Cylindrical plate-holder sleeve for removable-sleeve lithographic printing presses, in particular for printing on cylindrical bodies, and the like

Abstract

 Plate-holder skirt for removable-skirt lithographic printing presses, suitable for printing in many colours on cylindrical bodies and the like, constituted by a cylindrical body (1) having, along one of its generatrices, at least three radially-protruding pins (8) on which an equal number of holes present along a side of a plate are slid, said holes being obtained during the photoengraving process, by a punching preliminarily carried out on the same plate and on all of the plates which compose the image to be printed, by at least one bar for the fastening of the edge of said plate to the skirt (14), and by at least another bar (17, 17a), fastened to the opposite side of the plate, and fixable to the ends of two arch-shaped elements, hinged onto the front faces of the cylindrical body, so to be able to be turned against the same cylindrical body, thus carrying out the tensioning of the plate, in counteraction to spring elements, or the like, able to secure the regular tensioning of the same plate during the printing process.

Description

[0001] The present invention relates to a plate-holder cylindrical skirt for printing presses for the lithographic printing on cylindrical bodies, and the like, and, more precisely, for printing presses of the removable-skirt type.

[0002] It is known that at present the lithographic printing presses for printing on cylindrical bodies use a plurality of mould- or plate-holder cylindrical bodies (skirts); in substance, the plates are constituted by metal sheets (of steel, magnesium, zinc, and so forth), on which the images or characters to be printed on paper, or on the surfaces of solid bodies are obtained by photoengraving by starting from a photographic print exposed in negative and then developed in positive.

[0003] In case of a lithographic printing of many-colours images to be transferred, in particular, on cylindrical bodies, such as bottles, cans, vials, and the like, the printing presses use a number of plates, and therefore, a number of cylindrical skirts equal to the number of the colours which compose the full-colour image; in general, the plate-holder skirts are positioned according to the generatrices of a cylinder, and into contact with a roller, whose external surface is coated with rubber, or with a similar material; the plates are then inked up, in continuous, by special wavers-ink distributor rollers, which draw ink from suitable ink containers. By revolving the plate-holder rollers, and the rubber-coated roller around a revolution axis parallel to the axis of the plate-holder rollers, the portion of coloured image having the colour carried by each roller is sequentially transferred on the rubber-­coated roller, and from this latter to the outer surface of the cylindrical bodies on which the total image is transferred.

[0004] In order to prevent that the many-colours image transferred on the rubber-coated body, and then on the bodies which must receive it may show blurs and/or imperfections, in the matching in the mutual position of the various colours which compose the image, all of the plates which in their whole compose the many-colours image must be photoengraved in such a way that the image portions of each plate exactly correspond with each other, i.e., that the from-colour-to-colour printing register is correct and perfectly repetitive; it is furthermore essential that also the positioning and fastening of the plate-holder skirts on the removable-skirt printing press is at the same level of correctness and correspondence, i.e., in register.

[0005] According to the techniques known from the prior art, the positioning and the centering of each plate on its respective skirt are carried out by using optical systems which make it possible, by means of reference points correspondingly shown on all of the plates, the individual plates to be brought into register on their respective skirts.

[0006] More precisely, according to the prior art, on the photographic film exposed in negative, two small crosses, or similar marks, are provided, which are suitably spaced apart from each other along a side edge of the same film. Such reference marks or crosses are then transferred, during the development, on the positive film, and from this latter, by photoengraving, on the metal plate which constitutes the plate. At two opposite sides of the so-obtained photoengraved plate two bars are then fastened by means of screws, which clamp, between each other, the edge of the plate, and are used to anchor the plate round the outer surface of the cylindrical skirt. The fixing of the bars onto the skirt is carried out by hooking the opposite ends of said bars to the ends of four arch-shaped, crescent-­shape elements, hinged onto the two head ends of the skirt.

