Abstract: This method makes plastic book covers which have stiffer front and back panels and which have diminished plasticizer migration between the cover and any contacting cover or other adjacent surface. The covers are cross-linked to a limited extent to improve the elasticity of the hinge lines; and to a greater extent at the back and front cover areas to add stiffness to the plastic material. Laminated plastic covers are made with the different layers made of material that responds to cross-linking chemicals or radiation to different degrees, The covers can be made of expanded plastic and laminates.

Abstract: This invention provides an improved book and book cover, and apparatus for making book covers from laminated plastic material where one layer of the laminate is of sufficient stiffness for the front and rear panels of the book cover; and the other layer has good characteristics for hinges for the cover. Both layers are preferably coextruded to make a composite plastic sheet. The apparatus displaces material from the first layer down to the second layer to provide a groove over the hinge layer; and the apparatus is adjustable to make covers for books of different size and thickness. The covers have one layer that heats when exposed to a dielectric field of a predetermined frequency; and the hinge layer undergoes no consequential heating by the dielectric field that heats the first layer.

Abstract: For binding books with plastic covers, this invention cuts the covers from plastic stock such as calendered sheets or continuous webs; and the plastic is preferably one that can be cut from the stock with a die used with a high frequency electromagnetic field for softening the plastic. In the preferred method, a tear line is formed around the outline of the cover and the cover is torn from the sheet with a smooth tear. The leaves constituting the filler for the book are assembled, stabilized with adhesive and then trimmed before assembly with the cover. With plasticized covers, provision is made for preventing migration of the plasticizer into the adhesive with possible resulting loss of strength of the adhesive. By using electromagnetic adhesive to stabilize the filler, the adhesive can be activated by an alternating electromagnetic field when desired to secure the filler to the spine portion of the cover.