LT5394B - Method for the production of highly condensed polyester - Google Patents

Abstract

The present invention relates to latent-heat crystallised polyester and copolyester with a crystallisation degree of more than 38 percent, the production and use thereof for the production of polyester moulded bodies, whereby said granulate either, without prior addition of additives, or further cooling, is introduced directly into a solidphase polycondensation reactor, condensed to a higher viscosity and dealdehydised, or, without prior addition of additives, the granulate is dealdehydised and then introduced to the processing to give hollow bodies, or is directly applied to perform production for the production of hollow bodies, whereby before or/and after the polycondensation reactor additives, such as thermal stabilisers and/or acetaldehide reducing-aditives are added.

Description

The present invention relates to latent heat crystallized polyesters and copolyesters and their use in the manufacture of molded polyester products.

Known aromatic polyesters or copolyesters, in particular polyethylene terephthalate and its copolymers with a low content, such as isophthalic acid or cyclohexanedimethanol, polybutylene terephthalate and its copolyesters, polytrimethylene terephthalate, polyethylene terephthalate and their polyesters, for use as starting material, processed into medium viscosity granules. All of these polyesters and copolyesters are referred to in the present invention as polyesters.

The average degree of polycondensation of polyethylene terephthalate and its corresponding slightly modified copolyesters, after intrinsic viscosity (I.V.), ranges from 0.30 to 0.90 dl / g after melt polycondensation. It is a semi-crystalline granulate with a degree of crystallization of 9%. Because higher than 0.65 dl / g I.V. (intrinsic viscosity) granulate production, especially in conventional autoclaves, is difficult to achieve and high viscosity> 0.80 dl / g significantly limits the polycondensation capacity of the melt, while polyesters have to contain very little acetaldehyde for food packaging, state-of-the-art solid phase polycondensation. solid static polycondensation "(SSP) with upstream crystallization, which increases the IV by 0.05 - 0.4 dl / g (intrinsic viscosity) and from 25 to 100 to less than 1 min.m.d. reduces acetaldehyde content in PET (polyethylene terephthalate). Pre-crystallization and crystallization reactors attached to the main SSP reactor prevent the granules from sticking together in the SSP reactor. After the crystallization steps, the degree of crystallization is increased to 40-52% with a slight change in I.V. (intrinsic viscosity) and acetaldehyde content reduced to less than 10 min.m.d .. Crystallization proceeds from the outside to the inside.

Thus, the crystallinity at the periphery of the particles is higher than at the center of the particles.

In the SSP reactor, the average viscosity is increased so that the resulting resistance is appropriate to the intended use of the product, the amount of acetaldehyde in the food packaging is reduced to the required level and the amount of oligomers released is minimal. It is also important that acetaldehyde, also known as depot-aldehyde, still in the form of a vinyl ester, is removed to such an extent that only a minimal amount of acetaldehyde is recovered in the polyester by stretching and blowing and stretching and blow molding into packaging, especially polyester bottles.

Usually the processors of this granulate are manufacturers of hollow products. Often, die-casting molding machines produce semi-finished products, known as blanks, which are then molded into polyester bottles. Other forms of polyester granulate can also be obtained, for example by film and foil making machines.

The market for granulating plastics, for example, uses a spin granulation method. This method is characterized by the fact that in the continuous production process, relatively long plastic tails are pressed through the plate with the holes, then freely hanging over a short distance through the air, passing through a water bath. Due to the small surface of the plastic bore, which is relatively small compared to the granulate, it is possible to maintain a slight dip here. The cooled spinach is dried and fed to a granulator. In this method, the granulation takes place in a solid state. This is usually followed by re-drying as described, for example, in DE43 14 162 or in the plastics manual. With this granulation method, there is a great potential for dramatically increasing the reflux point temperature, thereby enhancing the polymer degradation phenomena and the uneven crystallization rates of the individual chips.

In this technology, chip cooling occurs from the outside to the inside.

