Styrene-based resin foamed articles, which are lightweight, have been used in a variety of applications including heat insulation applications for household electrical appliances, building materials, etc. and civil engineering applications such as an embankment method.
A styrene-based resin is made up of only carbon and hydrogen, and has a property of burning vigorously with evolution of black smoke once ignited. For this reason, it is imperative in some application fields to flameproof the resin by the addition of a flame retardant. For example, extrusion-foamed polystyrene molded articles to be used as a heat insulating material must pass a combustion test of JIS A 9511. Moreover, synthetic resin foamed articles having an oxygen index of less than 26.0 are designated as designated combustibles by the Fire Service Act, and storage, conveyance and transfer of a foamed article larger than 20 m3 are highly regulated and therefore such articles are not practically marketable.
Hexabromocyclododecane (HBCD), by which a desired flame retarding effect is attained at a relatively small addition amount, has heretofore been used for flameproofing of styrene-based resin foamed articles produced by an extrusion method. However, HBCD is poor in heat stability, and a decomposition product (HBr) generated when a resin composition containing HBCD is heated to the melting temperature causes deterioration in quality, such as coloring of the resin, and poses a problem of promoting corrosion of an apparatus. Moreover, although it is desirable that foamed articles and scraps generated during their production are recycled for the production of new foamed articles, a flame retardant being low in heat stability like HBCD promotes coloring and depolymerization of the resin during melting, and degrades the resin to be unsuitable for recycling.
Use of other bromine-based flame retardants instead of HBCD for styrene-based resin extrusion-foamed articles has been proposed, and one of such flame retardants is tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether). This has a flame retarding effect comparable to that of HBCD, but is low in heat stability. Accordingly, it has been proposed by the present applicant to replace part of (B1) tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) with (B2) tetrabromobisphenol A-bis(2,3-dibromopropyl ether) or tris(2,3-dibromopropyl) isocyanurate in order to attain flame retardancy represented by an oxygen index of 26.0 or more, thereby preventing degradation of the resin typified by decrease in molecular weight in comparison with the case of using (B1) alone. Use of the above-mentioned flame retardant mixture for extrusion-foamed articles of styrene-based resins has been proposed also in other patent documents.