Reversible and returnable envelope blanks are known wherein tabs or flaps are folded in one way to form an envelope sent by the sender to the receiver and then re-folded in another way to form a return envelope for re-mailing back to the sender. For example, U.S. Pat. No. 4,210,250 describes a generally cross-shaped envelope blank having a sending side and a returning side and two pairs of opposed flaps extending from a central panel. There are a total of five deposits of adhesive on various of the flaps, two of which are of an always-sticky gum-type releasable adhesive which once used and separated losed its adhesive properties, and three of which are of a moisture-activatable adhesive which become sticky only when moistened and which after drying forms a permanent bond. Such moisture-activatable adhesives have the disadvantage of being susceptible to unintentional activation from exposure to water or humidity. Also, release paper is typically used on the gum-type releasable pressure sensitive adhesives. Moreover, following the correct procedure in folding the flaps of this prior art blank together at the first mailing and then again upon re-mailing is by no means uncomplicated and if it is not done properly the first time the envelope must be discarded because none of the adhesive deposits can be used twice.
Other returnable envelopes disclosed in the prior art include that of U.S. Pat. No. 2,829,818 which involves stapling parts of the blank together when it is readied for re-mailing. Some prior art reversible envelope designs include tear strips such as those disclosed in U.S. Pat. Nos. 4,669,652 and 4,917,287.
It is a principal object of the present invention to provide a blank for forming a reversible and returnable envelope which avoids the use of staples and tear strips, avoids moisture-activated adhesive susceptible to unintended activation and avoids the use of release paper usually required for pressure-sensitive adhesives. A further object is to permit the envelope to be folded and re-folded such that if the folding is done mistakenly the flaps can be peeled apart and done again correctly, which is not possible with adhesives which can only be used once. The invention further includes among its purposes an economical use of both paper and adhesive, avoidance of the danger of tearing of the sheet material of the blank and avoidance of exposure of any adhesive not in use during sending or returning.