PROCESS FOR THE PRODUCTION OF THERMOPLASTIC POLYURETHANES

Description

[0001] The present invention relates to a process for treating thermoplastic polyurethane, the treated thermoplastic polyurethane and its use.

[0002] Thermoplastic polyurethanes (TPU) are widely used because they exhibit good elastomer properties and are easily thermoplastically processed. By appropriately selecting the components, a wide range of mechanical properties can be achieved. An overview of TPU, its properties, and applications is provided, for example, in Kunststoffe 68 (1978) 819, Kautschuk, Gummi, Kunststoffe 35 (1982) 569; G. Becker, D. Braun: Kunststoff-Handbuch, Vol. 7 "Polyurethane" Munich, Vienna, Carl Hanser Verlag 1983. An overview of the various manufacturing processes is provided in Plastikverarbeiter 40 (1989). The most important technical processes for producing TPU are the extruder process (DE 1 964 834) and the mixing head-belt process (GB 1,057,018).

[0003] TPUs are typically composed of linear polyols, such as polyester, polyether, or polycarbonate polyols, organic diisocyanates, and short-chain, mostly difunctional alcohols (chain extenders). Additives, catalysts, dyes, and fillers may also be used. TPUs can be produced batchwise or continuously.

[0004] Typically, after production, TPUs are discharged from a reaction extruder in the form of polymer strands, which are then cooled with water on a cooling belt and subsequently granulated in a granulator (strand granulation). Alternatively, granulation can also take place in a granulator directly connected to the reaction extruder, where granulation takes place in the presence of cooling water (e.g., underwater granulation). Due to these process steps, a certain amount of residual moisture remains on the resulting granules, so a drying process is often necessary. For this purpose, the granules can be dried in a downstream dryer. They can then be filled into the desired packaging.

[0005] However, this type of granule treatment often leads to fluctuations in product quality due to residual moisture and incompletely reacted reactive groups, particularly isocyanate groups. These residual isocyanate groups can react with remaining water molecules from the residual moisture in the granules, forming primary amino groups with the release of carbon dioxide. These amino groups can no longer contribute to further molecular weight buildup, meaning that the targeted final molecular weight of the TPU can no longer be achieved. This often negatively impacts the mechanical properties of the TPU, which depend significantly on its molecular weight. In a further possible reaction step, the amino groups can also react with any remaining, minimal amounts of free isocyanate groups to form urea groups.Compared to urethane groups, urea groups have a significantly higher melting point, which often leads to unmelted particles in films or foils during extrusion processing of TPU, which significantly reduces their quality or can even render the extruded articles unusable.

[0006] US 2005 / 043492 A1 discloses the drying of TPU pellets using a dehumidifying dryer at 70 °C for 5 hours. The inlet air dew point is specified as -70 °C.

[0007] JP 3 602668 B2 discloses the drying of polyurethane pellets at 80 °C for 10 hours. The atmospheric dew point is given as -30 °C.

[0008] US 2009 / 326108 A1 discloses the drying of TPU pellets using a dehumidifying dryer at 70 °C for 5 hours. The inlet air dew point is specified as -50 °C.

[0009] US 5,780,573 discloses the drying of polyurethane fibers at 80 °C for 10 hours. The atmospheric dew point is given as -30 °C.

[0010] The task was therefore to provide a process for the treatment of TPU that ensures that the TPU granules are chemically reacted as completely as possible before being packaged in suitable packaging containers and thus disadvantages such as fluctuating product quality, such as poor extrusion quality and inadequate mechanical properties, can be avoided.

[0011] According to the invention, this object is achieved by a method according to claim 1 for the treatment of thermoplastic polyurethane, wherein the treatment comprises the following steps: I) Providing the thermoplastic polyurethane (TPU-1) obtainable or obtained by reacting at least one polyisocyanate with at least one polyol, and II) Exposing the thermoplastic polyurethane (TPU-1) to a temperature in the range from 10 °C to 150 °C under a gas atmosphere, wherein the gas of the gas atmosphere has a dew point of ≤ - 10 °C, to obtain a treated thermoplastic polyurethane (TPU-2), characterized in that step II) takes place in a container or silo and the thermoplastic polyurethane (TPU-1) is fed via a hose and / or a pipe to the container or silo for step 11), wherein furthermore the hose and / or the pipe each have a gas atmosphere and the gas of the gas atmosphere has a dew point of < - 10 °C.

[0012] It was surprisingly found that thermoplastic polyurethane (TPU-2) treated in this way exhibits reproducible product quality and reproducible mechanical properties, as well as being almost completely chemically reacted. Furthermore, it was surprisingly found that the degree of polymerization is increased by the process according to the invention. It is essential to the invention that the thermoplastic polyurethane (TPU-1) is annealed in a gas atmosphere whose gas has a dew point of ≤ -10 °C.

[0013] Within the context of the present invention, the word "one" in connection with countable quantities is to be understood as a numeral only if this is explicitly stated (e.g., by the expression "exactly one"). For example, when "one polyol" is mentioned below, the word "one" is to be understood merely as an indefinite article and not as a numeral. Thus, it also encompasses an embodiment containing a mixture of at least two polyols.

[0014] According to the invention, the terms "comprising" or "containing" preferably mean "consisting essentially of" and particularly preferably "consisting of".

[0015] Within the scope of the invention, the thermoplastic polyurethane (TPU-1) can also be obtained or have been obtained by reacting several different polyisocyanates, preferably diisocyanates, with several different polyols. Within the scope of the invention, the thermoplastic polyurethane (TPU-1) can also be obtained or have been obtained by reacting several different polyisocyanates, preferably diisocyanates, with several different polyols and with one or more chain extenders, preferably diols with a molecular weight of less than or equal to 500 g / mol.

[0016] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1) has undergone a multi-stage process comprising the following steps before being provided in step I): a) extruding the thermoplastic polyurethane (TPU-1), b) granulating the extruded thermoplastic polyurethane (TPU-1) from step a), and c) drying the thermoplastic polyurethane (TPU-1) from step b).