Another modern possibility of polymer melt granulation after polycondensation is underwater granulation, in which the melt escaping from the granulator nozzles or perforated plates is immediately separated by knives in a connected water chamber. The separated granulate is still ductile and deforms due to surface tension when cooled in cold water, it also cools from the outside to the inside and takes a circular to lenticular shape. The cooled granulate is separated from the water by a stream of water in a water separator, dried and packed in large bundles or transported in bunkers for further processing (DE 35 41 500, DE 199 14 116, EP 0 432 427, DE 37 02 841). The peculiarity of this method is the principle of heat capacity drying.

The chips thus produced have a uniform degree of crystallization of less than 10%.

US 4, 436, 782 also describes a process for granulating and further processing PET into granules, wherein a mixture of 0.08 to 0.15 viscosity oligomers is pressed at 260 ° C to 280 ° C to form droplets passing through an inert gas. the atmospheric cooling section falls into a water bath or on a conveyor belt and freezes into amorphous granules. The granules obtained in this way also have many amorphous structures.

Granulates of low degree of crystallization, typically less than 12%, are obtained by all of the methods described. Increasing the crystallinity of the polymer granules, for example to obtain a pre-SSP step, is known to require high cost reaction steps. First of all, it is the cost of heating the supplied ambient temperature granulate to the crystallization temperature.

WO 01/81450 discloses a process and device for converting semi-finished thermoplastic polyesters and copolyesters into drops, which does not exhibit the crystallinity disadvantages of the granulation methods described above, which describes how to truncate conventional granulation methods and obtain monomers, oligomers, monomers. Semi-finished products in the form of droplets of crystallized surface, in the form of glycol mixtures or partially polycondensed materials. For this purpose, the product is placed in a gaseous medium, the droplet primary product entering the gaseous medium accelerates the crystallization process of the semi-finished product and accelerates the crystallization state if the droplet parent product is stored at > 100 ° C below its melting point for a period of time. crystallization of the drop surface. Here, too, the outer layer crystallizes more strongly, resulting in a non-sticky surface, which allows immediate processing of the polycondensate into the coarse polymer. The material obtained in this way is only relatively resistant to mechanical stress. Fragility compared to amorphous chips increases. Another disadvantage of this crystallization in the low molecular weight region is that after the SSP is a fully crystallized chip of rigid crystal structures that are dismantled in the melting process, for example, during the production of die-casting blanks, consuming much more energy. The high melting temperature of at least 300 ° C requires a substantial increase in the reforming and deterioration of the workpiece acetaldehyde, mainly due to the increased degradation reactions. In addition, there is a risk that the SSP stroke will be inhibited or even inhibited by the immobility of the ends of the chains when increasing the viscosity.

Another granulation method for producing crystallized chips in the granulation process is described in WO 01/05566. Fused nozzles flowing from the nozzles are immediately partially crystallized in a liquid medium at a certain temperature in the crystallization region, maintaining a glass transition temperature higher than the plastic tails in this liquid medium. The crystallization stretch is connected to a granulation unit. During the crystallization process, the plastic casing achieves sufficient resistance, so that after a short stretch of the appropriate temperature in the granulation unit, the plastic bobbins can be divided into granules without prior drying. There is also a more crystallized outer layer here. The disadvantage is that after granulation of the plastics, a mixture of granulate and liquid medium is obtained, which means that drying of granules by conventional means is necessary.

In the pending German patent application, registration no. DE 103 49 016, "Method of making a plastic granulate", describes that immediately after underwater granulation, the freshly obtained granules are rapidly separated from the water and the exposed heat tanks dry and crystallize. To prevent the chips from sticking, the pellets are transported over a period of time to a further bottling or treatment plant, after centrifugation of the water on a vibrating or oscillating conveyor. With this technology, the crystallization process takes place from the inside to the outside of the granule, ensuring a more uniform crystallization across the granulate cross-section.

This process is hereinafter referred to as the latent heat crystallization process. In addition to the process described in DE 103 49 016, latent heat crystallization is also referred to as any other process in which crystallization occurs solely due to the effect of the heat capacity of the polymer melt state. This means that no heat is externally supplied to the pellets between the granulation and the subsequent bottling plant or after-treatment plant. All media in contact with the pellets must be at or below the surface temperature of the pellets in order to prevent any heat from the outside. However, if the temperature of these media is too low, the granules release too much heat and the desired amount of latent heat crystallization cannot take place. The basic technological principles are described in DE 103 49 016.

