The present invention relates to a method of calen¬ dering lacquered sheet members such as carton sheets with printed fields to be punched for the forming of packing members.

Within the carton packing industry it is an almost absolute practice that the packing members are defined by print on large carton sheets with the largest possi¬ ble numbers thereon, whereafter the single blanks are made by being punched from the large sheets.

It occurs that some series of these sheets are de¬ sired in a lacquered version so that the surface of the packing members appear highly glossy, and it is already known that such a lacquering can be executed as a last operation in the printing machine, in which the blank fields are printed on the large sheets.

However, the surface gloss achieved hereby can be improved further if the sheets are subject to an extra operation in the form of a calendering, where they run through mating rolls and thus are exposed to both heat and pressure for extra smoothing of the lacquer surface. For this purpose special calender lacquers are develop¬ ed, which are usually applied by means of a lacquering device just before the calendering. To achieve the best result this double operation must be made on sheets which, after the printing and a first lacquering in the printing machine, have been stored for a certain period, for instance overnight, so that the sheets are complete¬ ly dry. On this background it has been a traditional technique that stored sheet piles are taken to a feeding unit on a combined lacquer and calendering machine, from where the sheets are delivered in piles, which after further re-storing, however, not necessarily for a long period, are taken to the feeding unit of a punching

machine for punching of the single blanks.

It is by the present invention realized that this technique can be simplified considerably, namely by the use of a relatively highly thermo-plastic lacquer alrea¬ dy in the lacquering device of the printing machine, as it is thus found possible to avoid the extra lacquering in connection with the calendering. In return, the ca¬ lendering itself is effected with increased heating and a longer pressing time than possible by a quick passing of the sheets through the gap between the calender cy¬ linder and a single pressure roller, while the sheets or at least the lacquer layer of these are exposed to heat and pressure through a considerably prolonged time, without this necessarily implying a reduction of the capacity of the system; the sheets can be exposed to a preheating at the infeed to the calender cylinder, and as a significant feature the sheets can be brought to engage the heated calender cylinder by being held against this not only in the gap between the two cylin¬ ders, but along an arched course around a part of the cylinder by using more pressure rollers. By such a rela¬ tively long impression against the very smooth calender cylinder a high quality surface gloss is achievable on the carton members.

At the outlet of the sheets from the cylinder the lacquer layer can be fixed by passing a cooling system, and the sheets will then be ready for immediately there¬ after, i.e. successively, to be fed to an aftercoupled punching machine for punching of the single blank mem¬ bers. Thus the punching machine can be directly coupled together with the calender unit, simplified in its enti¬ rety, whereby the normally used, separate feeding unit of the punching machine in principle can be entirely avoided; however, it may be desirable to use a feeding unit anyway, though only as a buffer for relative few sheets for securing of a high feeding accuracy.

It is an important part of the invention that the used lacquer is adapted to being used with the desired result in the said work cycle, but it has already been found that the indication of the desired work cycle has been sufficient for lacquer-experts to actually provide suitable lacquer compounds.

The invention also relates to a system for perfor¬ ming the method in question, by which the calender unit itself has more pressure rollers and means for preheat¬ ing and aftercooling of the sheets and is operatively integrated or coupled together with the said punching machine.

In the following the invention is explained with reference to the drawing, in which

Fig. 1 is a side view of an embodiment of a comple¬ te system according to the invention, while

Fig. 2 is a side view of a part thereof.

The system shown has, farthest to the right side, a feeding unit 2, to which in usual way is fed piles of pre-printed and lacquered sheets 4, which from the feed¬ er is delivered one by one to a following calender unit. While for a feeding unit of a punching machine it is usual that the sheets are layed out 'on stream', i.e. in scale-like formation, they should here be delivered fully in singles.

From the feeding unit the sheets are taken to an infeeder belt 8 for manoeuvring to a succeeding calender cylinder 10, which is done by means of an overlying holder belt 12 and lower holder rollers 13, whereby the sheets are taken down through a zone 14, above which is placed a heating unit 16 for preheating of the lacquer layer on the sheets. Thereafter the sheets are taken to direct surface touch with the calender cylinder, against which they are held by use of more pressure rollers 18, with or without surrounding pressure belts. These rol¬ lers are suspended in pressure chassises, which, by

means of hydraulic cylinders, enable a variable tighten¬ ing of the rollers, the surfaces of which are made by a compressible layer for reduction of the tolerance re¬ quirements to the cooperating cylinders. The sheets are taken around the lower half of the calender cylinder 10, but the entwining stretch may well be longer or shorter.

The sheets, which are of course supported by cylin¬ ders or belts on stretches where there are no actual pressure rollers 18, are removed from the cylinder 10 by means of a vacuum belt 20, after which is placed a sen¬ sor unit 22, which in case of non-slipping sheets pro¬ vokes a stop in the feeding of the sheets and a quick braking of the cylinder. This safety precaution is necessary to avoid damage of the calender cylinder.

