Printing apparatus and corresponding method

Abstract

 An apparatus for printing on a print support comprises a print head (13), for printing a print material on the print support, a feed device (11) and a recirculating unit (15) of the print material. The recirculating unit (15) comprises a first container (14), a second container (18), a first recirculating device (16) configured to generate a first stream of said print material from said first container (14) toward said print head (13) and said second container (18), and a second recirculating device (17) provided to transfer the print material from the second container (18) to the first container (14).

Description

FIELD OF THE INVENTION

[0001] The present invention concerns a printing apparatus for printing on supports such as paper, cardboard, textile materials, metal materials, wood materials, plastic materials, minerals or suchlike.

[0002] The present invention also concerns a printing method.

BACKGROUND OF THE INVENTION

[0003] Printing apparatuses are known, for printing on various types of support which comprise at least an accumulation tank for the print material, for example ink, paint, or enhancing material.

[0004] Printing apparatuses are also provided, comprising a plurality of tanks, each of which is suitable to supply a predetermined dye, paint or enhancing material.

[0005] The print material, taken from the tank, is transferred for example by a pumping device to a recirculating unit.

[0006] The function of the recirculating unit is to make the print material circulate continuously through a print head. The print head is configured to deposit the print material on the print support in a controlled manner.

[0007] The continuous movement of the print material through the print head is necessary to prevent the generation of incrustations and malfunctions therein due to the even partial solidification of the print material.

[0008] To this purpose recirculating units are known that comprise a container into which, according to needs, the print material arriving from the tank is introduced, and a pumping member suitable to confer the desired movement on the print material.

[0009] One disadvantage of known printing apparatuses is that turbulence is generated during the transfer of the print material from the accumulation tank to the intermediate container. In turn, the turbulence generates air bubbles which are incorporated in the print material and, if they start to circulate in the print head, they can affect the overall quality of the printing on the support and can lead to imperfections in the printing.

[0010] Units for recirculating print material are also known for example from documents US-A-2010/0177148, EP-A-2.127.883, EP-A-1.946.849 and US-A-2011/0279495, which comprise two containers, of which a first container is located upstream while a second container is located downstream of one or more print heads.

[0011] In particular, the first container is suitable to feed the print material to the one or more print heads while the second container is configured to receive the print material from the first container and allow it to recirculate toward the first container.

[0012] The recirculating units described in US-A-2010/0177148, EP-A-2.127.883 and US-A-2011/0279495 describe solutions in which the first container is located in a super-elevated position with respect at least to the at least one print head, while the second container is located in a position below the at least one print head. This difference in height is chosen to exploit the effect of gravity and to facilitate the flow of the fluid material from the first container to the print head and from the latter to the second container. However, as a consequence of this, these printing apparatuses are particularly bulky. Furthermore, during recirculating, the print material has to perform a rather extended travel, with the disadvantage that it has little stability and loses its properties, for example of viscosity or others. This requires that conditioning actions must be carried out, for example repeated heating or cooling of the print material, possibly in several zones along the recirculating path of the print material.

[0013] In document EP-A-1.946.849, a solution is described in which the first container and the second container are directly connected with each other by means of a pipe, and the transfer action of the fluid from the first container to the second container through the print head, and from the second container to the first container, occurs by generating different pressure conditions, alternated with each other over time, between the first and second containers.

[0014] However, with this solution, it is not possible to generate a continuous recirculating condition of the print material through the first container, the print head, the second container and subsequently again into the first container.

[0015] The conditions of pressure and depression in the first and second containers are modified alternatively to allow, on the one hand, the transfer of the print material through the print head and, on the other hand, the transfer of the print material from the second to the first container.

[0016] This solution does not ensure continuous recirculating conditions of the print material in the print head, so that the print material can possibly dry up in the latter. Furthermore, this solution is particularly complex and difficult to manage.

[0017] One purpose of the present invention is to obtain a printing apparatus that prevents the occurrence of air bubbles and turbulence in the print material, allowing to obtain high quality prints.

[0018] Another purpose of the present invention is to suitably control the quality of the print material before it is deposited on the print support.

[0019] Another purpose of the present invention is to obtain a printing apparatus that is simple and that reduces the maintenance operations required over time.