Granules obtained by latent heat crystallization can have a wide variety of properties. They depend not only on the conditions of the latent heat crystallization process but also on the properties of the polymer melt, for example, in the case of polyesters, the degree of polymerization, the intrinsic viscosity (I.V.) and the amount of acetaldehyde. The properties required will depend on the purpose of the latent heat, crystallized granulate, as these properties directly influence further processing steps.

Thus, the object of the invention is to obtain granules of high viscosity aromatic polyesters and their copolymers, which can be easily processed into hollow products and at the same time meet the extremely high quality requirements of polyester hollow products, especially bottles, with minimal investment and operating costs. .

The present invention solves this problem by employing a continuous or discontinuous polyester melt production process in a melt polycondensation reactor to obtain high intrinsic viscosities and economically transporting the melt to a granulator which produces more than 38% crystallization grade granulate by latent heat crystallization.

Further processing steps can be any of the uses of polyester granules. In addition to the solid phase polycondensation (SSP) described above, this may be the case for sufficiently large I.V. (intrinsic viscosity) dealdehyde (solid phase dealdehyde, DAH) or deformation processes of polyester granulate, in which, for example, semi-finished food prepackages are manufactured directly from the granulate. In the latter case, the granulate should have the necessary I.V. deformation immediately after the latent heat crystallization. (intrinsic viscosity) and the required amount of acetaldehyde.

This non-stick granulate can be:

A. transported directly to the solid phase polycondensation reactor without prior addition of additives and subsequent cooling and condensed to higher viscosity and dealdehyde or

B. is redirected to dealdehyde without prior addition of additives and then sent for processing into hollow products, or

C. is used immediately for the molding of semi-finished products of hollow products by the addition of additives, such as thermostabilizers and / or acetaldehyde reducing additives, before and / or after the polycondensation reactor.

Unexpectedly, latent heat crystallized granules have been found to be particularly suitable for all of the above-mentioned post-processing, where microscopic units, called spherolites, at the periphery of particles, i.e. in the outer layer, much smaller than in the middle of the samples, i.e. in the center of the particles. This can be clearly seen from the microphotos taken under these conditions (see examples). The maximum diameter of the spheroids in the middle of the samples is 20 µm, often much smaller.

Unexpectedly, the secret heat crystallized granules were found to be well suited for all of the above-mentioned further treatments even when the degree of crystallization at the fringes was the same or even lower than the middle of the samples.

The process contemplated is suitable for the preparation of granules of aromatic polyesters or copolyesters of an appropriate degree of crystallinity derived from one or more dicarboxylic acids or their methyl esters, such as terephthalic acid, isophthalic acid, naphthalene / or diethylene glycol.

In the known continuous or continuous esterification or transesterification process, using known catalysts and coupling with polycondensation, these parent compounds can be recycled to high viscosity polyester melt under vacuum, followed by granulation and crystallization at the same time.

During latent heat crystallization, the heat capacity in the polyester melt is used to crystallize the granulate. To achieve the required degree of crystallization it is important that the heat loss of the granulate obtained during the melt phase during transport and

Ί kept as small as possible during drying. The latent heat crystallization product of the present invention has a minimum degree of crystallization of 38%, preferably 38-60%, preferably 42-55%. It has a heat of fusion (HOF) of less than 60 kJ / kg, preferably less than 55 kJ / kg. Since the crystallization of the granule proceeds from the nucleus towards the shell, during the crystallization there is no high exothermic heat release characteristic of the conventional crystallization process, which causes undesirable agglomeration of the granulate, the granules obtained according to the invention do not adhere to each other in subsequent processing steps.

The polyester granulate obtained by the described latent heat crystallization is further recycled according to the technology of the polycondensation unit upstream.

Fig. depicts applications of latent heat crystallization in various polyester technologies.

Fig. shows micrographs of the middle and periphery of a PET chip specimen after two-stage crystallization according to the state of the art.

