Honeycomb core material for sandwich structure and method for manufacturing the same

A method comprising,

• filling a mixture comprising a phosphorus-containing acid material (a), a curing agent (b), a urethane prepolymer having NCO groups (d), water (e) and, optionally, a blowing agent (c), in cells of a paper honeycomb body having a cell size of from 5 to 50 mm and a porosity of from 92 to 99.5%, as stipulated in JIS-A6931, followed by
• foaming and
• curing, to produce a honeycomb core material having a flexibility of from 10 mm to 35 mm as measured by the deflection at the centerpoint of a 500 mm span of a 600×300 mm section of the material having a thickness of 40 mm.

A flexible material which comprises a honeycomb body and a filler filled in at least a part of cells thereof,

• wherein the honeycomb body has a cell size of from 3 to 100 mm and a porosity of from 92 to 99.5%, as stipulated in JIS-A6931,
• wherein the filler is a composite foam comprising an inorganic foam obtained from a phosphorus-containing acid material (a), a curing agent (b) and, optionally, a blowing agent (c), and an organic foam obtained from a urethane prepolyrner having NCO groups (d), and water (e), and
• wherein the flexible material has a flexibility of from 10 mm to 35 mm as measured by the deflection at the centerpoint of a 500 mm span of a 600×300 mm section of the flexible material having a thickness of 40 mm.