Hydrophilic, aliphatic polyurethane foams

A process for producing a hydrophilic aliphatic polyurethane foam, which comprises providing a composition comprising

• A) isocyanate-functional prepolymers obtained by reaction of
• A1) low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/mol with
• A2) di- to hexafunctional polyalkylene oxides having an OH number of 22.5 to 112 mg KOH/g and an ethylene oxide content of 50 to 100 mol %, based on the total amount of oxyalkylene groups present,
• B) alkali metal salts of weak inorganic acids,
• C) water,
• D) optionally heterocyclic 4-ring or 6-ring oligomers of low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/mol,
• E) optionally catalysts,
• F) optionally surfactants,
• G) optionally mono- or polyhydric alcohols, and
• H) optionally hydrophilic polyisocyanates obtained by reaction of
• H1) low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/ml and/or polyisocyanates obtained therefrom with an isocyanate functionality of 2 to 6, with
• H2) monofunctional polyalkylene oxides having an OH number of 10 to 250 and an ethylene oxide content of 50 to 100 mol %, based on the total amount of oxyalkylene groups present,
• foaming and curing the composition,
• wherein alkali metal salts of weak inorganic acids B) are used whose corresponding free acids have a pKa value of ≧4.0 in water at 25° C.

A composition comprising

• A) isocyanate-functional prepolymers, having a weight fraction of below 1.0 wt % for low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/mol, based on the prepolymer, obtained by reaction of
• A1) low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/mol with
• A2) di- to hexafunctional polyalkylene oxides having an OH number of 22.5 to 112, and an ethylene oxide content of 50 to 100 mol %, based on the total amount of oxyalkylene groups present,
• B) alkali metal salts of weak inorganic acids,
• C) water,
• D) optionally heterocyclic 4-ring or 6-ring oligomers of low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/mol,
• E) optionally catalysts,
• F) optionally surfactants,
• G) optionally mono- or polyhydric alcohols, and
• H) optionally hydrophilic polyisocyanates obtained by reaction of
• H1) low molecular weight aliphatic diisocyanates having a molar mass of 140 to 278 g/ml and/or polyisocyanates obtained therefrom with an isocyanate functionality of 2 to 6, with
• H2) monofunctional polyalkylene oxides having an OH number of 10 to 250 and an ethylene oxide content of 50 to 100 mol %, based on the total amount of oxyalkylene groups present,
• wherein the alkali metal salts of weak inorganic acids B) are compounds whose corresponding free acids have a pKA value of ≧4.0 in water at 25° C.