FR2577171A1 - MACHINES FOR OFFSET PRINTING OF METAL SHEETS - Google Patents

Abstract

1. Offset printing machine comprising a feeding device, a device for positioning the object to be printed on a feeding board (1), feeding hoops (2) ensuring the transfer of the object to be printed, a printing device constituted in particular of a blanket cylinder which presses the object to be printed against the surface of a feeding cylinder (4), whereas said object to be printed is held by means of clamps, and optionally at least one transfer cylinder (5), said feeding and transfer cylinders having diameters greater than about 60 cm, said machines performing the offset printing of one face of a metallic sheet of which the other face comprises at least one protective layer, said machines being characterized in that : - any surface of said machines, and in particular the surface of the feeding board (1) and of the feeding hoops (2), against which said protective layer of the sheet to be printed is liable to rub, is a perfectly polished chromium surface, - all the parts of said machines against which said protective layer of the sheet to be printed are liable to rub, or with which said sheet to be printed is liable to come into contact, are provided with inlet orifices (7) (8) for sequenced pressurized air.

Description

Machines for offset printing of metal sheets

  Machines for off-printing are known

  set-for example of the type VARIANT or SUPER VARIANT or VARIMAT of PLANETA in which one tried to optimize the

  various elements in order to achieve maximum speed

  precision and precision of mono or multi-color prints. These machines are successively formed of: - a feeding device (feeder),

  - a positioning sensor (position-

  front - cleats - and lateral - rectifier) located at the entrance of the first printing element; this positioning device which acts when the sheet is on the "margin table", is also called "rectifier",

  - margin arches that form the inter-

  intermediate between said margin table and the first cylinder said margin drum preceding the margin cylinder on which the paper is printed, the printing device itself, which consists, the sheet of paper being held by clamps which act on all the front of the sheet, to be brought into contact with at least

  a face of said sheet a carrier cylinder -

  inked characters, - at least one transfer device by which the sheet is transferred from a device

  to another printing device

  sion, - and output devices by which the

  printed sheets are neatly arranged.

  Of course, said machines comprise

  also the plates fixing devices, the devices

  supply of ink and water, the motors

  training equipment and the control and synchro-

necessary.

  Printing machines of this type have proven to be perfectly suited for offset printing

  ordinary paper, cardboard and metal sheets.

  But they are not directly usable for the printing of metal foils (mainly aluminum) intended, according to modern techniques, for the realization of the boxes of e-can, because of such

  leaves have on their face not intended for

  pressure, very sensitive protective layers

  we must at all costs ensure integrity.

  To date, metal sheets of this type can be printed according to techniques and with the aid of offset machines thanks to a particular choice, according to which said techniques and machines involve the passage of sheets "flat". Such machines are quite reliable, but they lack the possibility of locating one impression on the other and speed

  (limit about 1 sheet per second).

  It was found first of all that the machines of the VARIANT and SUPER VARIANT type mentioned above, could in principle be used for the printing of metal sheets, one of whose faces comprises at least one protective layer, despite the fact that, in these margin and transfer cylinders, the leaves do not remain "flat". This possibility is related to the fact that the cylinder - margin of said machines has a sufficient diameter to prevent any mechanical deformation of the sheet and any deterioration (cracks for example) 1-a protective layer. The diameter of the machines currently used is of the order of 85 cm; it may be thought that for such a machine to be usable it is necessary that the margin roll has a diameter greater than about 1 cm. But, besides this observation, it was found that the machine, as known and currently used, had to receive certain adaptations to maintain

  the integrity of the protective layers.

  These adaptations are essentially the following:

  - any surface, and more particularly the surface

  face of the margin table, roll bars and transfer devices, with which the protective layer is likely to rub, a perfectly polished chrome surface,

  - all parts of the machine on the

  the metal foil is in contact, by its face provided with protective layer, or is likely to come into contact will be provided with pressurized and sequential air supply orifices, this air having the function of either reducing the friction of the sheet with the contact surface, either

to prevent said contact.

  In addition to the essential adaptations mentioned above, it is desirable, in view of the high cost of the sheets to be printed, and consequently to optimize the economic results that can be obtained,

  to equip the printing machine with two other adapta-

  - to refine the fingers of the gripping tongs which hold and pull the sheets, so that said tongs exert their grip only to a depth of not more than 3 mm from the edge of the sheet, - adapt the rectifier of the machine so that, in spite of any pre-cutting of the metal foil, said foil can be suitably positioned with reference to its greater width; this implies the use of a rectifier whose reference plane can be suitably positioned at various points (in length as known and in width)

on the margin table.

  The invention will be better understood in terms of

  FIGS. 1 and 2, which schematically illustrate, in a nonlimiting manner, an example of

embodiment of the invention.

  FIG. 1 is a diagrammatic sectional view of the arrival devices of the plates to be printed

in the machine.

  FIG. 2 diagrammatically shows, from above, the principle of the initial positioning of the

  sheet to print on the margin table.

