EP0325535B1 - Method for mounting and positioning offset printing plates with a magnetic support, and the plates and offset printing machines used for realising the method - 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. <IMAGE>

Description

The present invention relates to offset printing machines, offset printing plates and a method for hanging and positioning offset printing plates in offset printing machines.

• l'existence d'un balourd (plus ou moins important selon la nature des mâchoires) sur le cylindre porte-plaque,
• un positionnement de la plaque nécessitant des ajustements précis et longs, et
• une certaine fragilisation de la plaque du fait de contraintes mécaniques, qui entraînent pour les plaques à base d'aluminium par exemple, des risques de casse lors de la mise en place au démarrage, ou pendant le roulage.

Offset plates are currently installed on printing machines using various mechanical devices. Among these devices, the most used consist of two jaws which clamp and tension the plates around the plate cylinder. These mechanical devices have various drawbacks, among which we can mention:

• the existence of an unbalance (more or less important depending on the nature of the jaws) on the plate cylinder,
• positioning of the plate requiring precise and long adjustments, and
• a certain embrittlement of the plate due to mechanical stresses, which cause for aluminum-based plates for example, risks of breakage during the positioning at start-up, or during rolling.

Such mechanical fastening devices are, despite the drawbacks mentioned above, used on a large scale insofar as at least 99% of the offset plates used today are based on aluminum - non-magnetizable material.

However, it seems for a few years that a new tendency is emerging in the industry of offset, consisting in using again as base of the plates, steel. The magnetic properties of this material are known; also, it may be desirable to use this property to hang, on offset machines, said offset plates with steel support (with magnetic support).

The principle of magnetically fixing a typo or flexo plate with steel support on the plate cylinder of a printing machine is known and has been advocated for a long time. For various reasons, this printing mode has never been used in the offset process. It was feared in particular that said method of attachment proves ineffective with thin plates which tend to deform and which are subjected to high pressures, due to the drawing of offset inks and the rubber blanket.

In addition, the magnetic fixing of the offset plates only proves advantageous insofar as one implements, for this fixing, means which allow not only a quick attachment of the plates but also a precise positioning of said plates in order to reduce the duration of the settings. These are the 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 drawn on the plate, lines of holes made on one edge of the plate ...) integral with this plate (or forming part of the plate). The means for exactly positioning the printer part on the plate are, as indicated above, known.

According to the invention, means are proposed for effective magnetic attachment of an offset plate to the plate cylinder.

• comporte des aimants,
• présente une largeur légèrement supérieure à celle dudit cylindre porte-blanchet et desdits rouleaux (cylindres immédiatement voisins),
• comporte sur au moins une partie ainsi débordante (débordant par rapport aux cylindres immédiatement voisins) une série de tétons de fixation.

According to a first aspect, the invention relates to offset printing machines comprising a plate cylinder, a blanket cylinder and a printing cylinder; said plate cylinder being intended to come into contact with said blanket cylinder and wetting and inking rollers. Typically, the plate cylinder of offset printing machines according to the invention:

• has magnets,
• has a width slightly greater than that of said blanket cylinder and said rollers (immediately adjacent cylinders),
• comprises on at least one part thus projecting (projecting with respect to the immediately neighboring cylinders) a series of fixing studs.

Another subject of the invention is offset printing plates intended for machines having the characteristics set out above. Said plates comprise a magnetizable support (they generally have a steel base) and along at least one of their lateral edges openings suitably arranged to cooperate with the pins arranged on the plate cylinder, in the vicinity of at least one of its edges.

• cintrée de façon à présenter une déformation permanente amenant ladite plaque à avoir la forme d'un cylindre ouvert dont le diamètre est de l'ordre de grandeur du diamètre du cylindre porte-plaque, de préférence légèrement inférieur ;
• puis enfilée sur les tétons de fixation ménagés sur ledit cylindre porte-plaque au voisinage d'au moins un bord dudit cylindre grâce aux ouvertures convenablement aménagées sur au moins un de ses bords latéraux ;
• et appliquée contre ledit cylindre porte-plaque grâce aux aimants que celui-ci comporte.

The invention finally relates to a method for hanging and positioning said offset plates on the plate cylinders of said offset machines. According to the said method, the plate, after exposure, development and possibly cooking, is:

• curved so as to have a permanent deformation causing said plate to have the shape of an open cylinder whose diameter is of the order of magnitude of the diameter of the plate cylinder, preferably slightly smaller;
• then threaded onto the fixing pins provided on said plate-carrying cylinder in the vicinity of at least one edge of said cylinder by means of the openings suitably arranged on at least one of its lateral edges;
• and applied against said plate cylinder by means of the magnets which the latter comprises.

The invention therefore proposes the use, in offset, of magnetic latching.

