FR2626214A1 - METHOD FOR HANGING AND POSITIONING OFFSET PRINTING PLATES WITH MAGNETIC SUPPORT, AS WELL AS OFFSET PRINTING PLATES AND MACHINES FOR USE THEREOF - Google Patents

Abstract

The present invention relates to a method for mounting and positioning printing plates with a magnetic support on an offset printing machine, characterised in that the plate, after being insulated, laid out and, where appropriate, baked, is bent in such a way as to have a permanent deformation causing said plate to have the form of an open cylinder, and is then slipped onto studs (5) formed on the plate cylinder (1) in the vicinity of at least one edge of said cylinder and in a plane perpendicular to the axis of the cylinder, this slipping on being made possible by the provision, along at least one lateral edge of the plate, of orifices suitably positioned to correspond to said studs, and is then laid against the plate cylinder by means of magnets flush with the surface of said cylinder.

Description

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  The present invention relates to a process and a provision

  sitive for the magnetic hanging of these offset plates.

  Offset plates are currently installed on printing machines with various mechanical devices; among these devices, the most used are constituted by two jaws which tighten and tighten the ones placed around the plate cylinder; these mechanical devices have various drawbacks among which one can mention the existence of an unbalance (more or less important depending on the nature of the jaws) on the plate cylinder, an ocsitionner of the plate requiring precise and long adjustments and a certain weakening of the plate due to mechanical stress, which leads, for aluminum-based plates for example, to the risk of breakage during installation when starting up, or during

rolling.

  These mechanical fastening devices seem, despite their drawbacks mentioned above, fully justified since at least 99% of the offset plates used today are based on aluminum.

  Now it seems for a few years that a new trend

  dance is taking shape in the offset industry which consists of using steel again as a base for the plates. The magnetic properties of this material are known; also it may be desirable to use this property to hang, on offset machines, offset plates with steel support (with magnetic support). The principle of fixing a standard plate to the flexo with steel support on the plate cylinder of a printing machine is known and has been advocated for a long time. Unfortunately for various reasons, this method of attachment has never been implemented

in the offset process.

  In addition, the magene tical fixing of the offset plates proves interesting only insofar as it is implemented, thanks to

  this fixation, means which not only allow an

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  quick loading of the plates but also precise positioning of the

  say plates in order to decrease the duration of the adjustments. These are

means which constitute the invention.

  In reality, what should be positioned is the printer part of the plate, that is to say the part of the plate which includes the ink-absorbing and aquaphile zones. It is therefore first of all necessary, by known means, to ensure that this printing part of the plate is exactly positioned in relation to the plate itself, that is to say in relation to fixed marks (sides of the plate, lines traced on the plate, lines of holes arranged on an edge of the plate ...) integral with this olaque (or forming part of the plate). As indicated above, the means for exactly positioning the printer part on the plate are known. Magnetic snapping is also known; it consists

  in that the plate cylinder comprises, flush with its surface

  face, a sufficient number of magnets for the plate to be soli-

  duly fixed. These magnets can have the most diverse shapes, they are generally in the form of studs or benches arranged along the Generators of the cylinders. It is desirable to take into account the specific nature of offset printing which is characterized by the presence of water on the plate,

  this dampening water which can, to a certain extent, infiltrate

  trer under the plate; to take this water into account, it may be useful to protect the surfaces of the magnets placed on the cylinder, this protection being able to be done, for example, by the use of a thin waterproof film or by depositing, on

  the surfaces to be protected, with a thin protective layer of a material

any waterproof riau.

  To achieve precise positioning of the plate, the following two means should be used: - prior bending of the plate, - threading of the plate on nipples formed on the plate cylinder, in the vicinity of a edge thereof, in a plane perpendicular to the axis of the cylinder, this threading being made possible by the arrangement, along one of the edges of the

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  plate, suitable openings Lerremert ost r 'rees correspond

to said nipples.

