The invention relates to an aqueous fire-retardant composition and improved method to impart fire-retardancy to wood- and cellulose-based materials for furniture and interior building constructions. Wood- and cellulose-based materials are widely used as construction materials and in furniture. Furthermore, decorative panels are commonly employed in the construction of furniture and in decorative interior finishing. These materials have to comply with high fire-retardancy standards. The European standard DIN EN 13823 is widely accepted for comparing the fire- retardant properties of different materials. Somewhat older methods which nevertheless yield reliable results are ISO 5658-2 (2006) and UNI 9174 (2010). Based on these methods, classifications can be assigned to the materials (e.g. Euroclass according to DIN EN 13501-1 (2019-05)).
To increase their fire-retardancy, wood- and cellulose-based materials can be treated with fire-retardant compositions and intumescent compositions. Fire-retardant compositions may slow the spread of a fire by absorbing energy that would otherwise serve the perpetuation of the combustion process. Intumescent compositions swell under the influence of heat to form a voluminous foam layer (intumescent char) that serves to insulate the substrate against heat, thereby slowing down pyrolysis of the substrate. Furthermore, the intumescent char prevents oxygen from contacting the substrate, thereby inhibiting combustion.
Typical intumescent compositions contain an acid donor, a carbon donor, and a blowing agent.
For environmental and economic reasons, it is desirable and advantageous to formulate water-based intumescent compositions, preferably compositions that are non-halogen. However, issues of solubility and compatibility have to be dealt with during their composition.
Different methods have been described for the treatment of substrates. These methods, however, require large amounts of active agents. Furthermore, raw materials that have been treated using an aqueous solution may be vulnerable to subsequent leaching of the active agents. Finally, issues of compatibility between the active agents and adhesives or resins used for forming a product from the treated raw materials may also arise.
A fire-retardant may be added as a granulate to wood particles in the case of preparing particle boards or added as a liquid suspension, dispersion or solution to fibers in the case of preparing fiberboards or oriented strand boards. In such cases, too, the compatibility between the active agents and the adhesive(s) may be an issue, and it is still necessary to employ large amounts of active agents.
The invention solves the identified problems by means of an aqueous fire- retardant composition, an aqueous intumescent composition, and a method for imparting fire-retardancy on a substrate. Materials exhibiting excellent fire-retardant properties can be obtained using only small amounts of active agents. In particular, the claimed invention achieves a notable reduction in the amounts of fire-retardants that are required to obtain a certain reaction-to-fire performance, such as a certain classification level in the Euroclass system. This reduction represents an improvement not only from an economic standpoint, but also from an ecological point of view. In addition, the composition is halogen-free. These compositions are generally considered safer, non-toxic and do not accumulate in the environment or in organisms.
- Aqueous resin solution: aqueous melamineformaldehyde 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 may be used. has dual functionality. On the one hand, the resin acts as a binder, which makes possible the formation of a stable coating. On the other hand, the melamine contained in the aqueous resin solution (A) acts as a blowing agent upon exposure to heat and thereby participates in the intumescent action of the coating.
- Acid donor: ammonium polyphosphate, guanylurea phosphate, guanidine phosphate and mixtures thereof. One or more selected from the group consisting of ammonium polyphosphate, guanylureaphosphate and guanidine phosphate, and preferably one or more selected from the group consisting of ammonium polyphosphate and guanidine phosphate. This is done from the viewpoint of maximizing the fire- retardancy of the coating, while at the same time avoiding the use of compounds exhibiting a high degree of acidity.
- Carbon donor: glucose, arabinose and other monosaccharides; lactose, maltose and other disaccharides; starch, cellulose, dextrin and other polysaccharides; sorbitol, erythritol, pentaerythritol, dipentaerythritol, tripentaerythritol, mannitol and other polyhydric alcohols; and mixtures thereof. Preferably one or more selected from the group consisting of starch, cellulose, dextrin and other polysaccharides; sorbitol, erythritol, pentaerythritol, dipentaerythritol, tripentaerythritol, mannitol and other polyhydric alcohols, and preferably is one or more selected from the group consisting of sorbitol, pentaerythritol and dipentaerythritol. The use of the indicated compounds also is believed to minimize health and environmental risks.
The acid donor and the carbon donor are typically employed in the form of particulate powders, wherein at least 90% of the particles present have a particle size which is smaller than 50 pm or at least 50% of the particles have a particle size of less than 10 pm.
- The composition and method of the present invention make it possible to obtain a coating that is sufficiently stable and durable to allow for the use of the treated product in interior construction applications, thereby eliminating the need for applying an additional overcoating.
- The dual functionality of the resin component makes it possible to eliminate the use of a polyvinyl acetate (PVA)/acrylate mixture, which previously has commonly been employed as a binder for intumescent compositions.
- The existence in dissolved form and the reduction in particle size that is associated therewith not only allow for a better distribution of the resin in the intumescent composition, but ultimately also serve to increase the reactivity of the intumescent coating, because the resin component exhibits a greater reaction surface and is more evenly distributed.
- However, the binder is not limited to such resin solutions, and any binder which does not impair the application of the aqueous intumescent composition may be used.
- Since partial phosphoric acid esters are comparably expensive, however, it would be desirable to find a means for lowering the needed amount or to be able to replace them altogether while maintaining adequate intumescent properties.