WO2010020841A1

WO2010020841A1 - Printing apparatus and printing process

Info

Publication number: WO2010020841A1
Application number: PCT/IB2009/005968
Authority: WO
Inventors: Danilo Bombardi
Original assignee: Ecociprea S.R.L.
Priority date: 2008-08-20
Filing date: 2009-06-17
Publication date: 2010-02-25
Also published as: ITMI20081527A1

Abstract

A printing apparatus comprises a printing machine (2) and a ventilation device (3) operatively coupled to the printing machine (2) and equipped with at least one recirculation circuit (4, 4a, 4b) to remove polluting and inflammable substances produced during printing. A plant (11) for removal of at least one polluting and inflammable substance from a gaseous-phase fluid flow, operatively acts on the ventilation device (3) and comprises: an entrance opening (13a) in fluid communication with the recirculation circuit (4, 4a, 4b); a thermal-head device (18) maintained to a lower temperature than the temperature of the gaseous-phase flow (F) to generate a Δt, said device (18) involving, during passage, condensing and/or freezing of part of the moisture and/or the polluting and inflammable substance contained therein; a drop separator (19) designed to collect drops or droplets present in the fluid passing therethrough; an exit opening (13b) in fluid communication with the recirculation circuit (4, 4a, 4b) to again admit into said recirculation circuit (4, 4a, 4b), the gaseous-phase flow from which at least part of the polluting and inflammable substance has been removed.

Description

PRINTING APPARATUS AND PRINTING PROCESS

D e s c r i p t i o n

The present invention relates to a printing apparatus and a printing process and in particular to a printing apparatus and process using an advantageous system for removal of the polluting and/or inflammable substances.

The present invention is not limited to particular types of print or particular supports to be printed but can apply to flexographic print, silk-screen print or heliographic print with rotary printing presses or sheet printing machines, intended for printing newspapers, magazines, packaging material, etc.

It is known that printing apparatuses generally comprise a printing machine provided with a true print region and possibly a drying region. During these printing and drying processes, polluting and inflammable substances (solvent mixtures containing acetone and ethyl acetate in addition to, possibly, ethanol, methoxypropyl alcohol, isopropyl alcohol, isobuthyl, etc. to percentages higher than 40%-60%) are produced by the printing inks, which substances must not be dispersed in the surrounding atmosphere and must not reach too high concentrations.

In this regard, known apparatuses further comprise a ventilation device provided with recirculation ducts adapted to continuously remove these substances from the print region and the drying region and to cause recirculation of same in an air flow through the same regions until concentration of these substances reaches a predetermined threshold, beyond which there is a risk for the mixture catching fire.

When this threshold measured by means of sensors has been reached, the air locks closing the ducts of the ventilation device are opened either automatically or manually, the whole mixture is discharged to the atmosphere through suitable filters and fresh air is admitted into the recirculation ducts. Once said air locks are closed again, circulation is started again until the predetermined threshold is reached again.

Disadvantageously, while the printing cycles can even last some hours (up to 5-8 hours) , the evacuation or discharge operation must be carried out every 10-20 minutes, because said threshold is reached very quickly.

The flow pressure, moisture and temperature conditions suddenly vary at each air exchange and can adversely affect the printing and drying processes.

In addition to the above, often a quick decay of the filters occur and they must be replaced/washed or at all events require a maintenance that is proportional in costs to their use.

Furthermore, frequent opening and closing of the air locks can give rise to problems involving interruption of the plant and also reduced mechanical reliability of the related mechanisms or, in case of manual operation, can also call for use of an operator dedicated to this operation .

In this context, the technical task underlying the present invention is to propose a printing apparatus and a printing process overcoming the above mentioned drawbacks of the known art.

In particular, it is an aim of the present invention to make available a printing apparatus and a printing process ensuring a minimum number of interruptions of the machine and discharge of the polluting substance and a better print quality.

It is a particular aim of the present invention to propose a printing apparatus and a printing process ensuring substantially constant conditions of the ventilation flow during the whole printing cycle (printing and drying) .

It is a further aim of the present invention to propose a more reliable printing apparatus requiring less maintenance interventions as compared with known apparatuses, referring in particular to the filters present therein and the moving parts belonging to the ventilation device.

The technical task mentioned and the aims specified are substantially achieved by a printing apparatus and a printing process comprising the technical features set out in one or more of the appended claims.

