Process for producing isocyanate-based foams

Isocyanate-based foams are produced by the reaction of polyisocyanates with compounds with molecular weights of from 400 to 10,000 and having at least two hydrogen atoms active towards isocyanates in the presence of hydrocarbons which are vaporizable under the foaming conditions as blowing agents. The active hydrogen component is a mixture of a) one or more nitrogen-free polyethers having at least two hydrogen atoms active towards isocyanates and containing oxyethylene residues, and b) one or more polyethers having at least two hydrogen atoms active towards isocyanates and containing no oxyethylene groups.

What is claimed is:

1. A process for producing isocyanate-based foams comprising reacting:

1) one or more polyisocyanates with

2) compounds having molecular weights of from 400 to 10,000 and having at least two hydrogen atoms active towards isocyanates in the presence of

3) hydrocarbons which are vaporizable under the foaming conditions as blowing agents, and

4) optionally in the presence of one or more compounds having a molecular weight of from 32 to 399 and having at least two hydrogen atoms capable of reacting with isocyanates,

wherein component 2) comprises a mixture of a) one or more nitrogen-free polyethers having at least two hydrogen atoms active towards isocyanates and containing oxyethylene residues, and b) one or more polyethers having at least two hydrogen atoms active towards isocyanates and containing no oxyethylene groups, and wherein the amount of all components is such that the isocyanate index is from about 90 to 130.

2. The process of claim 1, wherein hydrocarbons having from 3 to 7 carbon atoms are used as component 3).

3. The process of claim 1, wherein said component 3) is selected from the group consisting of n-pentane, isopentane, cyclopentane and mixtures thereof.

4. The process of claim 1, wherein component 3) is a mixture of a cycloalkane and a straight or branched alkanes.

5. The process of claim 1, wherein water, in a quantity of from 0.5 to 3.5% by weight, based upon the total weight of component 2) is included as a co-blowing agent.

6. The process of claim 1, wherein the polyether component 2a) is reacted with an excess of said polyisocyanate to produce a prepolymer having isocyanate groups, with said prepolymer then being reacted with the remaining components, to form said foam.

7. The process of claim 1, wherein said polyether component 2a) has a functionality of at most 4 and said polyether component 2b) has a functionality of at least 4.

8. The process of claim 1, wherein said polyether component 2a) is a polyether produced from trimethylolpropane and/or glycerol as starting material and said polyether component 2b) is a polyether from sucrose and/or sorbitol as starting material.

9. The process of claim 1, wherein from 5 to 40% by weight, based on the total weight of component 2), of a polyester having at least two hydrogen atoms active towards isocyanates is added to the polyether mixture 2).

10. The process of claim 9, wherein said polyester is a polyester of phthalic and/or terephthalic acid with an OH number of from 100 to 500.