WO2025168329A1 - Process for preparing polypropylene ether-containing thermoplastic polyurethanes - Google Patents

Abstract

The present invention relates to a process for preparing polypropylene ether-containing thermoplastic polyurethanes and to polypropylene ether-containing thermoplastic polyurethanes obtained or obtainable by these processes. The invention further relates to the use of these polypropylene ether-containing thermoplastic polyurethanes and to articles comprising or consisting of the polypropylene ether-containing thermoplastic polyurethane.

Description

Process for the preparation of polypropylene ether-containing thermoplastic polyurethanes

The present invention relates to a process for producing polypropylene ether-containing thermoplastic polyurethanes, as well as to polypropylene ether-containing thermoplastic polyurethanes obtained or obtainable by these processes. Furthermore, the invention relates to the use of these polypropylene ether-containing thermoplastic polyurethanes and to articles comprising or consisting of the polypropylene ether-containing thermoplastic polyurethane.

State of the art

Thermoplastic polyurethanes (TPUs) have been around for a long time. They are of great technical importance due to their combination of high-quality mechanical properties with the well-known advantages of cost-effective thermoplastic processability. By using different chemical components, a wide range of mechanical properties can be achieved. An overview of TPUs, their properties, and applications is provided, for example, in Kunststoffe 68 (1978), pages 819 to 825, or Kautschuk, Gummi, Kunststoffe 35 (1982), pages 568 to 584. TPUs are composed of linear polyols, usually polyethers or polyesters, organic diisocyanates, and short-chain diols (chain extenders). TPUs are usually solvent-free and can be produced continuously or batchwise. The best known technical manufacturing processes, which are also used technically, are the belt process (GB 1057018 A) and the extruder process (DE 1964834 A-l and DE 2059570 A-l).

To adjust the properties, the components can be varied within a relatively wide molar ratio. Molar ratios of macrodiols to chain extenders ranging from 1:1 to 1:12 have proven effective. The amount of chain extender allows the hardness of the TPU to be adjusted within a wide range. This results in products with hardnesses ranging from approximately 40 Shore A to approximately 85 Shore D.

To improve processing performance, especially cycle time, TPUs that exhibit a very high solidification rate after processing in injection-molded articles are of particular interest across the entire hardness range from approximately 40 Shore A to approximately 85 Shore D. Especially with hard TPUs and soft TPUs, problems often arise with the chemical coupling of the hard and soft segments due to excessive polarity differences between these phases. As a result, the full potential of the mechanical properties and processing characteristics cannot often be fully exploited. There has been no shortage of attempts to overcome these disadvantages using special processes. A process for producing thermoplastically processable polyurethanes is described by W. Bräuer et al. (EP-A 1757632). A multi-stage OH prepolymer process improves the homogeneity of the TPU. However, this improved homogeneity slows the solidification rate of the TPU.

A process for producing soft, easily demolded thermoplastic polyurethane elastomers with low shrinkage is described by W. Bräuer et al. (EP-A 1338614). The demolding behavior of TPUs with hardnesses between 45 Shore A and 65 Shore A was improved by pre-extension of the soft segments. At very high hardnesses, this process has significant disadvantages because it leads to incompatibilities between the hard and soft phases, preventing good coupling between these phases. As a result, the high molecular weight of the TPU required for good mechanical properties is not achieved. Furthermore, this process is very unstable in practice due to excessively high and fluctuating viscosities of the prepolymer stage, and it no longer functions satisfactorily below 60 Shore A, frequently leading to extruder downtimes.

To improve the low-temperature impact strength of polyester-based TPUs for ski boot applications, for example, polyether polyols with a molecular weight greater than 1600 g/mol are used as modifiers, such as polytetramethylene ether glycol (US4980445A) and polypropylene diol ether (WO/2018/158327). Due to the incompatibility of the hard and soft phases in the TPU, which leads to poor coupling between these phases, such polyethers are difficult to incorporate as a pure soft phase into TPUs harder than 60 Shore D. A hard TPU with good low-temperature impact strength is difficult to produce without a modifier.

