METHOD FOR PRODUCING THERMOPLASTIC POLYURETHANES

Abstract

The present invention relates to a process for the treatment of thermoplastic polyurethane, to the treated thermoplastic polyurethane and to the use thereof.

Claims

1. A process for the treatment of thermoplastic polyurethane, the treatment comprising: I) providing a thermoplastic polyurethane (TPU-1) obtained by reacting at least one polyisocyanate with at least one polyol, and II) subjecting the thermoplastic polyurethane (TPU-1) to a temperature in a range from 10° C. to 150° C. under a gas atmosphere, a gas of the gas atmosphere having a dew point of ≤−10° C., to obtain a treated thermoplastic polyurethane (TPU-2).

2. The process as claimed in claim 1, wherein, prior to being provided in step I), the thermoplastic polyurethane (TPU-1) has undergone a multi-stage process comprising: 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. The process as claimed in claim 1, wherein the gas of the gas atmosphere has a dew point of ≤−15° C.

4. The process as claimed in claim 1, wherein the thermoplastic polyurethane (TPU-1) is subjected to the temperature for a period of from 1 hour to 12 hours under gas atmosphere.

5. The process as claimed in claim 1, wherein the gas of the gas atmosphere is air, an inert gas, or a mixture of air and an inert gas.

6. The process as claimed in claim 1, wherein step II) is performed in an apparatus, wherein the apparatus is optionally a vessel or silo.

7. The process as claimed in claim 6, wherein the thermoplastic polyurethane (TPU-1) is supplied to the apparatus for step II) via a hose and/or a pipeline.

8. The process as claimed in claim 6, wherein the dew point of the gas of the gas atmosphere in step II) is kept constant on entry into the apparatus.

9. The process as claimed in claim 1, wherein the pressure of the gas atmosphere is in the range from 0.01 bar absolute to 5.0 bar absolute.

10. The process as claimed in claim 1, wherein the gas of the gas atmosphere flows around the thermoplastic polyurethane (TPU-1 and TPU-2).

11. The process as claimed in claim 1, wherein a 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.

12. The process as claimed in claim 1, wherein the NCO group content of the thermoplastic polyurethane (TPU-2) is at least 30% lower than the NCO group content of the thermoplastic polyurethane (TPU-1), the NCO group content being determined in accordance with DIN EN ISO 14896.

13. The process as claimed in claim 1, wherein the thermoplastic polyurethane (TPU-1) is subjected to a temperature in the range from 20° C. to 150° C. under a gas atmosphere.

14. A thermoplastic polyurethane (TPU-2) obtained by the process as claimed in claim 1.

15. A method of producing a composition, a thermoplastic molding compound, a molded article, a sheet, a film and/or a fiber, comprising: producing the composition, the thermoplastic molding compound, the molded article, the sheet, the film and/or the fiber, at least in part, with the thermplastic polyurethane (TPU-2) as claimed in claim 14.

16. (canceled)

17. The process as claimed in claim 5, wherein the inert gas is selected from the group consisting of nitrogen, carbon dioxide, argon, and a mixture of at least two of these.

18. The process of claim 7, wherein 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.

Description

EXAMPLES

[0077] TPU Products Used [0078] Desmopan 385S: aromatic, ester-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 85 [0079] Desmopan 2590A: aromatic, ester-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 90 [0080] Desmopan 192A: aromatic, ester-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 92 [0081] Desmopan 85085A: aliphatic, ester- and ether-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 85 [0082] Desmopan 9370AU: aromatic, ether-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 70 [0083] Desmopan 6080A: aromatic, ether-based thermoplastic polyurethane from Covestro AG with a Shore A hardness of 80 [0084] Desmopan 9665DU: aromatic, ether-based thermoplastic polyurethane from Covestro AG with a Shore D hardness of 65

[0085] To assess the influence of the conveying and drying air used on the properties of the respective TPU products, samples were taken immediately after the production, pelletization (strand pelletization or underwater pelletization, indicated in the following experiments) and subsequent pre-drying by means of a vibrating screen extractor or a centrifugal dryer (the nature of the pre-drying is indicated in the following experiments). The TPU samples were then dried for 30 minutes at 110° C., on the one hand with ambient air, the humidity of which fluctuates depending on the external climatic conditions, and on the other hand with dry air (dew point −25° C.). The dry air with a constant dew point of −25° C. was generated with a rotary dehumidifier. This involved passing the moist input gas stream (air stream) through a rotating sorption wheel coated with adsorbent and drying it in this way. The dew point of the gas (the air stream) at the exit of the rotary dehumidifier, i.e. after drying, was continuously measured by sensors so that the gas had a constant dew point at all times. A dry air dryer from Helios, on the one hand, and a “Turb etuve” circulating air dryer from Cerco-Semip, on the other, were used to dry the samples. The Helios dryer operated using dry air, with a constant dew point of −25° C. An air volume of 250 l/min was selected for drying the pellet samples. For drying, the Turb Etuve dryer from Cerco-Semip uses ambient air heated by a heating coil. A fan is used for circulating the air. In each case, 1 kg of sample was dried at 110° C. for 30 minutes. In both dryers, the respective air flowed around the respective pellets under standard pressure (1013.25 hPa). After drying, the NCO contents, the solution viscosities, the melt flow index (MVR), and the mechanical properties of the TPU samples were determined. In addition, the molecular weight distribution of some samples was determined by means of gel permeation chromatography. The corresponding values before drying were not determined because the starting sample for both drying methods was the same. Only the NCO content was determined before drying in order to determine the decrease as a result of the drying.

