PROCESS FOR PRODUCING ELASTIC AND TEAR-RESISTANT POLYURETHANE FOAMS AND USES

Abstract

The invention provides a process for producing polyurethane foams, the foams thus produced and the uses thereof. In the inventive process compositions comprising A) isocyanate-functional prepolymers obtainable by the reaction of A1) aliphatic, low molecular weight diisocyanates of molar mass from 140 to 278 g/mol with A2) polyalkylene oxides having an OH functionality of two or more, A3) optionally further isocyanate-reactive components not covered by A2), B) water in an amount of at least 2% by weight, based on the total weight of the composition; C) optionally heterocyclic 4-membered or 6-membered ring oligomers of low molecular weight, aliphatic diisocyanates having a molar mass of 140 to 278 g/mol; D) optionally catalysts; E) optionally salts of weak acids, the corresponding free acids of which have a pKA in water at 25? C. of ?3.0 and ?14.0; F) optionally surfactants; G) optionally mono- or polyhydric alcohols or polyols, and H) optionally hydrophilic polyisocyanates obtainable by reaction of H1) low molecular weight, aliphatic diisocyanates of molar mass from 140 to 278 g/mol and/or polyisocyanates preparable therefrom and having an isocyanate functionality of 2 to 6 with H2) monofunctional polyalkylene oxides of OH number from 10 to 250 and of ethylene oxide content from 50 to 100 mol %, based on the total amount of the oxyalkylene groups present,
are provided, foamed and cured, wherein the isocyanate-containing components, especially components A), C) and H), have a total isocyanate content within a range from 2% to 8% by weight and a content of urethane groups of 1.0 to 3.5 mol/kg, based in each case on the total amount of the isocyanate-containing components.

Claims

1. A process for producing polyurethane foams, in which compositions comprising A) isocyanate-functional prepolymers obtainable by the reaction of A1) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol with A2) polyalkylene oxides having an OH functionality of two or more, A3) optionally further isocyanate-reactive components not covered by A2); B) water in an amount of at least 2% by weight, based on the total weight of the composition; C) optionally heterocyclic 4-membered or 6-membered ring oligomers of low molecular weight diisocyanates having a molar mass of 140 to 278 g/mol, D) optionally catalysts; E) optionally salts of weak acids, the corresponding free acids of which have a pKA in water at 25? C. of ?3.0 and ?14.0; F) optionally surfactants; and G) optionally mono- or polyhydric alcohols or polyols; H) optionally hydrophilic polyisocyanates obtainable by reaction of H1) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol and/or polyisocyanates preparable therefrom and having an isocyanate functionality of 2 to 6 with H2) monofunctional polyalkylene oxides of OH number from 10 to 250 and of ethylene oxide content from 50 to 100 mol %, based on the total amount of the oxyalkylene groups present, are provided, foamed and cured, wherein the isocyanate-containing components, especially components A, C and H, have a total isocyanate content within a range from 2% to 8% by weight and a content of urethane groups of 1.0 to 3.5 mol/kg, based in each case on the total amount of the isocyanate-containing components.

2. The process according to claim 1, characterized in that component A) has a proportion by weight of low molecular weight diisocyanates having a molar mass of 140 to 278 g/mol of below 1.0% by weight, based on the prepolymer.

3. The process according to claim 1, characterized in that aliphatic isocyanates are used as component A1).

4. The process according to claim 1, characterized in that the following steps are conducted: I) preparing the prepolymer A) from components A1), A2) and optionally A3), D), II) optionally mixing components A), C) and H) and other isocyanate-containing components to obtain a prepolymer mixture, III) optionally adding A3) and optionally D), IV) optionally mixing component B) with all other components, especially D), E), F) and G), apart from the prepolymer mixture, V) mixing the prepolymer mixture obtained in I) to III) with the mixture from IV).

5. The process according to claim 1, characterized in that the ethylene oxide content of A2) is ?50% by weight.

6. The process according to claim 1, characterized in that the mixture of isocyanate-containing components has a molar ratio of urethane groups to isocyanate groups of 1.0 to 5.0.

7. The process according to claim 1, characterized in that there is a molar ratio of NCO to OH groups in the reaction of components A1) to A3) to give the isocyanate-functional prepolymer A) of <5.

8. The process according to claim 1, characterized in that the isocyanate-functional prepolymer A has a viscosity of ?50000 mPas.

9. The process according to claim 1, characterized in that at least some of the isocyanate-containing components have an isocyanate functionality of >2.

10. The process according to claim 1, characterized in that the polyalkylene oxide A2) has an OH number within a range from 40 to 450 mg KOH/g.