The use of polypropylene glycol or poly(propylene oxide) homopolymers (hereinafter also referred to as C3 polyether homopolymer polyol) as a polyol component in the production of thermoplastic polyurethanes is interesting, among other things, due to its low cost. The use of polypropylene glycol in the production of thermoplastic polyurethanes is known, for example, from WO 2020/109566 A1, in which polyols based on polypropylene glycol are reacted with polyisocyanates.

A disadvantage of using polypropylene glycol as a polyol component, however, is that so far only thermoplastic polyurethanes with relatively low Shore A hardnesses, or theoretical hardnesses, can be produced that exhibit sufficient mechanical properties and abrasion resistance. Hard thermoplastic polyurethanes based on polypropylene glycol generally exhibit these typical properties only to a limited extent or not at all, making them unsuitable for applications requiring significantly harder materials. Furthermore, these types of thermoplastic polyurethanes exhibit low low-temperature impact strength, which also precludes their use in articles exposed to low temperatures. Better hardness with good low-temperature impact strength can be achieved with polytetrahydrofurans (hereinafter also referred to as C4 polyether homopolymer polyols). However, these have the disadvantage of being significantly more expensive than the aforementioned C3 polyether homopolymer polyols and having a poorer CCT balance.

The object of the present invention was therefore to provide a process for producing polypropylene ether-containing thermoplastic polyurethanes with high hardness and improved mechanical properties, in particular increased tensile strength and increased low-temperature impact strength. In particular, a process for the more cost-effective production of polyether-containing thermoplastic polyurethanes is to be provided, which preferably has an improved CCE balance.

This object was surprisingly achieved by a process for the preparation of thermoplastic polyurethanes by reacting a composition comprising or consisting of the components:

(A) at least one polyol which

(Al) at least one C3 polyether homopolymer polyol and

(A2) optionally at least one C2 polyether homopolymer polyol and/or at least one C2/C3 polyether block copolymer polyol,

(B) at least one organic polyisocyanate,

(C) at least one chain extender,

(D) at least one non-oxidizing acid,

(E) optionally at least one catalyst,

(F) optionally at least one additive, auxiliary and/or adjuvant, and

(G) optionally at least one monofunctional chain terminator, characterized in that the process comprises or consists of the following steps:

1) Providing and reacting a first mixture M1 comprising the total amount of component (A), a partial amount of component (B) and optionally a partial amount or the total amount of component (E), component (F) and/or component (G) to form a second mixture (M2) containing at least one NCO-functional prepolymer, wherein in process step 1) a molar ratio of component (B) to component (A) is in the range from 1.1:1.0 to 5.0:1.0,

2) reacting the mixture M2 with the total amount of component (C) in the presence of component (D) and optionally in the presence of a further portion of component (E), Component (F) and/or component (G), to obtain a third mixture (M3) containing at least one OH-functional prepolymer, wherein components (C) and (D) are added separately or as mixture M2a to mixture M2, wherein i) mixture M2a has a pH of <6, preferably <5.5, more preferably <5.2 (at 23°C), or ii) when components (C) and (D) are added separately to mixture M2, component (D) is added in an amount such that a theoretical mixture of components (C) and (D) would have a pH of <6, preferably <5.5, more preferably <5.2 (at 23°C), wherein for the determination of the pH, a mixture corresponding to the theoretical mixture is prepared and measured,

3) reacting the mixture M3 with the remaining amount of component (B) and optionally the remaining amount of component (E), component (F) and/or component (G) to obtain the thermoplastic polyurethane, wherein over all process steps a molar ratio of component (B) to the sum of component (A) and component (C) in the range from 0.9:1.0 to 1.2:1.0 is present.

Furthermore, the invention relates to a thermoplastic polyurethane obtained or obtainable by the process according to the invention.