[0086] Test Conditions:

[0087] Tensile Test:

[0088] The tensile test was carried out on S1 bars [corresponds to type 5 test specimens in accordance with EN ISO 527-1 (02. 2012), stamped out from injection-molded slabs] or as directly injection molded bars in accordance with DIN 53504 (03. 2017) at a pulling rate of 200 mm/min.

[0089] Melt Flow Index (MVR)

[0090] Depending on the product, the MVR measurements were carried out at different temperatures under an applied weight of 10 kg (98 N) and with a preheating time of 5 min. in accordance with ISO 1133 (06. 2005) using an MVR instrument from Göttfert, model MP-D. The measurement temperatures are given in the following tables for the respective products.

[0091] Solution Viscosity

[0092] The solution viscosity was measured with a type 50110 Ubbelohde viscometer in accordance with DIN 51562-1 (01. 1999). 99.7 g of N-methyl-2-pyrrolidone with 0.1% dibutylamine and 0.4 g of TPU pellets were weighed out. The samples were stirred on a magnetic stirrer for about 1 hour at about 70° C. and cooled to room temperature overnight. The samples and a blank value (pure solvent) were measured at 25° C. on 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: AVS 400 viscosity measuring station, ASV/S measurement stand, glass thermostat, type 50110 Ubbelohde viscometer.

[0093] Nco Content:

[0094] In Accordance with DIN EN ISO 14896 (01. 2009) with the Following Differences:

[0095] Instead of toluene, N-methylpyrrolidone is used as solvent. The concentration of dibutylamine and hydrochloric acid is 0.5 mol/1. Dibutylamine is dissolved in dimethyl sulfoxide instead of in toluene. The hydrochloric acid is not dissolved in water but instead in a mixture of 85% isopropanol and 15% water.

[0096] Molecular Weights

[0097] The number-average molecular weights Mn and weight-average molecular weights Mw of the thermoplastic polyurethanes were determined, dissolved in HFIP (hexafluoroisopropanol), by means of GPC. The molecular weight was determined using a column combination of a precolumn and 3 consecutive GPC columns 30×8 mm. 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 to 400 ml)), Knauer Smartline 2300 RI detector. 100 μl of sample solution, concentration 2 mg/ml, are injected. The samples are passed through a 0.45 μm PTFE filter prior to measurement. Measurements are taken at room temperature, calibrated with a PMMA standard kit from PSS (from 102-981 000 g/mol at the peak maximum). As comparison gas, ambient air was used in the experiments. During the measurement period, the ambient air had a dew point of 17.2° C., with a relative humidity of 84%, at a pressure of 1014 hPa and a temperature of 20° C., the absolute humidity was 14.5 g/m.sup.3. During the measurement period, the dry process air, referred to as dry air, had a dew point of −25° C., with a relative humidity of 3.4%, at a pressure of 1014 hPa and a temperature of 20° C., the absolute humidity was 0.6 g/m.sup.3.

Example 1: Desmopan 2590A: Production in a Reactive Extruder, Underwater Pelletization, Pre-Drying Using a Centrifugal Dryer

[0098] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0099] Results:

TABLE-US-00001 TABLE 1 Results of the heat-treatment of Desmopan 2590A with ambient air and dry air. Pd refers to the polydispersity, obtained by dividing Mw by Mn. Residual Heat NCO MVR 100% Breaking Elongation GPC molecular treatment content Solution (190° C.) modulus strength at break weight distribution with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Mn Mw Pd Before heat 0.132 treatment 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

[0100] It can clearly be seen that a slightly higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is at a similar level after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable. This is also demonstrated by the results of the GPC molar weight distribution, with a higher molar weight of the sample that was heat-treated with dry air.

Example 2: Desmopan 385S: Production in a Reactive Extruder, Pelletization by Means of Strand Pelletization and Pre-Drying by Means of Vibrating Screen Extractor

[0101] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0102] Results:

TABLE-US-00002 TABLE 2 Results of the heat-treatment of Desmopan 385S with ambient air and dry air. Residual Heat NCO MVR 100% Breaking Elongation treatment content Solution (200° C.) modulus strength at break with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Before heat 0.186 treatment Ambient air 0.065 1.48 19 5.1 45.8 649 Dry air 0.068 1.56 13 5.1 51.2 527

[0103] It can clearly be seen that a higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is at a similar level after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable.