[0017] The reaction of the at least one polyisocyanate with the at least one polyol prior to extrusion in step a) can take place, for example, in a reactive extruder, a unit equipped with static mixers upstream of the extruder, or a mixing head. Preferably, both steps take place in a reactive extruder. The reaction and extrusion take place at temperatures in the range from 100°C to 250°C. Granulation is carried out, for example, by strand granulation or underwater granulation, with the extruded thermoplastic polyurethane (TPU-1) preferably being cooled to less than 100°C prior to granulation. Vibrating screen extractors and centrifugal dryers, for example, can be used to dry the granulated thermoplastic polyurethane.

[0018] To produce the thermoplastic polyurethane (TPU-1), at least one polyol and at least one organic polyisocyanate, preferably at least one diisocyanate and optionally at least one short-chain diol (chain extender), are used as main structural components. In a preferred embodiment, the thermoplastic polyurethane (TPU-1) is obtained by reacting at least one polyisocyanate with at least one polyol and with at least one chain extender. In another preferred embodiment, the thermoplastic polyurethane (TPU-1) is obtained by reacting at least one diisocyanate with at least one polyol and with at least one chain extender.

[0019] Catalysts can be added to accelerate the TPU formation reaction. Additives, auxiliaries, and additives may be used to achieve specific resistance to weathering, UV light, hydrolysis, oxidation, abrasion, and contamination, as well as to improve processing properties. Monofunctional chain terminators may also be used if necessary. To adjust the properties, the components can be varied within a relatively wide molar ratio. Molar ratios of polyols to chain extenders of 1:1 to 1:12 have proven effective. This results in products with hardnesses in the range of 45 Shore A to 85 Shore D.

[0020] The thermoplastic polyurethane (TPU-1) can be produced continuously using known processes, for example, with reaction extruders or the one-shot belt process or the prepolymer process, or discontinuously using the known prepolymer process. In these processes, the reacting components can be mixed with one another sequentially or simultaneously, with the reaction starting immediately. In the extruder process, the components and, if appropriate, catalysts and / or other auxiliaries and additives are introduced into the extruder individually or as a mixture, e.g., at temperatures of 100 to 280°C, preferably 140 to 250°C. The resulting TPU is extruded, cooled, and granulated.

[0021] Suitable production processes for thermoplastic polyurethanes are disclosed, for example, in EP 0 922 552 A1, DE 101 03 424 A1 or WO 2006 / 072461 A1. Production is usually carried out on a belt system or a reaction extruder, but can also be carried out on a laboratory scale, for example using the hand-casting process. Depending on the material properties of the components, these are all mixed together directly or individual components are premixed and / or pre-reacted, e.g. to form prepolymers, and only then are they subjected to polyaddition. In a further embodiment, a thermoplastic polyurethane is first produced from the components, optionally with a catalyst, into which auxiliary substances may also be incorporated. Homogeneous distribution is preferably carried out in an extruder, more preferably a twin-screw extruder.

[0022] To produce the thermoplastic polyurethanes according to the invention, the synthesis components are preferably reacted in the presence of catalysts and optionally auxiliaries and / or additives, usually in amounts such that the equivalence ratio of NCO groups of the diisocyanates to the sum of the hydroxyl groups of the components used is 0.95 to 1.05:1, preferably 0.97 to 1.03:1, more preferably 0.98 to 1.02:1.

[0023] Suitable polyols are all polyols known to those skilled in the art, preferably linear hydroxyl-terminated polyols with a number-average molecular weight (Mn) of 500 to 5000 g / mol. They are therefore often referred to as "essentially linear polyols." Polyesterdiols, polyetherdiols, polyetheresterdiols, polycaprolactonediols, polycarbonatediols, polyethercarbonatediols, or mixtures thereof are preferred. The molecular weights of such polyols are usually calculated from their OH number (hydroxyl number), which is known to those skilled in the art. The OH number is determined titrometrically according to DIN 53240. The molecular weight of polyols can be calculated from the OH number (OHN) using the following formula: Mn = 1000 mg / g ⋅ z ⋅ 56.106 g / Mol OHZ mg / g

[0024] Where z represents the number of OH groups in the macromolecule. For a linear diol, z = 2. Due to production reasons, these often contain small amounts of nonlinear compounds.

[0025] Suitable polyester diols can be prepared, for example, from dicarboxylic acids having 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, and polyhydric alcohols. Examples of suitable dicarboxylic acids include: aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, and sebacic acid, and aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid, and terephthalic acid. The dicarboxylic acids can be used individually or as mixtures, e.g., in the form of a succinic, glutaric, and adipic acid mixture. To prepare the polyester diols, it may be advantageous, where appropriate, to use the corresponding dicarboxylic acid derivatives, such as carboxylic acid diesters having 1 to 4 carbon atoms in the alcohol radical, carboxylic acid anhydrides, or carboxylic acid chlorides, instead of the dicarboxylic acids.Examples of polyhydric alcohols are glycols having 2 to 12, preferably 2 to 6, carbon atoms, such as ethylene glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 1,12-dodecanediol, 2,2-dimethyl-1,3-propanediol, 1,3-propanediol, and dipropylene glycol. Depending on the desired properties, the polyhydric alcohols can be used alone or, if appropriate, in mixtures with one another. Also suitable are esters of carbonic acid with the aforementioned diols, particularly those having 4 to 6 carbon atoms, such as 1,4-butanediol and / or 1,6-hexanediol. Such esters of carbonic acid are also referred to as polycarbonate diols. Also suitable as esters are condensation products of ω-hydroxycarboxylic acids, for example ω-hydroxycaproic acid and preferably polymerization products of lactones, for example optionally substituted ω-caprolactones.Preferred polyesterdiols are ethanediol polyadipates, 1,4-butanediol polyadipates, ethanediol-1,4-butanediol polyadipates, 1,6-hexanediol neopentylglycol polyadipates, 1,6-hexanediol-1,4-butanediol polyadipates, and polycaprolactones. The polyesterdiols have a number-average molecular weight (Mn) of 500 to 5000 g / mol, preferably 600 to 4000 g / mol, and particularly preferably 800 to 3000 g / mol. They can be used individually or in the form of mixtures. The molecular weights of such diols are usually calculated from their OH number, as explained above.