The magnetic snap is known per se. It consists of the fact that the plate cylinder has, flush with its surface, a sufficient number of magnets for the plate to be securely attached to it. These magnets can have the most diverse shapes, they are generally in the form of studs or benches arranged along the generatrices of the cylinders. In the context of the invention, 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 wetting water can, to a certain extent, infiltrate under the plaque ; 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 an impermeable thin film or by depositing on the surfaces to be protect with a thin protective layer of any waterproof material.

According to the invention, said magnetic coupling is implemented with pins, on the projecting part of a larger plate cylinder.

• de minimiser les pertes de papier,
• de minimiser les pertes de métal,
• de raccourcir considérablement la période de mise en route,
• de simplifier la machine.

The invention has many advantages. It allows in particular (compared to a mechanical coupling):

• minimize paper losses,
• minimize metal losses,
• to considerably shorten the start-up period,
• to simplify the machine.

This results in a significant reduction in the cost price.

• la figure 1 représente une vue longitudinale schématique d'un cylindre porte-plaque selon l'invention ;
• la figure 2 est une section selon II-II de la figure 1 ;
• la figure 3 est une section selon II-II d'un cylindre porte-plaque selon l'invention comportant une dépression.

Said invention is illustrated in Figures 1 to 3 appended to this description.

• Figure 1 shows a schematic longitudinal view of a plate cylinder according to the invention;
• Figure 2 is a section along II-II of Figure 1;
• Figure 3 is a section along II-II of a plate cylinder according to the invention comprising a depression.

• en 1 le cylindre porte-plaque,
• en 2 un rouleau encreur,
• en 3 un rouleau de mouillage.

In Figure 1, we see:

• in 1 the plate cylinder,
• in 2 an ink roller,
• in 3 a dampening roller.

• on a disposé selon des génératrices du cylindre des aimants 4 qui affleurent à la surface dudit cylindre,
• on a disposé au voisinage des bords dudit cylindre, des tétons 5 (qui coopèreront avec les ouvertures ménagées le long des bords des plaques) et, pour ne pas avoir à modifier les rouleaux 2 et 3, on a élargi le cylindre porte-plaque de façon à rejeter lesdits tétons à l'extérieur de l'emprise des rouleaux 2 et 3.

The plate cylinder 1 has, with respect to the plate cylinder of a corresponding current offset machine, the following characteristics:

• magnets 4 which are flush with the surface of said cylinder have been arranged along generatrices of the cylinder,
• was 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 rollers 2 and 3, the plate cylinder was enlarged by so as to reject said nipples outside the grip of rollers 2 and 3.

In FIG. 3, there is shown, in section along II-II, an improvement of the invention consisting in providing a slight depression 6 over a certain width of the cylinder. In this depression, for example and preferably, a magnet 4. When the offset plate 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 magnet 4. Obviously, the two ends of said plate can be attracted by magnet 4 (or by other magnets mounted in said depression 6).

The invention is described below in more detail.

• le cintrage préalable de la plaque,
• l'enfilage de la plaque sur les tétons ménagés sur le cylindre porte-plaque, au voisinage d'un bord de celui-ci, dans un plan perpendiculaire à l'axe du cylindre, cet enfilage étant rendu possible par l'aménagement, le long des bords de la plaque, d'ouvertures convenablement positionnées pour correspondre auxdits tétons.

To achieve the precise positioning of the plate, the following two means should be used:

• the prior bending of the plate,
• threading the plate on the pins provided on the plate cylinder, in the vicinity of an edge thereof, in a plane perpendicular to the axis of the cylinder, this threading being made possible by the arrangement, the along the edges of the plate, openings suitably positioned to correspond to said pins.

By prior "bending" is meant that the plate is subjected, before it is placed on the plate cylinder, to permanent deformation such that said plate, initially planar, is in the form of a cylinder whose diameter is of the order of magnitude of the diameter of the plate cylinder, and even preferably slightly smaller. This bending operation obviously implies that the nature of the steel which constitutes the base of the plate is suitably chosen, this choice being within the reach of any specialist in this material. It will also be noted that this bending operation involves a certain elongation of the outer surface portion of the plate; avoid any excessive deformation and make sure, by bending under identical or similar conditions for the various plates, to always have an identical elongation of said surface portion. This possibility, thanks to the prior bending to control and make reproducible from one plate to another, this elongation phenomenon is important because it allows the realization of a very precise positioning of the plate.

