MXPA06010093A - Method for production of a partly-crystalline polycondensate - Google Patents

Abstract

The invention relates to a method for production of a partly-crystalline polycondensate, in particular, a polyester or a polyamide, whereby a polycondensate prepolymer is firstly produced, which is prepared and formed into granules, by means of a die-face granulating device, with an average diameter of less than 2 mm, said granules being cut at the outlet from the die plate. The degree of crystallisation and the molecular weight are then increased in a solid-phase polycondensation process. For granulation, the polycondensate prepolymer melt is pressed through a die plate with a number of die perforations, preferably arranged on at least one annular track. The cutting is achieved by means of a circulating knife with a liquid jet.

Description

METHOD OF MANUFACTURING A PARTIALLY CRYSTALLINE POLYCONPENSATE The invention relates to a method for the production of partially crystalline polycondensate, especially a polyester or polyamide, by means of the following steps: a) manufacture of a polycondensate prepolymer melt; b) formation of granulates and solidification of the melt of the polycondensate prepolymer, by means of a granulation device, in which the granulates are cut at the outlet of a nozzle of the granulation device; c) raising the degree of crystallization of the prepolymer granules; and d) raising the molecular weight of the granulates by means of solid phase polycondensation.

Most Recent Basic Technique WO 01/42334 (Schiavone) describes a method that optimizes the manufacture of PET, so that a preform with improved properties can be produced, which is achieved by the addition of a high proportion of the comonomer. A relative optimization of the particle-making process, however, is performed and the possibility of producing properties improved by the correct selection of the particle size is not recognized. Thus, the process is limited to polyethylene terephthalate with a high proportion of the copolymer, which, on the one hand, has a negative influence on the treatment in the SSP and, on the other, limits the service interval of the PET thus manufactured. The publications DE 109 49 485, Geier et al., And DE 100 19 508 of atthaei et al,. Respectively, they describe a method for the dripping and crystallization of polyesters in a drip tower. In this drip tower, however, there is a risk that individual granules will collide with each other and stick together. The only possibility of carrying out such a method is to increase the separation of the distance of the drops, in such a way that the collisions of the granulate are reduced to a small acceptable amount. The resulting ratio of the size of the apparatus (diameter of the drip nozzle and drip tower) to achieve good performance is so great that, for a commercial scale installation, a multiplicity of expensive drip towers must be operated in parallel.

The Invention On the other hand, it is an object of the present invention to provide a method that can be employed for a multiplicity of polycondensates, which, in contrast to the state of the art, achieves improved properties of the product and can be carried out efficiently with simpler technologies. This object is solved by means of the method according to claim 1, in which the method, mentioned initially, according to the invention, in step b), granules are formed having an average diameter of less than 2 mm, Thus, a sufficiently large surface / volume ratio of the particles of the granulate is ensured, whereby an amount of diffusion per unit time and a rapid increase in the intrinsic viscosity (IV) or increase in the molecular weight of the polycondensate can take place. Also, the degradation reactions of the polycondensate can thus be suppressed to a large extent. Preferably, in step b), granulates with an average diameter of 0.4 to 1.7 mm, especially 0.6 to 1.2 mm, are formed.

For this purpose, the melt of the prepolymer of the polycondensate can be thought through a die plate, with a multiplicity of orifices of the nozzle, which are preferably arranged in at least one annular path. The cut in the granulation stage b) can be carried out by means of a circumferential knife. Preferably, the cutting takes place in step b) of granulation by means of a jet of fluid, especially by means of a jet of liquid. For polyester, it is a matter of a polyethylene terephthalate, a polybutylene terephthalate or one of its copolymers. Preferably, in the case of the melt of the prepolymer of the polycondensate, which relate to a polyester melt, especially the melt of polyethylene terephthalate or one of its copolymers, with a degree of polymerization consistent with the value of IV of 0.18 to 0.45 di / g. Preferably, upon entering the crystallization step c), the prepolymer granulate has a crystallinity of less than 10%.