[0026] Suitable polyether diols can be prepared by reacting one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene radical with a starter molecule containing two active hydrogen atoms. Examples of alkylene oxides that may be mentioned are: ethylene oxide, 1,2-propylene oxide, epichlorohydrin, 1,2-butylene oxide, and 2,3-butylene oxide. Ethylene oxide, propylene oxide, and mixtures of 1,2-propylene oxide and ethylene oxide are preferably used. The alkylene oxides can be used individually, alternately one after the other, or as mixtures. Examples of suitable starter molecules include: water, amino alcohols such as N-alkyldiethanolamines, for example N-methyldiethanolamine, and diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol. If necessary, mixtures of starter molecules can also be used. Suitable polyetherols also include the hydroxyl-containing polymerization products of tetrahydrofuran.Trifunctional polyethers can also be used in proportions of 0 to 20 wt.% based on the bifunctional polyethers, but no more than in an amount sufficient to produce a thermoplastically processable product. The essentially linear polyether diols have a number-average molecular weight (Mn) of 500 to 18,000 g / mol, preferably 750 to 12,000, and particularly preferably 900 to 4,200 g / mol. They can be used individually or in the form of mixtures. The molecular weights of such diols are usually calculated from their OH number, as explained above.

[0027] Suitable polyetheresters can be prepared, for example, by reacting short-chain polyetherdiols, such as polytetrahydrofurans with molecular weights of 250 to 1000 g / mol, with organic dicarboxylic acids, such as succinic acid or adipic acid. The polyetheresterdiols have a number-average molecular weight (Mn) of 600 to 5000 g / mol, preferably 700 to 4000 g / mol, and particularly preferably 800 to 3000 g / mol. They can be used individually or in the form of mixtures. The molecular weights of such diols are usually calculated from their OH number, as explained above.

[0028] Suitable polycarbonatediols can be prepared, for example, by reacting short-chain diols, such as 1,4-butanediol or 1,6-hexanediol, with diphenyl carbonate or dimethyl carbonate using catalysts and eliminating phenol or methanol. The polycarbonatediols have a number-average molecular weight (Mn) of 500 to 6000 g / mol, preferably 750 to 4000 g / mol, and particularly preferably 800 to 3000 g / mol. The molecular weights of such diols are usually calculated from their OH number, as explained above. They can be used individually or in the form of mixtures.

[0029] Suitable polyethercarbonatediols can be prepared, for example, by reacting short-chain polyetherdiols, such as polytetrahydrofurans having molecular weights of 250 to 1000 g / mol, with diphenyl or dimethyl carbonate with the aid of catalysts and eliminating phenol or methanol. Furthermore, polyethercarbonatediols can be prepared by copolymerizing alkylene oxides, such as ethylene oxide or propylene oxide, or mixtures thereof, with carbon dioxide with the aid of suitable catalysts, such as double metal cyanide catalysts. The polyethercarbonatediols have a number-average molecular weight (Mn) of 500 to 8000 g / mol, preferably 750 to 6000 g / mol, and particularly preferably 1000 to 4500 g / mol. The molecular weights of such diols are usually calculated from their OH number, as explained above.

[0030] Suitable polyisocyanates, preferably organic diisocyanates, include, for example, aliphatic, cycloaliphatic, araliphatic, heterocyclic, and aromatic diisocyanates, as described, for example, in Justus Liebig's Annalen der Chemie, 562, pages 75 to 136. It is irrelevant whether the polyisocyanates and diisocyanates were obtained by phosgenation or by a phosgene-free process. The polyisocyanates and diisocyanates and / or their precursor compounds can be obtained from fossil or biological sources. Preferably, 1,6-diisocyanatohexane (HDI) is prepared from 1,6-hexamethylenediamine, and 1,5-diisocyanatopentane is prepared from 1,5-pentamethylenediamine, with the 1,6-hexamethylenediamine and the 1,5-pentamethylenediamine being obtained from biological sources, preferably by bacterial fermentation.

[0031] The following may be mentioned as examples: aliphatic diisocyanates such as 1,6-hexamethylene diisocyanate, 1,5-pentamethylene diisocyanate and 1,10-decane diisocyanate, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4- and -2,6-cyclohexane diisocyanate and the corresponding isomer mixtures, 4,4'-, 2,4'- and 2,2'-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures and aromatic diisocyanates such as 2,4-tolylene diisocyanate, mixtures of 2,4- and 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 2,2'-diphenylmethane diisocyanate, mixtures of 2,4'-diphenylmethane diisocyanate and 4,4'-Diphenylmethane diisocyanate, urethane-modified liquid 4,4'-diphenylmethane diisocyanates and / or 2,4'-diphenylmethane diisocyanates, 4,4'-diisocyanatodiphenylethane-(1,2) and 1,5-naphthylene diisocyanate.Preferred diisocyanates are 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate isomer mixtures with a 4,4'-diphenylmethane diisocyanate content of greater than 96 wt.%, and especially 4,4'-diphenylmethane diisocyanate and 1,5-naphthylene diisocyanate. These diisocyanates can be used individually or in mixtures. They can also be used together with up to 15% (calculated based on total diisocyanate), but not more than the amount of a polyisocyanate needed to produce a thermoplastically processable product. Examples include triphenylmethane 4,4',4"-triisocyanate and polyphenyl polymethylene polyisocyanates.

[0032] Diols or diamines with a molecular weight of 60 to 500 can be used as short-chain chain extenders, preferably aliphatic diols with 2 to 14 carbon atoms, such as ethanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, diethylene glycol, dipropylene glycol and in particular 1,4-butanediol. However, diesters of terephthalic acid with glycols having 2 to 4 carbon atoms, such as terephthalic acid bis-ethylene glycol or terephthalic acid bis-1,4-butanediol, hydroxyalkylene ethers of hydroquinone, such as 1,4-di(β-hydroxyethyl)hydroquinone, ethoxylated bisphenols, such as 1,4-di(β-hydroxyethyl)bisphenol A, (cyclo)aliphatic diamines, such as isophoronediamine, ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, N-methylpropylene-1,3-diamine, N,N'-dimethylethylenediamine and aromatic diamines, such as2,4-Toluenediamine and 2,6-toluenediamine, 3,5-diethyl-2,4-toluenediamine and / or 3,5-diethyl-2,6-toluenediamine, and primary mono-, di-, tri-, and / or tetraalkyl-substituted 4,4'-diaminodiphenylmethanes. Mixtures of the above-mentioned chain extenders can also be used. Smaller amounts of triols can also be added, but no more than the amount of a triol required to produce a thermoplastically processable product.