Furthermore, the invention relates to the use of the thermoplastic polyurethane according to the invention for the production of injection-molded articles, extruded articles, pressed articles, compression-molded articles, 3D-printed articles, articles for mechanical engineering, road and rail construction, medical and dental articles, in particular splints for the treatment of malocclusions, shoes, in particular ski boots, articles for the automotive industry, articles for the electrical industry, in particular cable sheathing, housings and plugs, consumer articles, coatings, hoses, profiles, belts, films, fibers, nonwovens, textiles, damping elements, sealing materials.

Furthermore, the invention relates to an article which comprises or consists of the thermoplastic polyurethane according to the invention.

In the context of this invention, C2 polyether homopolymer polyol is defined as a polyol based on polyethylene glycol or poly(ethylene oxide), C3 polyether homopolymer polyol is defined as a polyol based on Based on polypropylene glycol or poly(propylene oxide), and C2/C3 polyether block copolymer polyol is understood to mean a polyol based on polyethylene glycol or poly(ethylene oxide) as well as polypropylene glycol or poly(propylene oxide). The "C" in "C2,""C3," etc., stands for a carbon atom, with the number following it indicating the number of carbon atoms in the repeating unit of the respective polymer.

In the method according to the invention, the

• C2 polyether homopolymer polyol has a number average molecular weight in the range from 500 to 4000 g/mol, preferably 1000 to 3000 g/mol;

• C3 polyether homopolymer polyol has a number average molecular weight in the range from 500 to 8000 g/mol, preferably 1000 to 4500 g/mol;

• C2/C3 polyether block copolymer polyol has a number average molecular weight in the range from 1000 to 4000 g/mol, preferably 1500 to 2500 g/mol;

If component (A2) is used, the mass ratio of component (Al) to (A2) is > 1:9, preferably > 3:7, in each case based on the total mass of components (Al) and (A2).

Preferably, component (A) consists exclusively of component (Al).

Suitable organic polyisocyanates of component (B) used in steps 1) and 3) include, for example, aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic polyisocyanates, as described in Justus Liebigs Annalen der Chemie, 562, pp. 75-136.

The following may be mentioned as examples: aliphatic diisocyanates such as 1,6-hexamethylene diisocyanate, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate and 1-methyl-2,6-cyclohexane diisocyanate and the corresponding isomer mixtures, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate and 2,2'-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures, aromatic diisocyanates such as 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate 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 2,4'-Diphenylmethane diisocyanates, 4,4'-Diisocyanatodiphenylethane-(1,2) and 1,5-Naphthylene diisocyanate. Preferably used are 1,6-Hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-Dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate isomer mixtures with a 4,4'- Diphenylmethane diisocyanate content of >96 wt.%, particularly 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 wt.% (calculated based on the total amount of diisocyanate) of a polyisocyanate, for example triphenylmethane-4,4',4"-triisocyanate or polyphenyl polymethylene polyisocyanates.

In a further preferred embodiment of the process according to the invention, a diphenylmethane diisocyanate isomer mixture having a 4,4-diphenylmethane diisocyanate content of greater than 96 wt.% based on the total weight of component (B) is used as component (B); preferably, 4,4-diphenylmethane diisocyanate is used as component (B).

In a further preferred embodiment of the process according to the invention, 1,6-hexamethylene diisocyanate is used as component (B).

Suitable as component (C) (chain extender) are all linear diols known to the skilled person with a molecular weight of 62 g/mol to 500 g/mol. The diols and/or their precursor compounds can be obtained from fossil or biological sources. Suitable diols are preferably aliphatic diols having 2 to 14 carbon atoms, such as ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, diethylene glycol, and dipropylene glycol. However, diesters of terephthalic acid with glycols containing 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-(hydroxyethyl)-hydroquinone, and ethoxylated bisphenols, are also suitable. Particularly preferred short-chain diols are ethanediol, 1,4-butanediol, 1,6-hexanediol, and 1,4-di-(hydroxyethyl)-hydroquinone. Mixtures of the aforementioned chain extenders can also be used. Small amounts of diamines and/or triamines can also be added.