The crystallization stage c) can take place in a fluid bed or a fluidized bed, by the action of a fluidizing gas. Preferably, the average temperature of the prepolymer granules (in ° C) at, the transition from granulation step b) to crystallization step c) should not be allowed to decrease below a value of 1/4 of the temperature of fusion (in ° C). In step b) of granulation, a liquid can be used for cutting, which, for the most part, is discarded from the polymer granules, before they reach stage c) of crystallization, in which the water like a liquid. In the polycondensate, a copolymer of polyethylene terephthalate may be involved, in that the dicarboxylic acid component comprises more than 96 mol% of terephthalic acid and the diol component comprises more than 94% or less than 84 mol% of the ethylene glycol. The polycondensate may involve a copolymer of polyethylene terephthalate, in which the diol component comprises more than 98 mol% of the ethylene glycol. The polycondensate may involve a copolymer of polyethylene terephthalate, wherein the dicarboxylic acid component comprises from 96 to 99 mole percent of the terephthalic acid. Preferably, simultaneously with step c) of crystallization, the stirring at a temperature suitable for the solid phase polycondensation takes place. The porous granulate can also be produced, in which the melt of the prepolymer, preferably in stage a) and / or in step b), employs a foaming agent. Other advantages, characteristics and possibilities of application of the invention arise from the following broad, non-limiting description.

Polycondensate The polycondensate involves a crystallizable thermoplastic polycondensate, such as, for example, polyamides, polyesters, polycarbonates or polylactides, which is produced by means of a polycondensation reaction by cleavage of a low molecular weight reaction product. The polycondensation can either take place directly between the monomers or by means of an intermediate stage, which is reacted to connect through the transesterification, where this transesterification can again take place by cleavage of a low molecular weight reaction product. or by ring opening polymerization. The polycondensate, thus produced, is essentially linear, in which a small amount of branching can be initiated. In the case of polyamides, a polymer is involved, which, by means of the polycondensation of its monomers, or a component of diamine and a component of dicarboxylic acid or a bifunctional monomer with an amine and a carboxylic acid group is produced. In the case of polyesters, a polymer is involved, which, through the polycondensation of its monomers, a diol component and a dicarboxylic acid component is produced. In a different way, most diol components, linear or cyclic, come into play. Similarly different, most aromatic dicarboxylic acid components come into use. Instead of the dicarboxylic acids, their corresponding dimethyl esters can also be used. Typical examples of polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT (and polyethylene naphthalate (PEN)), which may be in action either as copolymers or as copolymers.

In one embodiment, the polyester is comprised of a polyethylene terephthalate copolymer, in which: • the diol component comprises more than 98 mol% of the ethylene glycol or • the dicarboxylic acid component comprises more than 96 mol% of the acid terephthalic and the diol component comprises more than 94 mole% or less than 84 mole% of the ethylene glycol; or • the dicarboxylic acid component comprises from 96 to 99 mol% of the terephthalic acid.

Polymer Melt In a first stage, the polycondensate monomers are polymerized or polycondensed to a prepolymer in the liquid phase. Conventionally, the preparation of the melt of the prepolymer takes place in a continuous process, in which an esterification step follows a prepolycondensation step. The polycondensation stages used in the conventional polyester manufacturing process do not take place in the high viscosity reactor (also called Finisher [finishing]) (compare series in Modern Polyesters Wiley in Polymer Science, Edited by John Scheirs, J. Wiley & Sons, Ltd 2003, Figure 2.37).

The Degree of Polymerization (DP) achieved is still distinctly lower under the degree of polymerization of the polycondensate, after the subsequent exit phase treatment. Usually, the degree of polymerization of the prepolymer is below 60%, especially below 50% of the degree of polymerization of the polycondensate, then condensed in the solid phase. Preferably, the degree of polymerization of the prepolymer is between 10 and 50, especially between 25 and 40. In the case of .PET, a degree of polymerization analogous to an IV value of 0.18 to 0.45 dl / g is achieved. For Pet, a value of IV between 0.30 and 0.42 dl / g is preferred. For the calculation of the degree of polymerization from the IV value of a PET, the ratio DP = 155.5 ° IV1-466 of the US Patent 5,532,333 Stouffer et al. Is used. The process generally takes place at a high temperature, whereby the prepolymer is formed as a melt of the prepolymer. However, the melt of the prepolymer can also be produced by heating to a prepolymer, previously solidified. Mixtures of different prepolymers can also be considered as the melt of the prepolymer, in which recycled raw materials can also be used.

The melt of the prepolymer can contain various additives, such as, for example, catalysts, stabilizers, coloring additives, reactive chain elongation additives, etc.