[0033] The catalysts commonly used in polyurethane chemistry can be used as catalysts. Suitable catalysts are conventional tertiary amines known per se, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo-[2,2,2]octane, and the like, and in particular organic metal compounds such as titanium compounds, iron compounds, bismuth compounds, zinc compounds, zirconium compounds, tin compounds, e.g. tin diacetate, tin dioctoate, tin dilaurate or the tin dialkyl salts of aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate or the like. Preferred catalysts are organic metal compounds, in particular titanic acid esters, bismuth compounds, zirconium compounds, iron or tin compounds. Dibutyltin dilaurate, tin dioctoate and titanic acid esters are very particularly preferred.

[0034] Additives, auxiliaries, and additives that can be used include, for example, lubricants such as fatty acid esters, their metal soaps, fatty acid amides, and silicone compounds, antiblocking agents, inhibitors, stabilizers against hydrolysis, light, heat, and discoloration, flame retardants, dyes, pigments, inorganic or organic fillers, nucleating agents, and reinforcing agents. Reinforcing agents are, in particular, fibrous reinforcing materials such as inorganic fibers, which are manufactured using state-of-the-art technology and can also be coated with a size. Further information on the auxiliaries and additives mentioned can be found in the specialist literature, for example JH Saunders, KC Frisch: "High Polymers", Volume XVI, Polyurethanes, Parts 1 and 2, Interscience Publishers 1962 and 1964 respectively, R.Gächter, H.Müller (Ed.): Taschenbuch der Kunststoff-Additive, 3rd Edition, Hanser Verlag, Munich 1989, or DE-A 29 01 774.

[0035] Monofunctional chain terminators such as monoalcohols such as 1-butanol, 1-hexanol, 1-octanol, and stearyl alcohol, or monoamines such as 1-butylamine or stearylamine, can be used to adjust a specific TPU molecular weight. These also sometimes serve as demolding aids.

[0036] A gas atmosphere with a dew point of ≤ -10 °C can be achieved by dehumidifying or humidifying the gas, depending on the dew point of the gas before treatment. The dew point of the gas can be determined using a mirror dew point hygrometer, for example. Dehumidification of the gas can be achieved using a variety of dryers, such as condensation dryers or absorption dryers. The use of rotary dehumidifiers as adsorption dryers has proven particularly effective. The moist gas stream is passed through a rotating sorption wheel coated with adsorbent and thus dried. On the opposite side, the wheel is regenerated to effectively ensure the continuous processing of the gas to be dried.By expanding the system technology, for example, with pre- and aftercooler modules, dew points down to -65 °C and thus a relative process gas humidity of 0.05% can be achieved. The dew point of the gas atmosphere can be set as the desired dew point directly on the adsorption dryer. The adsorption dryer then operates continuously, generating a process gas with the selected dew point. Adsorption dryers have special functions, e.g., drying occurs until a specified dew point (°C) is reached, which is measured with external sensors connected to the device.

[0037] In a preferred embodiment of the process according to the invention, the gas in the gas atmosphere has a dew point of ≤-15 °C, preferably ≤-20 °C, and particularly preferably ≤-25 °C. In a further preferred embodiment of the process according to the invention, the gas has a dew point in the range from -10 °C to -40 °C, preferably in the range from -15 °C to -35 °C, and particularly preferably in the range from -20 °C to -30 °C.

[0038] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1) is exposed to the temperature for a period of 1 hour to 12 hours, preferably a period of 2 hours to 10 hours, particularly preferably a period of 3 hours to 9 hours, very particularly preferably a period of 4 hours to 8 hours and even more preferably a period of 4 hours to 7 hours under a gas atmosphere.

[0039] In a preferred embodiment of the process according to the invention, the gas of the gas atmosphere is air, an inert gas, or a mixture of air and an inert gas, wherein the inert gas is preferably selected from the group consisting of nitrogen, carbon dioxide, argon and / or a mixture of at least two thereof.

[0040] In a preferred embodiment of the method according to the invention, the dew point of the gas in the gas atmosphere in step II) is kept constant upon entry into the device. Preferably, the dew point of the gas in the gas atmosphere in step II) and the dew point of the gas in the gas atmosphere in the hose and / or pipe through which the thermoplastic polyurethane (TPU-1) is fed to the device for step II) are substantially constant, i.e., the gas atmosphere in the device for step II) and the feed means (hose and / or pipe) has a substantially constant dew point at the set temperature in the device.

[0041] This has the advantage that the thermoplastic polyurethane (TPU-2) exhibits even better product consistency. This is particularly noticeable after processing of the (TPU-2) in the mechanical properties and extrusion quality of extruded foils and films.

[0042] In a preferred embodiment of the process according to the invention, the pressure of the gas atmosphere is in the range from 0.01 bar absolute to 5.0 bar absolute, preferably in the range from 0.1 bar absolute to 4.5 bar absolute, and particularly preferably from 0.2 to 3.5 bar absolute. "Bar absolute" in the sense of the invention means the measured pressure relative to zero pressure in empty space (vacuum).

[0043] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1) is exposed to a temperature in the range from 20 °C to 150 °C, preferably in the range from 25 °C to 130 °C, particularly preferably in the range from 30 °C to 110 °C and most preferably in the range from 30 °C to 100 °C under a gas atmosphere.

[0044] In the process according to the invention, step II) takes place in a container or silo. For example, after granulation and drying in a downstream dryer, the thermoplastic polyurethane (TPU-1) can be conveyed through conveyor lines into, for example, a silo and tempered for several hours with circulation at temperatures of 10 to 100 °C in the presence of air that has been supplied to the silo via pipelines with a previously set, preferably constant, dew point of ≤ - 10 °C. It is advantageous if a gas with a previously set, preferably constant, dew point of ≤ - 10 °C is also used to transport the thermoplastic polyurethane (TPU-1) through the transport lines to the device, for example a tempering silo.The thermoplastic polyurethane (TPU-1) can, for example, be moved and conveyed by an air flow caused either by applying a vacuum to a transport line, whereby an air flow with a previously set dew point of ≤ - 10 °C enters the line, or by compressed air.