[0020] The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

[0021] The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

[0022] In accordance with the above purposes, the present invention concerns an apparatus for printing on a print support made of a material chosen for example from paper, cardboard, textile materials, metal materials, wood materials, plastic materials, mineral materials or ceramic materials.

[0023] A printing apparatus according to the present invention comprises a print head for printing a print material on the print support, a feed device configured to feed the print material to the print head, and a recirculating unit configured to generate a recirculating of the print material through the print head.

[0024] The recirculating unit comprises:

• a first container to contain the print material, fluidically connected to the feed device and upstream of the print head;
• a second container to contain the print material, fluidically connected downstream of the print head and configured to contain the print material;
• a first recirculating device configured to generate a first stream of the print material from the first container toward the print head and the second container, and a second recirculating device connected between the second container and the first container and configured to transfer the print material from the second container to the first container.

[0025] In particular, the first stream of print material arriving from the first container allows to store the part of print material not used by the print head in the second container.

[0026] The second stream of print material from the second container to the first container allows to reuse the print material and to create an additional feed source with respect to that coming from the feed device.

[0027] According to one feature of the present invention, the first container and the second container are located substantially at the same height as the print head. This condition allows to obtain an extremely compact printing apparatus compared to known solutions, also allowing, at the same time, a reduction of the recirculating travel that the print material has to complete during functioning. This allows to keep optimal properties of the ink during printing, ensuring its stability over time and not requiring further conditioning actions, for example heating and/or cooling.

[0028] According to another feature of the present invention, the first recirculating device comprises a suction member connected to the second container and configured to generate at least a negative pressure in the second container suitable to determine a movement of the print material from the first container to the second container through the print head. The suction member can be connected to the first container and also be configured to generate a positive pressure in the first container or, in a variant, the first container can be kept at atmospheric pressure.

[0029] The difference in pressure between the first container and the second container ensures a uniform and constant transfer of the ink through the print head, preventing the generation of turbulence and bubbles that could alter the print quality.

[0030] By positive pressure, here and hereafter in the description, we mean a pressure equal to or higher than atmospheric pressure, for example 101kPa, while by negative pressure we mean a pressure lower than atmospheric pressure, for example comprised between 1kPa and -15kPa.

[0031] The presence of the suction member combined with the positioning at the same height of the two containers prevents the print head from generating unwanted accumulations of print material with consequent deterioration of the printing quality.

[0032] The drive of the suction member is maintained both during the whole printing process and also when the print heads are not working, in order to preserve the properties of the ink over time and prevent it from drying up.

[0033] The present invention also concerns a printing method that comprises feeding, by means of a feed device, a print material to a print head to print the print material on a substrate, and recirculating the print material through the print head, by means of a recirculating unit.

[0034] During the recirculating a first stream of print material is generated from a first container toward the print head and toward a second container, and a second stream of print material is generated from the second container toward the first container.

[0035] The printing method according to the present invention provides that during the recirculating the first container and the second container are located substantially at the same height as the print head and that a negative pressure is induced in the second container to generate the first stream of print material through the print head. According to one form of embodiment, during the recirculating in the first container a positive pressure is induced through the suction member or the first container is kept at a condition of atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] These and other characteristics of the present invention will become apparent from the following description of some forms of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

• fig. 1 is a schematic illustration of one form of embodiment of a printing apparatus according to the present invention.

[0037] It is understood that elements and characteristics of one form of embodiment can conveniently be incorporated into other forms of embodiment without further clarifications.

DETAILED DESCRIPTION OF SOME FORMS OF EMBODIMENT

[0038] We shall now refer in detail to the various forms of embodiment of the present invention, of which one or more examples are shown in the attached drawing/s. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one form of embodiment can be adopted on, or in association with, other forms of embodiment to produce another form of embodiment. It is understood that the present invention shall include all such modifications and variants.

[0039] Fig. 1 is used to describe forms of embodiment of a printing apparatus 10 configured to print a print material, for example ink, on a print support (not shown).

[0040] The print material can comprise an ink, a paint or an enhancing material suitable to confer, for example, a shiny or opaque effect or other graphic effect, such as glitter, sequins or similar conferred for example by respective paints.

[0041] Hereafter in the description reference will be made to the use of ink, although the present invention is applicable to any type of print material.