Granulation For granulation, the melt of the prepolymer is pressed through a nozzle, which has a multiplicity of openings and is then cut. This nozzle preferably comprises at least one nozzle body and one die plate. In the nozzle body, the melt of the prepolymer is distributed in the area of the die plate, in which the openings are located, where the uniform, temperate distribution and flow rate are measured, which are found on the plate. the nozzle in which a plurality of openings (orifices of the nozzle) are located. Through which the melt of the prepolymer flows. The dimensions of the hole are frequently constant over the entire plate of the nozzle. In order to equalize the irregularities in the flow through the openings, it may be advantageous, depending on the position of the holes, to provide different lengths of openings and diameters of openings. These openings can be made wider on the entrance side. On the outlet side, a straight cutting edge is an advantage, where also a widening and / or rounding of the opening is conceivable. The die plate must be heated sufficiently (for example electrically or with a medium that carries heat) in order to prevent freezing vaporization of the melt of the prepolymer and block if the openings. At the same time, the outer side of the nozzles must be insulated in order to reduce heat loss. The die plate may consist, for example, of metal, ceramic or a combination of metal and ceramic. The openings are usually round, but may have another profile, such as, for example, openings in the form of slots. The resulting granules are, for example, spherically or ball-shaped, lens-shaped or cylindrical in shape. Likewise, porous granulates are conceivable, for example when the melt of the prepolymer is treated with a foaming agent (gas or a chemical foam producing agent that produces gas). The size of the granulate, measured as an average diameter of individual granulates should be less than 2 mm, preferably 0.4 to 1.7 mm, especially 0.6 to 1.2 mm.

The cutting must take place according to the invention at the outlet of the nozzle. For cutting, a rotary cutting device, such as, for example, a rotary cutting head can be used. On the head of the cutter, one or a plurality of cutting elements (eg blades) are fastened, which separate the melt from the prepolymer leaving the openings of the nozzle. Between the nozzle plate and the cutting elements, there may be a small gap, so as to prevent constant "grinding" of the cutting elements on the nozzle plate. The cutting elements can be made of various materials, such as, for example, metal, glass or ceramic, in which, however, metal blades are preferred. The separation can also be carried out according to the invention, by means of one or a plurality of high pressure fluid jets or liquid jets (water jet cutting system, jet cutting). Optionally, an abrasive cutting agent can be added. Likewise, a combination of gas jets and liquid jets can be used as the "mixed fluid jet" of cutting.

Likewise, the granulation can be carried out using one or a plurality of laser decorums (laser jet cutting or laser cutting). The number of holes and the cutting frequency must be adjusted, eliminating the production of the desired granule size, in that through the use of a plurality of cutting elements, the cutting frequency can be a multiple of the circulation frequency of the cutting device. The following table presents the resulting strong dependence Preferred productions are 0.1 - 2 kg // (h * hole) and cutting frequencies of 80-400 Hz. In order to prevent the agglomeration of the cutting granules, they are immediately surrounded by a liquid. So that the granulation can take place in the liquid or the granulates can be centrifuged in a liquid ring. Suitable granulation devices are known under the term "head granulation" or "hot face granulation", "underwater granulation" and "water ring granulation". Despite the use of the term "water" in the designation of granulation devices, other fluids, mixtures of fluids, liquids, mixtures of liquids or liquids, with dissolved, emulsified or suspended substances can be used. The fluid or liquid is generally used, at least partially, in a loop in which the conditions (temperature, pressure, composition) are maintained for a regenerated application for granulation. The polycondensate melt solidifies upon cooling. This preferably occurs by means of the liquid used in the granulation process. The use of other cooling means or the combination of a plurality of cooling means, however, is conceivable. The cooling may take place at a temperature, which is under the glass transition temperature of the polycondensate, which allows the storage and / or transport of the granulates over a longer period of time. The average temperature of the polycondensate granulates can also, however, be maintained at a higher level in order to improve the energy efficiency of the process. For this it is possible to raise the temperature of the cooling medium and / or choose the retention time in the cooling medium correspondingly short (shorter than 5 seconds, especially shorter than 2 seconds) The average temperature of the granulate (in ° C) C) must thus be greater than 1/4 Tmpp especially 1/3 Tmpp in which Tmpp represents the melting temperature (in ° C) of the polycondensate prepolymer. While the granulate of the prepolymer is in contact with the liquid, at least partial crystallization can take place. Preferably, the contact conditions (temperature and time) between the granulate of the prepolymer and the liquid are selected so that there is essentially no adverse effect on the reaction rate in the subsequent solid phase polycondensation process. For example, the contact time of a PET prepolymer in water, at a temperature between 1 and 25 ° C, below the boiling point, should not add more than 10 minutes, preferably not more than 2 minutes. In accordance with the present invention, selected contact conditions are provided so that the degree of crystallization of the polymer granulate adds up to less than 10% before entry into the subsequent crystallization step.