On a succeeding vacuum belt 24 the sheets are taken out from the calender unit for infeed to a following unit, which could be a punching machine, but in this case is a special feeding unit 27 of a punching machine 28. The belt 24 stretches through a cooling tunnel 30 for effective cooling of the heated lacquer layer on the sheets, preferably by the use of a cold-air blowing sys¬ tem with nozzles 31. The cooling can start right after the sheets have left the calender cylinder 10. Above the belt 24 may be placed a parallel running overbelt 32, the lower run of which combines with the active cooling system.

The punching machine 28, conventionally, will be adapted to receive scale-layed sheets, and though the machine could well be modified to receiving free single sheets, then it is preferred, according to the inventi¬ on, to arrange a scale-like laying of the sheets in connection with their exit from the cooling zone 30 and the associated delivery on an infeeder belt 35 to the feeder 27. For this purpose a unit 34 may be used, see fig. 2, consisting of conveyor belts 36 placed between the separated belts, of which the belt 24 is formed, and

which are fitted with wedge-shaped blocks 38. The belt 36 works with lower speed than the exit belt 24, whereas the following belt 35 runs with even slower speed. The blocks 38 may hereby form a stop for the projected sheets on the belt 24 and furthermore wedge themselves in below the rear of the previous sheet delivered, to the belt 35, so that the sheets succeedingly will be scaled in a desired manner. In fig. 1 it is indicated that this transfer system may be power steered by means of motors 39, which, however, will not be explained in more detail here. The holder belt 12 at the entrance to the calender unit is made of the lower run of a gently sloping belt section, which is pivotal mounted about a transverse arbour 13 above the calender cylinder 10. By means of a control cylinder 17 this belt section may be pivoted slightly downwards into a position, in which it can receive on its top side the sheets delivered from the feeder 2. Hereby the sheets can be guided overhead of the calender cylinder 10 on the top side of the said belt 32, as the corresponding belt section is corre¬ spondingly downwards pivotal about the transverse arbour 13 into a position, in which sheets from the top side of this section may be delivered directly to the exit belt 24. Such a direct passing by of sheets past or above the calender cylinder 10 may be desirable in production sequences, where it is of current interest to use the punching machine 28 for processing of sheets that are not to be calendered.

From the drawing it would seem necessary for the downwardly pivoting of the belt sections 12 and 32 that also the underlying belt sections are pivoted downwards, but this will not be necessary, when the belts in ques¬ tion are made of a number of mutually spaced belts.

In fig. 1 it is shown in dotted lines that the belt section 12 can be pivoted upwards to an upright positi¬ on, in which there is free access to servicing the heat-

ing unit 16, which is mounted on this conveyor section. The calender cylinder 10 is kept appropriately heated in one of many possible ways, and it is made with an extre¬ mely even surface, for instance with a chromium or tef¬ lon layer. Though the effective entwining stretch of the sheets needs not be of large extension, it will, how¬ ever, be desirable for the cylinder to be of a conside¬ rably "oversize", for instance with a diameter of the magnitude of one meter, considering the mechanical sta¬ bility of the cylinder.

It may be possible for the calender cylinder 10 to be arranged above the throughlet belt lane 12, 32 or for that sake in centre height with the entrance and exit belts, as the free by-pass 12, 32 may then extend through a curve above or below the cylinder 10.

The calender cylinder is contemplated heated to a temperature of approximately 110-130 degrees, and it should be kept heat insulated at the non-operative are¬ as.

By the invention it is particularly interesting to use a calender cylinder 10, which has a "slip-layer" of teflon or the like. Such layers will typically be heat insulating to some degree, and it will thus become topi¬ cal to attach extra importance to the preheating stretch 14,16 even with the possibility of completely sparing the internal heating of the calender cylinder. Optional¬ ly, a stationary unit for external preheating of the cylinder surface just before it receives the sheets may be added to the system. Preferably the heating of the sheets is conducted in such a way that it is mainly the lacquer layer itself that is heated. It is here a speci¬ al possibility that by use of infrared irradiation, i.e. by use of infrared lamps in the heating unit 16, it is possible to perform a selective heating by adjustment of the wavelength of the irradiation, as it is found possi¬ ble to hereby achieve that so to speak the entire energy

is absorbed in the thin lacquer layer. As an example it can be mentioned that this effect has been demonstrated at a wavelength of 3300 nm for a certain lacquer type, but the ideal wavelength for lacquers within the rele¬ vant compound area is expected to be in the area of 3000-4000 nm. By a spectrum analysis of a lacquered sheet it is quite easy to state an optimal, narrow wave¬ length range for the heat radiation, which for just that lacquer will be ideal for an effective heating of the lacquer layer without an associated unnecessary heating of the basic carton material.