In a further preferred embodiment of the process according to the invention, one or more diols selected from the group consisting of 1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-di-(beta-hydroxyethyl)hydroquinone or a mixture of at least two of these are used as component (C), preferably 1,2-ethanediol, 1,4-butanediol or mixtures thereof are used as component (C) and particularly preferably 1,4-butanediol is used as component (C).

Phosphoric acid, p-toluenesulfonic acid monohydrate and adipic acid can be used as non-oxidizing acids (D).

The catalysts commonly used in polyurethane chemistry can be used as catalysts (E). Suitable catalysts are known and common tertiary amines, such as E.g., triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo[2,2,2]octane, and the like, as well as, in particular, organic metal compounds such as titanic acid esters, iron compounds, bismuth 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, iron or tin compounds. Dibutyltin dilaurate, tin dioctoate, and titanic acid esters are very particularly preferred.

Additives, auxiliaries, and additives (F) 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 may also be coated with a size. Further information on the aforementioned auxiliaries and additives can be found in the specialist literature, for example, J.H. Saunders, K.C. Frisch: "High Polymers", Volume XVI, Polyurethanes, Parts 1 and 2, Interscience Publishers 1962 and 1964, respectively, R.Gächter, H.Müller (Ed.): Handbook of Plastics Additives, 3rd Edition, Hanser Verlag, Munich 1989, or DE-A 29 01 774.

Monoalcohols such as 1-butanol, 1-hexanol, 1-octanol and stearyl alcohol or monoamines such as 1-butylamine and stearylamine can be used as monofunctional chain terminators (G) to adjust a specific TPU molecular weight.

The amounts of the reaction components for the NCO-functional prepolymer formation in step 1) are selected such that the NCO/OH ratio of polyisocyanate to polyol in step 1) is 1.1: 1 to 5.0: 1.

The components are thoroughly mixed and the NCO prepolymer reaction in step 1) is preferably brought to complete conversion (based on the polyol component).

Subsequently, component (C) is mixed in as a chain extender (step 2) and an essentially OH-functional prepolymer is formed.

“Essentially” in this context means that at least 95 mol%, preferably at least 98 mol%, particularly preferably at least 99 mol% and even more preferably at least 99.5 mol%, even more preferably at least 99.8 mol% and most preferably 100 mol% of the total amount of the prepolymers formed are OH-functional prepolymers. Component (D) is mixed in with component (C) or as a single component.

In the first case, the pH of the mixture is adjusted to the values mentioned in claim 1 by means of component (D).

In the second case, component (D) is added to the reactor in such amounts that the pH of a theoretical mixture of components (C) and (D) corresponds to the values stated in claim 1. To determine the pH, a mixture corresponding to the theoretical mixture is prepared and measured.

The pH values are determined electrochemically at 23°C in accordance with DIN 19268:2021-10. The measurement is performed using the pH electrode "Solvotrode Easy Clean 6.0229.010" from Methrom AG. The Solvotrode is supplied with 2 mol/L LiCl in ethanol as the reference electrolyte.

In step 3), the remaining amount of component (B) is added, maintaining an NCO/OH ratio of 0.9:1 to 1.2:1. Preferably, the same component (B) is used in step 3) as in step 1).

In a preferred embodiment of the process according to the invention, the molar ratio of NCO-functional prepolymer to component (C) in process step 2) is less than 1.0. Component (C) is thus present in molar excess.

