Patent Publication Number: US-8985750-B2

Title: Ink jet printing process using gas with molar mass lower than air during ink deposition

Description:
The present invention relates to inkjet printing techniques. 
     Inkjet printing techniques are especially used in the field of printers and, more generally, in graphic application. 
     At the present time it is desired to apply inkjet printing techniques to fields other than graphic application, such as, for example, to microtechnology and/or nanotechnology. 
     This is because known inkjet printing devices are inexpensive and reliable. It would therefore be desirable to be able to benefit from these advantages in fields other than that of graphic design. 
     However, certain applications have specific needs that known inkjet printing devices are not able to meet. 
     Thus, in the nanotechnology field, the use of known inkjet printing devices is limited by problems relating to the resolution of the inkjet printing technique with respect to the resolution of the techniques, such as photolithography, conventionally used in this field. Specifically, known inkjet printing devices do not allow ink to be deposited on a substrate with a print quality comparable in precision to that obtained with the techniques conventionally used in the field of nanotechnology. 
     Similar problems are generally encountered in the microtechnology field. 
     One objective of the invention is to provide an inkjet printing device capable of obtaining, in particular in fields other than graphic application, a higher resolution than existing inkjet printing devices. 
     In particular, one objective of the invention is to provide such an inkjet printing device for microtechnology and/or nanotechnology applications. 
     Another objective of the invention is to provide such an inkjet printing device, said device being inexpensive and reliable. 
     To achieve at least one of these objectives, the invention provides an inkjet printing device comprising a chamber containing at least one inkjet head, an inlet orifice for a gas having a molar mass lower than the molar mass of air, and at least one outlet orifice for this gas, said head being placed in the chamber such that the gas can be injected around the head and ejected out of the chamber with the ink delivered from the head. 
     The device will possibly have other technical features, whether in isolation or in combination:
         a member is provided to support the inkjet head, said supporting member comprising a means for controlling its temperature, for example a resistive heater or a heating circuit;   the supporting member comprises at least one channel for removing fluid;   a means is provided for controlling the temperature of a target surface on which the ink delivered from the inkjet head is intended to be deposited;   the chamber is funnel-shaped, in order to increase the velocity of the gas around the inkjet head; and   a means is provided for controlling the gas flow rate.       

     To achieve at least one of these objectives, the invention also provides an inkjet printing process for printing on a target surface, comprising the following steps:
         depositing ink on the target surface with at least one inkjet head placed in a chamber, said ink comprising a solvent that is liable to evaporate when it makes contact with the target surface; and
           injecting a gas having a molar mass lower than the molar mass of air into the chamber, said head being placed in this chamber so that the gas thus injected flows around the head and is then ejected out of the chamber with the ink delivered from the head.   
               

     The process will possibly have other technical features, whether in isolation or in combination:
         the temperature of the target surface is controlled;   the gas comprises an additive capable of modifying the contact angle between the ink deposited on the target surface and this target surface;   the gas comprises an additive capable of functionalizing particles contained in the ink after evaporation of the solvent from the ink;   the gas flow rate is controlled; and   the gas ejected out of the chamber increases the velocity of the ink drops via a driving effect.       

    
    
     
       Other features, aims and advantages of the invention will become apparent from the following detailed description given with reference to the following figures: 
         FIG. 1(   a ) is a schematic cross-sectional view of a first embodiment of an inkjet printing device according to the invention; 
         FIG. 1(   b ) is a partial view from below of the device shown in  FIG. 1(   a ); 
         FIG. 1(   c ) is a schematic showing, from below, the orifice of the device shown in  FIG. 1(   a ); 
         FIG. 1(   d ) is a schematic showing a view of the cross section A-A of the part of the device shown in  FIG. 1(   c ); 
         FIG. 2  shows various lines of ink printed on a substrate with the device shown in  FIGS. 1(   a ) to  1 ( d ); 
         FIG. 3(   a ) is a schematic cross-sectional view of a second embodiment of an inkjet printing device according to the invention; 
         FIG. 3(   b ) is a schematic of the device shown in  FIG. 3(   a ), illustrating an enlarged view of the inkjet head; 
         FIG. 4  shows various lines of ink printed on a substrate with the device shown in  FIGS. 3(   a ) and  3 ( b ), with injection of helium and hydrogen, for the same substrate temperature; and 
         FIG. 5  shows the variation in the velocity of the ink drops delivered from an inkjet head as a function of the voltage applied to a piezoelectric actuator of this head. 