Further features and advantages of the present invention will become more apparent from the description given hereinafter by way of non-limiting example of a preferred but not exclusive embodiment of a printing apparatus and a printing process, as illustrated in the accompanying drawings, in which: - Fig. 1 is a diagram showing operation of a printing apparatus according to the present invention; - A -

Fig. 2 is a plan view of an embodiment of the printing apparatus in accordance with the present invention;

- Fig. 3 is an elevation side view of the apparatus seen in Fig. 2;

- Fig. 4 diagrammatically shows a plant for removal of a polluting substance from a gaseous-phase fluid, which is part of the apparatus seen in the preceding figures;

- Fig. 5 shows a block diagram of a further embodiment of the plant seen in Fig. 4; and

- Fig. 6 is a more detailed view of the plant seen in Fig. 5.

With reference to the accompanying drawings, a printing apparatus in accordance with the present invention has been generally identified with reference numeral 1.

Apparatus 1 comprises a printing machine 2 known by itself and therefore herein not described in detail, and a ventilation device 3 operatively coupled in a circuit to the printing machine 2 and provided with at least one recirculation circuit 4 for removal of polluting and inflammable substances produced during printing .

The machine 2 comprises a true print region 5 of the rotary (shown) or sheet (not shown) type for example, and a drying region 6.

The machine 2 can be a flexographic, silk-screen or heliographic, etc. printing machine for example, for printing packaging material or publishing material

(newspapers, magazines, books, pamphlets, etc.), for example . In the embodiment shown, each of the two regions 5, 6 is coupled to a respective recirculation circuit 4a, 4b equipped with one or more devices 7 (fans, pumps), adapted to generate a gaseous-phase fluid flow (air) . The fluid flow grazes the print 5 and drying 6 regions for removing the polluting and inflammable substances contained in the inks and prevent these substances from becoming concentrated giving rise to dangerous fire triggering sources.

Each recirculation circuit 4a, 4b is provided with return ducts so that the gaseous-phase fluid flow goes on grazing the respective regions 5, 6.

Each of the recirculation circuits 4a, 4b further has an inlet 8 provided with air locks for selectively bringing the circuit itself into fluid communication with the external environment and enabling air admission from the outside, and an outlet 9 also provided with air locks for selectively bringing said circuit into fluid communication with the external environment and enable discharge of the gaseous-phase fluid flow contained in circuits 4a, 4b. A filtering device 10 of known type and therefore not further described is installed at the outlet 9, which filtering device in this example is common to both circuits 4a, 4b.

Apparatus 1 further comprises at least one plant 11 for removal of at least one polluting and/or inflammable substance from a gaseous-phase fluid flow, operatively acting on said ventilation device 3.

In the embodiment shown, a single removal plant 11 is in fluid communication with both the aforesaid recirculation circuits 4a, 4b. In alternative embodiments not shown of the apparatus, each circuit 4a, 4b can comprise one or more removal plants 11, according to specific design choices.

Advantageously, , the removal plant 11 is adapted to treat the whole gaseous-phase fluid flow passing through the recirculation circuits 4a, 4b or, preferably, a fraction of said fluid flow. This fraction is included between about 15% and about 40% and more preferably is of about 20% of the flow rate of said fluid flow.

In more detail, in accordance with the non-limiting embodiment shown, apparatus 1 comprises a branching- off circuit 12 which has 12a terminal ends 12a in fluid _ connection with both the recirculation circuits 4a, 4b. The removal plant 11 is installed on said branching-off circuit.

The branching-off circuit 12 allows a fraction of the gaseous-phase fluid passing through the recirculation circuits 4a, 4b to be drawn, which fraction then passes through the removal plant 11 and is subsequently re- admitted into the recirculation circuits 4a, 4b themselves .

Identified as a whole in Figs, 4, 5 and 6 is plant 11 enabling the gaseous-phase polluting fluid "F" to be purified.

Still by way of example only, plant 11 that will be hereinafter described is intended for removal and recovery of solvents such as alcohols, ketones, aromatic compounds, esters or aliphatic compounds. Obviously, removal as referred to in the claims is capable of operating not only with the mentioned solvents, but also with other polluting substances not listed in the following table (given by way of example only) .

Turning back to Fig. 4, the gaseous-phase fluid flow "F" generally consisting of air and at least one (or more than one) polluting substance present in the form of vapour, droplets and/or fumes within this flow will be forced to enter the plant through an entrance opening 13a so as to pass through the plant itself along the advancing direction 14 of the flow. An exit opening 13b in fluid communication with the recirculation circuit 12 allows the gaseous-phase flow devoid of at least part of the polluting and inflammable substance to be admitted again into such a recirculation circuit 12.