The reaction is preferably carried out at an isocyanate index of 0.9 to 1.2, more preferably from 0.95 to 1.1, and particularly preferably from 0.97 to 1.03. The isocyanate index (also called index, NCO/OH index, or isocyanate index) is understood here as the quotient of the actual amount of isocyanate groups used [mol] and the actual amount of isocyanate-reactive groups used [mol]. In other words, the index indicates the percentage ratio of the actual amount of isocyanate used to the stoichiometric amount of isocyanate, i.e., the amount calculated for the conversion of the OH equivalents. An equivalent amount of NCO groups and NCO-reactive hydrogen atoms corresponds to an NCO/OH index of 1. The isocyanate index is calculated using the following formula:

Index = [(mol isocyanate groups) / (mol isocyanate-reactive groups)]

The process according to the invention can be carried out in solvent or solvent-free. It is preferred that the process be carried out solvent-free.

The thermoplastic polyurethane polymers can be produced discontinuously (hand-casting process) or continuously using the process according to the invention, with a continuous process being preferred, especially on an industrial scale (for example, as an inline one-shot process). The best-known technical production processes for producing TPU are the belt process (GB-A 1 057 018) and the extruder process (DE-A 1 964 834, DE- A2 059570 and US-A 5 795 948). Conventional mixing units, preferably those operating with high shear energy, are suitable for producing thermoplastically processable polyurethane polymers. Examples for continuous production include co-kneader machines, preferably extruders, such as twin-screw extruders and Bus kneaders.

The thermoplastic polyurethane polymers can be produced, for example, on a twin-screw extruder by preparing the prepolymer in the first part of the extruder and subsequently adding the chain extender and polyisocyanate in the second part. According to the invention, the chain extender (component (C)) must be added before the other polyisocyanate. The chain extender and polyisocyanate must not be added simultaneously into the same metering opening of the extruder.

However, the NCO and OH prepolymer can also be produced outside the extruder in a separate, upstream prepolymer reactor, discontinuously in a vessel or continuously in a tube with a static mixer or a stirred tube (tube mixer).

An OH prepolymer produced in a separate prepolymer reactor can also be mixed with the diisocyanate using a first mixing device, e.g., a static mixer, and with the remaining polyisocyanate using a second mixing device, e.g., a mixing head. This reaction mixture is then continuously applied to a carrier, preferably a conveyor belt, analogously to the known belt process, where it is allowed to react until the material solidifies, optionally with heating of the belt.

In a preferred embodiment, the process is carried out at a reaction temperature in the range of 140 °C to 240 °C. In a further preferred embodiment, the process is carried out in an extruder at a reaction temperature in the range of 140 °C to 240 °C.

It has proven advantageous to carry out the process according to the invention in the presence of nitrogen. The advantage here is that oxidation processes during TPU production at high temperatures of, for example, 180 to 240 °C are minimized, resulting in a significantly lower color number of the TPU granules. In the hand-casting process, it is sufficient to fill the reaction vessel with nitrogen and to apply a nitrogen blanket at a rate of 1 to 10 liters of nitrogen per hour during the metered addition of the individual components. In the extruder process, it is advantageous to feed a nitrogen stream into an initial barrel of the extruder, for example barrel 1 to barrel 3. The amount of nitrogen fed in is in the range of 10 to 1000 liters per hour, preferably 100 to 750 liters per hour, and particularly preferably 100 to 500 liters per hour.

Preferably, the theoretical hardness of the thermoplastic obtained according to the invention is

Polyurethane > 30%, whereby the theoretical hardness is calculated using the following formula: Theoretical hardness = (n(chain extender)*M(polyisocyanate)+m(chain extender))/ _m total with n = amounts of components, M = molar mass of components and m = masses of components.

The thermoplastic polyurethane according to the invention preferably has

• a tensile strength greater than 17 MPa, preferably at least 18 MPa, more preferably at least 20 MPa, measured according to ISO 53504 (2009-10); and/or

• a Charpy impact strength of at least 30 KJ/m ² , preferably 50 to 140 KJ/m ² , measured at -20 °C according to DIN EN ISO179/leA (2010).