[0042] The print support can be made for example of a material chosen from paper, cardboard, textile materials, metal materials, wood materials, plastic materials, mineral materials or ceramic materials, although other types of material can also be used, and are not important for the purposes of the present invention.

[0043] According to a possible form of embodiment, the printing apparatus 10 comprises a feed device 11 configured to feed the print material toward a recirculating unit 15 which in its turn is configured to generate, in a print head 13, a continuous recirculating of the print material.

[0044] The print head 13 can be selectively commanded, in a substantially known way, to deposit the print material on the print support according to a prefixed pattern.

[0045] According to a possible form of embodiment, the feed device 11 can comprise an accumulation tank 12 into which the ink is deposited before it is used for printing, and a first pumping device 22 configured to transfer the ink from the accumulation tank 12 toward the recirculating unit 15.

[0046] A possible implementation of the invention, shown in fig. 1 for example, provides that the first pumping device 22 is configured to take the ink from the accumulation tank 12 through a first suction pipe 41 and transmit it to the recirculating unit 15 through a first delivery pipe 42.

[0047] The first suction pipe 41 and/or the first delivery pipe 42 can be provided with a filtering device 21, for example a filter, or similar or comparable devices.

[0048] In possible forms of embodiment, the feed device 11 can comprise a mixing member 30 configured to mix the ink contained in the accumulation tank 12 periodically or continuously.

[0049] According to one form of embodiment of the present invention, the recirculating unit 15 comprises a first container 14 containing the print material, fluidically connected to the feed device 11 to receive the ink. The first container 14 can be connected to the feed device 11 by means of the first delivery pipe 42.

[0050] In one possible solution, it can be provided that the first delivery pipe 42 comprises an end 42a, connected to the first container 14 in an upper portion of the latter. The introduction of the ink from the upper portion of the first container 14 allows to reduce the turbulence that can be induced in the ink already contained in the first container 14 and prevents the onset of air bubbles sent toward the print head 13.

[0051] The first container 14, in its turn, is also connected fluidically upstream of the print head 13 to supply the necessary ink to the latter.

[0052] A possible implementation of the invention provides that the first container 14 is fluidically connected to the print head 13 by means of a first pipe 43a.

[0053] In a possible implementation, the first pipe 43a is connected with one of its ends in correspondence to a lower portion, or bottom, of the first container 14. The connection of the first pipe 43a in the lower part of the first container 14 allows to remove the ink already in a stable condition, that is, not turbulent and which does not incorporate air bubbles for example, which could compromise the printing quality.

[0054] The recirculating unit 15 also comprises a second container 18 containing the print material, fluidically connected downstream of the print head 13 and configured to contain the print material.

[0055] A possible implementation of the invention provides that the second container 18 is fluidically connected to the print head 13 by means of a second pipe 43b.

[0056] According to a possible form of embodiment, the second pipe 43b is connected with its end portion to a lower portion of the second container 18, so as to prevent the ink contained in the second container 18 from incorporating air bubbles.

[0057] The first pipe 43a and the second pipe 43b can be connected to the print head 13 by means of connectors that allow the rapid connection/disconnection of the print head 13 or allow to invert the direction of circulation of the ink in the print head 13.

[0058] In one formulation of the present invention, the recirculating unit 15 comprises a first recirculating device 16 configured to generate a first stream of the print material from the first container 14 toward the print head 13 and toward the second container 18.

[0059] According to one possible solution, the first container 14 and the second container 18 are both located at a same height as the print head 13 so that the levels of ink in the first 14 and the second container 18 are substantially at the same reciprocal height, or kept at slightly different heights, for example 5 mm up to 15 mm, acting on the pressure conditions generated in the first 14 and second container 18 as described hereafter.

[0060] This solution allows to contain the overall bulk of the recirculating unit 15, with consequent reduction in the travel that the print material has to complete in order to be recirculated. Thanks to the limited size of the recirculation travel it is possible to ensure the preservation over time of optimal properties of the print material for subsequent deposition on the substrate.

[0061] According to one possible solution, both the first container 14 and the second container 18 are located above the print head 13. This positioning allows to exploit the gravitational effect to which the ink is subjected to facilitate the flow of the latter from the first container 14 to the print head 13.