11. A polyurethane foam obtainable by a process according to claim 1.

12. A polyurethane prepolymer mixture comprising the following components: A) a polyurethane prepolymer obtainable from A1) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol with A2) polyalkylene oxides having an OH functionality of two or more, A3) optionally further isocyanate-reactive components not covered by A2), C) optionally heterocyclic 4-membered or 6-membered ring oligomers of low molecular weight diisocyanates having a molar mass of 140 to 278 g/mol, D) optionally catalysts; H) optionally hydrophilic polyisocyanates obtainable by reaction of H1) low molecular weight diisocyanates of molar mass from 140 to 278 g/mol and/or polyisocyanates preparable therefrom and having an isocyanate functionality of 2 to 6 with H2) monofunctional polyalkylene oxides of OH number from 10 to 250 and of ethylene oxide content from 50 to 100 mol %, based on the total amount of the oxyalkylene groups present, wherein the polyurethane prepolymer mixture, especially components A, C and H, have an isocyanate content within a range from 2% to 8% by weight and a content of urethane groups of 1.0 to 3.5 mol/kg, based in each case on the total amount of the polyurethane prepolymer mixture.

13. Use of a polyurethane prepolymer mixture according to claim 12 of a wound dressing, a cosmetic article or an incontinence product.

14. A polyurethane foam having at least the following properties: a) a quotient of breaking strength and stress at 20% elongation (F20) of at least 3.5; b) a liquid absorption ?300%; c) a density between 50 and 300 g/l; d) a breaking strength of at least 50 kPa; e) an F20 of at most 50 kPa.

15. A wound dressing, a cosmetic article or an incontinence product obtainable using polyurethane foams according to claim 11.

Description

EXAMPLES

Example 1 (Inventive)

[0186] To a mixture of 1680 g of HDI and 5.0 g of dibutyl phosphate were added dropwise at 80? C., within 30 min, 2960 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 9.1% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.7 mbar. The mixture had an NCO content of 5.0% and a viscosity of 5140 mPas. The calculated urethane content is 2.4 mol/kg.

Example 2 (Inventive)

[0187] To a mixture of 662 g of HDI and 1.8 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1167 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 9.1% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.4 mbar. A prepolymer having an NCO content of 5.0% and a viscosity of 4500 mPas was obtained. The calculated urethane content is 2.4 mol/kg. Subsequently, 5% Desmodur N 3300 was added. The mixture had an NCO content of 5.7% and a viscosity of 3700 mPas. The calculated urethane content is 2.3 mol/kg.

Example 3 (Inventive)

[0188] To a mixture of 531 g of HDI and 1.6 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1169 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 5.8% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.6 mbar. A prepolymer having an NCO content of 3.7% and a viscosity of 11500 mPas was obtained. The calculated urethane content is 2.4 mol/kg. Subsequently, 5% Baymedix? FP520 was added. The mixture had an NCO content of 4.1% and a viscosity of 15700 mPas. The calculated urethane content is 2.3 mol/kg.

Example 4 (Inventive)

[0189] To a mixture of 541 g of HDI and 1.5 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1059 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 7.3% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.6 mbar. A prepolymer having an NCO content of 4.5% and a viscosity of 6690 mPas was obtained. The calculated urethane content is 2.4 mol/kg. Subsequently, 5% Baymedix? FP520 was added. The mixture had an NCO content of 4.7% and a viscosity of 9800 mPas. The calculated urethane content is 2.3 mol/kg.

Example 5 (Inventive)

[0190] To a mixture of 662 g of HDI and 1.8 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1167 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 9.1% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.4 mbar. A prepolymer having an NCO content of 5.0% and a viscosity of 4500 mPas was obtained. The calculated urethane content is 2.4 mol/kg. Subsequently, 5% Baymedix? FP520 was added. The mixture had an NCO content of 5.2 and a viscosity of 7030 mPas. The calculated urethane content is 2.3 male.

Example 6 (Inventive)

[0191] To a mixture of 4616 g of HDI and 12 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 7384 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 10.4% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.3 mbar. A prepolymer having an NCO content of 5.5% and a viscosity of 3450 mPas was obtained. The calculated urethane content is 2.4 mol/kg. Subsequently, 5% Baymedix? FP520 was added. The mixture had an NCO content of 5.9% and a viscosity of 4100 mPas. The calculated urethane content is 2.3 mol/kg.

Example 7 (Inventive)

[0192] To a mixture of 4984 g of HDI and 12 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 7016 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 12.5% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.3 mbar. A prepolymer having an NCO content of 5.7% and a viscosity of 2670 mPas was obtained. The calculated urethane content is 2.3 mol/kg. Subsequently, 5% Baymedix? FP520 was added. The mixture had an NCO content of 6.1% and a viscosity of 3220 mPas. The calculated urethane content is 2.2 mol/kg.

