Universal under-packing for rubber-coated fabrics on offset printing press cylinders

Abstract: Sheets of rubber-coated fabric are mounted on the cylinders of offset printing presses. An under-packing formed from the combination of a flexible supporting sheet (12), which may however be dispensed with, and a multiplicity of flexible graded sheets (14) has to be interposed between the cylinder surface and the rubber-coated fabric to obtain a predetermined total thickness which varies as the type of printing press varies. The total thickness of the universal under-packing (10) according to the invention is equal to a predetermined maximum thickness. The thickness of the sheets (12, 14) of the universal under-packing (10) is chosen such that by removing from the universal under-packing (10) one or more graded sheets (14), the thickness which has to be obtained for any specific case can be sufficiently approximated to. That face of each of the graded sheets (14) of the universal under-packing (10) which, when the under-packing is mounted on the impression cylinder, faces inwards, but with the exception of the face of the most inner graded sheet (14) if the supporting sheet (12) is not present, is treated with a sticker of the type which, while maintaining the sheets (12, 14) united, enables them to be separated from each other.

Description: The present invention relates to so-called under-packing for rubber-coated fabrics mounted on offset printing press cylinders. As known to the expert of the art, an offset printing press cylinder consists of a hollow metal cylinder rotatable about its axis and carrying on its lateral surface a rubber-coated fabric sheet (the so-called printing blanket) provided on each of its opposing sides with a metal bar, normally of aluminium, of U cross-section to enable it to be mounted over the corresponding edge of the rubber-coated fabric and then fixed to it. The two metal bars serve to fix the rubber-coated fabric sheet to said cylinder. The rubber-coated fabric from which said sheet is obtained comprises two layers, of which one is the fabric and the other is rubber (normally caoutchouc). For each model of offset printing press its manufacturer indicates the total thickness to which the blanket cylinder has to be covered, this covering consisting not only of the aforesaid rubber-coated fabric sheet (printing blanket) but also of so-called under-packing, traditionally formed from a supporting sheet of fairly thin rubber-coated fabric (the so-called under-blanket) and a certain number of graded paper sheets of various thicknesses which the user has to choose to obtain the necessary under-packing thickness. The supporting sheet (under-blanket) may also be not present, particularly in the more modem printing presses, so that in this case the under-packing is formed only from the graded paper sheets. These graded paper sheets are stored in various boxes, each containing a multiplicity of graded paper sheets of the same thickness. All the graded paper sheets of the same thickness have the same colour, which is different from that of the graded paper sheets of other thicknesses in order to facilitate identification. The user covers the under-packing (consisting of the under-blanket and the graded paper sheets) with the sheet of rubber-coated fabric (printing blanket), and fixes it to the impression cylinder by the said end metal bars. As will be apparent, the aforedescribed operation is lengthy and requires a certain care, all of which affects to a certain degree the operating costs of the printing press. The object of the present invention is to substantially simplify and accelerate such an operation, with the advantage of substantially reducing said costs. This object is attained by the universal under-packing of the present invention, comprising a determined number of superposed flexible sheets, characterised in that: the total thickness of the universal under-packing is equal to a predetermined maximum thickness; the thickness of the sheets of the universal under-packing is chosen such that by removing from the universal under-packing one or more graded sheets, the thickness which has to be obtained for any specific case can be equalled or sufficiently approximated to; that face of each of the graded sheets of the universal under-packing which, when the under-packing is mounted on the impression cylinder, faces inwards, but with the exception of the face of the most inner graded sheet if the supporting sheet is not present, is treated with an sticker which, while maintaining the sheets united, enables them to be separated from each other. The most inner sheet of the universal under-packing can be a traditional supporting sheet (an under-blanket), but can also be of other suitable synthetic material of adequate thickness. By virtue of the present invention the user can be provided with a manufactured universal under-packing as a single unit, comprising (if requested) not only the graded sheets but also a supporting sheet. The user can then, according to the type of printing press available, detach from the universal under-packing those graded sheets which need to be removed in order to obtain an under-packing of the required thickness as determined for the specific case. It should be noted that the component sheets of the universal under-packing of the present invention can still be of paper (but treated on one of their faces with sticker), although better results can be obtained by using sheets of a suitable flexible synthetic material (for example polyurethane sheets) which are normally more resistant while being detached (if care is not taken, the paper sheets can tear), so that they are sure to remain whole and reusable. Except for the possible support sheet, the other (graded) sheets of the universal under-packing can be all of the same thickness, provided that this is sufficiently small to enable the predetermined required thickness to be approximated to the required extent, in order to ensure proper operation of the impression cylinder. This obviously does not mean that graded sheets of different thicknesses cannot be used. The constituent sheets of the universal under-packing can have a specific colour, indicative of a determined sheet thickness. Each sheet can also carry a number and/or letter indicating the specific thickness. In this manner it is extremely simple for the user to how many and which graded sheets to be removed from the universal under-packing to obtain the total thickness required to cover the cylinder of a determined offset printing press. The invention will be more apparent from the ensuing description of one embodiment thereof. In this description reference is made to the accompanying drawing, in which: Figure 1 is a partial perspective view of an under-packing according to the present invention; Figure 2 is an enlarged view thereof in the direction of the arrow 2 of Figure 1. As can be seen from the figures, the piece of universal under-packing 10 comprises, in this specific case, a support sheet 12 and a multiplicity of graded sheets 14. Although as stated the sheets 14 can be of paper, they are preferably of a suitable synthetic material, of adequate flexibility and strength, they all being of the same thickness in this specific case. In particular, it has been found that a thickness of the graded sheets 14 not exceeding 0.10 mm enables those effective thicknesses encountered in practice to be approximated to a sufficiently precise extent. The supporting sheet 12 can either be a traditional under-blanket or an adequate thickness sheet of the same material as the graded sheets 14. Before forming the universal under-packing 10, a sticker layer is applied to one of the faces of the graded sheets 14 (that which is to face downwards with reference to the figures) to enable the various sheets (12 and 14) forming the universal under-packing 10 to stay together. If the supporting sheet 12 is not present, the lowest sheet 14 (again with reference to the figures) is not treated with sticker. The sticker used is of the type which enables a sheet (12, 14) to be detached from the adjacent sheet, as indicated by the raising of the edge of the upper sheet 14 in Figure 1. To facilitate detachment of one or more of the graded sheets, one or more edge regions of that surface of the graded sheets which is treated with sticker (for example a small comer region) has no sticker applied. It has been found that by producing the universal under-packing of the present invention in two suitable different thicknesses, all requirements of any user which arise in practice can be covered. This also avoids having to remove an excessive number of graded sheets when small thicknesses are required. In particular, a first thickness can be 1.65 mm and a second thickness 0.70 mm. The universal under-packing of 1.65 mm is composed for example of a supporting sheet 12 of 1.05 mm plus several graded sheets 14 of 0.05 or 0.1 mm (preferably all equal), in such a number as to arrive at the total thickness of 1.65 mm. Likewise the under-packing of 0.70 mm can be composed of a supporting sheet of 0.35 mm and a number of graded sheets (preferably all equal) of 0.05 or 0.1 mm. In both cases, by removing one or more graded sheets 14 an under-packing of the thickness necessary for a specific case can be obtained. As already stated, those graded sheets 14 which have been removed can be reused either to form a new universal under-packing or to be added to the aforedescribed second under-packing (of lesser thickness) to obtain one of greater thickness. Finally, it should be noted that the supporting sheet 12 can be dispensed with, especially in the case of the second under-packing (of lesser thickness).

