GB2151551A - Device for delivering viscous fluids, in particular ink - Google Patents

Abstract

A device for distributing viscous fluids, for example glues or inks comprises a delivery nozzle (7) that is mounted in a way whereby able to move towards and away from the roller (4), is provided with a work part (9) virtually in close contact, for a determinate distance, with the cylindrical surface of the roller (4), and has a control part (12), opposite the work part, shaped to act as a piston and in direct contact with the liquid being delivered, in such a way that the pressure exerted by the nozzle (7) on the spreader roller (4) be a function of the pressure of the liquid being delivered. The pressure of the liquid is arranged to be dependant upon the viscosity. <IMAGE>

Description

SPECIFICATION Device for delivering viscous liquids, in particular ink The invention relates to a device for delivering viscous liquids, in particular ink.

As is known, printing inks have to be supplied to spreader rollers in such a way as to form thereon thin films of ink. The thickness of the said films or layers of ink is determinant in defining the quality of the print. If, in fact, the film of ink is too thin, or broken, the print too can have parts that are missing and in consequence be unacceptable.

On the other hand, should the film of ink be too thick, the print is blemished and overimpressed, thus equally being unacceptable.

Use is currently made, to deliver inks and similar viscous liquids with precision, of devices that comprise a supply unit provided with a tank for the liquid to be delivered, and with means able to deliver the said liquid to a delivery nozzle virtually in contact with a first spreader roller. The position of the said delivery nozzle, placed more or less close to the said roller, determines the thickness of the film or layer of ink and, therefore, the final quality of the print.

With the present art, the position of the delivery nozzle is fixed once and for always at the time the device is mounted. The said position can be rigid or even be set by springs that are also put into place and calibrated at the time of mounting.

The foregoing technical solution, apparently simple and precise, is, instead, a source of serious problems whilst the printing is in progress. This is because, as is known, inks, just as liquids in general, do not have a viscosity that is constant with changes in the temperature and, more particularly, the said viscosity decreases as the temperature rises.

The variations in temperature to which the ink in the devices of the considered type is subjected, are determined by ambient and seasonal causes, as well as, in the course of one and the same work shift, by the progressive heating of the mechanical parts undergoing movement.

The duration of the storage period and the type of more or less hermetically sealed container can also produce quite unforseeable variations in the viscosity.

All this results in the pre-established pressures of the said nozzles being, with respect to the said spreader rollers, in many cases unsuitable for the formation of the optimal film to which prior reference has been made.

In particular, when the said nozzles are pressed on the said rollers by calibrated springs, what happens is that the greater the fluidity of the liquid delivered, the closer the said nozzles are carried by the springs up against the spreader rollers with the said liquid offering resistance directly proportional to the viscosity thereof.

In this situation, a break can also occur in the film of ink on the rollers when the ink is very fluid.

On the other hand, when high viscosity ink is being delivered, the pressure generated between the nozzle and the roller by the said springs can be quite insufficient to form on the said spreader roller, a uniform film of ink of optimal thickness. Consequently, the amount of ink is excessive and the results are those mentioned previously.

It is, therefore, apparent that the described devices for delivering viscous liquids can give fully satisfactory results only in particular situations chosen at the time the said devices are calibrated.

The general object of the invention is to overcome the problems mentioned above through the creation of a device for delivering viscous liquids, able to operate under optimal conditions independently of the viscosity characteristics of the liquid delivered.

Within the framework of the said general object, one important object of the invention is to devise a device of a structure that is particularly simple and easy to construct, with use being made, to a considerable extent, of elements in themselves already known for the said devices.

The foregoing objects are attained by the device according to the invention for delivering viscous liquids, in particular ink, of the type comprising a supply unit placed upstream of at least one spreader roller and provided with a tank for one said liquid, and with means able to deliver the said liquid at a pressure substantially proportional to the viscosity thereof, as well as with a delivery nozzle placed virtually in contact with the said roller, characterized by the fact that the said nozzle is mounted in a way in which it is able to oscillate in the direction of the said roller, and that it has a work part virtually in close contact, for a determinate distance, with the cylindrical surface of the said roller, and a control part, opposite the said work part, shaped essentially in the form of a piston and directly in contact with the liquid being delivered; the pressure of the said liquid on the said control part determining the position of the work part.

One preferred embodiment for the device according to the invention will now be described with reference to the accompanying drawings, in which: -Figure 1 shows, in a perspective view and in detail, one part of the said device; -Figure 2 shows, in vertical median sectional form, a delivery nozzle forming part of the device depicted in Fig. 1, placed in contact with a spreader roller; -Figure 3 shows, diagrammatically and in global form, the device in question.

With reference to the said figures, the device according to the invention is shown overall at 1. It is placed immediately consecutive to the rollers 2, 3 and 4 (Fig. 3) and, in particular, to a first spreader roller 4.

The device 1 comprises a supply unit 5, provided with a casing 6 in which provision is made for a tank for the liquid to be delivered, in this specific case ink, and for means able to deliver the ink at a pressure proportional to the viscosity thereof. The said means are, for example, constituted by pumps.

The supply unit 5 also comprises a nozzle 7 that projects partially from the casing 6 in order to place itself in frontal engagement with the roller 4.