Fig. shows micrographs of the respective locations of the PET chip after further crystallization in a standard SSP reactor.

Fig. shows micrographs of the respective locations of the PET chip obtained by crystallization of latent heat according to the invention.

Option A:

According to the invention, the granulate crystallized in latent heat having a temperature of more than 100 ° C, preferably not less than 115 ° C, preferably not less than 130 ° C, I.V. (specific viscosity) greater than 0.53 dl / g, crystallization rate greater than 38%, acetaldehyde content 20 to 70 min.md, preferably 20 to 55 min.md, transported continuously by conveyor, if necessary through an intermediate storage bin, straight into an SSP reactor to extend the polymer chain and reduce AA (acetaldehyde).

The PET granulate produced in this way meets the market requirements: crystallization rate less than 60%, preferably less than 55%, HOF values less than 60 kJ / kg, acetaldehyde content less than 1 min.m.d. Incoming I.V. (specific viscosity) will depend on the purpose of the product. Since the temperature of the granule entering the SSP reactor is 160 - 210 ° C significantly lower than the standard values of the standard crystallizer, a 10% increase in the standard 8-18 hour residence time or a 2-3 K increase in the SSP temperature over the standard equipment or both. By eliminating conventional intermediate storage and crystallization steps, and by reducing operating costs, and the associated partial heat from granulation to the SSP reactor, this technique offers significant economic advantages. In addition, the granulate obtained by this inventive process has a very uniform quality of all chips, which results in easier and more reliable recycling into preforms and bottles, since the chip has a much more uniform melting behavior compared to prior art products.

Option B:

According to the invention, in the following dealdehydification step (DAH), a latent heat crystallized granulate from a high viscosity ("DHI") polycondenser having a temperature greater than 100 ° C, preferably not less than 115 ° C, preferably not less than 135 ° C, I.V. (intrinsic viscosity) greater than 0.65 dl / g, crystallization rate greater than 38%, acetaldehyde content of 20-100 min.m.d., preferably 30-60 min.m.d., reduction of acetaldehyde content and increase of I.V. (intrinsic viscosity). At this stage, as described for example in German Patent Application DE 102004010680.0, at a temperature of 190-220 ° C for at least 5 hours with minor mechanical interference and using purposefully selected nitrogen at <10 ° C as the carrier gas, the amount of AA (acetaldehyde) decreases to less than 1 min.md and, if necessary, the I.V. of the resulting granulate. (intrinsic viscosity) is adjustable according to the purpose of the product. I.V. (intrinsic viscosity) may be unchanged or increased by 0.1 dl / g. The granulate so produced has an AA (acetaldehyde) content of less than 1 min.m.d., and a degree of crystallization less than 55% of the HOF value is less than 55 kJ / kg. The crystalline structure is much brighter compared to granules obtained in standard processes, which makes it easier to use for the preparation of blanks, and has lower energy consumption. Acetaldehyde recovery values are up to 15% lower than standard sizes when optimally adjusted. An additional advantage of this technology is the savings in equipment and energy.

Option C:

The addition of acetaldehyde-reducing additives or thermostabilizers on the market prior to and / or after the melt polycondensation reactor and / or in the melt immediately prior to granulation according to the invention produces a polyester of a quality that can be used immediately for further processing. for example for the manufacture of hollow products. The granulate produced in this way has a degree of crystallization of greater than 38%, with an acetaldehyde content of 0.5 - 8 million m.d., preferably 0.5 - 3 min.m.d., preferably 0.5 - 1 min.m.d. Granule I.V. (specific viscosity) is at least 0.68 dl / g, depending on the application.

PET granules for hollow products are often not produced by the processor itself. Because packaged and transported granules can absorb moisture from the air, they are dried just before melting to form blanks. The processor can immediately dry this relatively low-crystallization granulate, which has no tendency to adhere, in its dryer at standard 160-180 ° C air flow prior to production

4-6 hours.

Because the crystalline structure of the granulate crystallized in latent heat according to the invention is significantly shorter, this molding process requires much less energy in the preforming machine, reduces PET degradation and AA (acetaldehyde content) regeneration, and easily maintains the preform bindings <8 million. amounts of acetaldehyde.