[0045] In the process according to the invention, the thermoplastic polyurethane (TPU-1) is fed to the container or silo for step II) via a hose and / or a pipeline, wherein the hose and / or the pipeline each have a gas atmosphere and the gas of the gas atmosphere has a dew point of ≤- 10 °C. According to a preferred embodiment, the hose and / or the pipeline each have a temperature in the range of 10 °C to 100 °C. This has the advantage that the pre-dried thermoplastic polyurethane (TPU-1) no longer comes into contact with moisture and / or fluctuating ambient conditions during transport to the device of step II), thus preventing fluctuating product qualities and thus a loss of quality due to uncontrolled side reactions.Such a loss of quality is particularly noticeable when the dew point of the gas atmosphere fluctuates greatly and / or is above -10 °C, i.e. when there are no constant ambient conditions, such as those caused by the seasonal influence of the weather at the production site.

[0046] In a preferred embodiment of the method according to the invention, the device, the hose, the pipeline and / or the gas atmosphere has a temperature in the range of 10 °C to 100 °C.

[0047] In a further preferred embodiment of the method according to the invention, the pressure of the gas atmosphere in the device, the hose and / or the pipeline is constant.

[0048] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1 and TPU-2) is surrounded by the gas of the gas atmosphere, preferably circulated by the gas. This has the advantage that the thermoplastic polyurethane is heated evenly and has a uniform heat distribution. The circulation prevents dead spaces from occurring between the thermoplastic polyurethane (TPU-1 and TPU-2), in particular the thermoplastic polyurethane granules, and thus ensures uniform and efficient drying. Furthermore, the circulation prevents the individual thermoplastic polyurethane granules from sticking together and thus prevents the thermoplastic polyurethane granules from clumping together.

[0049] In a preferred embodiment of the process according to the invention, the ratio of the volume of the gas in the gas atmosphere to the volume of the thermoplastic polyurethane (TPU-1) is in the range from 1 to 1000, preferably in the range from 1.5 to 500, and particularly preferably in the range from 2 to 100. In a further preferred embodiment of the process according to the invention, the ratio of the volume of the gas in the gas atmosphere to the volume of the thermoplastic polyurethane (TPU-1 and TPU-2) is in the range from 1 to 1000, preferably in the range from 1.5 to 500, and particularly preferably in the range from 2 to 100.

[0050] In a preferred embodiment of the process according to the invention, the NCO group content of the thermoplastic polyurethane (TPU-2) is at least 30%, preferably at least 40% and particularly preferably at least 50% lower than the NCO group content of the thermoplastic polyurethane (TPU-1), the NCO group content being determined based on DIN EN ISO 14896.In a further preferred embodiment of the process according to the invention, the NCO group content of the thermoplastic polyurethane (TPU-2) is at least 30%, preferably at least 40%, and particularly preferably at least 50% lower after the thermoplastic polyurethane has been exposed to a temperature in the range from 10°C to 100°C under a gas atmosphere, based on the NCO group content of the thermoplastic polyurethane (TPU-1) before it has been exposed to a temperature in the range from 10°C to 100°C under a gas atmosphere, wherein the NCO group content is determined based on DIN EN ISO 14896. Based on DIN EN ISO 14896 (January 2009) means that this procedure was carried out with the following deviations: N-methylpyrrolidone is used as the solvent instead of toluene. The concentration of dibutylamine and hydrochloric acid is 0.5 mol / l. Dibutylamine is dissolved in dimethyl sulfoxide instead of toluene.The hydrochloric acid is not dissolved in water, but in a mixture of 85% isopropanol and 15% water.

[0051] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1) is exposed to a temperature in the range from 20 °C to 100 °C, preferably in the range from 30 °C to 100 °C, particularly preferably in the range from 50 °C to 100 °C and most preferably in the range from 50 °C to 90 °C under a gas atmosphere.

[0052] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1 and / or TPU-2) is a granulate and has an average size in the range of 2 mm to 8 mm, preferably in the range of 3 mm to 7 mm, and particularly preferably in the range of 3.5 mm to 6.5 mm.

[0053] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1 and / or TPU-2) is a granulate and has a surface area in the range from 12 mm 2< to 201 mm 2<, preferably in the range from 28 mm 2< to 154 mm 2< and particularly preferably in the range from 38 mm 2< to 133 mm 2<.

[0054] In a preferred embodiment of the process according to the invention, the thermoplastic polyurethane (TPU-1 and / or TPU-2) has a diameter in the range of 2 mm to 8 mm in the case of spherical granules and a diameter in the range of 1 mm to 7.5 mm in the case of strand granules.

[0055] In a preferred embodiment of the method according to the invention, the treatment comprises the following steps: I) Providing the thermoplastic polyurethane (TPU-1) obtainable or obtained by reacting at least one polyisocyanate with at least one polyol, and II) exposing the thermoplastic polyurethane (TPU-1) to a temperature in the range of 10 °C to 100 °C under a gas atmosphere for a period of 1 hour to 12 hours, wherein the gas of the gas atmosphere has a dew point of ≤ - 10 °C, to obtain a treated thermoplastic polyurethane (TPU-2).

[0056] In a preferred embodiment of the method according to the invention, the treatment comprises the following steps: I) Providing the thermoplastic polyurethane (TPU-1) obtainable or obtained by reacting at least one polyisocyanate with at least one polyol, and II) Exposing the thermoplastic polyurethane (TPU-1) to a temperature in the range of 10 °C to 100 °C under a gas atmosphere for a period of 1 hour to 12 hours in a silo, wherein the gas of the gas atmosphere has a dew point of ≤ - 10 °C, to obtain a treated thermoplastic polyurethane (TPU-2).

[0057] In a preferred embodiment of the method according to the invention, the treatment comprises the following steps: I) Providing the thermoplastic polyurethane (TPU-1) obtainable or obtained by reacting at least one polyisocyanate with at least one polyol, and II) Exposing the thermoplastic polyurethane (TPU-1) to a temperature in the range of 50 °C to 90 °C under a gas atmosphere for a period of 1 hour to 12 hours, wherein the gas of the gas atmosphere has a dew point in the range of -15 °C to -35 °C, to obtain a treated thermoplastic polyurethane (TPU-2).