Plant 11 is provided with at least one device 15 for generating an air flow inside the plant itself. This flow is already created by the ventilation device 3 by means of the fans or pumps 7 within the region where the vapours of polluting substances are generated exactly to cause said substances to be diluted in the air .

At all events, plant 11 is equipped with said further device 15 because it causes strong flow resistance during passage of the fluid and therefore, in order not to reduce the inner suction of the ventilation device 3 of apparatus 1, one or more fans are used for full recovery of the additional pressure loss caused by the plant 11 itself.

As can be viewed from the drawings, also present is control means 16 designed to drive the device 15 in order to enable the fluid flow passing through plant

11 to be varied, in particular at least depending on a control parameter of the fluid, as better clarified in the following in the explanation concerning operation of plant 11. This control means 16 can comprise different types of known systems, such as a microcontroller or CPU, a PLC or other structures capable of receiving a signal as an input which is a function of the control parameter and in turn generating a command for the suction fan/fans (device 15) in order for example to vary the driving torque thereof as well as the rotation speed or inclination of the vanes so as to consequently vary the flow of the fluid passing through the plant 11.

Generally, the air flow entering plant 11 of the embodiment shown in Fig. 4 will exactly have the same temperature it has on coming out of the work region inside the establishment. In case of flexographic printing processes the air can even reach temperatures of about 5O⁰C.

At all events, the plant in Fig. 4 is not generally designed for heat treatment of the air before removal of the polluting substances; in particular it is not designed to vary the temperature of the air at the inlet and therefore it will be necessary to modify the working power and temperatures of the different devices as a function of the temperature of the inlet air.

Obviously, exceptionally, should it be absolutely necessary to lower the temperature of the air entering the plant, it would be possible to also use a heat exchanger with well water or similar apparatus of known type, having rather reduced costs.

Still referring to the first embodiment, the inlet air first of all passes through a flow humidifier 17 designed to selectively transfer a given substance into the gaseous-phase flow passing therethrough. In particular, the humidifier therein used is of the adiabatic type by coalescence, of the kind presently known on the market.

The adiabatic humidifier 17 actually is not always essential for operation of plant 11 and its use essentially depends on the conditions and the type of flow of the inlet air. For instance, in flows with a too much reduced pollution, problems occur (also depending on the solvents used) because the solvents have a varying curve of vapour pressure on varying of the temperature.

Obviously the plant aims at bringing the vapour pressure to values close to zero (i.e. it aims at obtaining full liquefaction of the solvent) .

Actually, the observance of the operative parameters for admission into the external environment is reached through obtaining very low values of the vapour pressure, i.e. about 0.001, which allow the regulations in force not to be overcome, also with very volatile solvents (some ketones or alcohols, for example) .

It is however to be pointed out that varying of the vapour pressure with the temperature also depends on the saturation curve of the product. Therefore, if there are high percentages of pollutant in the flow, greater reductions are obtained; on the contrary, if flows have small amounts of pollutant, a much more marked temperature lowering is necessary as compared with situations with higher percentages.

For instance, working with isopropyl acetate it is sufficient that the temperature be reduced to about -30°C with saturated flows (200-3000 milligrams per normal m³) ; on the contrary, in the presence of only 50-100 milligrams per normal m³ it would be necessary to reach temperatures of about -85° with clear energy problems, frosting problems and generally the necessity to provide very complicated cryogenic plants suitable for reaching such temperatures.

Under this situation the adiabatic humidifier 17 can be used for admitting additional polluting agent into the flow so as to reduce the temperatures required for removal thereof.

Obviously, also when very high amounts of pollutants are present, which therefore can generate difficulties for obtaining sufficient drainage of same, it is necessary to introduce an intermediate medium into the flow which enables the necessary reductions to be obtained. Generally an azeotrope will be created in the flow so that it can be drained more easily.

The same situation also occurs in the presence of very volatile or very hot polluting products in which the vapour pressure is very high and such that these products are not allowed to be frozen. Under this situation use of the adiabatic humidifier 17 may be suitable for introducing carrying substances such as water for example, or alternatively 2 , 2 , 4-trimethyl- 1, 3-pentanediol monoisobutyrate, which enable rising of the freezing temperature through creation of suitable azeotropic mixtures, to such a degree that the polluting substances can be removed.

In the presence of chloromethane solidifying to a temperature of -3O⁰C, it is not generally necessary to add any further carrier through the adiabatic humidifier.

