DESCRIPTION

The present invention relates to an impregnation tank of a fabric and manufacturing device of a cylinder for a printing machine which includes said impregnation tank.

In the sector of printing machines, in particular but not exclusively in the sector of flexographic printing, printing cylinders are used that have various layers of fabric impregnated with resin. To realise the printing cylinder the fabric is unwound from a reel and wound spiral-fashion on a rotating spindle.

To impregnate the fabric, in general a dispenser is used that translates along the spindle and is provided with a spout which pours the resin onto the fabric.

To ensure a correct impregnation, in general an operator uses a brush to hand-spread the resin uniformly on the fabric.

This impregnation system has various drawbacks.

Firstly, it leads to a high amount of waste of resin which falls to earth as it drips from the fabric. Secondly, the success of the impregnation operation is subordinated to the experience and professional skills of the operator.

Thirdly, the inclusion of various steps for manual intervention lengthens the realising times of the final product, thus causing an inevitable increase in production costs for the finished product. The technical task of the present invention is, therefore, to realise an impregnation tank of a fabric and a manufacturing device of a cylinder for a printing machine which includes said impregnation tank, which enable obviating the technical drawbacks noted in the prior art.

Within the scope of this technical task an object of the invention is to create an impregnation tank having a construction adapted for the use of as small a quantity as possible of resin for carrying out a correct impregnation.

A further aim of the invention is to realise a productive impregnation system configured for eliminating or reducing waste of resin in carrying out the impregnation.

A further aim of the invention is to realise an extremely efficient and highly productive impregnation system.

A further aim of the invention is to realise an impregnation system which guarantees a uniform impregnation of the fabric.

A further aim of the invention is to realise an automated impregnation system which eliminates or limits the human error factor to a minimum.

A further aim of the invention is to realise an impregnation system which can at the same time be compact and highly productive.

The technical task, as well as these and other aims of the present invention, are attained by realising an impregnation tank for impregnating a fabric, characterised in that it comprises an impregnation roller for impregnating a fabric with a resin, a chamber that can be filled with a resin and that extends all around the impregnation roller, an entrance channel for the fabric to enter said chamber and an exit channel for the fabric to exit said chamber, said impregnation roller having ridges on the external cylindrical surface so as to delimit uniformly distributed storage cavities for the resin, said chamber having an impregnation zone for impregnating the fabric, a regeneration zone for regenerating the resin in the storage cavities, a first connecting zone connecting to said entrance channel, a second connecting zone connecting to said exit channel, said first and second connecting zones being interposed between said impregnation zone and said regeneration zone, said regeneration zone being smaller in volume than said impregnation zone.

Said impregnation zone is preferably configured in the form of a sector of a cylinder.

Said regeneration zone is preferably configured in the form of a sector of a cylinder. Said regeneration zone preferably has a thickness that is smaller than the thickness of said impregnation zone.

Said regeneration zone preferably has an angular amplitude that is smaller than the angular amplitude of said impregnation zone.

The first and second connecting zones preferably tangentially connect said impregnation zone to said entrance channel and said exit channel.

Said entrance channel and said exit channel are preferably flat.

Said entrance channel and said exit channel preferably extend rectilinearly.

The angular amplitude of said impregnation zone is preferably no greater than 180° and no less than 90°.

Said impregnation roller can be freely rotatable or can be motorised with a direction of rotation opposite the feed direction of said fabric into said chamber.

Said tank preferably has cooling means for cooling the walls of the impregnation tank and the impregnation roller.

Said entrance channel preferably has dehumidifying means for dehumidifying said fabric.

Said exit channel preferably has smoothing means for smoothing said impregnated fabric.

The present invention also relates to a device for manufacturing a cylinder for a printing machine, comprising a rotating spindle and a frame in translational motion along said rotating spindle and supporting an impregnation tank.

The tank of the invention is optimally usable with a resin having an exothermic polymerisation (or not) during the polymerisation step, for example an epoxy resin.

In fact, as the volume of the chamber and consequently the volume of resin which can occupy the chamber, the thermal energy unleashed from the resin during the polymerisation step is minimum and this enables conserving the fabric from heat degradation as temperatures in the chamber never reach very high levels. Further characteristics and advantages of the invention will more fully emerge from the description of a preferred but not exclusive embodiment of the impregnation tank of the invention, illustrated by way of non-limiting example in the accompanying figures of the drawings, in which:

figure 1 is an axono metric view of the impregnation tank;

figure 2 is an axonometric view in cross section of the impregnation tank;

figure 3 is a section view in lateral elevation of the impregnation tank; and

figure 4 illustrates the manufacturing device of a cylinder for a printing machine which incorporates said impregnation tank.