Claims: A universal under-packing (10) for rubber-coated fabrics mounted on offset printing press cylinders, on the lateral surface of the cylinder there being mounted a rubber-coated fabric sheet fixed by two metal bars applied to two of the parallel sides of the rubber-coated fabric sheet, to ensure proper operation of the impression cylinder the thickness of the under-packing used being equal or sufficiently close to the predetermined thickness required to fill the space existing between the lateral surface of the cylinder and the rubber-coated fabric sheet, the universal under-packing (10) comprising a multiplicity of superposed flexible sheets (12, 14), characterised in that : the total thickness of the universal under-packing (10) is equal to a predetermined maximum thickness; the thickness of the sheets of the universal under-packing (10) is chosen such that by removing from the universal under-packing (10) one or more graded sheets (14), the thickness which has to be obtained for any specific case can be equalled or sufficiently approximated to; that face of each of the graded sheets (14) of the universal under-packing (10) which, when the under-packing is mounted on the impression cylinder, faces inwards, but with the exception of the face of the most inner graded sheet (14) if the supporting sheet (12) is not present, is treated with an sticker which, while maintaining the sheets (12, 14) united, enables them to be separated from each other. A universal under-packing (10) as claimed in claim 1, wherein that sheet thereof which, when the under-packing is mounted on the printing press cylinder, is the most inner is a traditional supporting sheet (12). A universal under-packing (10) as claimed in claim 1, wherein the graded sheets (14) are of a flexible synthetic material. A universal under-packing (10) as claimed in claim 1, wherein the supporting sheet (12) is of a material equal to that of the graded sheets (14). A universal under-packing (10) as claimed in claim 1, wherein the graded sheets (14) all have the same thickness, provided that this is sufficiently small to enable the necessary predetermined thickness to be approximately equalled in order to ensure proper operation of the impression cylinder. A universal under-packing (10) as claimed in claim 1, wherein the graded sheets (14) are also of different thicknesses. A universal under-packing (10) as claimed in claim 6, wherein the graded sheets (14) of different thickness have a different colour indicative of the specific thickness. A universal under-packing (10) as claimed in claim 6, wherein the graded sheets (14) of different thickness comprise a number and/or a letter indicative of the specific thickness. A universal under-packing (10) as claimed in claim 1, wherein in order to facilitate the detachment of the sheets of the universal under-packing (10), one or more edge regions of that surface of the graded sheets treated with sticker are without sticker. A universal under-packing (10) as claimed in claim 1, which is produced in at least two different thicknesses to cover all user requirements arising in practice, to avoid having to remove an excessive number of graded sheets (14). A universal under-packing (10) as claimed in claim 10, which is produced in two different thicknesses, namely in a first thickness of 1.65 mm and in a second thickness of 0.70 mm. A universal under-packing (10) as claimed in claim 11, wherein the under-packing (10) of 1.65 mm thickness is composed of a supporting sheet (12) of 1.05 mm plus a number of graded sheets (14) of 0.05 or 0.10 mm. A universal under-packing (10) as claimed in claim 11, wherein the under-packing (10) of 0.70 mm thickness is composed of a supporting sheet (12) of 0.35 mm plus a number of graded sheets (14) of 0.05 or 0.10 mm.

Inventors: LEVI ACOBAS ROBERTO, LEVI, ACOBAS ROBERTO
Applicants: PRINTGRAPH WATERLESS S R L, PRINTGRAPH WATERLESS S.R.L.
Application year: 2001
Main classification: B41F30
IPC codes: B32B7, B41N10, B41F30