Another situation in which the adiabatic humidifier 17 can be used is in case of working operations during which peaks of pollutants are generated under some work conditions. In this case, the adiabatic humidifier 17 will be only and exclusively used when the air flow is greatly charged with pollutants while it is deactivated when the flow will again have a smaller percentage of pollutants .

Obviously, the adiabatic humidifier 17 will be connected to a pump for wetting and causing coalescence of the screens. This pump can be activated by a timer

(that is after a given time interval the screen is wetted for a given period of time) or also connected to a pollutant detector that automatically decides on switching the pump on or off.

Still referring to the plant in Fig. 4 it is possible to see that immediately downstream of the adiabatic humidifier 17 a thermal-head device 18 is present which is maintained to a lower temperature than the temperature of the gaseous-phase fluid flow "F" for generating a very important Δt .

The device is passed through by the gaseous-phase fluid and causes formation of the condensate and/or freezing of at least part of the moisture and/or part of the polluting agent.

It is clear that the first battery of the thermal-head device 18 passed through will mainly freeze water and the polluting portion that is mixed with the water itself .

Obviously, this exchanger will also force part of the vapours, fumes or droplets to condense, which droplets will coalesce downwards and will help to a greater degree in absorbing part of the pollutants coming into the flow.

It is also apparent that where substances that are very miscible with water are present (acetone, for example) the first battery will also draw an important part of the polluting agent; on the contrary, where the solvent is not very miscible with water (methylene chloride, for example) the first battery will be fundamentally used for greatly lowering the moisture of the air flow.

Obviously, the geometry and exchange surfaces of the thermal-head device 18 can be studied as a function of the sizes of the plant and the air and pollutant flows passing therethrough; however generally they can be studied in such a manner that the gaseous-phase flow passes through the thermal-head device 18 at an average speed between 1 and 2 m/s and preferably to the limit of the heat exchange between 1.2 and 1.5 m/s.

At this point it is to be pointed out that obviously the ice will tend to close the batteries over time and therefore at each predetermined time interval (30- 50 minutes, for example; however this time interval will obviously depend on the operating conditions and sizes of the plant), it will be necessary to release the thermal-head device 18 from the plant for the purpose of defrosting it using a water jet, for example. Generally a thermal head of about 15 C could be sufficient for the first freezing/condensing operation. Actually, the thermal head used is more important even if generally due to the water enthalpy the first heat exchange battery does not generally fall under -5/-1O⁰ C, at all events generally working below 0⁰C.

Immediately downstream of the heat exchange device 18 there is at least one drop separator 19 designed to collect drops or droplets already present in the flow or created during passage through the adiabatic humidifier and/or the thermal head device 18.

Generally this drop separator 19 is of the turbulent type to allow a better drop collection and is maintained to substantially the same temperature as that of the thermal-head device for increasing efficiency of same.

In this regard the drop separator 19 is made of metal material such as steel for example and is directly connected to the thermal-head device so that it is maintained cold (in other words, for acting as a further condensation means) .

Alternatively, it is possible to think of using a drop separator of a nature different from the turbulent type such as ceramic or sintered ceramic drop separators.

Generally the flow humidifier 17, thermal-head device 18 and drop separator 19 define a first module A of the plant; generally said plant comprises at least two modules A, B and usually three modules A, B, C sequentially in engagement with each other so that they are passed through by the flow to be treated. Obviously the subsequent modules are of the same structure as the previously described one and will exclusively change the air flow conditions at the inlet and outlet and the operating temperatures.

Generally the module having more problems for ice creation will be the second. On the contrary, the third module will be passed through by substantially dehumidified and already cold air and the third thermal-head device 18 will work at temperatures between -25°C and -35°C for example, even being able to reach temperatures of -100⁰C.

Obviously, suitable refrigerating means 20 is provided which is adapted to generate the appropriate low temperatures in the thermal-head device 18.

Generally this means 20 consists of a compressor and a circuit using Freon as the working gas.

Turning to the embodiment of the plant shown in Figs. 5 and 6, it is possible to first of all notice, immediately downstream of the means 15 for generating the air flow inside said plant 11, the presence of a heat exchange unit 21 generally consisting of an air- air exchanger.

This heat exchange unit 21 can be, by way of example, a tube-nest heat exchanger or a finned-pack heat exchanger or others to enable a thermal interaction between the incoming polluted fluid flow "F" and part of the low-temperature flow coming out of plant 11 after being purified.

In this manner the heat exchange unit 21 will act as a heat recuperator to enable energy recovery and will start lowering of the temperature and creation of the condensate (at least with reference to moisture and aqueous vapour) of the polluted fluid flow "F" that is wished to be treated.