Crystallization The increase in the degree of crystallization of the prepolymer granules takes place in accordance with the known state of the method of the art. In order for the granules of the prepolymer to be treated at the appropriate crystallization temperature in the crystallization, at least one degree of crystallization must be achieved, which allows the treatment in the subsequent solid phase polycondensation, without being significantly above the degree of crystallization of the polycondensate cooled through a rapid cooling. The appropriate temperature range is evident if the half-period (t? / 2) of the crystallization is recorded as a function of temperature. It is limited up and down and below through the temperature which reaches the crystallization half-period, approximately 10 times the minimum crystallization half-period. Since very short semi-periods of crystallization (ti2) are difficult to determine, t? / 2 = 1 minute is set as a minimum value. For PET, the temperature range is between 100 and 220 ° C and a degree of crystallization of at least 20%, preferably at least 30%, is achieved. After achieving partial crystallization, the granulate can be brought to a temperature outside the range of the crystallization temperature. Cooling to a temperature below the crystallization range should, however, preferably be avoided. If the temperature of the prepolymer granulate is below the suitable crystallization temperature, after it is separated from the liquid used in the granulation process, then the granules of the prepolymer must be heated. This can, for example, be carried out by means of a heated wall of the crystallization reactor, by means of the components heated in the radiation crystallization reactor or by bubbling in a hot process gas. The suitable crystallization time follows from the time necessary to heat the product to the crystallization temperature, more at least the half-period of crystallization at a given temperature, in which preferably from 2 to 20 half-periods are taken for the time of encouragement , in order to achieve a sufficient mixture between the crystalline and amorphous product. In order to prevent the granules of the crystallization polymer from sticking together, they keep moving in mutual relation. This can be carried out, for example, by means of an agitator, a moving container or the action of a fluidized bed gas. Especially suitable crystallization reactors are fluid bed or fluidized bed crystallizers, since they do not have to form powder. At the same time as the degree of crystallization increases, possible residues of the liquid are removed from the granulation process. If a process gas is used in the loop of the crystallization process, in order to prevent excessive adsorption of fresh enough liquid gas or purified process gas they must be added. The process gases used in the solid phase polycondensation can also be used in the crystallization stage, in which different process gases can also be used in the different stages of the process.

Solid Phase Condensation The molecular weight of the polycondensate granules is brought to a greater degree of polymerization through a solid phase polycondensation, in which at least 1.67 times, especially at least 2 times, the degree of polymerization increases. For PET, an increase in IV value of at least 0.6 dl / g results, usually at least 0.7 dl / g. The solid phase polycondensation takes place in accordance with the known state of the methods of the art, and comprises at least the steps of heating to a postcondensation temperature and the postcondensation reaction. Optionally, other steps can take place before the subsequent crystallization or cooling. Therefore, continuous processes can be used as well as in batch processes, which, for example, take place in apparatuses, such as fluid bed, fluidization of bubbles or solid bed reactors, as well as in reactors with devices stirring or self-moving reactors, such as rotary kilns or reciprocating vessels.

The solid phase polycondensation can be carried out at elevated pressure or under vacuum, as well as at a normal pressure. In the known state of the methods of the technique, in which the heating stage and the stage of the reaction of post condensation by the action of a process gas takes place, the separation between the heating stage and the reaction stage The post-condensation is thus provided so that the heating step is carried out with a high amount of gas (mg / mp = 2 -15, especially 2.5-20). Therefore, the temperature of the product essentially approaches the temperature of the gas and the stage of the condensation reaction is carried out with a smaller amount of gas (mg / mp = 0.1 - 2, especially 0.3 - 0.8) whereby the temperature of the gas essentially approximates the temperature of the product. Thus, mp is the sum of the product streams fed into the process, and mg is the sum of all gas streams fed into the process. As the process gas, air or inert gases, such as, for example, nitrogen or C02, as well as mixtures of process gases, come into consideration. The process gas may contain additives, which either actively react with the heated product or are passively deposited on the product to be treated.

Preferably, the process gas is at least partially fed in a loop. In order to decrease an adverse effect on the polycondensation reaction, the process gas can be purified from undesirable products, especially the cleavage products of the polycondensation reaction. Typical cleavage products such as water, diols (for example ethylene glycol, butanediol) diamines or aldehydes (for example acetaldehyde) should be reduced to levels below 100 ppm, especially at levels below 10 ppm. The purification can be carried out by means of known gas purification systems of the prior art, such as, for example, catalytic combustion, gas washing systems, adsorption systems or cold traps. The suitable postcondensation temperature is in the temperature range which is limited on the low side by a minimum reaction rate of the polycondensation and at an upper end is limited by the temperature which is slightly below the melting temperature of the polycondensate As the minimum reaction regime, the reaction regime is considered with which the desired increase in the degree of polymerization can be achieved in an ergonomically acceptable time period.