[0007] By turning the crescent-shaped elements until they come to lay upon the skirt heads, the tensioning is achieved of the plate, which remains therefore wound around the same skirt. To be able to centre the plates on their respective skirts, such that all of the plates forming the image to be transferred correspond with each other, viz., they are in register, each plate-holder skirt is positioned inside an optical-type equipment, able to determine fixed reference points with which the reference crosses engraved on the plates have to be made coincide. The bringing into register is carried out by acting on screws associated with the skirt and acting on a bar fastened onto a plate side; one of such screws is prearranged to shift the plate, by a short distance, along the generatrices of the cylindrical skirt, and the other screw is prearranged to shift the plate, by a short distance, along the directrices of the same skirt. The adjustment is stopped when the reference crosses on the plate coincide with the fixed reference points of the optical system. By repeating this process for all of the plate-holder skirts, a corresponding positioning, in register, is obtained, of all of the plates, relatively to their corresponding skirts. After the positioning of the plates on their respective skirts, these latter are installed on relevant seats provided on the printing press, such seats being provided with corresponding hollows or slots and related latches making it possible the ends of the skirts to be slack-free locked onto the shaft ends, and the same skirts to revolve. After installing the skirts, usually a further manual adjustment is carried out in the position of the same skirts, before the end fastening thereof is carried out.

[0008] In practice, the positioning and the bringing into register of the plates on their respective skirts, carried out up to date according to the above described technique, involve several drawbacks and limitations; in fact, the operation of positioning of the plates on the skirts and the centering thereof by means of optical systems require various hours and a specialized staff; furthermore, the long times required by such steps make it presently impossible to accept printing orders for small amounts, due to cost reasons.

[0009] Therefore, a purpose of the present invention is to provide a plate-holder skirt having such a structure as not to require the plates to be brought into register on their respective skirts by means of an optical equipment, to allow a considerable saving, ranging from one to two, or even more hours, to be achieved in the time required by the processes of positioning and centering of the plates, and hence with the advantage that orders for the lithographic printing of even small amounts can be accepted.

[0010] Another purpose of the present invention is to provide a plate-holder skirt able to result interchangeable with the skirts known from the prior art, and, hence, to be installed on the printing presses of known type, without any modifications thereof being necessary and, above all, without requiring the use of specialized staff.

[0011] These purposes, and still further purposes which will be more clearly evidenced by the following disclosure, are achieved by a plate-holder skirt for lithographic printing presses of removable-skirt type, particularly suitable for the many-colours printing on cylindrical bodies, or the like, and provided at its ends with usual engagement means, to be fastened onto, to revolve with the revolving shaft of the printing press, which skirt is constituted, according to the instant invention:
- by an internally hollow cylindrical body, provided along one of its generatrices, and in the nearby of the longitudinal slot, provided to enable it to be positioned on the printing press revolving shaft, with at least three radially protruding pins, suitable for being engaged inside three corresponding holes provided on one side edge of the photoengraved plate, and provided, during the photoengraving process, by a punching preliminarily carried out, in a corresponding position, on all of the plates which constitute the many-colours image to be printed, such that said image is always equally positioned relatively to said three holes provided on the plates,
- by at least a fastening bar, making it possible the plate edge to be locked, by screws, to the skirt;
- by a further bar, fastened to the edge of the opposite side of the same plate, and suitable for being anchored onto the end of two arch-shaped, crescent-­shaped elements, frontally hinged onto the opposite heads of the skirt, and such to make it possible them to be turned until they come to lay upon the same heads, and to be thereto fastened, the turning of said arch-shaped elements causing the plate to be tensioned around the skirt, in counteraction to spring members, interposed between the bar and a seat destined to receive said bar provided on said arch-shaped elements, said spring members being such to secure a regular tensioning of the plate on the skirt during the printing process.

[0012] The invention, as relates to a preferred and non-­exclusive form of practical embodiment thereof, is hereunder disclosed in greater detail, by referring to the hereto attached drawing tables, supplied for indicative and non-limitative purposes, wherein:

Figure 1 shows a schematic side view of the plate-­holder skirt realized according to the invention, positioned on a plate laying in a flat condition, and ready to be fastened onto the outer surface of the skirt, and

Figure 2 shows a schematic view of a head of the skirt of Figure 1, with an arc-shaped element, shown separated from the same head, in order that its structure may be more easily understood.