Example 8 (Inventive)

[0193] To a mixture of 420 g of HDI and 1.6 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1021 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 23.5% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.4 mbar. A prepolymer having an NCO content of 7.5% and a viscosity of 905 mPas was obtained. The calculated urethane content is 2.2 mol/kg. Subsequently, 5% Baymedix? FP520 was added. The mixture had an NCO content of 8.0% and a viscosity of 1440 mPas. The calculated urethane content is 2.2 mol/kg.

Example 9 (Inventive)

[0194] To a mixture of 710 g of HDI and 0.5 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 200 g of polyethylene glycol having a molar mass of 400 g/mol (OH number 281 mg KOH/g), and stirring of the mixture was continued until an NCO content of 7.5% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.4 mbar. A prepolymer having an NCO content of 5.0% and a viscosity of 15 900 mPas was obtained. The calculated urethane content is 3.2 mol/kg. Subsequently, 5.0% Baymedix? FP520 was added. The mixture had an NCO content of 5.1% and a viscosity of 23 100 mPas. The calculated urethane content is 3.0 mol/kg.

Example 10 (Inventive)

[0195] To a mixture of 361 g of HDI and 2.1 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1216 g of a polyalkylene oxide having a molar mass of 998 g/mol (OH number 112 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 89%, and stirring of the mixture was continued until an NCO content of 15.8% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.4 mbar. A prepolymer having an NCO content of 4.9% and a viscosity of 1360 mPas was obtained. The calculated urethane content is 1.5 mol/kg. Subsequently, 5.0% Baymedix? FP520 was added. The mixture had an NCO content of 5.5% and a viscosity of 2020 mPas. The calculated urethane content is 1.5 mol/kg,

Example 11 (Non-Inventive)

[0196] To a mixture of 1260 g of HDI and 2.0 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 1972 g of a polyalkylene oxide having a molar mass of 3951 g/mol (OH number 28.4 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 78%, and stirring of the mixture was continued until an NCO content of 18.1% had been attained (3.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.5 mbar. A prepolymer having an NCO content of 2.0% and a viscosity of 3690 mPas was obtained. The calculated urethane content is 0.5 mol/kg. Subsequently, 5.0% Baymedix? FP520 was added. The mixture had an NCO content of 2.6% and a viscosity of 4250 mPas. The calculated urethane content is 0.5 mol/kg.

Example 12 (Non-Inventive)

[0197] The isocyanate-containing mixtures from Examples 10 and 11 were mixed in a ratio of 1:1. The mixture had an NCO content of 4.3% and a viscosity of 2940 mPas. The calculated urethane content is 0.97 mol/kg.

Example 13 (Non-Inventive)

[0198] To a mixture of 1130 g of HDI and 1.78 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 652 g of tetraethylene glycol (OH number 580 mg KOH/g), and stirring of the mixture was continued until an NCO content of 15.7% had been attained (3.5 h). The calculated urethane content is 3.8 mol/kg. During cooling to room temperature, there was crystallization to form a white solid. Owing to the solid character, it was not possible to process the material to give the foam.

Example 14 (Non-Inventive)

[0199] To a mixture of 998 g of HDI and 1.9 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 873 g of tetraethylene glycol (OH number 580 mg KOH/g), and stirring of the mixture was continued until an NCO content of 6.4% had been attained (7 h). The calculated urethane content is 4.8 mol/kg. During cooling to room temperature, there was crystallization to form a white solid. Owing to the solid character, it was not possible to process the material to give the foam.

Example 15 (Non-Inventive)

[0200] To a mixture of 1184 g of HDI and 2.58 g of dibutyl phosphate were added dropwise, at 80? C. within 2 h, 1395 g of a polyalkylene oxide having a molar mass of 4680 g/mol (OH number 36 mg KOH/g), started from glycerol, a proportion by weight of ethylene oxide of 72% and a proportion by weight of propylene oxide of 28%, and stirring of the mixture was continued until an NCO content of 21.4% had been attained (2.5 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.1 mbar. A prepolymer having an NCO content of 2.5% and a viscosity of 3500 mPas was obtained. The calculated urethane content is 0.6 mol/kg.

Example 16 (Non-Inventive)

[0201] The commercial product Baymedix? FP505 was used with a polyol content of 69% by weight (as Example 3), an NCO content of 5.3% and a viscosity of 3000 InPas; the calculated urethane content is 0.8 mol/kg.

Example 17 (Non-Inventive)

[0202] To a mixture of 2805 g of HDI and 3.25 g of dibutyl phosphate were added dropwise, at 80? C. within 30 min, 649 g of a polyalkylene oxide having a molar mass of 591 g/mol (OH number 190 mg KOH/g), started from 1,3-propylene glycol, and a proportion by weight of ethylene oxide of 87%, and stirring of the mixture was continued until an NCO content of 37.6% had been attained (1 h). The excess HDI was removed by thin-film distillation at 140? C. and 0.5 mbar. A prepolymer having an NCO content of 9.1% and a viscosity of 700 mPas was obtained. The calculated urethane content is 2.2 mol/kg. Subsequently, 5.0% Desmodur N 3300 was added. The mixture has an NCO content of 9.3% and the calculated urethane content is 2.1 mol/kg.