[0062] According to one formulation of the present invention, the first container 14 and the second container 18 are made in a single body with each other and are located one adjacent to the other. In other words, the first container 14 and the second container 18 comprise a single containing body provided with a separation wall to define respectively the first 14 and second container 18.

[0063] One possible solution of the present invention provides that the first recirculating device 15 is the pneumatic type and comprises a suction member 24 connected fluidically, by means of a pneumatic circuit 19, to the first container 14 and second container 18.

[0064] According to one possible solution, the suction member 24 is configured to put a gas, for example air, in a condition of positive pressure inside the first container 14 and to take from the second container 18 the air present therein, generating a depression, or negative pressure. According to a variant embodiment, the suction member 24 can be configured to make only a depression action in the second container 18.

[0065] The difference in pressure that is established between the first container 14 and the second container 18 induces the movement of the ink from the first container 14 to the second container 18, passing through the print head 13.

[0066] According to one possible solution, to ensure the desired pressure conditions in the first container 14 and second container 18, both of them or at least the second container 18 can be hermetically closed with respect to the outside.

[0067] The suction member 24 can possibly comprise a flow adjuster 29 configured to regulate the stream of air which is sent to the first container 14 and the second container 18.

[0068] According to a possible form of embodiment, the pneumatic circuit 19 comprises a first pipe 46 connecting the suction member 24 to the first container 14, and a second pipe 47 connecting the suction member 24 to the second container 18.

[0069] According to one possible form of embodiment, a super-pressure valve 26 can be connected to the first connection pipe 46 to regulate the stream of air that is sent to the first container 14 from the suction member 24.

[0070] According to another possible form of embodiment, a differential pressure sensor or a counter pressure sensor 50 can be connected to the second connection pipe 47, suitable to detect the conditions of pressure that persist in the second connection pipe 47, and therefore control the stream of suction air that is induced in the second container 18.

[0071] The pneumatic circuit 19 can also comprise safety devices 55 disposed upstream and downstream of the suction member 24 and configured to prevent, due to malfunctioning, the ink present in the first container 14 and/or the second container 18 from entering into the suction member 24 and damaging it.

[0072] According to one possible solution the safety devices 55 comprise tanks 25a, 25b interposed between the first container 14 and the second container 18 and the suction member 24, connected for example in an intermediate position along the first connection pipe 46 and the second connection pipe 47.

[0073] In particular, it is provided that in the tank 25a, connected to the first container 14, the air is put in a condition of positive pressure while in the tank 25b, connected to the second container 18, a condition of negative pressure, or depression is generated.

[0074] The tanks 25a, 25b can be provided with discharge valves, not shown in the drawings, to discharge the condensation that can be generated or possible ink that can be present inside them. Moreover, the tanks 25a, 25b can be provided with ink detection sensors which if activated command or supply a signal for the deactivation of the suction member 24. In this way it is possible to prevent damage to the suction member 24.

[0075] In the form of embodiment in fig. 1, the suction member 24 is connected by means of a first pipe 48a to a distribution valve 27. The distribution valve 27 is connected in its turn by means of a second pipe 48b and a third pipe 48c respectively to the tanks 25a and 25b of the safety devices 55.

[0076] One implementation of the invention provides that the recirculating unit 15 also comprises a second recirculating device 17 provided to transfer the print material from the second container 18 to the first container 14.

[0077] The second recirculating device 17 comprises a pumping member 23 connected fluidically, by means of a fluidic circuit 28, to the first container 14 and second container 18, and configured to transfer the ink from the second container 18 to the first container 14.

[0078] One possible solution provides that the fluidic circuit 28 comprises a suction pipe 44 that fluidically connects the second container 18 to the pumping member 23, and a delivery pipe 45 that fluidically connects the pumping member 23 to the first container 14.

[0079] In a possible form of embodiment, the suction pipe 44 is connected with its first end to the lower portion of the second container 18. This solution prevents air from being sucked in through the suction pipe 44.

[0080] In one possible solution it is provided that the delivery pipe 45 is connected with its first end to the lower portion of the first container 14. The introduction of the ink from the lower portion of the first container 14 allows to obtain at least a stable ink accumulation zone, that is, quiet and without turbulence or air bubbles.