[0013] Referring to said figures, the plate-holder skirt is substantially constituted, as in the types known from the prior art, by a cylindrical body 1 provided, at its opposite ends, with two inner and coaxial seats 2 suitable for being positioned on the revolving shaft of a lithographic printing press of the removable-skirt type, with the relevant fastening taking place by means of keys, or the like, inserted inside the radial seats 3 (see Figure 2). Still like in the forms known from the prior art, a plate 4 (see Figure 1) is wound and laid round the outer surface of the skirt 1, with such positioning and centering on the same skirt that during the overlapping of the various plates to the rubber-­coated, image transfer roller, a perfect matching is obtained in the position of the different colour patterns of all of the concerned plates.

[0014] In order that according to the invention a perfect positioning of the plates, and an as perfect centering thereof on the skirt 1 may be achieved, the same plates 4 (Figure 1) are preliminarily provided with reference elements able to make it possible the same plates to be automatically positioned and centered on their related skirt, with no need for any subsequent adjustments.

[0015] More precisely, during the plate preparation process, on the negative film three (or more) holes 5, 6, 7 (Figure 1) are provided by punching, with the same punching pattern being repeated on the positive film and on the plate. Such punching is carried out on all of the plates composing the full-colour image to be transferred; in such a way, the image of each single-­colour plate is positioned always at the same distance relatively to the above-mentioned three holes, and that secures an easy assemblage and a perfect centering on the skirt which, for that purpose, is provided with pins having dimensions corresponding, and with no slack, to the dimensions of the referene slots provided on the plate.

[0016] In order to facilitate the centering of the plates, the holes provided on the plates 4 are then preferably given a non-circular shape; e.g., by giving the external holes 5 and 6 an elongated configuration, with the long axis parallel to the generatrices of the cylinder 1, and giving the central hole 7 an elongated configuration, with the long axis perpendicular to the generatrices of the cylinder 1.

[0017] The pins provided on the skirt, indicated by the reference numeral 8 on the figures, are realized radially protruding from the skirt and are positioned along a generatrix of the cylindrical body 1 which is close to the usual slot 9 longitudinally provided on the skirt, to make it possible the same skirt to be inserted on, and removed from, the printing press shaft.

[0018] Furthermore, the three pins 8 are positioned on a surface portion 1a which is lowered relatively to the cylindrical surface of the skirt, so to prevent the pins from interfering with the image transfer rubber-­coated roller. The skirt 1 is then equipped, at its opposite ends, with an arch-shaped, crescent-shaped element 10, and, respectively 10a; the arch-shaped elements 10, 10a are hinged in 11 on the two front heads of the skirt 1, so that they can be opened wide, on the plane of the same heads, towards the outside of the cylindrical surface of the skirt and then turned until they come to mate the same heads, and are fastened onto said heads by means of screws passing through bores 12, 12a. The hinging of the arch-shaped elements is carried out by means of a single shaft passing through the skirt and rotatable on it, at whose ends the arch-shaped elements are integral in 11; in such a way, when one acts on one of the two arch-shaped elements, the turning of the opposite arch-shaped element is also obtained.

[0019] At the free end of the two arch-shaped elements 10 and 10a a fork-shaped recess 13, and, respectively, 13a, is provided; its function will be clarified in the following. At the basis of said recess a hollow 14a is provided, which is destined to house a cylindrical or helical spring 14, whose function is also clarified in the following.

[0020] The centered positioning of a plate 4 on the skirt 1 is therefore carried out by sliding the holes 5, 6, 7 on the pins 8 of the skirt, and clamping the plate on the same skirt by means of a bar 15, which is also provided with holes 15a in positions corresponding to the positions of the pins 8 and which, in its turn, is fastened to the skirt by means of screws 16, passing through the bar in 16a, and the underlying plate 4, and engaged inside the screw-threaded bores 16b provided on the skirt.