[0203] Production of Foams from the Examples

[0204] The prepolymer mixtures from the examples were each introduced into a 500 ml PP cup from Sarstedt and homogenized by means of a stirrer from Pendraulik (Disperlux green 037) at a speed of 930 rpm for 15 seconds. Subsequently, a defined amount (Table 1) was added. The water phase consisted of 93.5% water, 1.3% sodium hydrogencarbonate, 0.4% citric acid monohydrate and 4.8% Pluronic. Then the mixture was stirred for a further 7 seconds. The mixture was applied with the aid of a coating bar (gap height 1500 ?m) to a release paper from Felix Schoeller (Y05200). After 60 seconds (based on the start of the experiment), a needled release paper from Felix Schoeller (Y05200) was applied. The resultant foam was left to stand at room temperature for drying overnight.

TABLE-US-00001 TABLE 1 Properties of foams produced from the examples NCO content of Mass ratio of the isocyanate- the isocyanate- Swelling containing Urethane containing Foam Breaking Elongation Breaking (length mixture content mixture* to thickness Density strength at break F20 strength/ Absorption expansion) Example [%]* [mol/kg] aqueous phase [mm] [g/l] [kPa] [%] [kPa] F20 [%] [%] 1 5.0 2.4 5:1 5.5 113 339 515 46.0 7.4 1818 30.8 2 5.7 2.3 7:1 5.0 88 147 437 9.3 15.8 1762 25.0 3 4.1 2.3 5:1 5.7 120 170 456 14.1 12.1 1462 26.0 4 4.7 2.3 5:1 5.5 106 167 577 11.7 14.3 1751 23.4 5 5.2 2.3 5:1 6.0 96 131 476 9.8 13.4 1824 21.4 6 5.9 2.3 5:1 7.3 85 92 338 12.9 7.1 1382 22.3 7 6.1 2.2 5:1 7.1 76 134 288 22.6 5.9 922 21.3 8 8.0 2.2 4:1 15.8 61 68 165 17.2 4.0 738 19.9 9 5.1 3.0 5:1 8.0 89 140 277 21.6 6.5 858 15.0 10 5.5 1.5 7:1 10.7 85 106 458 8.7 12.2 2600 36.8 11 2.6 0.5 5:1 1.5 492 519 564 78.0 6.7 961 74.5 12 4.3 0.97 5:1 1.6 401 495 475 67.6 7.3 866 59.8 13** 15.7 3.8 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 14** 6.4 4.8 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 15 2.5 0.6 5:1 1.9 316 155 46 80.0 1.9 724 52.5 16 5.3 0.8 5:1 7.4 123 83 124 17.0 4.9 1800 44.4 17 9.3 2.1 5:1 13.4 57 34 59 18.7 1.8 445 12.4 *the isocyanate-containing mixture is based on the sum total of all isocyanate-containing components, especially components A), C) and H) **Examples 13 and 14 were not processible to give a foam owing to their solid character.

[0205] As already mentioned in the introduction to the application, it is desirable to provide a foam suitable, for example, for production of a wound dressing having optimized properties. These optimized properties include maximum flexibility coupled with high elongation at break and maximum absorption capacity. It can be seen from the values in Table 1 that the F20 values of the inventive examples are all below 50 kPa with a quotient of breaking strength and the F20 values of greater than 3.5. By contrast, the non-inventive examples do not have such a combination in any case and are therefore much less flexible and/or insufficiently tear-resistant and hence unsuitable for use as wound dressing. Moreover, it was easily possible to use the isocyanate-containing examples according to the invention to produce foams within the desired density range from 60 to 300 g/l, especially within the preferred range from 62 to 200 g/l.

[0206] Furthermore, the person skilled in the art would expect the swelling of a polyurethane foam to correlate with the proportion of hydrophilic polyol, especially the proportion of hydrophilic ethoxyethylene units. However, comparison of Inventive Example 3 with Non-inventive Example 16 shows that, contrary to expectation, this is not the case. In both isocyanate-containing mixtures, the proportion of hydrophilic polyols was 69% by weight. The proportion of ethoxyethylene units based on the total mass of the isocyanate-containing mixture was 60% by weight for Inventive Example 3 and 55% by weight for Non-inventive Example 16. Contrary to expectation, the foam produced from Example 3 showed a length expansion of 26.0%, whereas the foam produced from Example 16 showed a length expansion of 44.4%. It has been found that, surprisingly, polyurethane foams according to the invention have particularly low swelling or length expansion without losing other important properties for a wound dressing, as already described above.