Recording materials that utilize color formation resulted by reaction of a color-forming compound and a color-developing agent makes it possible to carry out recording in a short time with a relatively simple device without conducting cumbersome treatments such as developing/fixing. Such recording materials are thus widely used for thermal recording papers used for output recording such as for a facsimile and a printer, as well as for pressure sensitive copying papers used for the simultaneously copying multiple ledger sheets. As for these recording materials, those recording materials are desired in which color is formed swiftly, whiteness of the no color-forming part (hereinafter referred to as “background”) is retained, and toughness of the colored image is high. Especially, recording materials with a superior light resistance of the background are awaited in view of the long-term storage stability. For this purpose, efforts have been made to develop color-forming compounds, color-developing agents, storage stabilizers, etc. In spite of such efforts, those recording materials that are sufficiently satisfactory with well balanced color-formation sensitivity, storage property for the background and the image, etc. have not yet been found.
Further, 2,4′-dihydroxydiphenylsulfone and 4-isopropoxy-4′-hydroxydiphenylsulfone have conventionally been known as a recording material with a superior background storage property, but the background light resistance thereof has not yet been satisfactory.
The present inventors have already proposed a recording material with a superior background light resistance comprising a cinnamic acid amide-based compound as a color-developing agent (see Patent Document 1), which, however, is not yet sufficiently satisfactory. Hence, practically usable recording materials have not yet been obtained.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2003-305959
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