The Charpy impact strength measured at -20 °C according to DIN EN ISO 179/11A (2010) is understood in this invention as a measure of low-temperature impact strength. The injection-molded parts undergo Charpy impact strength testing according to DIN EN ISO 179/11A (2010) at -20 °C. The test specimen has the following dimensions: 80 ± 2 mm length, 10.0 ± 0.2 mm width, and 4.0 ± 0.2 mm thickness. The test specimen is notched. The notch root radius rN is 0.25 ± 0.05 mm.

Experimental part

Examples and comparison examples:

The present invention is discussed below with reference to examples, but is not limited to them.

Components used:

• Polyol 1 = polypropylene glycol (C3 polyether homopolymer polyol), starter propylene glycol (poly(propylene oxide) homopolymer); OH number approx. 56: proportion of secondary terminal OH groups: >90%;

• Polyol 2 = poly(propylene oxide)-poly(ethylene oxide) block copolymer (C2/C3 polyether block copolymer polyol): propylene glycol (starter) with polymerized alkylene oxides (molar ratio of ethylene oxide units to propylene oxide units of approximately 51:49); OH number approximately 56, proportion of primary terminal OH groups: >90%), KOH catalyzed

• Polyol 3 = polypropylene glycol (C3 polyether homopolymer polyol), starter propylene glycol (poly(propylene oxide) homopolymer); OH number approx. 28: proportion of secondary terminal OH groups: >90%

• Polyol 4 = Terathane®1000 (commercial product from Invista: polytetramethylene glycol; molecular weight approx. 2000g/mol

• Polyol 5 = Terathane®2000 (commercial product from Invista: polytetramethylene glycol; molecular weight approx. 2000g/mol

• BDO = 1,4-butanediol (BDO, purity > 99 wt%) was purchased from Ashland.

• MDI = 4,4‘-diphenylmethane diisocyanate (MDI, purity > 99 wt%) was purchased from Covestro AG.

Measurement methods used:

• Titration of the OH numbers according to DIN 53240-2:2007-11

• Tensile test: Measurement according to ISO 53504 (2009-10) with a tensile speed of 200 mm/min;

• Charpy impact strength test (low-temperature impact strength): The injection-molded specimens were subjected to Charpy impact strength tests according to DIN EN ISO179/1eA (2010) at -20°C. The specimen has the following dimensions: 80±2mm length, 10.0±0.2mm width, and 4.0±0.2mm thickness. The specimen is notched. The notch root radius rN is 0.25±0.05mm.

• pH value measurement: based on DIN 19268:2021-10

10g of the acid is dissolved in 90g of 1,2-ethanediol aqueous solution (10% water content). The solution is diluted with butanediol to the concentration used for TPU production. The pH values of this mixture are measured. Instruments used: Titrando 905 with two Dosino 800, Tiamo 2.5 software, with Solvotrode Easy clean electrode 6.0229.010, Metrohm AG

Examples:

Table 1 illustrates the invention with some examples. The manufacturing processes used are described below.

Production (discontinuous process):

Step 1: Partial amount 1 (see Table 1) of the MDI is brought to a conversion of > 90 mol-%, based on the polyol, at approx. 140°C with 1 mol of polyol or polyol mixture while stirring.

Step 2: The chain extender is added to the stirred reaction mixture and stirred vigorously for approximately 10 seconds. The acid is then added in defined amounts (Table 1).

Step 3: Part 2 (see Table 1) of the MDI is added to the stirred reaction mixture. The reaction mixture is stirred for another 20 seconds, then poured onto a tray and annealed for 30 minutes at 120°C.

The resulting TPU cast sheets were cut and granulated. The granules were processed into rods (mold temperature: 40°C; rod size: 80x10x4 mm) or sheets (mold temperature: 70°C; size: 125x50x2 mm) using an Arburg Allrounder 470S injection molding machine at a temperature range of 180°C to 230°C and a pressure range of 650 to 750 bar with an injection flow rate of 10 to 35 cm3/s.

The mechanical values (tensile strength and tensile elongation) as well as the low-temperature impact strength according to Charpy were determined for the TPU products manufactured.