With reference to the figures mentioned, an impregnation tank is illustrated, of a fabric denoted in its entirety by reference number 1.

The impregnation tank 1 comprises an impregnating roller 2 for impregnating the fabric 3 and a chamber 6 that can be filled with a resin and that extends all around the impregnation roller 2. The impregnation roller 2 can be freely rotatable or can be motorised with a direction of rotation opposite the feed direction of said fabric 3 into said chamber 6.

The motorisation can be used for improving the impregnation performance as the rotation of the impregnation roller 2 contrary to the advancement direction of the fabric 3 performs the function of creating a light squeezing and a consequent deaeration of the fabric 3 which facilitates the following incorporation of the resin.

The impregnation tank 1 further comprises an entrance channel 7 for the fabric 3 to enter said chamber 6 and an exit channel 8 for the fabric 3 to exit said chamber 6.

The impregnation roller 2 having ridges 9 on the external cylindrical wall so as to delimit uniformly distributed storage cavities 10 for the resin.

The storage cavities 10 enable correct impregnation of the face of the fabric in direct contact with the impregnation roller 2. The ridges 9 are formed by fiat, pointed or appropriately bevelled teeth or by longitudinal formations, for example formations that wind in a spiral about the external cylindrical wall of the impregnation roller 2.

The chamber 6 has an impregnation zone 11 for impregnating the fabric, a regeneration zone 12 for regenerating the resin in the storage cavities 10, a first connecting zone 20 connecting to said entrance channel 7, and a second connecting zone 21 connecting to said exit channel 8.

The first connecting zone 20 and the second connecting zone 21 are interposed between the impregnation zone 11 and the regeneration zone 12.

The regeneration zone 12 advantageously has a smaller volume than the impregnation zone 11, so as to limit the volume of the chamber 6 and consequently the volume of resin used for the impregnation zone.

The chamber 6 for the resin is a closed chamber delimited between the external cylindrical lateral wall of the impregnation roller 2, walls 4, 5 of the tank 1 which surround the external cylindrical wall of the impregnation roller 2, and walls 22, 23 of the tank 1 which surround the base walls opposite the impregnation roller 2.

The impregnation zone 11 is configured in the form of a sector of a cylinder.

The wall 4 of the tank 1 is consequently arched with the centre of curvature located on the axis of the impregnation roller 2.

The angular amplitude of the impregnation zone 11 is defined between the point P' of first contact of the fabric 3 with the impregnation roller 2 and the point P of detachment of the fabric 3 from the impregnation roller 2.

The impregnation zone 11 has an angular amplitude a measured between the point of first contact and the point of detachment P that is no greater than 180° and no less than 90°.

The regeneration zone 12 is also configured in the form of a sector of a cylinder.

The wall 5 of the tank 1 is consequently arched with the centre of curvature located on the axis of the impregnation roller 2.

The thickness of the regeneration zone 12 is less than the thickness of the impregnation zone 11. The angular amplitude of the regeneration zone 12 is smaller than the angular amplitude of the impregnation zone 11.

The first connecting zone 20 and the second connecting zone 21 tangentially connect the impregnation zone 11 to the entrance channel 7 and the exit channel 8.

The entrance channel 7 and the exit channel 8 are flat for minimising the volume of resin present therein.

The entrance channel 7 and the exit channel 8 further extend in a rectilinear direction so that the fabric 3 never comes into contact with the walls thereof.

The entrance channel 7 has a sleeve 24 for connection to a supply tank of the resin by means of a supply pump (not illustrated).

The entrance channel 7 further has dehumidifying means of the fabric 3 for facilitating the impregnation.

In the illustrated case, the dehumidifying means comprise a roller 26 having a hot external surface on which the fabric 3 slides.

The dehumidifying means can alternatively comprise for example two opposite hot plates between which the fabric slides. In this case, though there is a slight structural complication, a better efficiency of dehumidification is obtained as both faces of the fabric 3 can be contemporaneously heated.

The exit channel 8 is provided with a sleeve 25 in which a resin level sensor is insertable.

The exit channel 8 further has smoothing means for smoothing the impregnated fabric 3.

The smoothing means, in the illustrated case, are formed by doctor blades 27 that are opposite one another and have rounded ends, each for acting on a corresponding face of the fabric 3. Said tank 1 preferably has cooling means (not illustrated) for cooling the walls 4, 5, 22, 23 of the impregnation tank itself and of the impregnation roller 2.