Immediately downstream of the heat exchanger 21 a flow mixer 22 is also provided. In particular, the polluted fluid flow "F" will be physically mixed with part of the cold air flow coming out of plant 11, as shown in a circuit in Fig. 5.

In particular, the two flows will be brought into mutual contact at a region 23 immediately upstream of the flow mixer 22 and will then pass through a mixing chamber enabling optimal mixing.

For instance, the flows will be able to be mixed in a 1 to 1 ratio and the overall flow will pass through a series of septa or surfaces acting as barriers for the condensate or freezing of the moisture/aqueous vapour as well as for part of the polluting products to be retained.

It is apparent that this process will involve creation of ice at the mixer surfaces and that therefore periodical defrosting cycles will be necessary to enable percolation of the solidified products.

It is also to be noted that the air flow coming out of the plant that will be mixed in the inlet region 23 will be able to even have temperatures in the range of -70, -8O⁰C. Then the polluted fluid flow "F" enters an air cooling battery 24 shown in Fig. 5 and detailed in Fig. 6. This air cooling battery 24 can be equivalent to a module A of the previously described type, and will in detail comprise at least said thermal-head device 18 and drop separator 19.

However in the embodiment shown in Fig. 6 different elements will be present along the advancing direction 14 of the air flow.

A first space 25 is in particular provided which can be used for possible accessories to be introduced into the plant. A de-atomiser 26 is provided immediately downstream and it is immediately followed by a deflector 27.

Then the flow enters the thermal-head devices 18 of the type described above and then meets the drop separator 19, also of the above discussed type.

Optionally, a further space to be used for further accessories 28 can be provided.

Adoption of the heat exchange unit 21 and the flow mixer 22 will help, together with the suitable refrigerating means described in the following, in reaching temperatures even of -100⁰C in the thermal- head device.

The dry air clear of the pollutants and at a low temperature can be partly bled (by a bleeding and recirculation fan 29, for example) to be sent to the inlet region 23 and then further mixed with the polluted fluid flow "F" entering the device.

The portion of cleaned air not used for recirculation will be, on the contrary, sent to the heat exchange unit 21 for performing the above described functions and then will be admitted to the environment.

It should be noted that use of the heat exchanger 21 and mixer 22 enables an important energy recovery because a great amount of energy is required by the plant when temperatures have to be lowered to a great extent .

It is apparent that obtaining a good energy recovery allows an important cost reduction and therefore makes the plant competitive.

In this regard, it should be pointed out that the plant shown in Figs. 5 and 6 will be able to operate in the region of the thermal-head device 18 at temperatures even reaching -100⁰C with a clean air flow at the outlet having temperatures between -70⁰C and -90⁰C.

It is also to be pointed out that in plants of the type shown in Figs. 5 and 6 the cold-generating method too is of the greatest importance.

Obviously, with temperatures reaching -100⁰C, technologies exploiting liquid nitrogen or cryogenic systems of known type can be utilised.

In this particular case, use of refrigeration compressors for average temperatures (about -50⁰C, as the working temperature) has been selected, which compressors are of the screw type or also of the single-stage or two-stage piston type with use of Freon gas R 507. In order to obtain the cold with this type of compressors, a liquid receiver is placed downstream of the compressor for receiving the very hot and high- pressure Freon coming out of the compressor.

Due to an inner pipe coil for heat exchanger the outgoing Freon is cooled with Freon of the same circuit coming from the battery expansion in the cold production cycle (to temperatures of about -7O⁰C) .

In this manner a first cooling of the Freon entering the circuit is advantageously obtained and also heating of the Freon that on the contrary enters the compressor (in this way the Freon entering the compressor will no longer be to a temperature of -7O⁰C but it will be to temperatures of -30 or -40⁰C) .

The compressor (positive-displacement pump) will have a differential pressure enabling it to give refrigerating power.

Downstream of the liquid receiver the hot high-pressure Freon starts being cooled for reaching the lamination member. In particular, the Freon can be brought from about 70⁰C to temperatures in the range of 5-10⁰C corresponding to pressures of about 8 bars.

In detail, a pre-expansion phase is carried out with a plate-type heat exchanger on part of the Freon so that the latter is expanded and mixed with the other Freon for cooling it in order to reach lamination at temperatures of about -2O⁰C.

By so doing it is possible to cause lamination of the Freon R 507 until pressures of about 0.45 bars so as to reach temperatures included between -80 and -90⁰C.