Production (continuous process e.g. reaction extruder):

Analogous to the discontinuous experiments, the TPU can also be produced continuously, e.g. using a twin-screw reaction extruder (however, the production is not limited to this form of presentation, see “belt process”).

Using a gear pump, the MDI portion 1, preheated to 60°C, was metered into a tube equipped with a spiked mixer. Using a second gear pump, a polyol or polyol mixture heated to 140°C was pumped into the same tube. The tube had a length/diameter ratio of 8:1. The reaction mixture flowed continuously into a connected twin-screw extruder, which was heated externally to 140°C to 220°C. The acid was metered into the chain extender, and the chain extender and portion 2 of the MDI were added in the middle of the screw. The screw shaft speed was 300 rpm. At the end of the screw, the hot melt was granulated and cooled. The granules were Injection molded into test specimens on which the properties listed in the table were measured.

Examples 9, 11 and 12 describe a continuous process (extruder process).

Table 1

Table 2

* Comparative example not according to the invention; ** No processing possible;

^# Theoretical hardness (TH) is the weight fraction of the hard segment in the TPU: TH = (n(KV)*M(ISO)+m(KV))/m _ge s with KV = chain extender and ISO = isocyanate (here MDI)

- Comparative Examples 1 and 2 (Table 1) are TPU formulations without added acid. Comparative Example 1 has a very low tensile strength. With increased theoretical hardness (Comparative Example 2), TPU cannot be produced and/or processed by injection molding.

- Examples 3-12 (Table 1) show TPU formulations with addition of the acids with good tear strength.

Examples 3, 10, 11, and 12 (Tables 2 and 1) show TPU formulations with increased theoretical hardness with the addition of the acids, with good tensile strength and good low-temperature impact strength (Charpy impact strength). The Charpy impact strength is comparable to TPUs based on C4 polyether homopolymer polyols. However, the use of C3 polyether homopolymer polyols is more cost-effective and has a better CCU balance than C4 polyether homopolymer polyols.