[0021] Onto the opposite end of the plate 4 another bar is applied, which is constituted by two superimposed half-­bars 17, 17a, which clamp the end edge of the plate 4, and are tightened to each other by means of screws 18. The bar constituted by the two half-bars 17 and 17a is then slid into the fork-shaped recess 13, with the arch-shaped element 10 being in its opened wide position, so that the plate 4 is wound around the skirt; the two arch-shaped elements are then turned until they come into juxtaposition to the skirt heads, wherein the elements 10 are fastened by means of screws in 12, 12a. During the closure turning of the arch-­shaped elements 10, 10a, the plate 4 is laid on the skirt, and the spring 14, inserted inside the hollow 14a, and into contact with the free end of the bar 17-­17a inserted inside the fork 13, contributes to control the tension of the plate during the printing process. Therefore, in practice, the presence, as reference points, of holes equally positioned on all of the plates forming the many-colours image, and their sliding on the retainer pins provided on the skirt, causes an automatic and corresponding positioning of all of the plates on their respective skirts, the control of the tensioning of the plates being guaranteed by the spring tensioning system provided at the end of the arch-shaped elements 10, 10a.

[0022] Furthermore, the skirt according to the invention is so realized as not to have sharp edges in the plate bending areas, in order to prevent sharp-edge bends - ­which would cause difficulties in the bringing into register and in the adjustment - from occurring in the same plates.

[0023] The skirt as above disclosed is then installed on the printing press, as in case of the skirts of type known from the prior art, i.e., making protrusions, provided for that purpose, enter corresponding hollows provided on skirt supports, and by means of the above mentioned radial keys 3 (Figure 2).

[0024] As a consequence, the subject skirt of the present invention results interchangeable with the skirts known from the prior art and is hence directly installable on the already existing printing presses, with no modifications.

[0025] Finally, the adjustment in position of the various skirts on the printing press is carried out by hand, as it occurs at present, by observing the images initially printed on the bodies which must receive them.

Claims

1. Plate-holder skirt for lithographic printing presses of removable-skirt type, particularly suitable for the many-colours printing on cylindrical bodies, or the like, characterized in that it is constituted
- by an internally hollow cylindrical body, provided, along one of its generatrices, and in the nearby of the longitudinal slot, provided to enable it to be positioned on the printing press revolving shaft, with at least three radially protruding pins, suitable for being engaged inside three corresponding holes provided on one side edge of the plate, and provided, during the photoengraving process, by a punching preliminarily carried out, in a corresponding position, on all of the plates which compose the many-colours image to be printed, such that said image is always equally positioned relatively to said three holes provided on the plates,
- by at least a fastening bar, making it possible to lock, by screws, the plate edge to the skirt;
- by a further bar, fastened to the edge of the opposite side of the same plate, and suitable for being anchored onto the end of two arch-shaped, crescent-­shaped elements, frontally hinged onto the opposite heads of the skirt, and such that they can be turned until they come to lay upon the same heads, and can be thereto fastened, the turning of said arch-shaped elements causing the plate to be tensioned around the skirt, in counteraction to spring members, such to secure a regular tensioning of the plate on the skirt during the printing process.

2. Skirt according to claim 1, characterized in that said three or more holes provided along a side of the plate to be wound around the skirts are obtained by punching the negative film and correspondingly punching the positive film and the printing plates.

3. Skirt according to claim 1, characterized in that said spring elements for the regular tensioning of the plate on the skirt are constituted by at least a helical spring, or the like, housed inside a seat provided inside the end of said arch-shaped, crescent-­shaped elements, and interposed between the basis of the said seat and said bar housed inside the end of the arch-shaped elements.

4. Skirt according to claim 1, characterized in that said three or more holes provided along a plate side are given substantially elongated shapes, or flattened-­ring shapes, with a portion of said holes being positioned with its longer axis being parallel to the generatrices of the cylindrical skirt, and the balance thereof being positioned with its longer axis being perpendicular to the generatrices of the cylindrical skirt, with the anchoring pins destined to enter said holes being on the contrary given a circular outer shape.

5. Skirt according to claim 1, characterized in that said pins radially protruding from the skirt are provided on a surface region which is lowered relatively to the cylindrical surface of the same skirt, to enable the skirt to freely revolve against the usual rubber-coated roller for the image transfer.

6. Skirt according to claim 1, characterized in that said two opposite arch-shaped, crescent shaped elements are mounted onto, and integral with, the ends of a shaft which, in its turn, is longitudinally rotatably mounted inside the body of the skirt.

7. Skirt according to claim 1, characterized in that it is dimensioned and structured in such a way that it results interchangeable with the skirts presently used on the normal lithographic printing presses.

Drawing