruder is connected to a variable speed gear pump, the molten polymer material is pumped under pressure at a flow rate of 22.7 kg / h (50 lbs / h) to a ROTOFORMERR droplet former 60 cm wide (approximately 2 feet), manufactured by Sandvik Process Systems, Totowa, NJ. The holes, aligned in rows along the ROTOFORMERR, are 1.5 mm in diameter. The feed temperature of the molten polymeric material at the entrance of the ROTOFORMERR is approximately 285 ° C. The molten polymeric material is formed into droplets on a conveyor 13, 2.43 m (8 ft.) In length, which consists of a continuously moving steel strip, which is also manufactured by Sandvik Process Systems. The band is heated by the convection formed from an air blower which heats the bottom of the band about its full length to about 160 ° C. The molten polymer droplets are solidified on the web to provide hemispherical particles which are transported to a collection tray. Based on the experimental runs, in which the band was not heated to an elevated temperature according to the present invention; it can be estimated that the speed of the cylinder head, the speed of the belt, and the average weight of the particles, if they occur under the conditions described in this example, could be as follows:TABLE IExample Speed < of the Weight Speed of theNo. Head Particle Band (m / min) (m / min) Average (g) 1 7.89 9.14 0.0369 2 10.15 9.14 0.0236 3 8.50 9.14 0.0221 4 26.70 18.29 0.0140It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.
Having described the invention as above, property is claimed as contained in the following