Example 3: Desmopan 192: Production in a Reactive Extruder, Pelletization by Means of Strand Pelletization and Pre-Drying by Means of Vibrating Screen Extractor

[0104] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0105] Results:

TABLE-US-00003 TABLE 3 Results of the heat-treatment of Desmopan 192 with ambient air and dry air. Pd refers to the polydispersity, obtained by dividing Mw by Mn. Residual Heat NCO MVR 100% Breaking Elongation GPC molecular treatment content Solution (190° C.) modulus strength at break weight distribution with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Mn Mw Pd Before heat 0.223 treatment 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

[0106] It can clearly be seen that a higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is below 0.1% after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable. This is also demonstrated by the results of the GPC molar weight distribution, with a higher molar weight of the sample that was heat-treated with dry air.

Example 4: Desmopan 85085A: Production in a Reactive Extruder, Underwater Pelletization, Pre-Drying Using a Centrifugal Dryer

[0107] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0108] Results:

TABLE-US-00004 TABLE 4 Results of the heat-treatment of Desmopan 85085A with ambient air and dry air. Pd refers to the polydispersity, obtained by dividing Mw by Mn. Residual Heat NCO MVR 100% Breaking Elongation GPC molar treatment content Solution (180° C.) modulus strength at break weight distribution with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Mn Mw Pd Before heat 0.226 treatment Ambient air 0.087 1.52 49 6.2 37.8 918 123470 244200 1.98 Dry air 0.065 1.71 32 6.4 50.0 846 223820 427500 1.91

[0109] It can clearly be seen that a higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is at a similar level after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable. This is also demonstrated by the results of the GPC molar weight distribution, with a higher molar weight of the sample that was heat-treated with dry air.

Example 5: Desmopan 9370AU: Production in a Reactive Extruder, Pelletization by Means of Strand Pelletization and Pre-Drying by Means of Vibrating Screen Extractor

[0110] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0111] Results:

TABLE-US-00005 TABLE 5 Results of the heat-treatment of Desmopan 9370AU with ambient air and dry air. Residual NCO content Heat before heat MVR 100% Breaking Elongation treatment treatment Solution (190° C.) modulus strength at break with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Before heat 0.188 treatment Ambient air 0.072 1.41 30 2.7 27.2 836 Dry air 0.068 1.44 20 2.8 31.3 787

[0112] It can clearly be seen that a slightly higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is at a similar level after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable.

Example 6: Desmopan 6080A: Production in a Reactive Extruder, Pelletization by Means of Strand Pelletization and Pre-Drying by Means of Vibrating Screen Extractor

[0113] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0114] Results:

TABLE-US-00006 TABLE 6 Results of the heat-treatment of Desmopan 6080A with ambient air and dry air. Pd refers to the polydispersity, obtained by dividing Mw by Mn. Residual Heat NCO MVR 100% Breaking Elongation GPC molecular treatment content Solution (190° C.) modulus strength at break weight distribution with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Mn Mw Pd Before heat 0.330 treatment Ambient air 0.143 1.404 25.8 5.9 23.9 672 159100 369500 2.32 Dry air 0.144 1.468 11.3 6.0 26.8 552 226600 602700 2.66

[0115] It can clearly be seen that a higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is at the same level after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable. This is also demonstrated by the results of the GPC molar weight distribution, with a much higher molar weight of the sample that was heat-treated with dry air.

Example 7: Desmopan 9665DU: Production in a Reactive Extruder, Pelletization by Means of Strand Pelletization and Pre-Drying by Means of Vibrating Screen Extractor

[0116] The TPU sample was divided and one portion of the TPU sample was heat-treated with ambient air and the other portion of the TPU sample was heat-treated with dry air, as described above.

[0117] Results:

TABLE-US-00007 TABLE 7 Results of the heat-treatment of Desmopan 9665DU with ambient air and dry air. Residual NCO content Heat before heat MVR 100% Breaking Elongation treatment treatment Solution (210° C.) modulus strength at break with [% by wt.] viscosity [ml/10 min] [MPa] [MPa] [%] Before heat 0.343 treatment Ambient air 0.126 1.50 12 27.6 53.0 836 Dry air 0.131 1.62 8 29.0 54.7 787

[0118] It can clearly be seen that a higher solution viscosity, a lower MVR value and higher breaking strength are obtained in the case of heat treatment with dry air. This points to a linear increase in the molar weight during heat treatment. The residual NCO content decreases considerably after heat treatment compared to the initial value and is at a similar level after both types of heat treatment. Since the use of dry air during the heat treatment results in a higher solution viscosity and a higher breaking strength, the reduction in the residual NCO content can be attributed to a linear molecular weight increase. In the case of the reduction in the residual NCO content after the heat treatment with ambient air, some of the NCO groups must accordingly also have reacted with water, which is undesirable.

[0119] Examples 1-7 reported clearly show the advantage gained when TPU samples are treated with dry air instead of ambient air.