The post-condensation temperature of the PET is in the range of 190 ° C to 245 ° C. The conditions of the polycondensation must be chosen so that the granulate can be processed subsequently to the final product under most of the available conditions. The corresponding interrelationships for the manufacture of PET are, for example, explained in the application PCT / CH03 / 00686, which is included here as reference. The suitable post-condensation time is in the range of 2 to 100 hours, in which the retention times based on the efficiency are preferred, of 6 - 30 hours. Optionally, the crystallization step and the boost stage can take place simultaneously at a suitable post-condensation temperature, or at least in the same reactor, in which the reactor used therefor can be divided into a plurality of process chambers, in that different process conditions (for example temperature and retention time) may prevail. It is thus an advantage if the heating rate at which the polycondensate is heated in the range of the subsequent condensation temperature is sufficiently large to prevent excessive crystallization before starting the polycondensation reaction. For the PWT the heating rate should be at least 10 ° C / minute, preferably at least 50 ° C / minute.

Product Manufacturing Following completion of the solid phase polycondensation, the polycondensates can be processed into various products, such as, for example, fibers, webs, films or injection molded parts. PET is largely processed to hollow bodies, such as, for example, bottles.

Claims (17)

1. CLAIMS 1. A method for manufacturing a polycondensate, partially crystalline, especially a polyester or polyamide, this method comprises the following steps: a) manufacture of a melt of polycondensed prepolymer; b) formation of granulates and solidification of the polycondensate prepolymer melt, by means of a granulation device, in which the granulates are cut off from a nozzle of the granulation device; c) raising the degree of crystallization of the prepolymer granules; and d) raising the molecular weight of the granulates, by means of solid phase polycondensation, characterized in that in step b), the granules with an average diameter of less than 2 mm are formed.
2. 2. The method according to claim 1, characterized in that, in step b), the granules with an average diameter of 0.4-7 mm, especially 0.6-1.2 mm, are formed.
3. 3. The method, according to one of the present claims, characterized in that the melt of the polycondensate prepolymer is pressed through a die plate, with a multiplicity of nozzle orifices, which are preferably arranged on at least one path cancel.
4. 4. The method according to one of the present claims, characterized in that the cutting in step b) of granulation is carried out with a circumferential knife.
5. 5. The method according to one of the present claims, characterized in that the cutting, in step b) of granulation, is carried out with a fluid jet, especially with a jet of liquid.
6. 6. The method according to one of the present claims, characterized in that the polyester comprises a polyethylene terephthalate, a polybutylene terephthalate, a polyethylene naphthalate or one of its copolymers.
7. 7. The method according to one of the present claims, characterized in that the melt of the polycondensate prepolymer involves a polyester melt, especially the melt of the polyethylene terephthalate, or one of its copolymers, with a degree of polymerization consistent with a value of the intrinsic viscosity of 0.18 to 0.45 dl / g.
8. 8. The method according to one of the present claims, characterized in that the granules of the prepolymer have a crystallinity of less than 10% at the entrance to the crystallisation stage c).
9. 9. The method according to one of the present claims, characterized in that the crystallisation step c) is carried out in a fluidized bed reactor or a fluidized bed, with the action of a fluidizing gas.
10. 10. The method, according to one of the present claims, characterized in that the average temperature of the granules of the prepolymer, (in ° C), in the transition from stage b) of granulation to stage c) of crystallization, does not fall below of a value corresponding to 1/4 of the melting temperature Tmprp (in ° C)
11. 11. The method, according to one of the present claims, characterized in that in step b) of granulation, a liquid is used for cutting, which is mostly separated from the granules of the prepolymer, before feeding in the stage c) crystallization.
12. 12. The method, according to one of the present claims, characterized in that water is used as the liquid.
13. 13. The method, according to one of the present claims, characterized in that the polycondensate involves a copolymer of polyethylene terephthalate, wherein the dicarboxylic acid component comprises more than 94 mol% or less than 84 mol% of the ethylene glycol.
14. 14. The method according to one of the present claims, characterized in that the polycondensate involves a copolymer of polyethylene terephthalate, in which the polyol component comprises more than 98 mol% of the ethylene glycol.
15. 15. The method according to one of the present claims, characterized in that the polycondensate involves a copolymer of polyethylene terephthalate, wherein the dicarboxylic acid component comprises 98 mol% to 99 mol% terephthalic acid.
16. 16. The method according to one of the present claims, characterized in that, simultaneously with stage c) and crystallization, heating takes place at a temperature suitable for the solid phase polycondensation.
17. 17. The method according to one of the present claims, characterized in that a porous granulate is produced, in which, preferably in step a) and / or in step b), a foaming agent is added to the melt of the polymer.