The invention is further illustrated by some non-limiting examples of the invention. The property values reported were calculated as follows:

The intrinsic viscosity (I.V.) of a 500 mg solution of polyester in 100 ml of phenol / 1.2 dichlorobenzene (3: 2 parts by weight) was measured at 25 ° C.

Acetaldehyde content (AA) was determined by removing acetaldehyde from the polyester by heating in a sealed vessel, acetaldehyde was determined in a gas chamber of the vessel by gas chromatography Perkin Elmer's Head space injection system H540 with carrier gas: nitrogen, column: 1.5 m alloy steel, filler: Poropack Q, 80-100 mesh, sample size: 2g, heating temperature: 150 ° C, heating time: 90 min.

To determine the degree of crystallization a (= CTG), determine the density of 30 chips in triplicate with a mixture of tetrachloroethane and heptane at 23 ° C in triplicate and calculate with ρΛρ-ρ.) P (p <-p 'Y where

The density of 100% crystalline PET: p _c = 1.455 and the density of amorphous PET: p _c = 1.332.

Heat of Fusion (HOF) was determined on a Mettler DSC instrument according to American Society for Testing of Materials ASTM E 793 at 100 to 200 ° C at 50 K / min for 5 minutes at this temperature. a heating rate of 10 K / min to 300 ° C; the energy consumed is determined in kJ / kg.

During micrographs, the chips were placed cold and cut with a microtome 10 µm thick. Photographs were taken under a light microscope with polarization contrast. The close-up and mid-detail photos are taken with 10, 20 and 40 lenses.

Examples

All samples were made with 15.5 mg spherical granule, spherical to lens form. The polyester from the last melt polycondensation reactor had the following comonomer composition: comonomer - 2% by weight of isophthalic acid (IPA); diethylene glycol 1.4% by weight. Catalyst content - 200 min.m.d. Sb 1 in the reference sample and 230 min.m.d. Sb in Examples 2-4.

reference example in sample amorphous chips with I.V. (intrinsic viscosity) from a melt polycondensation of 0.61 dl / g were crystallized and polycondensed in the solid phase for the preparation of lightly modified PET for the dispensing of sweetened beverages. The conventional BKG AH 2000 underwater granulator produces the following chips: I.V. (intrinsic viscosity) = 0.61 dl / g, AA content = 40 min.m.d., CTG = 8%. In the first stage of crystallization, chips were obtained in a pseudosized liquid layer having a residence time (VWZ) of 60 min and a temperature of 200 ° C, having I.V. (intrinsic viscosity) = 0.62 dl / g, AA content = 12.3 min.m.d., CTG = 46.1%. In the second stage of crystallization, in a shaft crystallizer, chips with an I.V. (intrinsic viscosity) = 0.63 dl / g, AA content = 8.8 min.m.d., CTG = 53.1%.

for the parent material and are therefore given in the table. They were fed into a standard SSP reactor (carrier gas: -75 ° C dew point nitrogen). The SSP reactor was set at a temperature of 207.5 ° C and a residence time of 12 hours. Microphotos of these chips are shown in Figure 3. The results of Example 1 are shown in the table.

Examples 2-4 utilized and further processed latent heat crystallization chips.

example (Option A)

Both stages of crystallization were abandoned. The latent heat crystallization granule at 140 ° C (see micrographs of these chips in Figure 4) was fed directly to a standard SSP reactor (carrier gas: -75 ° C dew point nitrogen) on an appropriate conveyor without intermediate storage. Temperature in SSP reactor - 210 ° C, residence time -12 hours.

example (Option B)

The 140 ° C granulate obtained by latent heat crystallization was fed to a solid phase dealdehydeization step (DAH) (carrier gas: -30 ° C dew point nitrogen) via a suitable conveyor without intermediate storage or intercooling. The temperature during the solid phase dealdehyde step is 213 ° C and the residence time is 6.7 hours.

example (variant C)

