Translucent polyurethane or polyisocyanurate foams

1. A process for producing translucent polyurethane and polyisocyanurate foams by reaction of a component A comprising or consisting of

A1 at least one polyol reactive with the component B;

A2 optionally at least one amine;

A3 water and optionally formic acid;

A4 at least one foam stabilizer

A5 optionally auxiliary and/or additive substances;

A6 optionally at least one flame retardant;

A7 at least one catalyst;

and a component B comprising

B1 at least one aliphatic or cycloaliphatic polyisocyanate component or a combination thereof; and

B2 optionally at least one hydrophilized isocyanate; and

B3 less than 20 parts by weight of an aromatic polyisocyanate component, wherein the parts by weight of B3 are based on the sum of the parts by weight of B1 to B3 which are normalized to 100 parts by weight, wherein the reaction of the component A with the component B is performed at an isocyanate index of at least 150,

wherein substantially no gaseous nucleating agents introduced by the mixing process are present during the reaction and

wherein the translucent polyurethane and polyisocyanurate foams have a light transmission according to EN ISO 13468-2:2006 of at least 10% and a haze of at least 70% determined according to ASTM D1003-13 in each case measured at a thickness of 20 mm.

2. The process as claimed in claim 1 , wherein the translucent polyurethane or polyisocyanurate foam has a thermal conductivity measured according to DIN 52612:2-1984-06 of less than 100 mW/(m*K).

3. The process as claimed in claim 1 , wherein the translucent polyurethane or polyisocyanurate foam have a degree of NCO modification of at least 30 mol %.

4. The process as claimed in claim 1 , wherein the translucent polyurethane or polyisocyanurate foam is colorless to white and has a yellowing index (measured according to ASTM E 313:2015) of less than 10 based on a thickness of the foam of 20 mm.

5. The process as claimed in claim 1 , wherein the polyurethane or polyisocyanurate foam is in the form of a polyurethane or polyisocyanurate foam having a closed-cell content of at least 40%.

6. The process as claimed in claim 1 , wherein the polyurethane or polyisocyanurate foam has an average cell size between 1 mm and 20 mm determined using an optical microscope, wherein the cell size is defined as the greatest distance between two cell edges.

7. The process as claimed in claim 1 , wherein the polyurethane or polyisocyanurate foam has an apparent density of the obtained foam of not more than 300 kg/m 3 determined according to DIN EN ISO 845:2009-10.

8. The process as claimed in claim 1 , wherein the polyurethane or polyisocyanurate foam has an average cell wall thickness of at least 0.05 mm determined using an optical microscope, wherein cell wall thickness is defined as the thickness of a cell wall centrally between two nodes.

9. The process as claimed in claim 1 , wherein the component A

10 to 99.3 parts by weight of A1;

0 to 10 parts by weight of A2;

0.1 to 80 parts by weight of A3;

0 to 50 parts by weight of A5;

0 to 80 parts by weight of A6;

wherein the sum of A1 to A7 is 100 parts by weight.

10. The process as claimed in claim 1 , wherein

0.5 to 25 parts by weight of A4;

0.1 to 60 parts by weight of A7 are present based on 100 parts by weight made up of the sum of A1 to A7.

11. A translucent polyurethane or polyisocyanurate foam obtained by a process of claim 1 .

12. A multilayer composite element in which the translucent polyurethane or polyisocyanurate foam as claimed in claim 11 is arranged between two elements.

13. An article comprising the translucent polyurethane or polyisocyanurate foam as claimed in claim 11 .

14. The multilayer composite element as claimed in claim 13 , wherein the two elements are transparent films or sheets.