  By “bending” beforehand we mean that the plate is subjected before its installation, on the plate holder plate, a permanent deformation such that said initially flat layer is in the form of 'a cyLirore whose diameter is of the order of magnitude of the diameter of the plate holder cy.irore, and even preferably the slightly lower. This bending operation implies that the nature of the steel which constitutes the base of the plate smit ct n n e.erer; tc w-cîe, this choice being within reach This all spaLe - this mazer at. It will be noted moreover that this operation this bending irpLiqae a certain lengthening of the portion suoerificeLve e ,, térie e of the plate; we will avoid any deformation too imnortarte and we will make sure, by realizing the cirntraqe darn s oe coniilons identical or neighboring for the various pLaaues, always adding an identical extension of said corticr sCercieL.This possibility, thanks to bending prerequisite, to control and make it reproducible from one slap to the next this phenomenon of lengthening, is important because it is the first and the realization of a

  very precise positioning of the plate.

  To carry out the threading of the pLauje on the nipples, one will obviously use a plate provided, along and in the vicinity of one of its lateral edges at least, with suitable openings. The shape, dimensions (generally the diameter, tre) and the relative position of these openings must correspond to the nipples with

  which these openings will have to cooperate. Given the pro-

  high mechanical properties of steel-supported plates and taking into account the prior bending under controlled conditions, it is possible to provide very precise adamtation of said openings with said nipples. The pins on which the plate openings are threaded are arranged on the plate cylinder, in the vicinity of a bcra of said cylinder and in a plane perpendicular to the axis cu cyLindre. So that there are no particular difficulties due to the presence of these

  nipples and neighboring cylinders and rollers (

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  blanket and inking and wetting rollers) it will suffice, and this constitutes a secondary aspect of the invention, to provide that the olaque-carrying cylinder will be slightly wider than the cylinders

and neighboring rollers.

  The offset plates most often have, on their edges, openings intended to ensure the positioning of the printing part of the plate with respect to said plate. We can obviously use these openings to, in cooperation with back nipples fitted on the cylinder, position the plate, but '' experience proves that, in the current racnines (es, such

  nipples will not be positioned beyond the cylinders and

  leaux see-ns of the plate cylinder, which would require sometimes expensive arrangements of said cylinders and rollers. So, most often, we prefer to use other openings, often

  in greater number, to ensure the positioning of the sticks.

  The present invention therefore relates to a method allowing the attachment and positioning of offset plates on (the plate cylinders of offset machines by using a magnetic attachment, characterized in that a plate is used in the vicinity of at least one of its lateral edges of the apertures suitably arranged, in that said plate-carrying cylinder comprises, in the vicinity of at least one of its edges, a series of pins arranged in a plane perpendicular to the axis of the cylinder, said pins being adapted to said openings and that

  A pre-bending of the plate is carried out before positioning

  cut it on said cylinder by using said pins

and said openings.

  The present invention also relates to

  - offset plates usable for the implementation of the pro-

  assigned hooking and positioning according to the invention, said plates being characterized in that they have a

  steel base and a series of openings in the vicinity

  swimming of at least one of the longitudinal edges of said plates,

  - offset machines for implementing the ac-

  hooking and positioning according to the invention, characterized in that their plate cylinder has a width slightly greater than that of the immediately adjacent cylinders and that said cylinder-placed holder has on its 5arn-e projecting relative to the cylinders and rollers immediately neighbors one

series of nipples.

  It will be noted that, according to the invention, the pLacies are main-

  held and positioned by these nipples located near the edge of the plate cylinder and no longer by means (macho: -es by

  example) arranged according to a Judit cyL-n-re generator. They-

  follows that the sides of La placue which are arranged, ar-es position-

  The length of a generator of said cvLincre are free, that is to say, are only maintained by means of the magnets located on

  The cylinder. In general, this provision is not difficult.

  cultured (all the more cue in the fall this art diszose-a magnetizable on said cylinder) but it can be cue tors manipulations of the plate the edges of it (-ords Dositionnes

  along the generators) are slightly deformed; this deformation

  This could result when rolling the back plate. To overcome this difficulty, it was pre;, according to one of the aspects of the invention, that the pore-cylinder could

  include, on a portion of said cylinder corresponding to the ends

  Mites of the plate, a slight depression in which at least one magnet is arranged. It is understood that thanks to this depression the ends of the plates will always be slightly re-entrant (that is to say will be kept inside the theoretical hoop formed by the plate cylinder) and cannot, therefore, undergo damage, even in the event of accidental deformation of the

ends of the plate.

  The following nonlimiting example illustrates the invention; this example will itself be illustrated by FIGS. 1 to 3:

  - Figure 1 shows a schematic longitudinal view

  tick of a plate roller according to the invention; - Figure 2 is a section along II-II of 'Figure 1; - Figure 3 is a section along II-It of a cylinder

  of the plate holder comprising a depression according to the invention.