     
    
    
     A first embodiment is shown in  FIGS. 1(   a ) to  1 ( d ). 
     The inkjet printing device  1  comprises a reservoir  110  of ink, which ink contains a solvent that is liable to evaporate when it makes contact with a substrate  100  on which this ink is intended to be deposited. It also comprises an inkjet head  10 , one end of which is fluidically connected to the reservoir  110  of ink via a duct  11 . 
     The other end of the inkjet head  10  terminates in an ink ejecting nozzle  101 , placed facing the target surface  100 . 
     The inkjet head  10  is actuated by a system (not shown) allowing a succession of independent ink drops to be generated. In particular, this may be what is called a “drop on demand” piezoelectric system allowing drops to be generated on demand by way of suitable choice of the control amplitude and frequency of this system, thereby allowing drop size and production rate to be controlled. 
     However, an inkjet head allowing other forms of drop to be generated, especially a spray of drops, could be envisioned. 
     The inkjet printing device  1  also comprises a chamber  60  in which the inkjet head is housed. 
     This chamber GO is defined by the sides of a member  20  that supports the inkjet head  10 , this supporting member  20  in this case being made up of a number of parts. 
     Specifically, this supporting member  20  comprises a supporting body  201 , a vertical wall  202  that is mounted on the upper side  24  of the supporting body  201 , and a cover  203  mounted on the vertical wall  202 . 
     One end of the inkjet head  10  is mounted on the cover  203  and the weight of this head  10  is then transmitted from the cover  203  to the vertical wall  202  and then to the supporting body  201 , which body is mounted on a frame (not shown). 
     The inkjet head  10  thus passes through the supporting member  20  and extends into the chamber  60  and in particular into the supporting body  201 , the latter containing a housing  23  for this purpose. 
     The chamber  60  is separated into two parts  60   a ,  60   b  sealed from each other by virtue of an O-ring  63  placed both around the inkjet head  10  and against the internal part of the vertical wall  202 . 
     The cover  203  may be movably mounted relative to the vertical wall  202 , in order to permit this cover to move in translation relative to the vertical wall  202 . This movement occurs along the longitudinal axis A of the inkjet head  10 . It is shown by the arrow F 1  in the appended figures. 
     This allows the position of the inkjet head  10  relative to the target surface  100  to be controlled. 
     In this case, the upper part  60   a  of this chamber  60  advantageously comprises an elastic means  65 , such as a spring, placed between a plate  64 , mounted on the internal part of the cover  203 , and the vertical wall  202 . This spring  65  allows a force that is liable to be exerted on the upper part of the cover  203  to be opposed, thereby making it possible for the inkjet head  10  to return to a reference position. 
     As a variant, it is possible to envision a simpler device in which the position of the inkjet head  10  cannot be adjusted. 
     Moreover, the lower part  60   b  of the chamber  60  comprises an inlet orifice  66  for a gas and an outlet orifice  21  for this gas, the head  10  being arranged in the chamber  60  so that the gas can be injected around the head  10  and ejected out of the chamber with the ink delivered from the head. 
     The outlet orifice  21  is formed in the lower wall  22  of the supporting body  201 , this lower wall  22  lying opposite the upper wall  24  of this supporting body  201 . 
     The inlet orifice  66  of the chamber  60  is connected to a reservoir  30  containing a pressurized gas, by way of various means. 
     Specifically, the gas reservoir  30  is connected by a duct  80  to a means  40 , such as a regulator, for setting the gas in motion. 
     The gas contained in the reservoir has a molar mass lower than the molar mass of air. It will be recalled that the molar mass of air is 29 g/mol. 
     Thus, the gas contained in the reservoir may be qualified a “light” gas. This gas may for example be helium or hydrogen. 
     The diffusion coefficient of the vapor of the solvent of the ink in the gas contained in the reservoir  30 , because of the molar mass of said gas, is higher than the diffusion coefficient of the same solvent vapor in air. This may be observed whatever the nature of the solvent, the nature of the solvent having a secondary effect on the value of the diffusion coefficient of the vapor of the solvent in the gas in question. 
