Process for preparing a free rise or slabstock flexible polyurethane foam

A process for preparing a free rise or slabstock flexible polyurethane foam with a free rise density of 20 to 35 kg/m3 and a high resilience at an NCO index of 70-120 by reacting:

• (a) a polyisocyanate composition having an isocyanate functionality below 2.15 and consisting of diphenylmethane diisocyanate and optionally homologues thereof having an isocyanate functionality of 3 or more, the amount of diphenylmethane diisocyanate being 81 to 100% by weight calculated on the amount of diphenylmethane diisocyanates and homologues, and the diphenylmethane diisocyanate comprising 40-60% by weight, calculated on the weight of diphenylmethane diisocyanate, of diphenylmethane diisocyanate containing at least one NCO group in the ortho position, and the amount of homologues having an isocyanate functionality of 3 or more being 19-0% by weight, and
• (b) a polyol composition comprising:
• (i) a polyoxyethylene-polyoxypropylene-polyol, having an average nominal hydroxyl functionality of 2-8, an average equivalent weight of 1000-4000 and containing 10-25% by weight of oxyethylene groups;
• (ii) 3 to 8 parts by weight of water as the sole blowing agent or optionally together with CO2 as the sole blowing agents;
• and
• (iii) 2 to 20 parts by weight of a polyether polyol having an average nominal hydroxyl functionality of 2-6, an average equivalent weight of 200-600 and containing at least 60% by weight of oxyethylene groups;
• and optionally
• (iv) up to 30 parts by weight of particulate material which is dispersed in said polyol composition;
• the amounts of (b)(ii) to (b)(iv) being calculated per 100 parts by weight of (b)(i);
• and optionally
• (v) auxiliaries and additives.