It is also to be pointed out that the plant will also comprise at least one tank for collecting the polluting substances and the water separated from the flow (not shown) . The tank allows possible at least partial separation of the water and the polluting substance by decantation .

In particular, most of the solvents have a substantial immiscibility with water and therefore three phases are generated in the tank by decantation, a heavier phase at the bottom of the container consisting of the pure heavier substance, an interference of sizes depending on the miscibility of the liquids and a third upper phase consisting of the less heavy liquid in a pure form.

For instance, with a mixture of water and isopropyl acetate, the latter that is lighter will be at the upper part in the tank, while the water will be gathered at the bottom generating an intermediate interference region.

At the bottom at least one outlet to enable discharge of the heavy substance will be present.

Using a suitable electric conductivity/resistivity sensor applied to the outgoing fluid it will be possible to calibrate this probe on the heavier phase; at the moment the conductivity starts changing it means that part of the interference is being drained and therefore the outlet can be selectively closed exactly as a function of the signal detected by the sensor. In this manner it is possible to separate the heavier phase from the lighter one and it becomes necessary to exclusively treat the interference portion.

When the plant is switched on, or at each restart of same after a given time of non operation, the device 8 (i.e. the fan/fans) generates the suitable suction action so that the created pressure difference allows generation of a flow within the plant, overcoming the flow resistance in the machine.

The control means 16 will start receiving the signal/s from the suitable sensors 16a adapted to measure the control parameter/s of the fluid. Generally, the preferential control parameter will consist of the temperature of the fluid passing through the plant, at least at the module where the air reaches the lowest temperature .

Obviously, it will be possible to have more than one temperature measurement in the different regions of the concerned plant.

In addition or alternatively, measurement of other parameters of the fluid can be provided such as the speed of the fluid passing through or also the fluid pressure or moisture, for example.

Referring in particular to the temperature in the last stage C of the plant, it is apparent that the same will start from a condition at which it is substantially the same as the fluid inlet temperature, becoming progressively lower until reaching the operating temperature under normal running conditions. The temperature variation of the gaseous-phase fluid passing through the plant also involves an important volume variation while passing through. In particular, the presence of an important temperature variation (ΔT) involves volume reductions even exceeding 50% relative to the volume of the inlet fluid.

It is therefore apparent that the optimal suction conditions at the plant start will be completely different relative to the optimal suction conditions under normal running conditions.

Should not suitable expedients be adopted for obviating the above, the overall yield of the plant would be submitted to a great decay.

Under this situation the control means 16 acts on device 15 capable of generating the flow within the plant for varying an operating parameter thereof, so as to take into account the volume variations of the gas within said plant.

In particular, as the temperature decreases within the different modules, the control means 16 will send a signal to the fan, varying the driving torque thereof, for example. Variation of the driving torque of the fan allows the plant to be maintained in operation under optimal yield conditions, maintaining the generated pressure difference too within the best operation range.

It is apparent that it will be possible to come to the conclusion of intervening on other operating parameters of the fan such as the rotation speed of the fan or the orientation of the thrust vanes, also for the purpose of reaching the aims highlighted above.

It is finally to be pointed out that the air flow coming out of the plant will be a completely dry low- temperature flow. Said flow can be suitably heated, through exploitation of the heat produced by the refrigerating means for example for generating low temperatures and therefore it can be used again for drying articles of manufacture or given closed environments where the working operations occur so as to allow recovery of part of the heat that otherwise would be lost by dissipation.

Alternatively, it will be possible to use heat created by the pump for generation of the cold, in order to heat the air utilised for heating the environment inside the establishment so that part of the consumed energy can be once more recovered.

It should be also appreciated that there is an important possible use of the above described plants in particular in the presence of big amounts of polluted fluid flows 3 (flows exceeding 15,000 normal/m³ per hour, for example) . With flows of such a nature the electric consumption becomes very high and it may happen that use of the plant is not advantageous and/or the available current is insufficient.

In this case it is possible to use common removal and filtering machines exploiting absorption on activated carbon filters where in particular two or more activated carbon beds are used.

On the contrary, the plant shown in Figs. 4, 5 or 6 can be used with a reduced air flow (500-2000 normal/m³ per hour) for obtaining deabsorption of the exhausted activated carbons.

In particular, by removing the activated carbon bed exhausted for the presence of polluting substances, it will be possible to obtain deabsorption of same making an air flow devoid of humidity pass therethrough (in this manner the activated carbons will have a longer residual life because the same suffer from humidity) and then using the plant in accordance with the invention for removing the pollutants from the flow coming from the activated carbons.

