This invention relates to temporarily bonded construction utilizing a non-pressure sensitive hot melt adhesive which comprises specific A-B-A block copolymers and relatively high levels of plasticizing oil.
There has been an increasing need in recent years for adhesives to be used in applications requiring temporary bonding properties, i.e., adhesives which will bond an item to a substrate for a unlimited period, which bond may be easily broken when desired. One of the largest applications for such adhesives is for the attachment of plastic cards (e.g., credit cards) to paper stock for mailing to a customer. Upon receipt, the card can be readily removed by peeling it from the paper stock.
Previous attempts to provide temporary bonding involved the use of non-pressure sensitive rubber latex adhesives or hot melt pressure sensitive adhesives, i.e., adhesives which are permanently tacky at room temperature and which adhere on mere contact with the surfaces to which they are applied. In the case of both types of adhesive, removal of the card from the paper stock was often accompanied by some tearing of the paper and it was necessary for the customer to scrape or otherwise remove the residual tacky adhesive, and often some paper, from the card prior to use. While some of these problems could be overcome using specially treated release paper, this coated stock is costly and generally cannot be printed upon.
There is therefore a continuing need for an adhesive capable of forming temporary bonds, and in particular, capable of forming temporary bonds between plastic and preprinted stock. The latter requirement is especially important in applications where, after removal of the card, the customer is to sign and return the preprinted paper substrate for further processing either by hand or on automated equipment and wherein tearing of the paper or the presence of residual tacky adhesive either on the card or the paper stock would be unacceptable.