  In Figure 1 is schematized: - in 1 the margin table which collects the metal sheet from the feeder; this sheet is oriented so that its face to be printed is on the top and that its face coated with a layer

  sensitive protector either below, that is,

  say in touch with the surface of the table

margin.

  - In 2 margin arches, through which it ensures the transfer of the sheet from the margin table to a first drum cylinder 3; the metal sheets are then held, all over the front of each

  sheet, by not shown pliers.

  in 4 the margin cylinder against which the sheets are pressed when they are printed, which is produced by a blanket (cylinder

  rubber surface) not shown.

  - In 5 a transfer cylinder bringing the sheets1 held by new clamps, from the margin cylinder 4 to another printing device similar to that

schematized in this figure.

  in 6 there is shown a device of the invention which is a tube in which air under pressure is admitted; the role of 6

will be explained later.

  It has been indicated above that the fundamental element of the invention lies in the fact that all the surfaces with which the protective layer is capable of rubbing must be perfectly polished chrome surfaces; if we consider the figure these surfaces are essentially the surface of the margin table 1 and the surface of the arches 2; the surface of the cylinder 4 is also polished chrome, but it will be noted that, given that the plates are driven (by the clamps in particular) at a speed substantially equal to that of the cylinder, there is no real friction of the surface of the plate, having the protective layer on the surface of this cylinder 4. In the present application, when indicating the existence

  Polished chrome surface should be understood as

  face having been coated with a hard chromium, the surface of which has been made as smooth (polished) as possible by any

  medium (chemical and / or mechanical).

  We also mentioned the parts of the

  machine on which the metal foil is likely to

  to rub through its coated surface, o the parts of the machine with which the foil can

  coming into contact unduly are provided with

  nee air under pressure. This is particularly the case

  the extremity 7 of the margin table, this is also the case

  8 at the level of the hoops 2, this is finally the case at the exit of the margin cylinder o the presence of various housings required the proper positioning of a

  tube with pressurized air supply ports 6.

  In machines of the type of trans-

  formed according to the invention, there are often areas of air blowing; but this blowing is performed with air at low pressure, (a few hundred grams cm2) while in the invention blowing is performed with air under pressure ie pressures of 3 to 10 kg / cm 2. Given the use of pressurized air, it is not acceptable to blow said air

  permanently, as this could present various

  vantages; It has therefore been provided with an electro-

  valves, controlled by the movement of the metal plates

  printable, which only delivers air when the plate arrives at the proper place. This sequential release of pressurized air into various parts of

  the machine is one of the features of the invention.

  Other improvements of the existing machines have been made to take into account, at the economic level,

  the high cost of the metal sheets to be printed. How-

  these improvements, if they are of interest

  certain, may not appear on some machines.

  It has previously been indicated that one of these improvements is the refinement of the ends of the fingers of the plate grippers, in order to reduce the area of the plate on which there can be no impression; in this area, with pliers fingers that have been tapered to the end, at the end, a thickness

  0.5 mm, it has been possible to reduce the

  take the clip on the sheet to a width of about 2.5 mm and bring the edges of the "prints" closer to a distance of about 5 mm from the edge of the sheet. Another improvement is schematically and

in principle in Figure 2.

  In this figure we have schematized: - in 1 the margin table

  - in 9 retractable cleats which, at the end -

  of the margin table, allow a posi-

  in x of the metal plate 10 - 11 the device (ectificator) according to the invention for positioning in

y of the plate 10.

  On the current machine the positioning therein is achieved by a stop 12 (rectifier plate) that can be moved longitudinally (along y) on the axis 13, which includes the necessary marks; according to the invention said stopper 12 can be moved and marked, not only along the axis 13, but also along the axis 14 (x) so as to take into account any cuts (such as 15) on the edge of the plate.

Claims (3)

  l .. Offset printing machines with   a feeding device, a positioning device   the object to be printed on a margin table, margin arches transferring the object to be printed, a printing device consisting in particular of a blanket that presses the object to be printed against the surface of the object; a margin cylinder, while said object to be printed is held by means of clamps, characterized   in that said machines have received, for the purpose of printing   offset of one side of a metal sheet, the other side of which comprises at least one protective layer, the following adaptations: - any surface of said machines, in particular the surface of the margin table and margin arches, on which said protective layer of the sheet to be printed is   likely to rub, is a chromatic surface   perfectly polished, - all the parts of said machines on which said protective layer of the sheet to be printed is likely to rub, or with which said sheet to be printed is likely to come into contact, are   provided with air supply ports under pres- sequence.   2. Machines according to claim 1, characterized   in addition, in that the rectifying device ensuring the positioning of the sheet on the margin table is positionable and detectable according to two   perpendicular directions on the margin table.   3. Machines according to one of claims 1 and   2, characterized in that they comprise clips of which   the fingers have been refined in such a way as to allow a pre-   heightening of the sheet to be printed at most 3mm from from the edge of said sheet.