The cooling means are useful for opposing the raising of the temperature due to exothermic reaction in the polymerisation of some resins.

The cooling means can comprise, for example, a cooling liquid that can be subjected to forced circulation in a special circuit realised internally of the walls 4, 5, 22, 23 of the tank 1 and internally of the impregnation roller 2.

To improve the efficiency of heat exchange the walls 4, 5, 22, 23 of the tank 1 and the impregnation roller 2 are made of a heat conductive material, for example the walls 4, 5, 22, 23 of the tank 1 are made of stainless steel which is, among other things, also easy to clean, while the impregnation roller 2 can be formed by an internally hollow structure made of aluminium. In the tank 1 the impregnation roller 2 is positioned low down with a horizontal axis, the entrance channel 7 extends from up towards down, and the exit channel 8 extends from down upwards.

To prevent the air bubbles from remaining trapped in the regeneration zone 12 during the filling of the chamber 6, the wall 5 of the tank 1 is equipped with a breather valve for the air (not illustrated).

The impregnation tank 1 is advantageously incorporated in a device 30 for manufacturing a cylinder for a printing machine, in particular a sleeve for a flexographic printing machine.

The flexographic sleeve is formed by a series of layers comprising at least a lower layer destined to contact the support spindle of the sleeve, at least a compressible intermediate layer and at least an upper layer destined to contact the printing plate.

At least the lower and higher layer are realised using a woven or non-woven fabric, typically polyether, impregnated with a resin, typically an epoxy resin, while the compressible intermediate layer is for example made of polyurethane.

For realising a flexographic sleeve, it has been seen to be particularly suitable to include an impregnation tank 1 provided with an impregnation roller 2 having an external diameter of 10 cm ± 20%, a thickness of the impregnation zone 11 of 1 cm ± 20%, a thickness of the regeneration zone 12 of 0.5 cm± 20%.

The device 30 comprises a fixed frame 34, rested on the ground 35, a rotating spindle 31, a reel 36 of fabric 3 to be impregnated, a mobile frame 32 for supporting the tank 1 and the reel 36, a linear guide 33 supported by a fixed frame 34 and in turn supporting the support frame 32 along the rotating spindle 31 in translation, and a motorisation of the mobile frame 32.

The mobile frame 32 has a first part constrained in translation (horizontal) to the linear guide 33 and a second part constrained to the first part with a rotational degree of freedom about an axis that is perpendicular (vertical) to the direction of translation.

The reel 36 is provided with a pneumatic brake (not illustrated) while a special stretcher 37 provided with a load cell controls the pressure of the pneumatic brake of the reel 36 for retroactively regulating the stretch imparted on the fabric 3 when the spindle 31 rotates.

The functioning of the device 30 clearly emerges from what is described and illustrated and, briefly, is as follows.

The spindle 31 is activated in rotation and the mobile frame 32 is activated in translation 32 along the rotating spindle 31.

By effect of the relative motion between the spindle 31 and the frame 32, the fabric 3 winds in spiral- fashion about the spindle 31.

The mobile frame 32 makes a first pass along the spindle 31, and then, when it arrives at the end of the spindle 31, the second part of the mobile frame 32 is rotated (by an appropriate motor or by hand) with respect to the first part of the mobile frame so as to appropriately re-orientate the tank 1 - reel 36 group and carry out a second pass along the spindle 31 in the opposite direction to the first.

The process halts on reaching the number of passes necessary for realising the desired thickness of the layer.

Naturally, in order to realise the various layers the resin and/or the reel of fabric can be replaced. Plant productivity, which can be regulated by modifying the velocity of rotation of the spindle 31, can be appreciably increased due to the fact that the impregnating resin is very plentiful though the impregnation system is very compact.

In fact, the impregnation is carried out on both faces of the fabric 3 from when the fabric 3 enters into the entrance channel 7 to when it leaves the exit channel 8 due to the fact that the face of the fabric 3 in contact with the impregnation roller 2 can collect the resin from the storage cavities 10, and the storage cavities 10, rotating in the impregnation zone 11, are replenished with resin when they cross the regeneration zone 12.

The impregnation tank has the advantage of containing a minimum quantity of resin.

This, on the one hand, reduces consumption and waste and, on the other hand, ensures preservation of the structural integrity of the fabric even when a resin is used that has a high degree of polymerisation exothermic reaction.

The impregnation tank as conceived herein is susceptible of numerous modifications and variants, all falling within the scope of the inventive concept; furthermore, all the details are replaceable by technically equivalent elements.

In practice the materials used, as well as the dimensions, can be any according to needs and the state of the art.