This invention relates to the art of printing-platemaking in general and, in particular, to a gravure printing cylinder of the type having a printing sleeve wrapped around a core roll. The invention also particularly concerns a method of, and apparatus for, the assembly of such a gravure printing cylinder.
Iron rolls with suitable claddings have long been used as gravure cylinders. Such cylinders have been heavy to handle and costly to prepare. Another problem has arisen from the need for holding the gravure cylinders in storage in the case of printing jobs that might be reordered. Thus, in large-scale printing factories, a considerable number of gravure cylinders has had to be constantly kept in storage, demanding considerable space. The transportation of the cylinders from the place of storage to the printing presses, or vice versa, has also been troublesome.
Gravure printing sleeves have recently entered the field to remedy the problems attendant on the solid cylinders. Such sleeves are formed by electroplating one or more thin layers of nickel, copper, chromium, etc., on what is called a mother cylinder, which is of iron with a cladding of stainless steel, nickel, chromium or the like. After grinding the surface of the plated-on sleeve, ordinary ink-retaining cells or depressions characteristic of gravure printing are etched or engraved therein by any known or suitable method, and then the sleeve is withdrawn from over the mother cylinder. The thus-prepared sleeve is fitted over a core roll to provide a gravure printing cylinder for use on a printing press. After each printing run the sleeve is dismounted from the core roll and placed in storage by itself. Such lightweight sleeves are easier to handle than solid cylinders and make it unnecessary to store the expensive cylinders themselves for extended lengths of time.
We have previously proposed in our Japanese patent application No. 55-94265 a method of mounting and dismounting a printing sleeve on and from a core roll. This prior art method dictates the heating of the sleeve to cause its increase in diameter. Since the sleeve of nickel, copper, chromium, etc., is more thermally expansible than the core roll of iron or the like, the former can be readily mounted on the latter with a tight fit and removed therefrom. As has later proved, however, this method is open to further improvement.
The printing sleeve must fit over the core roll tightly enough to preclude the possibility of their relative angular displacement during printing, in spite of the pressure exerted thereon from the impression cylinder. No such angular displacement will normally take place when the sleeve-type cylinder is printing on film or like smooth surfaces, because of relatively low printing pressure required. The printing pressure rises to as high as 10 to 20 kilograms per centimeter when the cylinder prints on rough paper, titanium paper or like poor receptors of ink. The printing sleeve then tends to turn about the core roll because of the high pressure from the impression cylinder as well as the possible deformation of the core roll.
Japanese Patent Laid-Open (Kokai) No. 54-4601, suggests a method of obtaining a firm bond between printing sleeve and core roll. This known method calls for the use of cement, lead alloy or like substance, which is poured in molten state into a space intentionally created between printing sleeve and core roll. This method requires the core roll to be of minimal out-of-roundness, and the filler demands a prolonged length of time for solidification. An even more serious disadvantage is that, once the printing sleeve and core roll are bonded together with such a filler, they cannot possibly be disassembled unless the sleeve is torn apart or the filler is broken as by hammering. In either way the printing sleeve cannot be dismounted in reusable form.