     As for the regulator  40  it is connected to a flow meter  50  by way of a duct  81 . Lastly, the flow meter  50  is connected by a duct  82  to the inlet orifice  66  leading to the lower part  60   b  of the chamber  60 . 
     The flow meter  50  allows the flow rate of gas delivered from the gas reservoir  30  to be measured and allows this flow rate to be set to a value chosen by the operator. 
     Other means of setting the gas in motion could be employed. 
     After it has entered the lower part  60   b  of the chamber  60 , the gas flows along the inkjet head  10 , in the housing  23  of the supporting body  201 , before exiting via the orifice  21  formed in the lower wall  22  of the supporting body  201 . 
     This gas is then sprayed against the target surface  100  at the same time as the ink delivered from the nozzle  101  of the inkjet head  10 . This gas therefore flows around and travels in the same direction as the ink drops delivered from the nozzle  101 , the ink being intended to be deposited on the target surface  100 . 
     The path travelled by the gas delivered from the reservoir is shown by the arrows F. 
     In operation, for microtechnology or nanotechnology applications, the fluid contained in the volume located between the lower side  22  of the supporting body  201  and the upper side  105  of the target surface  100  is saturated with a fluid comprising, on the one hand, the gas coming from the reservoir  30 , and on the other hand, solvent vapor coming from the ink. 
     Specifically, the ink used in these applications may be formed by a mixture of a powder, microparticles or nanoparticles depending on the circumstances, and a solvent. In these applications, the target surface  100  is generally a substrate. 
     Thus, when a drop  101 ′ of ink is deposited on the substrate  100 , the solvent contained in the drop evaporates in order to leave only the desired deposit, the solvent vapor then mixing with the fluid contained in the volume located between the supporting member  20  and the substrate  100 . 
     The rate at which the solvent evaporates is an important factor affecting whether the resolution of the deposit is improved. 
     It has been demonstrated, as will be explained below, that the injection of a gas having a molar mass lower than the molar mass of air allows the resolution of this deposit to be improved. 
     The device  1  advantageously comprises a means  104  for heating the substrate  100  to a desired temperature. This means  104  will generally be placed on the lower side  106  of the substrate  100 , opposite what is called the upper side  105  of said substrate  100 , on which upper side the ink  101 ′ is deposited. Specifically, heating the substrate  100  accelerates evaporation of the solvent. 
     The orifice  21  may have a cross shape, the longitudinal axis of the nozzle  101  then advantageously passing through the center of this orifice  21 , as is shown in  FIGS. 1(   b ) and  1 ( c ). 
     Advantageously, the supporting member, and more precisely the supporting body  201 , also comprises at least one, for example circular, channel  70  opening into the lower wall of the supporting body  201 , allowing turbulence in the fluid contained in the volume located between the supporting body  201  and the substrate  100  to be reduced. 
     This channel  70  improves the quality of the deposit produced on the substrate  100  especially enabling quality deposits to be produced with wider ranges of flow rates of gas coming from the gas reservoir  30 . Other means for limiting this turbulence may be provided. 
     Lastly, the supporting body  201  generally comprises a heating means (not shown) with which it is possible to control the temperature of said supporting body  201 , and therefore that of the nozzle  101 , in order to influence the size of the ink drops delivered from the nozzle  101 . This heating means may be a resistive heater, a circuit in which a fluid heated to the desired temperature is able to flow, or any other means capable of fulfilling this function. 
     The device  1  according to the invention allows the resolution of the ink deposit obtained on the substrate  100  to be improved relative to known inkjet printing devices. 
     Specifically, the Applicant has carried out tests demonstrating the benefits of the invention. The results of these tests are shown in  FIG. 2 . 
       FIG. 2  shows four lines A, B, C and D of ink deposited on the substrate substrate  100  using the device described with reference to  FIGS. 1(   a ) to  1 ( c ), under partially different test conditions. 
     For the lines A, B, C and D, the following experimental conditions were the same. 
     The ink was formed by mixing zinc oxide nanoparticles in a concentration by weight of 10% in the solvent, namely ethylene glycol, and a given amount of ink was deposited. 