[0081] One possible solution provides that at least the delivery pipe 45 is provided with a filter device 59 provided to filter the stream of ink that is introduced into the first container 14 from the second container 18.

[0082] According to one form of embodiment of the present invention, the recirculating unit 15 comprises detection devices 56 provided to detect the quantity of ink present in the first container 14 and second container 18, so as to allow the correct activation of the first 16 and second 17 recirculating devices.

[0083] According to possible forms of embodiment, for example shown in fig. 1, the detection devices 56 comprise a first level sensor 31 configured to detect the level of ink in the first container 14, and a second level sensor 32 configured to detect the level of ink in the second container 18.

[0084] The first level sensor 31 and the second level sensor 32 can be chosen from a group comprising optical sensors, magnetic sensors, inductive sensors, capacitive sensors, floating members, or possible combinations thereof.

[0085] The first level sensor 31 and the second level sensor 32 can provide useful indications for the functioning modes of the recirculating unit 15. In particular, depending on the levels of ink present in the first container 14 and the second container 18, it will be possible to determine the activation of the pumping member 23 to maintain desired levels of ink.

[0086] The recirculating unit 15 can comprise conditioning devices 60 connected to at least one of either the first container 14 or the second container 18 and configured to modify the physical characteristics in a desired way, for example temperature, viscosity of the ink that is made to circulate through the print head 13.

[0087] In some forms of embodiment, the conditioning devices 60 can comprise a system to regulate the temperature, for example obtained with a heat-carrying circuit, able to modulate the temperature of the ink contained in at least one of either the first container 14 or the second container 18, for example by heating and/or cooling action.

[0088] According to a possible form of embodiment, the conditioning devices 60 comprise a cooling member 52 mounted inside at least one of either the first container 14 or the second container 18 to heat the ink contained in the latter according to pre-set modes.

[0089] The heating member 52 can comprise, for example, an electric resistance 58 as shown in fig. 1, a heat conditioning circuit or other device suitable to the purpose.

[0090] According to another possible form of embodiment, the conditioning devices 60 comprise a cooling member 61 configured to induce in at least one of either the first container 14 or the second container 18 a cooling of the ink contained therein, and to adjust its temperature to the temperature of use by the print head 13. One possible implementation provides that the cooling member 61 comprises a fluid-dynamic conditioning circuit that exploits the principles of a cooling cycle.

[0091] According to other solutions, the conditioning device 60 can comprise an activator member, for example a UV lamp, an ultrasound exciter, an ionizer or similar to activate specific components of the ink before printing.

[0092] Thanks to the fact that the first container 14 and the second container 18 are installed at the same height and possibly adjacent to each other, it is possible to provide that at least one of the conditioning devices 60, described above, can be installed between the first container 14 and the second container 18, exerting a conditioning action on the property of the ink both in one container and the other.

[0093] The printing apparatus 10 can comprise a control unit 33, in this case a PLC, configured to monitor and manage at least the functioning mode of the first recirculating device 16 and the second recirculating device 17.

[0094] In particular, possibly also depending on the signals detected by the first level sensor 31 and the second level sensor 32, the control unit 33 is able to suitably manage the activation of the first pumping device 22 and the pumping member 23 in order to maintain in the first container 14 and the second container 18 a predetermined level of ink so as to guarantee the correct supply to the print head 13.

[0095] In some forms of embodiment, the control unit 33 is connected to the components of the apparatus 10 to be controlled and managed through electric connections 36, such as electric cables or electric tracks, in the case where the control device comprises integrated boards or PCB.

[0096] According to other forms of embodiment, the control unit 33 can be served by user interface devices 34 to allow the user to selectively set some print parameters and monitor alarms and print operations.

[0097] In other forms of embodiment, the interface devices 34 can be provided external to the printing apparatus 10, for example made by means of an electronic calculator such as a PC, or similar device.

[0098] It is clear that modifications and/or additions of parts may be made to the printing apparatus 10 as described heretofore, without departing from the field and scope of the present invention.

[0099] For example, even if the present invention has been described with reference to a printing apparatus 10 comprising a single print head 13, an application of the invention to a printing apparatus with more than one print head 13 is not excluded. In this case, for each print head 13 it is necessary to provide its own feed device 11 and its own recirculating unit 15, in the same way as described above.