The delivery nozzle 7 can be seen particularly in Figs. 1 and 2. It is obvious from the said figures that the said nozzle has an infeed channel 8, substantially in the form of a slot, stretching parallel to the axis of rotation of the roller 4. Furthermore, the nozzle 7 is provided with a work part or front face 9 virtually in close contact, for a determinate distance, with the cylindrical surface of the roller 4, that essentially defines a sliding block.

On the front face or work part 9 there is a bevel 10 at the top and an indent 11 at the bottom, the function of which will be clarified below.

Furthermore, Fig. 2 shows that the nozzle 7 is mounted in a way whereby able to oscillate inside the casing 6 in the direction of the roller 4. Directly in contact with the liquid to be delivered, the nozzle 7 is provided with a control part 1 2 that is opposite the work part 9 and is virtually of piston shape.

The control part 1 2 is, therefore, directly sensitive to the delivery phase pressure of the ink. Additionally, the said piston shaped control part expands for a distance clearly predominating the development in breadth of the nozzle 7.

With respect to the said predominating area, the development in breadth of the slot 8 is extremely limited and thus a very modest local loss of pressure is determined by the said slot.

In Fig. 3 it can also be seen that the said rollers are provided, at least in part, with not only a rotary but also translatory movement, parallel to the axis of rotation thereof. This allows the ink to be distributed over the full working surface of the said rollers without increasing excessively the longitudinal dimensions of the slot 8 and, therefore, without making provision for nozzles 7 of a size that is excessive for the supply unit 5 to which they are fitted.

The operation of the above described device takes place as follows.

The supply unit 5 furnishes pressurized ink at a pont corresponding to the work part 1 2 of the nozzle 7. Use can be made for this purpose, as already specified, of pumps whose head becomes greater as the viscosity of the ink increases, or also of ordinary pumps, the operation of which is graduated by means able to detect the viscosity of the ink.

From the control part 12, the ink flows through the infeed channel or slot 8 and then passes on to the first roller 4, and thence on to the successive rollers.

As shown in Figs. 1 and 2, the nozzle 7 is provided with a bevel 10 at the top, above the infeed channel or slot 8. The said bevel 10 is provided to receive any eventual residua of ink carried with the rotation of the first roller 4 that passes across the work part or front face 9, from the top to the bottom thereof.

Underneath the infeed channel 8 is placed a base indent 11, and this collects any excess ink delivered by the infeed channel 8.

The pressure of the nozzle 7 on the first roller 4 is determined by the pressure of the fluid delivered which, as stated, varies in proportion to the viscosity of the fluid.

Prior to discharging through the infeed channel 8, the fluid exerts, in fact, an action on the control part 1 2 of the nozzle 7 and thrusts the said nozzle in the direction of the roller 4.

Thus it is obvious that the greater the fluidity of the ink, or in general of the liquid delivered, the lesser is both the pressure thereof and the thrust exerted in the region of the control part 12.

A lesser thrust obviously means a decrease in the pressure exerted by the nozzle 7 on the roller 4, with a consequent reduction in the danger of a break in the film of ink, though the greater the fluidity of the ink, the greater becomes the said danger.

In this way, the invention attains the objects proposed. Stress, in particular, is laid on the immediacy of the operation of the device and on the extreme sensitivity thereof, since the thickness of the film of fluid on the spreader roller 4 is controlled, at the delivery phase, by the fluid itself when in the final physical condition.

All parts may be substituted with technically equivalent elements, and the materials used, as also the shapes and sizes thereof, may vary according to the requirements.

Claims (7)

1. Device for delivering viscous liquids, in particular ink, of the type comprising a supply unit placed upstream of at least one spreader roller and provided with a tank for one said liquid, and with means able to deliver the said liquid at a pressure substantially proportional to the viscosity thereof, as well as with a delivery nozzle placed virtually in contact with the said roller, characterized by the fact that the said nozzle is mounted in a way in which it is able to oscillate in the direction of the said roller, and that it has a work part virtually in close contact, for a determinate distance, with the cylindrical surface of the said roller, and a control part, opposite the said work part, shaped essentially in the form of a piston and directly in contact with the liquid being delivered; the pressure of the said liquid on the said control part determining the position of the work part.

2. Device according to Claim 1, characterized by the fact that the said delivery nozzle has running through it, an infeed channel virtually shaped in the form of a slot and directed parallel to the axis of rotation of the said spreader roller.

3. Device according to Claim 1, characterized by the fact that the said work part defines the front face of the said nozzle and is shaped in the form of a block.

4. Device according to Claim 3, characterized by the fact that the said work part has a bevel in the region of the upper extremity thereof, and an indent in the region of a lower extremity, the said spreader roller rotating from the said bevel to the said indent, these being provided to channel the residua of the liquid on to the said roller and to collect the excess liquid spread on to the said roller, respectively.

5. Device according to Claim 2, characterized by the fact that the said infeed channel is of a thickness, perpendicularly to the direction in which the said slot extends, that is particularly thin compared to the breadth of the said control part.

6. Device according to Claim 1, characterized by the fact that the said delivery nozzle is in direct engagement with a spreader roller and able to be oscillated in a direction parallel to the axis of rotation of the said roller.

7. Device for delivering viscous liquids, in particular ink, substantially as hereinbefore described with reference to the accompanying drawings.