To thread the plate onto the nipples, use will obviously be made of a plate provided, along and in the vicinity of at least one of its lateral edges, with suitable openings. The shape, dimensions (generally the diameter) and the relative position of these openings must correspond to the pins with which these openings must cooperate. Given the high mechanical properties of the steel-supported plates and taking into account the prior bending under controlled conditions, it is possible to provide a very precise adaptation 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 an edge of said cylinder and in a plane perpendicular to the axis of the cylinder. So that there is no particular difficulties due to the presence of these pins and neighboring cylinders and rollers (blanket cylinder and inking and wetting rollers), it will suffice, and this constitutes the main aspect of the invention, to provide that the plate cylinder is slightly wider than the neighboring cylinders and 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. It is obviously possible to use these openings to, in cooperation with pins arranged on the cylinder, position the plate, but experience proves that in current machines, such pins would not be positioned beyond the cylinders and rollers neighboring the plate cylinder, which would require sometimes expensive arrangements of said cylinders and rollers. Thus, most often, it is preferred to use other openings, often in greater numbers, to ensure the positioning of the plates.

It will be noted that, according to the invention, the plates are maintained and positioned by pins located in the vicinity of the edge of the plate cylinder and no longer by means (jaws for example) arranged along a generator of said cylinder. It follows that the sides of the plate which are arranged, after positioning, along a generator of said cylinder are free, that is to say are only held by means of the magnets arranged on the cylinder. In general, this arrangement does not give rise to difficulties (all the more so as a person skilled in the art will have the magnets suitably on said cylinder) but it may happen that, when handling the plate, the edges of that -this (edges positioned along the generatrices) are slightly deformed; this deformation could cause the plate to tear off during rolling. To overcome this difficulty, it has been provided, according to one aspect of the invention, that the plate cylinder could comprise, on a portion of said cylinder corresponding to the ends of the plate, a slight depression in which at least one magnet is willing. It is understood that thanks to this depression, the ends of the plates will always be slightly reentrant (that is to say will be maintained within the theoretical circle 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.

EXAMPLE

Consider a 4-color sheetfed offset machine from OCMSA, reference Aurélia 700, using 775 x 1,035 mm plates and capable of printing a maximum paper area of 710 x 1,020 mm.

The plate cylinder of this machine is 1045 mm wide.

Although this plate cylinder is of sufficient width to be able to use there in the vicinity of the edges of the fixing studs according to the invention, said cylinder has been replaced by a plate cylinder (of perfectly cylindrical shape) of 1,100 mm in width comprising, flush with its surface, magnets arranged along 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 the method according to the invention.

As offset plate with magnetic support (steel), use will be made, for example, of a plate comprising a black iron support whose mechanical qualities are those of European standard T 61 and whose thickness is 25/100. This black iron support was covered with a layer of hydrophilic matt chromium and a positive photosensitive encrophilic layer.

This plate has the particularity of comprising, on its two sides, openings which correspond exactly to the pins present on the plate cylinder.

This plate, after insolation, development and cooking, is passed through a rolling machine which makes it undergo a permanent deformation such that in the state of rest said plate is in the form of an open cylinder whose diameter is order of magnitude (and even preferably slightly smaller) of the diameter of the plate cylinder.

The plate is then placed around the plate cylinder by inserting the plate through the pressure end side and then placing this plate so as to thread the pins into the holes in the plate.

This process provides rapid and precise positioning of the plate.

It will be noted that in the example above, the width of the plate is the same as that of the plate cylinder and that said plate includes openings on its two lateral sides. This arrangement is not essential since it is possible to use for a plate cylinder with a width L two plates each having a width a little less than L / 2; each of these plates will have active openings only on one of its lateral sides.

Claims (3)

1. Offset printing machines comprising a plate-carrying cylinder (1), a blanket-carrying cylinder and a printing cylinder; said plate-carrying cylinder (1) being designed to come into contact with said blanket-carrying cylinder and wetting (3) and inking (2) rollers, characterized in that:

   - said plate-carrying cylinder (1) comprises magnets (4);

   - the width of said plate-carrying cylinder (1) is slightly greater than that of said blanket-carrying cylinder and of said rollers (2, 3);

   - the plate-carrying cylinder (1) comprises on at least one part overlapping in this way, a series of fastening lugs (5).
2. Offset printing plates for machines according to claim 1, characterized in that they comprise a magnetizable support and along at least one of their lateral edges, openings suitably arranged so as to cooperate with lugs (5) provided on the plate-carrying cylinder (1), close to at least one edge of said cylinder.
3. Method for fastening and positioning an offset printing plate according to claim 2, in machines according to claim 1, characterized in that the plate, after insolation, processing and optionally baking is:

   - bent so as to present a permanent deformation which causes said plate to have the shape of an open cylinder whose diameter is in the order of size of the diameter of the plate-carrying cylinder (1), preferably slightly less;

   - then threaded on the fastening lugs (5) provided on said plate-carrying cylinder (1) close to at least one edge of said cylinder, owing to the openings suitably arranged on at least one of its lateral edges;

   - and applied against said plate-carrying cylinder (1) owing to the magnets (4) provided on the latter.

Images