[0058] In a preferred embodiment of the method according to the invention, the treatment comprises the following steps: I) Providing the thermoplastic polyurethane (TPU-1) obtainable or obtained by reacting at least one polyisocyanate with at least one polyol, and II) Exposing the thermoplastic polyurethane (TPU-1) to a temperature in the range of 50 °C to 90 °C under a gas atmosphere for a period of 1 hour to 12 hours in a silo, wherein the gas of the gas atmosphere has a dew point in the range of -15 °C to -35 °C, to obtain a treated thermoplastic polyurethane (TPU-2).

[0059] Also disclosed is a thermoplastic polyurethane (TPU-2) obtained or obtainable by the process according to the invention.

[0060] Also disclosed are the thermoplastically processable polyurethanes (TPU-2) produced by the continuous process according to the invention and their use for producing molded parts by injection molding, as well as producing films, foils, hoses, pipes and cable sheathing by extrusion and producing coatings by calendering.

[0061] Furthermore, the use of the thermoplastic polyurethane (TPU-2) according to the invention for producing a composition, a thermoplastic molding compound, a molded article, a foil, a film and / or a fiber is disclosed.

[0062] Furthermore, the use of the process according to the invention for producing thermoplastic polyurethane (TPU-2) is disclosed.

[0063] Furthermore, the use of the process according to the invention for converting thermoplastic polyurethane (TPU-1) into thermoplastic polyurethane (TPU-2) is disclosed.

[0064] Furthermore, the use of the method according to the invention for the treatment of thermoplastic polyurethane (TPU-1) is disclosed.

[0065] Further embodiments of the present invention can be found in the claims and the examples.

[0066] The following examples serve to illustrate the invention. Examples TPU products used

[0067] Desmopan 385S: Aromatic, ester-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 85 Desmopan 2590A: Aromatic, ester-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 90 Desmopan 192A: Aromatic, ester-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 92 Desmopan 85085A: Aliphatic, ester- and ether-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 85 Desmopan 9370AU: Aromatic, ether-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 70 Desmopan 6080A: Aromatic, ether-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 80 Desmopan 9665DU: Aromatic, ether-based thermoplastic polyurethane from Covestro AG with a Shore D hardness of 65

[0068] To assess the influence of the conveying and drying air used on the properties of the respective TPU products, samples were taken immediately after production, granulation (strand granulation or underwater granulation, as specified in the subsequent tests), and subsequent pre-drying using a vibrating screen extractor or a centrifugal dryer (the type of pre-drying is specified in the subsequent tests). The respective TPU samples were then dried for 30 minutes at 110 °C using ambient air, the humidity of which fluctuates according to the external climatic conditions, and dry air (dew point -25 °C). The dry air, with a constant dew point of -25 °C, was generated using a rotary dehumidifier. The moist inlet gas stream (air stream) was passed through a rotating sorption wheel coated with adsorbent and thus dried.The dew point of the gas (the air stream) at the outlet of the rotary dehumidifier, i.e., after drying, was continuously measured using sensors to ensure the gas maintained a constant dew point at all times. A Helios dry air dryer and a Cerco-Semip "Turb etuve" circulating air dryer were used to dry the samples. The Helios dryer operated with dry air with a constant dew point of -25 °C. An air flow of 250 l / min was selected for drying the granulate samples. The Cerco-Semip Turb etuve dryer uses ambient air heated by a heating coil for drying. A fan circulates the air. 1 kg of sample was dried for 30 minutes at 110 °C. In both dryers, the air flowed around the granulate at atmospheric pressure (1013.25 hPa).After drying, the NCO content, solution viscosities, melt flow index (MVR), and mechanical properties of the TPU samples were determined. The molecular weight distribution of some samples was also determined using gel permeation chromatography. The corresponding values ​​before drying were not determined because the same starting sample was used for both drying methods. Before drying, only the NCO content was determined to determine the decrease due to drying. Test conditions: Tensile test:

[0069] The tensile test was carried out on S1 bars [corresponding to test specimen type 5 according to EN ISO 527-1 (02. 2012), punched out from injection molded sheets] or as bars directly injected according to DIN 53504 (03. 2017) at a tensile speed of 200 mm / min. Melt flow index (MVR)

[0070] The MVR measurements were taken at different temperatures, depending on the product, with a 10 kg (98 N) contact weight and a 5-minute preheating time according to ISO 1133 (June 2005) using a Göttfert MP-D MVR device. The measurement temperatures for the respective products are listed in the tables below. Solution viscosity

[0071] The solution viscosity was measured using an Ubbelohde viscometer type 50110 in accordance with DIN 51562-1 (January 1999). 99.7 g of N-methyl-2-pyrrolidone with 0.1% dibutylamine and 0.4 g of TPU granules were weighed. The samples were stirred on a magnetic stirrer at approximately 70 °C for approximately 1 hour and cooled to room temperature overnight. The samples and a blank value (pure solvent) were measured at 25 °C using a Schott viscosity measuring station. The relative solution viscosity is calculated from the time (solution) divided by the time (solvent). The Schott viscosity measuring station consists of an AVS 400 viscosity measuring station, an ASV / S measuring stand, a glass thermostat, and a Ubbelohde viscometer type 50110. NCO content:

[0072] Based on DIN EN ISO 14896 (January 2009) with the following deviations: N-methylpyrrolidone is used as the solvent instead of toluene. The concentration of dibutylamine and hydrochloric acid is 0.5 mol / l. Dibutylamine is dissolved in dimethyl sulfoxide instead of toluene. The hydrochloric acid is dissolved in a mixture of 85% isopropanol and 15% water, rather than water. Molecular weights