In addition, working on carbons at low temperatures also avoids dangerous isothermal reactions.

In use, at the beginning of the printing process the air locks of the inlet 8 and outlet 9 are opened for filling the recirculation circuits 4a, 4b with air from the external environment. During the printing process, the action of fans 7 generates the gaseous-phase fluid flow (admitted air) through the recirculation circuits 4a, 4b.

At the print regions 5 and drying regions 6, the fluid removes and entrains polluting and inflammable substances originating from the printing inks.

A fraction of the flow with polluting and inflammable substances passes in the branching-off circuit 12 and through plant 11 where at least part of the polluting and inflammable substances is removed from the passing fraction. The treated fraction is admitted into the recirculation circuits 4a, 4b again. The amount of polluting and inflammable substances removed from the flow is sufficient to delay reaching of the predetermined threshold, beyond which there is the risk of the mixture catching fire.

In accordance with an embodiment of the process, only at the end of the printing cycle the air locks closing the ducts of the ventilation device 3 are opened automatically or manually and the whole mixture is discharged outwardly through the filtering device 10, fresh air being admitted into the recirculation circuits .

Alternatively, during printing, the percentage of pollutants in the flow is measured through suitable sensors and once the predetermined threshold has been reached the whole mixture is discharged outwards. The interval of time between one discharge and the subsequent one at all events is very large, typically included between 4 and 8 hours.

The invention reaches the intended purposes and achieves important advantages.

First of all the invention allows a better print quality to be obtained due to the fact that the condition of the ventilation flow are maintained substantially constant during the whole printing cycle (printing and drying). In fact, the full ventilation air exchange, which is the cause of sudden pressure changes is carried out between one cycle and the subsequent one during the necessary machine interruptions for changing the printing setting for instance, or at all events for a limited number of times during printing. In addition, the apparatus of the invention is more reliable than known apparatuses because the opening and closing air locks are actuated few times.

The plant made in accordance with the invention is of simpler construction and management as compared with known techniques involving afterburning or use of activated carbons.

The plant itself is suitable for recovery of a wide variety of solvents and polluting substances to such an extent that it can be used for many types of working operations .

Due to the presence of the control means acting on the suction fan, optimal operating conditions can be ensured during all steps of the transient of the plant from start to the normal running conditions.

Furthermore, the control means are operative independently of the optimal temperatures for removal of the polluting agents and irrespective of the speeds and fluid masses at the plant inlet.

Moreover, use of one or more of the modules inserted in the plant can be provided through activation of exclusively the devices which, among those inserted therein, are strictly required for observance of the regulations in force. By way of example, only one, two or more of the adiabatic humidifiers can be utilised depending on flows and requirements.

Finally, management of the plant involves simpler and less expensive operations as compared with the plants presently on the market.

Claims

C L A I M S

1. A printing apparatus, comprising:

- a printing machine (2); - a ventilation device (3) operatively coupled to the printing machine (2) and equipped with at least one recirculation circuit (4, 4a, 4b) to remove polluting and inflammable substances produced during printing; characterised in that it further comprises at least one plant (11) for removal of at least one polluting and/or inflammable substance from a gaseous-phase fluid flow, operatively acting on said ventilation device (3) and comprising:

- an entrance opening (13a) in fluid communication with the recirculation circuit (4, 4a, 4b) to enable entry of a gaseous-phase fluid flow (F) containing at least one polluting and inflammable substance;

- at least one thermal-head device (18) maintained to a lower temperature than the temperature of the gaseous- phase flow (F) to generate a Δt, said device (18) being passed through by the gaseous-phase flow and causing during passage, condensing and/or freezing of part of the moisture and/or the polluting and inflammable substance contained therein; - at least one drop separator (19) preferably placed downstream of the thermal-head device (18) along an advancing direction (14) of the gaseous-phase flow (F), designed to collect drops and droplets present in the fluid passing therethrough; - an exit opening (13b) in fluid communication with the recirculation circuit (4, 4a, 4b) to again admit into said recirculation circuit (4, 4a, 4b), the gaseous- phase flow from which at least part of the polluting and inflammable substance has been removed.

2. An apparatus as claimed in claim 1, wherein, the printing machine (2) comprises a print region (5) and a drying region (6), each provided with a respective recirculation circuit (4a, 4b) preferably drivable independently of each other.

