Use of non-halogen fire retardant composition for indirect fire protection layers on substrates

An intumescent carrier comprising a kraft paper that has been subjected to coating with an intumescent composition comprising an acid source, a charring agent and a blowing agent, wherein the kraft paper has been subjected to coating with an aqueous intumescent composition (C), comprising:

• an aqueous resin solution (A) selected from the group consisting of aqueous melamine-formaldehyde resin solutions, aqueous melamine-urea-formaldehyde resin solutions, mixtures thereof and mixtures thereof with aqueous urea-formaldehyde resin solutions and/or aqueous phenol-formaldehyde resin solutions,
• the aqueous resin solution (A) is a mixture of an aqueous melamine-formaldehyde resin solutions with an aqueous phenol-formaldehyde resin solution, wherein a mass ratio of a solids content (aMF) derived from the aqueous melamine-formaldehyde resin to a solids content (aPF) derived from the phenol-formaldehyde aqueous resin is from 2:1 to 10:1;
• an acid donor (b) selected from the group consisting of ammonium polyphosphate, urea phosphate, guanylurea phosphate, guanidine phosphate and mixtures thereof;
• and
• a carbon donor (c) selected from the group consisting of glucose, arabinose and other monosaccharides, lactose, maltose and other disaccharides, starch, cellulose, dextrin and other polysaccharides, sorbitol, erythritol, pentaerythritol, dipentaerythritol, tripentaerythritol, mannitol other polyhydric alcohols and mixtures thereof;
• wherein
• the aqueous resin solution (A) exhibits a total melamine content of from 20 to 45 wt. % relative to a total weight of the aqueous resin solution (A);
• a mass ratio of acid donor (b) to carbon donor (c), (b):(c), is in a range of from 10:1 to 1:1;
• and
• the acid donor (b) and the carbon donor (c) are included in an amount such that a mass ratio of the solids content (aA) of the aqueous resin solution (A), as determined according to DIN 53216, to the total amount of acid donor (b) and carbon donor (c), (aA):((b)+(c)), is in a range of from 0.25:1 to 5:1
• the aqueous intumescent composition (C) exhibits a solids content (aC), as determined according to DIN 53216, of from 50 to 80 wt. % relative to a total weight of the aqueous intumescent composition (C).