Claims

Claims 1. Process for the preparation of thermoplastic polyurethanes by reacting a composition comprising or consisting of the components: (A) at least one polyol which (Al) at least one C3 polyether homopolymer polyol and (A2) optionally at least one C2 polyether homopolymer polyol and/or at least one C2/C3 polyether block copolymer polyol, (B) at least one organic polyisocyanate, (C) at least one chain extender, (D) at least one non-oxidizing acid, (E) optionally at least one catalyst, (F) optionally at least one additive, auxiliary and/or adjuvant, and (G) optionally at least one monofunctional chain terminator, characterized in that the process comprises or consists of the following steps: 1) Providing and reacting a first mixture M1 of the total amount of component (A), a partial amount of component (B) and optionally a partial amount or the total amount of component (E), component (F) and/or component (G) to form a second mixture (M2) containing at least one NCO-functional prepolymer, wherein in process step 1) a molar ratio of component (B) to component (A) is in the range from 1.1:1.0 to 5.0:1.0, 2) reacting the mixture M2 with the total amount of component (C) in the presence of component (D) and optionally in the presence of a further portion of component (E), component (F) and/or component (G), to obtain a third mixture (M3) containing at least one OH-functional prepolymer, wherein components (C) and (D) are added separately or as mixture M2a to the mixture M2, wherein i) the mixture M2a has a pH of <6, preferably <5.5, more preferably <5.2 (at 23°C), or ii) when components (C) and (D) are added separately to the mixture M2, component (D) is added in an amount such that a theoretical mixture of components (C) and (D) would have a pH of <6, preferably <5.5, more preferably <5.2 (at 23°C), whereby a mixture corresponding to the theoretical mixture is prepared and measured to determine the pH value, 3) reacting the mixture M3 with the remaining amount of component (B) and optionally the remaining amount of component (E), component (F) and/or component (G) to obtain the thermoplastic polyurethane, wherein over all process steps a molar ratio of component (B) to the sum of component (A) and component (C) in the range from 0.9:1.0 to 1.2:1.0 is present. 2. Process according to claim 1, characterized in that the C3 polyether homopolymer polyol has a number-average molecular weight in the range from 500 to 8000 g/mol, preferably 1000 to 4500 g/mol. 3. Process according to claim 2, characterized in that the C2 polyether homopolymer polyol has a number-average molecular weight in the range from 500 to 4000 g/mol, preferably 1000 to 3000 g/mol and/or the C2/C3 polyether block copolymer polyol has a number-average molecular weight in the range from 1000 to 4000 g/mol, preferably 1500 to 2500 g/mol. 4. Process according to one of claims 1 to 3, characterized in that the theoretical hardness of the thermoplastic polyurethane is > 30%, the theoretical hardness being calculated using the following formula: Theoretical hardness = (n(chain extender)*M(polyisocyanate)+m(chain extender))/ _m total with n = amounts of components, M = molar mass of components and m = masses of components. 5. Process according to one of claims 1 to 4, characterized in that the polyisocyanate of component (B) is selected from the group comprising or consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate, 1-methyl-2,6-cyclohexane diisocyanate, and the corresponding isomer mixtures, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures, 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate 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 2,4'-diphenylmethane diisocyanates, 4,4'-diisocyanatodiphenylethane-(1,2), 1,5-naphthylene diisocyanate and mixtures thereof. 6. The process according to any one of claims 1 to 5, characterized in that the chain extender of component (C) is selected from the group comprising or consisting of ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, diethylene glycol, dipropylene glycol, 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(hydroxyethyl)hydroquinone, and ethoxylated bisphenols, and mixtures thereof. 7. Process according to one of claims 1 to 6, characterized in that the non-oxidizing acid of component (D) is selected from the group comprising or consisting of phosphoric acid, p-toluenesulfonic acid monohydrate, adipic acid and mixtures thereof. 8. Method according to one of claims 1 to 7, characterized in that - the catalyst of component (E) is selected from the group comprising or consisting of tertiary amines, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo-[2,2,2]-octane, organic metal compounds such as titanic acid esters, iron compounds, bismuth 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, and mixtures thereof, and/or - the additive, auxiliary and/or additive of component (F) is selected from the group comprising or consisting of: 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, and mixtures thereof, and/or - the monofunctional chain terminator of component (G) is selected from the group comprising or consisting of: monoalcohols such as 1-butanol, 1-hexanol, 1-octanol and stearyl alcohol or monoamines such as 1-butylamine and stearylamine, and mixtures thereof. 9. Process according to one of claims 1 to 8, characterized in that the reaction is carried out at an isocyanate index of 0.9 to 1.2, preferably of 0.95 to 1.1, particularly preferably of 0.97 to 1.03. 10. Thermoplastic polyurethane obtained or obtainable by a process according to any one of claims 1 to 9. 11. Thermoplastic polyurethane according to claim 10, characterized in that the thermoplastic polyurethane has a tensile strength greater than 17 MPa, preferably at least 18 MPa, more preferably at least 20 MPa, measured according to ISO 53504 (2009-10), and/or a Charpy impact strength of at least 30 KJ/m ² , preferably 50 to 140 KJ/m ² , measured at -20 °C according to DIN EN ISO179/leA (2010). 12. Use of a thermoplastic polyurethane according to claim 10 or 11 for the production of injection-molded articles, extruded articles, pressed articles, compression-molded articles, 3D-printed articles, articles for mechanical engineering, road and rail construction, medical and dental articles, in particular splints for the treatment of malocclusions, shoes, in particular ski boots, articles for the automotive industry, articles for the electrical industry, in particular cable sheathing, housings and plugs, consumer articles, coatings, hoses, profiles, belts, films, fibers, nonwovens, textiles, damping elements or sealing materials. 13. An article comprising or consisting of thermoplastic polyurethane according to claim 10 or 11.