EP-4225822-B1 - METHOD FOR PRODUCING POLYURETHANE FOAMS OR HYDROGELS BY EMPLOYING DIOL CONTAINING FORMULATIONS

Inventors

• THOMPSON-COLON, JAMES, A.
• SUETTERLIN, Jan
• WEISER, MARC-STEPHAN
• LORENZ, KLAUS
• PLUG, SASCHA

Dates

Publication Date

20260513

Application Date

20210930

Claims (14)

1. A process for producing polyurethane foams or polyurethane hydrogels, 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) from 1.1 to 4.9% by weight C 2 to C 12 diols based on the total amount of the isocyanate-reactive components A2) to A4) wherein component A3) differs from component A2), A4) optionally further isocyanate-reactive components differing from A2) and A3); B) water in an amount of at least 2% by weight, based on the total weight of the composition; C) optionally polyisocyanates obtainable by reaction of at least two low molecular, preferably aliphatic diisocyanates, wherein the 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 average isocyanate-functionality of 2 to 6 with H2) monohydroxyfunctional polyalkylene oxides of OH number from 10 to 250 and of oxyethylene unit content from 50 to 100 mol%, based on the total amount of the oxyalkylene groups present, are provided, optionally foamed and cured wherein the isocyanate containing components, especially components A), C) and H), do not exceed a residual diisocyanate content of 8% by weight, based on the total weight of the polyurethane foam or hydrogel.
2. The process according to either of the preceding claims, wherein the isocyanate-containing components, especially components A), C) and H), have a total isocyanate content within a range from 2% to 12% by weight, based on the total amount of the isocyanate-containing components, especially on the total amount of components A), C) and H).
3. The process according to either of the preceding claims, wherein prepolymer 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 total mass of the prepolymer A).
4. The process according to either of the preceding claims, wherein aliphatic diisocyanates are used as component A1).
5. The process according to either of the preceding claims, wherein linear diisocyanates are used as component A1).
6. The process according to either of the preceding claims, wherein unbranched diols are used at least partly as component A3).
7. The process according to any of the preceding claims, wherein the isocyanate-functional prepolymer A has a viscosity at RT/ 23°C/ 25°C, determined according to DIN 53019, of ≤ 50 000 mPas.
8. The process according to any of the preceding claims, wherein the following steps are conducted: I) preparing the prepolymer A) from components A1), A2), A3) and optionally A4) and optionally D), II) optionally mixing components A), C) and H) and other isocyanate-containing components to obtain a prepolymer mixture, III) optionally adding A4) 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).
9. The process according to any of the preceding claims, wherein the oxyethylene unit content of A2) is ≥ 50% by weight, based on the total amount of the oxyalkylene groups present.
10. The process according to any of the preceding claims, wherein the polyalkylene oxide A2) has an OH number within a range from 25 to 770 mg KOH/g.
11. A polyurethane foam or a polyurethane hydrogel obtained by a process according to any of the preceding claims.
12. A polyurethane prepolymer mixture comprising the following components: A) a polyurethane prepolymer 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) from 1.1 to 4.9% by weight of C 2 to C 12 diols based on the total amount of the isocyanate-reactive components A2) to A4) wherein component A3) differs from component A2), A4) optionally further isocyanate-reactive components differing from A2) or A3), C) optionally polyisocyanates obtainable by reaction of at least two low molecular, preferably aliphatic diisocyanates, wherein the 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 average isocyanate functionality of 2 to 6 with H2) monohydroxyfunctional polyalkylene oxides of OH number from 10 to 250 and of oxyethylene unit 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), has 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. The use of a polyurethane prepolymer mixture according to claim 12 or of a polyurethane foam or hydrogel according to claim 11 for production of a wound dressing, a cosmetic article or an incontinence product.
14. A wound dressing, a cosmetic article or an incontinence product obtainable using polyurethane foams or hydrogels according to any of claims 11 or 12, or produced according to any of claims 1 to 10.

Description

The invention provides a process for producing polyurethane foams or polyurethane hydrogels, 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 and A3) from 1.1 to 4.9% by weight C2 to C12 diols based on the total amount of the isocyanate-reactive components A2) to A4) wherein component A3) differs from those of component A2) and optionally A4) further isocyanate-reactive components differing from A2) and A3); B) water or a nonaqueous isocyanate-reactive component; C) optionally polyisocyanates composed of at least two low molecular weight, preferably aliphatic diisocyanates; 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; H) optionally hydrophilic polyisocyanates, are provided, and also the foams and hydrogels thus produced and the uses thereof. Water absorbing polyurethanes are useful for many applications such as foam or hydrogel based wound dressings, incontinence pads or hydrogel contact lenses. Foams are highly porous materials with low density. In the case of wound dressing foams, densities are often around 100 g/L. With increasing density the material may be called a porous hydrogel until it is a pure and compact hydrogel without any visible pores. There is no sharp boundary between the two extremes. Regardless of terminology, regarding foams and hydrogels, important mechanical properties, such as tensile strength at break, drastically decline upon swelling of the foams or hydrogels when coming into contact with fluids. Especially, for the application in wound dressings, water absorbing polyurethanes in the form of foams or hydrogels that retain high wet-tensile-strength-at-break (σB,wet) despite good water absorption are desirable. Since the density of the material, like foams or hydrogels, has also a strong influence on the mechanical properties it is not easy to say which basic materials would directly reach the goal of retaining wet high wet-tensile-strength-at-break (σB,wet) and good water absorption. Solely, comparing absolute values of wet-tensile-strength-at-break (σB,wet) for the different materials like low density foams, high density foams and hydrogels, does not allow for assessing the mechanical performance of the polymer material they are made of. However, dividing σB,wet by density (D) delivers a value that accounts for density differences and therefore normalizes the value of wet-tensile-strength-at-break (σB,wet) with respect to the density. However, it is not desirable to increase wet-tensile-strength-at-break (σB,wet) by simply reducing water absorption of the material because water absorption is an essential feature for the application in wound dressings and incontinence pads of these polymeric materials. Consequently, a material at low density with high water absorption that displays high σB,wet is desirable. When absorbing water, the material swells. Here, swelling was described as an expansion factor S in one dimension, i.e., the increase of a cross-section of a sample can be described by a factor S2. Since tensile stress depends on the tensile force per cross-sectional area and water does not contribute to the tensile stress it is expected that wet-tensile-strength-at-break (σB,wet) drops by at least the factor S2. Based on these considerations the term (σB,wet/D)·S2 is useful to assess the performance of the material of the foam or hydrogel in the wet state independent from density and extent of swelling. Foams with good wet-tensile-strength-at-break (σB,wet) are already known. For instance, a foam from prepolymer example 4 of US2006142529 was synthesized (comparative example 17 in this document) and used to obtain a foam with an excellent (σB,wet/D)·S2 value of 0.61. However, all foams in US2006142529 were synthesized from prepolymers that were not distilled after synthesis, hence, containing more than at least 8% residual diisocyanate. Due to the low vapor pressure of diisocyanate monomers foam or hydrogel manufacturers require an exhaustion system for safe manufacturing of foams and hydrogels. Another disadvantage of prepolymers in US2006142529 is that they are based on aromatic isocyanates. Furthermore, for many manufacturing processes it is desirable to use prepolymers with viscosities lower than 25000 mPas, preferably lower than 10000 mPas. Many aromatic prepolymers do not meet this requirement. Moreover, removing the residual diisocyanate by distillation will lead to a further drastic increase of viscosity. An additional disadvantage of aromatic prepolymers is that foams produced from aromatic prepolymers are inherently yellowing. All foams in US2006142529 are based on aromatic isocyanates and cont