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: An improved method of making hard and semi-rigid book covers, and the product obtained, provides a multi-layer plastic book with any desired ratio of flexibility to stiffness in the different parts of the cover such as the front and back panels, the hinge lines and the backbone panel that connects the front and back panels. A first layer of plastic is cast or extruded on a casting paper or belt or other supporting surface, and additional plastic material is applied to the first layer over areas that will form the front and back panels, and to the backbone area if the desired cover is one that is to have a stiffened backbone panel. A second layer is applied under conditions that insure a highly effective bonding and freedom from distortion when a curing step is necessary. The operation is continuous and the laminate formed is severed into separate covers as it is delivered from the laminating operation.

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.