[0073] The number-average molecular weights (Mn) and weight-average molecular weights (Mw) of the thermoplastic polyurethanes were determined by GPC, dissolved in HFIP (hexafluoroisopropanol). The molecular weight was determined using a column combination consisting of a guard column and three 30 × 8 mm GPC columns connected in series: 1000 Å PSS PFG 7µ, 300 Å PSS PFG 7µ, and 100 Å PSS PFG 7µ. Flow rate: 1 ml / min HFIP (fluorochem, 99.9%) with potassium trifluoroacetate from Aldrich, 98% (3 g per 400 ml), Smarline RI detector 2300 Knauer. 100 µl of sample solution were injected, concentration 2 mg / ml. The samples are passed through a 0.45 µm PTFE filter before measurement. Measurements are performed at room temperature, calibrated with a PMMA standard kit from PSS (from 102 - 981000 g / mol at the peak maximum). Ambient air was used as the reference gas in the experiments.During the measurement period, the ambient air had a dew point of 17.2 °C, a relative humidity of 84%, a pressure of 1014 hPa, and a temperature of 20 °C; the absolute humidity was 14.5 g / m 3 . The dry process air, referred to as dry air, had a dew point of -25 °C, a relative humidity of 3.4%, a pressure of 1014 hPa, and a temperature of 20 °C; the absolute humidity was 0.6 g / m 3 . Example 1: Desmopan 2590A: Production in a reaction extruder, underwater granulation, pre-drying using a centrifugal dryer.

[0074] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0075] Results: Table 1: Results of annealing Desmopan 2590A with ambient air and dry air. Pd refers to the polydispersity, which is calculated by dividing Mw by Mn. Tempering with Residual NCO content Solution viscosity MVR (190 °C) 100% module Tear resistance Elongation at break GPC molecular weight distribution [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Mn Mw Pd Before tempering 0,132 Ambient air 0,012 1,472 18,6 11,9 40,1 448 63540 125200 1,97 Dry air 0,007 1,487 14,8 11,5 43,2 474 72660 138300 1,90

[0076] It is clearly evident that annealing with dry air results in a slightly higher solution viscosity, a lower MVR value, and higher tear strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is at a similar level after both annealing types. Since using dry air during annealing results in higher solution viscosity and higher tear strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. Therefore, the reduction in the residual NCO content after annealing with ambient air must also have resulted in a reaction of some of the NCO groups with water, which is undesirable. This is also confirmed by the GPC molecular weight distribution results, with a higher molecular weight for the sample annealed with dry air. Example 2: Desmopan 385S: Production in a reaction extruder, granulation by strand granulation and pre-drying by vibrating screen suction.

[0077] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0078] Results: Table 2: Results of tempering Desmopan 385S with ambient air and dry air. Tempering with Residual NCO content Solution viscosity MVR (200 °C) 100% module Tear resistance Elongation at break [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Before tempering 0,186 Ambient air 0,065 1,48 19 5,1 45,8 649 Dry air 0,068 1,56 13 5,1 51,2 627

[0079] It is clearly evident that annealing with dry air results in higher solution viscosity, lower MVR, and higher ultimate tensile strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is at a similar level after both annealing types. Since the use of dry air during annealing results in higher solution viscosity and higher ultimate tensile strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. Therefore, the reduction in the residual NCO content after annealing with ambient air must also have resulted in a reaction of some of the NCO groups with water, which is undesirable. Example 3: Desmopan 192: Production in a reaction extruder, granulation by strand granulation and pre-drying by vibrating screen suction.

[0080] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0081] Results: Table 3: Results of annealing Desmopan 192 with ambient air and dry air. Pd refers to the polydispersity, which is calculated by dividing Mw by Mn. Tempering with Residual NCO content Solution viscosity MVR (190 °C) 100% module Tear resistance Elongation at break GPC molecular weight distribution [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Mn Mw Pd Before tempering 0,223 Ambient air 0,073 1,476 32,2 9,0 52,6 611 97030 246200 2,11 Dry air 0,092 1,503 25,2 9,2 55,8 605 116800 207700 2,14

[0082] It is clearly evident that annealing with dry air results in higher solution viscosity, a lower MVR value, and higher tear strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is below 0.1% after both annealing types. Since the use of dry air during annealing results in higher solution viscosity and higher tear strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. Therefore, the reduction in the residual NCO content after annealing with ambient air must also have resulted in a reaction of some of the NCO groups with water, which is undesirable. This is also confirmed by the GPC molecular weight distribution results, with a higher molecular weight for the sample annealed with dry air. Example 4:Desmopan 85085A: Production in a reaction extruder, underwater granulation, pre-drying using a centrifugal dryer.

[0083] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0084] Results: Table 4: Results of annealing Desmopan 85085A with ambient air and dry air. Pd refers to the polydispersity, which is calculated by dividing Mw by Mn. Tempering with Residual NCO content Solution viscosity MVR (180 °C) 100% module Tear resistance Elongation at break GPC molecular weight distribution [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Mn Mw Pd Before tempering 0,226 Ambient air 0,087 1,52 49 6,2 37,8 918 123470 244200 1,98 Dry air 0,085 1,71 32 6,4 50,0 846 223820 427500 1,91

[0085] It is clearly evident that annealing with dry air results in higher solution viscosity, a lower MVR value, and higher tear strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is at a similar level after both annealing types. Since using dry air during annealing results in higher solution viscosity and higher tear strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. Therefore, the reduction in the residual NCO content after annealing with ambient air must also have resulted in a reaction of some of the NCO groups with water, which is undesirable. This is also confirmed by the GPC molecular weight distribution results, with a higher molecular weight for the sample annealed with dry air. Example 5:Desmopan 9370AU: Production in a reaction extruder, granulation by strand granulation and pre-drying by vibrating screen suction.

[0086] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0087] Results: Table 5: Results of tempering Desmopan 9370AU with ambient air and dry air. Tempering with Residual NCO content before tempering Solution viscosity MVR (190 °C) 100% module Tear resistance Elongation at break [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Before tempering 0,188 Ambient air 0,072 1,41 30 2,7 27,2 836 Dry air 0,068 1,44 20 2,8 31,3 787

[0088] It is clearly evident that annealing with dry air results in a slightly higher solution viscosity, a lower MVR value, and higher tear strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is at a similar level after both annealing types. Since the use of dry air during annealing results in a higher solution viscosity and higher tear strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. The reduction in the residual NCO content after annealing with ambient air must therefore also have resulted in a reaction of some of the NCO groups with water, which is undesirable. Example 6: Desmopan 6080A: Production in a reaction extruder, granulation by strand granulation and pre-drying by vibrating screen suction.