     The ejection nozzle used had a diameter of 50 μm and said nozzle was heated to a temperature of 47° C. 
     A line was formed by depositing drops in succession every 50 μm. 
     The inkjet head was actuated by a piezoelectric actuator, at a voltage V 1 =35 volts. 
     The nozzle was moved relative to the substrate at a speed of 450 μm/s. 
     The drops were delivered from the nozzle  101  with a velocity of 1.3 m/s. In order to determine this velocity, a stroboscopic detector was integrated into the device  1 . 
     The substrate  100  used had a contact angle, measured beforehand with a drop of water, of 40°. 
     The orifice  21  was cross-shaped with a length L=5 mm and a width 1=1 mm, the parameters L and  1  being shown in  FIG. 1(   c ). This orifice  21  received at its center the nozzle  101  the outside diameter of which was about 500 μm. 
     Lastly, the distance between the nozzle  101  and the substrate  100  was about 1 mm. 
     In contrast, the tests differed in the temperature of the substrate and/or in the presence or absence of fluid coming from the gas reservoir  30 . 
     Thus, line A corresponds to deposition of the ink on a substrate at a temperature T substrate =65° C., without injection of fluid coming from the gas reservoir  30 . Line B corresponds to deposition of the ink on a substrate at a temperature T substrate =65° C., with injection of helium coming from the gas reservoir  30  with a flow rate of 374 ml/mn. Line C corresponds to deposition of the ink on a substrate at a temperature T substrate =90° C., without injection of gas coming from the gas reservoir  30 . Line D corresponds to deposition of the ink on a substrate at a temperature T substrate =95° C., without injection of gas coming from the gas reservoir  30 . 
     Line A was not straight and contained regions in which the ink had spread because the temperature (65° C.) of the substrate  100  was too low preventing the solvent from evaporating quickly enough. As a result, the ink had a tendency, in certain regions, to spread over the substrate  100 . 
     In contrast, line B was straight and very uniform, and moreover its width was measured to be 56 μm, for a substrate  100  at an identical temperature (65° C.). 
     The beneficial influence of injecting helium into the volume formed between the supporting member  20  and the substrate  100  may be noted by comparing lines A and B. 
     This beneficial influence is due to the fact that the diffusion coefficient of the vapor of the solvent, in this case ethylene glycol vapor, in helium is higher than the corresponding coefficient in air. This is due to the lower molar mass of helium so that a result of the same nature would be obtained with any other type of solvent. 
     Moreover, the inventors also consider this beneficial influence to be due to the velocity of the gas, in this case helium, which blows away the solvent vapor surrounding the ink deposited on the substrate. 
     After having carried out the tests corresponding to lines A and B, a number of tests were carried out without injecting helium into the volume located between the supporting member  20  and the substrate  100 , the temperature of the substrate  100  being increased 5° C. each time, in order to identify the substrate temperature above which it was possible to achieve approximately the same deposition quality as obtained with the test having led to line B. 
     Thus, lines C and D show the results obtained, in the absence of helium injection into the volume located between the supporting member  20  and the substrate  100 , for substrate temperatures of 90° C. and 95° C., respectively. 
     Line C deposited on the substrate was relatively straight and had a width of about 70 μm. 
     Line D was a little less uneven than line C but contained rings that made the deposit nonuniform. The width of line D was also about 70 μm. 
     At temperatures strictly below 90° C., evaporation of the solvent contained in the ink was too slow, so that the line of ink deposited on the substrate was not straight. Moreover, at temperatures strictly above 95° C., evaporation of the solvent contained in the ink was too fast and the quality of the deposit was unacceptable. 
     From these tests, it is therefore deduced that injecting helium into the volume located between the supporting member  20  and the substrate  100  makes it possible to obtain a better resolution (deposited line width of 56 μm) than the resolution liable to be obtained in the absence of helium injection (line width of about 70 μm), while simultaneously allowing the heating temperature of the substrate to be decreased by 25° C. to 30° C. 
     An additional test was also carried out with hydrogen replacing helium, the hydrogen flow rate and the substrate temperature being identical to the test carried out with helium and the other test conditions remaining the same and conforming to the conditions given above. 