According to the invention, a suspension of a commercially available acetaldehyde reducing additive of Color Matrix was added to the melt stream for 120 seconds before latent heat crystallization. The granulate obtained from the latent heat crystallization at 140 ° C was cooled to about 50 ^° C and sent for processing into blanks. Prior to the preparation of the blanks, the granulate was dried under standard drying conditions (5 hours at 170 ° C) in a standard air dryer. No adhesion was found. The blanks were made on a Husky billet forming machine with two cavities LX 160 P. The AA content of the blanks was 7 min.md

Table:

An example 1 2 3 4 Primary material I.V. [dl / g] 0.63 0.60 0.74 0.80 AA [Md.m] 8.8 41 43 1.0 KTG [%] 53.1 42.0 42.0 42.0 HOF [kJ / kg] 41.6 43.8 42.7 For further processing conditions Variant Benchmark (SSP reactor) A (SSP reactor) B (DAH) C (straight) VWZ [h] 12th 12th 6.7 0 T [° C] 207.5 210 213 0 Δ I.V. [dl / g] 0.19 0.20 0.06 0 Rear 'product I.V. [dl / g] 0.80 0.80 0.80 - AA [Md.m] 0.5 0.8 0.9 KTG [%] 55.2 51.5 50.0 - HOF [kJ / kg] 58.6 52.0 52.0

Claims (13)

DEFINITION OF INVENTION 1. Polyester or copolyester granulate having a degree of crystallization of at least 38%, containing 0.5 to 100 ppm, preferably 0.5 to 70 ppm, preferably 0.5 to 60 ppm, with an enthalpy of acetaldehyde and less than 50 kJ / kg of melt. the fact that under the light microscope, the visible microstructure units in the polarization contrast of the granule outer layer are smaller than in the center of this granule. Polyester or copolyester granulate according to claim 1, characterized in that it is obtained by crystallization of latent heat. Polyester or copolyester granulate according to claims 1 and 2, characterized in that it has a minimum intrinsic viscosity of 0.53 dl / g. Use of a polyester or copolyester granulate according to claims 1-3, characterized in that the amount of acetaldehyde ranges from 20 to 70 ppm, preferably from 20 to 55 ppm, in solid phase polycondensation (SSP). The use according to claim 4, wherein the polyester or copolyester granulate has a minimum intrinsic viscosity before entering the solid phase polycondensation (SSP) of 0.53 dl / g. Use according to claim 4, characterized in that the constant minimum temperature of the surface of the polyester or copolyester granulate between the latent heat crystallization unit and the solid phase polycondensation (SSP) is 100 ° C, preferably -115 ° C, preferably 135 ° C. Use according to claim 4, characterized in that the enthalpy of granulate melt after solid phase polycondensation (SSP) is less than 60 kJ / kg, preferably less than 55 kJ / kg. Use of a polyester or copolyester granulate according to claims 1-3, characterized in that the amount of acetaldehyde is from 20 to 100 ppm, preferably from 30 to 60 ppm, for solid phase dealdehyde (DAH). Use according to claim 8, characterized in that the polyester or copolyester granulate has a minimum intrinsic viscosity against solid phase dealdehyde (DAH) of 0.65 dl / g. Use according to claim 8, characterized in that the polyester or copolyester granulate has a constant minimum temperature between the latent heat crystallization unit and the solid phase dealdehyde (DAH) of 100 ° C, preferably -115 ° C, preferably 135 ° C. Use according to claim 8, characterized in that the enthalpy of granulate melt after solid phase dealdehyde (DAH) is less than 55 kJ / kg. 12. Use of a polyester or copolyester granulate according to claims 1-3 for the direct production of molded articles, characterized in that they have a degree of crystallization of more than 38%, 0.5-3 ppm, preferably 0.5-1 ppm, acetaldehyde, when introduced into the forming unit. less than 50 kJ / kg of melt enthalpy. 13. A process for the preparation of a granulate according to claims 1-3 from a continuous or discontinuous melt in a polycondensation reactor melt having a high viscosity polyester or a copolyester melt, characterized in that it comprises a latent heat crystallization step yielding a granulate having a degree of crystallization 5-100 ppm, preferably 0.5-70 ppm, preferably 0.5-60 ppm, acetaldehyde.