[0089] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0090] Results: Table 6: Results of annealing Desmopan 6080A with ambient air and dry air. Pd refers to the polydispersity, which is calculated by dividing Mw by Mn. Tempering with Residual NCO content Solution viscosity MVR (190 °C) 100% module Tear resistance Elongation at break GPC molecular weight distribution [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Mn Mw Pd Before tempering 0,330 Ambient air 0,143 1,404 25,8 5,9 23,9 672 159100 369500 2,32 Dry air 0,144 1,488 11,3 6,0 26,8 552 226600 602700 2,66

[0091] It is clearly evident that annealing with dry air results in higher solution viscosity, a lower MVR value, and higher tear strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is at the same level after both annealing types. Since using dry air during annealing results in higher solution viscosity and higher tear strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. The reduction in the residual NCO content after annealing with ambient air must therefore also have resulted in a reaction of some of the NCO groups with water, which is undesirable. This is also confirmed by the results of the GPC molecular weight distribution, with a significantly higher molecular weight for the sample annealed with dry air. Example 7:Desmopan 9665DU: Production in a reaction extruder, granulation by strand granulation and pre-drying by vibrating screen suction.

[0092] The TPU sample was split and, as described above, one part of the TPU sample was annealed with ambient air and the other part of the TPU sample was annealed with dry air.

[0093] Results: Table 7: Results of tempering Desmopan 9665DU with ambient air and dry air. Tempering with Residual NCO content before tempering Solution viscosity MVR (210 °C) 100% module Tear resistance Elongation at break [Wt.%] [ml / 10 min] [MPa] [MPa] [%] Before tempering 0,343 Ambient air 0,126 1,50 12 27,6 53,0 836 Dry air 0,131 1,62 8 29,0 54,7 787

[0094] It is clearly evident that annealing with dry air results in higher solution viscosity, lower MVR, and higher ultimate tensile strength. This indicates a linear increase in molecular weight during annealing. The residual NCO content decreases significantly after annealing compared to the initial value and is at a similar level after both annealing types. Since the use of dry air during annealing results in higher solution viscosity and higher ultimate tensile strength, the reduction in the residual NCO content is due to a linear increase in molecular weight. Therefore, the reduction in the residual NCO content after annealing with ambient air must also have resulted in a reaction of some of the NCO groups with water, which is undesirable.

[0095] Examples 1-7 clearly demonstrate the advantage achieved when TPU samples are treated with dry air instead of ambient air.

Claims

1. Process for the treatment of thermoplastic polyurethane, wherein the treatment comprises the following steps: I) providing the thermoplastic polyurethane (TPU-1) obtainable or obtained by reacting at least one polyisocyanate with at least one polyol, and II) subjecting the thermoplastic polyurethane (TPU-1) to a temperature in the range from 10°C to 150°C under a gas atmosphere, wherein the gas of the gas atmosphere having a dew point of ≤ -10°C, to obtain a treated thermoplastic polyurethane (TPU-2), characterized in that step II) is carried out in a vessel or silo and the thermoplastic polyurethane (TPU-1) is supplied to the vessel or silo for step II) via a hose and / or a pipeline, wherein in addition the hose and / or the pipeline each comprise a gas atmosphere and the gas of the gas atmosphere has a dew point of ≤ -10°C.

2. Process according to Claim 1, wherein the thermoplastic polyurethane (TPU-1) prior to being provided in step I) has undergone a multi-stage process comprising the following steps: a) extruding the thermoplastic polyurethane (TPU-1), b) pelletizing the extruded thermoplastic polyurethane (TPU-1) from step a), and c) drying the thermoplastic polyurethane (TPU-1) from step b).

3. Process according to either of Claims 1 and 2, characterized in that the gas of the gas atmosphere has a dew point of ≤ -15°C, preferably of ≤ -20°C, and particularly preferably of ≤ -25°C.

4. Process according to any of Claims 1 to 3, characterized in that the thermoplastic polyurethane (TPU-1) is subjected to the temperature for a period of from 1 hour to 12 hours, preferably a period of from 2 hours to 10 hours, particularly preferably a period of from 3 hours to 9 hours, very particularly preferably a period of from 4 hours to 8 hours and even more preferably a period of from 4 hours to 7 hours under gas atmosphere.

5. Process according to any of Claims 1 to 4, characterized in that the gas of the gas atmosphere is air, an inert gas, or a mixture of air and an inert gas, wherein the inert gas is preferably selected from the group consisting of nitrogen, carbon dioxide, argon and / or a mixture of at least two of these.

6. Process according to any of Claims 1 to 5, characterized in that the hose and / or the pipeline each have a temperature in the range from 10°C to 100°C.

7. Process according to any of Claims 1 to 6, characterized in that the dew point of the gas of the gas atmosphere in step II) is kept constant on entry into the vessel or silo.

8. Process according to any of Claims 1 to 7, characterized in that the pressure of the gas atmosphere is in the range from 0.01 bar absolute to 5.0 bar absolute, preferably in the range from 0.1 bar absolute to 4.5 bar absolute and particularly preferably in the range from 0.2 to 3.5 bar absolute.

9. Process according to any one of claims 1 to 8, characterized in that the thermoplastic polyurethane (TPU-1 and TPU-2) is flowed around by the gas of the gas atmosphere, preferably circulated by the gas.

10. Process according to any of Claims 1 to 9, characterized in that the ratio of the volume of the gas of the gas atmosphere to the volume of the thermoplastic polyurethane (TPU-1) is in the range from 1 to 1000, preferably in the range from 1.5 to 500, and particularly preferably in the range from 2 to 100.

11. Process according to any of Claims 1 to 10, characterized in that the NCO group content of the thermoplastic polyurethane (TPU-2) is at least 30%, preferably at least 40% and particularly preferably at least 50% lower than the NCO group content of the thermoplastic polyurethane (TPU-1), wherein the NCO group content being determined in accordance with DIN EN ISO 14896.

12. Process according to any of Claims 1 to 11, characterized in that the thermoplastic polyurethane (TPU-1) is subjected to a temperature in the range from 20°C to 150°C, preferably in the range from 25°C to 130°C, particularly preferably in the range from 30°C to 110°C and very particularly preferably in the range from 30°C to 100°C under a gas atmosphere.