PROCEDURE FOR SEALING TOGETHER LIGNOCELLULOSIC MATERIALS

1,123,526. Seaming non-metallic sheet material. E. L. BACK, K. G. NORBERG, and F. I. JOHANSON. 17 March. 1967 [30 March, 1966], No. 12751/67. Heading B5K. Cellulosic or lignocellulosic materials are sealed together or to another material without using an added adhesive by heating the bonding surface, i.e. the surface to be bonded, of the cellulosic or lignocellulosic material to at least 250‹ C. and maintaining it at this temperature for a maximum of 30 seconds and then bringing the bonding surfaces of the two materials into contact with each other before, during or irnmediately after heating, while pressure is applied. Preferably, the bonding surface of the cellulosic or lignocellulosic material is maintained at at least 325‹ C. for a maximum of 1 second and the applied pressure is in the range of 20-250 kg./cm.2 Heating of the bonding surface of the second may or may not be effected. Lap joints are specified. Heating of the bonding surface(s) may be effected by conduction of heat through the material from clamps or tongs having constant temperature bars or impulse heated bars having smooth or grooved clamping surfaces. A constant press gap may be maintained by spacers or stop screws. Alternatively, the bonding surface(s) may be heated directly by (a) passing the material(s) over a wedge-shaped heating tool followed by pressure rollers, (b) passing the bonding surface(s) over electrically, gas or oil heated, and possibly driven, rollers or cylinders preferably augmented by spring-loaded steel bands running parallel to the webs of material, (c) blowing a heated gas, e.g. air or an inert gas, on to the bonding surface(s), (d) applying radiant heat or other radiant energy, e.g. a laser beam, prior to applying pressure, (e) using a high frequency electrical field, (f) pressing the bonding surfaces together while cold and rotating one relative to the other using a spindle to generate heat by friction, or (g) bringing the bonding surfaces in contact with a number of thin electrical resistance wires inserted into the bonding region and passing an electric current through the wires. The bond may be cooled by contact with cold rollers or plates or by a stream of cold air or inert gas. Preferably, the sealing operation is carried out in an inert atmosphere, e.g. in nitrogen or water vapour.