3. An apparatus as claimed in the preceding claim, wherein a single removal plant (11) is in fluid communication with both said recirculation circuits (4a, 4b), or alternatively comprises a removal plant (11) for each of said recirculation circuits (4a, 4b) .

4. An apparatus as claimed in claim 1, wherein the removal plant (11) is adapted to treat a fraction of the overall fluid flow in the gaseous phase (F) flowing in the recirculation circuits (4, 4a, 4b), preferably said fraction being included between about 15% and about 40%.

5. An apparatus as claimed in claim 1, wherein the recirculation circuit (4, 4a, 4b) further comprises an inlet (8) selectively in fluid communication with the external environment and an outlet (9) selectively in fluid communication with the external environment.

6. An apparatus as claimed in the preceding claim, further comprising at least one filtering device (10) operatively disposed at the outlet (9) .

7. An apparatus as claimed in claim 1, comprising a branching-off circuit (12) having terminal ends (12a) in fluid connection with said recirculation circuit (4, 4a, 4b), wherein the removal plant (11) is installed on said branching-off circuit (12) .

8. An apparatus as claimed in claim 1, wherein the removal plant (11) comprises a device (15)- for generating a fluid flow in the gaseous phase through at least the thermal-head device (18) and the drop separator (19), and control means (16) adapted to operate the device (15) in order to vary the fluid flow passing through the plant (11) as a function of at least one control parameter of the fluid itself.

9. An apparatus as claimed in claim 1, wherein the removal plant (11) further comprises at least one flow humidifier (17) designed to selectively transfer, preferably by coalescence, a predetermined substance into the gaseous-phase flow (F) passing therethrough, said humidifier (17) being for instance an adiabatic humidifier, preferably an adiabatic humidifier by coalescence .

10. An apparatus as claimed in the preceding claim, wherein said humidifier (17) is placed upstream of the thermal-head device (18) along the flow advancing direction (14 ) .

11. An apparatus as claimed in anyone of claims 8 to 10, wherein the device (15) for generating a gaseous- phase fluid flow through the thermal-head device (18) and the drop separator (19) is defined by one or more fans and is preferably able to create at least one pressure increase in the flow, equal to the flow resistance values of the flow through the apparatus.

12. An apparatus as claimed in the preceding claim, wherein the control means (16) acts on said fan so as to vary an operation parameter of the latter and preferably the driving torque.

13. An apparatus as claimed in claim 8, comprising at least one sensor (16a) adapted to detect a control parameter, the control parameter being the temperature of the fluid passing therethrough.

14. An apparatus as claimed in anyone of the preceding claims, further comprising a heat-exchange unit (21) placed upstream of the thermal-head device (18) along a flow advancing direction (14) .

15. An apparatus as claimed in anyone of the preceding claims, further comprising a flow mixer (22) placed upstream of the thermal-head device (18) along a flow advancing direction (14) and adapted to mix the fluid flow (F) with a fluid flow having a lower temperature.

16. An apparatus as claimed in claim 11, wherein the flow humidifier (17), thermal-head device (18) and drop separator (19) define a first module (A) of the plant (11), said plant (11) comprising at least two modules (A, B) and preferably three modules (A, B, C) sequentially in engagement with each other.

17. An apparatus as claimed in anyone of the preceding claims, wherein the printing machine (2) is a rotary printing press or a sheet printing machine, or a flexographic, silk-screen or heliographic printing machine .

18. A printing process, comprising the steps of: printing a plurality of supports in a printing machine (2 ) ;

- submitting the supports to drying in said printing machine (2 ) ; - generating a recirculation of a gaseous-phase fluid flow (F) grazing a print region (5) and/or a drying region (6) of the printing machine (2) to remove polluting and/or inflammable substances produced during printing; characterised in that it further comprises the steps of: forcing passage of -at least one fraction of said gaseous-phase fluid flow through a thermal-head device

(18) maintained to a temperature lower than the temperature of the gaseous-phase flow for generating a

ΔT; condensing and/or freezing at least part of the moisture and/or the polluting and inflammable substances during passage; - separating drops/droplets from the gaseous-phase flow by use of at least one drop separator (19), said separating step preferably taking place after said condensing and/or freezing step;

- admitting said at least one fraction again into the recirculation circuit.

19. A process as claimed in the preceding claim, further comprising the step of discharging into the surrounding atmosphere all the gaseous-phase fluid at each predetermined time interval, said time interval being included between about 4 and about 8 hours.

20. A process as claimed in claim 18, further comprising a control step of a device (15) for varying the fluid flow passing through the plant (11) as a function of at least one control parameter of the fluid itself.