Method and apparatus for drying and setting the adhesive on books by vaporization of water using RF energy

An improved method for drying and setting an adhesive layer applied to the backs of book blocks by passing the book blocks by means of clamps along a travel path through a high frequency leakage field to vaporize the water in the adhesive, the improvement comprising the steps of:

• subjecting the adhesive layer on the back of said book blocks to a high frequency leakage field of high strength to heat the adhesive layer to a desired vaporization and drying temperature;
• maintaining said desired temperature until said adhesive layer is completely dried and set by varying the strength of said high frequency leakage field along said travel path, said field strength initially being substantially reduced following heating of said adhesive layer to said desired temperature and thereafter continuously increased in inverse proportion to the dielectric loss factor of said adhesive layer, said high energy leakage field being produced by a plurality of RF electrodes spaced-apart along one side of the travel path of said book blocks in an oblique manner relative to said travel path and wherein said step of subjecting and maintaining comprises varying the spacing between said electrodes along said travel path, said electrodes being spaced relatively close together at the beginning and end of said travel path and being spaced further apart in the center range of said travel path, with the spacing between said electrodes decreasing from said center range to the end of said travel path, and wherein adjacent electrodes are fed with 180.degree. phase displaced voltages so that the voltage difference between adjacent electrodes is larger than between an electrode and a clamp.