Example

  Let's consider a 4 colors sheetfed offset machine from OCMSA reference AuréLia 700 using 775 x 1 G35 mm plates and able to print a maximum paper surface of

710 x 1 02C mm.

  The plate cylinder of this machine has a Width

1045 mm.

  Although this plate cylinder is of sufficient width

  Fisarte to be able to use it in the vicinity of the edges of the fixing nipples according to the invention, the said cylinder has been replaced by a cylindrical toe-plate (perfectly cylindrical in shape) of 1,100 mm. Width including, flush with its surface

  magnets placed according to generatrices of said cylinder.

  About 15 mm from each of the edges of said cylinder, regularly distributed pins were placed. The offset machine, thus transformed, is ready to make prints using

te process according to the invention.

  We have schematized this transformation of the machine on

Figures 1 and 2.

  In Figure 1 we see - in 1 the plate cylinder - in 2 an ink roller

- in 3 - dampening roller.

  The plate cylinder 1 has, with respect to the plate cylinder of a current corresponding offset machine, the following characteristics: - magnets 4 which are flush with the surface of said cylinder are placed on the surface of said cylinder - we have arranged in the vicinity of the edges of said cylinder pins 5 (which will cooperate with the openings formed along the

  edges of the plates) and, so as not to have to modify the

  Leaux 2 et 3, we enlarged the plate cylinder so that

  reieter said nipples outside the grip of the rou-

Leaux 2 and 3.

  In Figure 3 there is shown, in section along II-II, a

  improvement of the invention consisting in providing on a certain

  taine cylinder width a slight depression 6. In this-

  depression, for example and this preference, a aimart L has been placed. When the offset offset is placed around the cylinder at least one of the ends of said plate (the end capable of being torn off during rolling; will be attracted by the magnet 4. Obviously the two ends of the said plate can be attracted by the magnet 4 (or by other magnets mounted in the said

depression 6.

  As offset plate with magnetic support (steel) used

  will read, for example, in the invention a plate comprising a s-

  black iron port whose mechanical qualities are those of European standard T 61 and whose thickness is 25, LW0. This black iron support has been covered with a layer of matt chrome.

  and an encrophilic positive photosensitive layer.

  This plate has the oarricularity of comprising, on its two sides, openings which correspond exactly to the pins present on the plate cylinder. This plate after exposure, development and cooking, is passed through a rolling machine which makes it undergo a permanent cefcrmcaior such that in the state of rest said plate is in the form of an open cylinder whose diameter is of the order of magnitude (and even preferably slightly less) of

diameter of the plate cylinder.

  The plate is then placed around the cylinder

  plate by inserting the plate from the pressure end side and then placing this plate so as to thread the nipples into the

plate holes.

  This process provides rapid positioning and

precise of the plate.

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  Note that in the example above the width of the plate is the same as that of the plate cylinder and that said plate has openings on its two lateral sides. This provision is not essential because it is possible to use

  for a plate cylinder of width L two plates present

  both being slightly less than L / 2 in width; each of these plates will have active openings only on one of its lateral sides.

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Claims (3)

R E V E N D I C A T I 0 N S   1. Method for hanging and positioning printing plates with magnetic support on an offset printing machine, characterized in that the plate after exposure, development and possibly baking is - bent so as to present a permanent deformation bringing said plate to have the shape of an open cylinder then - threaded on pins (5) formed on the cylinder (1) plate holder, in the vicinity of at least one edge of said cylinder and in a plane perpendicular to the axis of the cylinder, this threading being made possible by the arrangement, along at least one lateral edge of the plate, of apertures suitably positioned to correspond with said pins, then - applied against the plate cylinder thanks to   magnets flush with the surface of said cylinder.   2. offset printing plates usable for implementing the method of hanging and positioning according to claim 1, characterized in that: - they comprise a magnetic support - they comprise along at least one of their edges   side of suitably arranged openings.   3. Offset printing machines which can be used for implementing the method of hanging and positioning pre-bent printing plates with magnetic support according to claim 1, characterized in that their plate cylinder comprises magnets and that said cylinder has a width slightly greater than the width of the immediately neighboring cylinders and rollers and comprises on at least one part thus   overflowing a series of fixing nipples.