[0100] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of printing apparatus, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims

1. Apparatus for printing on a print support comprising a print head (13) for printing a print material on said print support, a feed device (11) configured to feed said print material to said print head (13), and a recirculating unit (15) configured to generate a recirculating of said print material through said print head (13), said recirculating unit (15) comprising:

- a first container (14) to contain said print material fluidically connected to said feed device (11) and upstream of said print head (13);

- a second container (18) to contain said print material fluidically connected downstream of said print head (13);

- a first recirculating device (16) configured to generate a first stream of said print material from said first container (14) toward said print head (13) and said second container (18);

- a second recirculating device (17) connected between said second container (18) and said first container (14) and configured to transfer said print material from said second container (18) to said first container (14), characterized in that said first container (14) and said second container (18) are located substantially at the same height as said print head (13), and in that said first recirculating device (16) comprises a suction member (24) connected to said second container (18) and configured to generate at least a negative pressure in said second container (18) suitable to determine a movement of said print material from said first container (14) to said second container (18) through said print head (13).

2. Apparatus as in claim 1, characterized in that said suction member (24) is connected to said first container (14) and is configured to generate a positive pressure in said first container (14).

3. Apparatus as in claim 1 or 2, characterized in that said second recirculating device (17) comprises a pumping member (23) connected between said first container (14) and said second container (18) to transfer the print material from said second container (18) to said first container (14).

4. Apparatus as in any claim hereinbefore, characterized in that said first container (14) and said second container (18) are both located above said print head (13).

5. Apparatus as in any claim hereinbefore, characterized in that said first container (14) and said second container (18) are made in a single body with respect to each other and are located adjacent to each other.

6. Apparatus as in any claim hereinbefore, characterized in that said suction member (24) is connected to said second container (18) and to said first container (14) by means of a pneumatic circuit (19), and in that said pneumatic circuit (19) comprises safety devices (55) disposed upstream and downstream of said suction member (24) and configured to prevent said print material present in said first (14) and/or in said second container (18) from entering into said suction member (24).

7. Apparatus as in any claim hereinbefore, characterized in that said feed device (11) comprises an accumulation tank (12) in which said print material is disposed, and a first pumping device (22) configured to transfer said print material from the accumulation tank (12) to said first container (14).

8. Apparatus as in any claim hereinbefore, characterized in that said first container (14) is connected to said feed device (11) by means of a first delivery pipe (42) provided with an end (42a) connected in an upper portion of said container (14).

9. Apparatus as in any claim hereinbefore, characterized in that said first container (14) is connected to said print head (13) by means of a pipe (43a) provided with an end connected to a lower portion, or bottom, of said first container (14).

10. Apparatus as in any claim hereinbefore, characterized in that said recirculating unit (15) comprises devices (56) provided to detect the quantity of ink present in said first (14) and said second container (18).

11. Apparatus as in claim 10, characterized in that said detection devices (56) comprise a first level sensor (31) configured to detect the level of said print material in said first container (14), and a second level sensor (32) configured to detect the level of said print material in said second container (18).

12. Apparatus as in any claim hereinbefore, characterized in that said recirculating unit (15) comprises at least one of either a heating member (52) or a cooling member (61), connected to at least one of either said first (14) or said second container (18) and configured to heat and/or cool said print material.

13. Printing method that comprises feeding, by means of a feed device (11), a print material to a print head (13) for printing said print material on a substrate, and recirculating the print material, at least during printing, through said print head (13), by means of a recirculating unit (15), and in which during the recirculating, a first stream of print material from a first container (14) is generated to the print head (13) and to a second container (18), and a second stream of print material from the second container (18) to the first container (14), characterized in that during the recirculating the first container (14) and the second container (18) are located substantially at the same height as the print head (13), and in that a negative pressure is induced in the second container (18) to generate said first stream of print material through said print head (13).

14. Method as in claim 13, characterized in that during the recirculating, a positive pressure is induced in the first container (14), greater than atmospheric pressure.

15. Method as in claim 13, characterized in that during the recirculating, said first container (14) is maintained in a condition of atmospheric pressure.

Drawing