     This test showed that hydrogen enabled a deposition quality comparable to that obtained with helium to be achieved. In particular, the line deposited under these conditions with hydrogen was straight and had a width of about 56 μm. 
     A second embodiment is shown in  FIGS. 3(   a ) and  3 ( b ). 
     In the second embodiment, the device  1 ′ differs from the device  1  of the first embodiment in that the shape of the sidewalls of the housing  23 ′ and therefore the shape of the housing  23 ′ itself, produced in the supporting member  20 ′, is different. 
     Thus, the shape of the chamber  60 ′ is also modified. 
     This is also the case for the shape of the orifice  21 ′. 
     Specifically, the housing  23 ′ produced in the supporting member  20 ′ has a funnel shape. This shape allows a Venturi effect to be generated between the inkjet head and the walls of the housing  23 ′. 
     The funnel ends in the orifice  21 ′ which therefore has, when observed from below, a circular shape in which the nozzle  101  of the inkjet head  10  is located. 
     Example shapes for the housing  23 ′ and orifice  21 ′ are shown in greater detail in  FIG. 3(   b ). 
     The housing  23 ′ comprises a cylindrical part  230 ′, under which another part  231 ′, taking the form of a narrowing, is provided. The orientation of the walls in this part  231 ′ where the housing  23 ′ narrows may be defined, in the vertical cross-sectional plane of  FIG. 3(   b ) by an angle a, for example of 120°. This angle a is chosen to limit turbulence. 
     As for the orifice  21 ′, it has a first cylindrical part  210 ′, of diameter l 2  and height h 2 , under which another part, having a conical shape, of height h 1 , is located. The angle α 1  made between the walls of this conical part, defined in the vertical cross-sectional plane of  FIG. 3(   b ), is advantageously chosen to limit turbulence. However, the orifice  21 ′ could have a simpler shape, it could, for example, be completely cylindrical. 
     The other features of this second embodiment V of the device are the same as the features described for the first embodiment 1 of the device, identical references in the two embodiments relate to the same elements. 
     The Applicant has carried out tests allowing the benefit of this second embodiment of the invention to be demonstrated. The results of these tests are shown in  FIG. 4 . 
       FIG. 4  shows two lines of ink A′ and B′ deposited on a substrate  100  with the device  1 ′ described with reference to  FIGS. 3(   a ) and  3 ( b ), under partially different test conditions. 
     For the two lines A′ and B′ the following experimental conditions were the same. 
     The ink was formed by mixing zinc oxide nanoparticles in a concentration by weight of 10% in the solvent, namely ethylene glycol, and a same amount of ink was deposited. 
     The ejection nozzle used had a diameter of 50 μm and said nozzle was heated to a temperature of 47° C. 
     The line was formed by depositing drops in succession every 50 μm. 
     The inkjet head was actuated by a piezoelectric actuator, at a voltage V 1 =50 volts. 
     The nozzle was moved relative to the substrate at a speed of 450 μm/s. 
     The drops were delivered from the nozzle  101  with a velocity of 3.2 m/s. This velocity was measured using a stroboscopic detector. It should be noted that in these tests the velocity of the gas increased the velocity of the drops relative to that obtained in the absence of this gas. Specifically, in the absence of gas, this velocity was 1.3 m/s, in accordance with the tests carried out with the device  1  of the first embodiment. 
     The substrate  100  used had a contact angle of 40°, measured beforehand with a drop of water, and its temperature was set to 65° C. 
     The flow rate of the fluid coming from the reservoir  3  was 510 ml/mn. Moreover, the position of the inkjet head  10  was adjusted so that the passage cross section of the fluid between the inkjet head  10  and its housing  23 ′ equaled 4.7 mm 2 . This adjustment was carried out by moving the cover  203  in translation relative to the vertical wall  202 . 
     For these tests, the distance between the nozzle  101  and the substrate  100  was between 2 mm and 3 mm. This distance was larger than in the tests carried out using the first embodiment of the device because movement of the inkjet head  10  in the conical part of the housing  23 ′ was limited. 
     Lastly, the orifice  21 ′ had the following geometrical characteristics: h 1 =2.5 mm; h 2 =1.5 mm; l 2 =2.5 mm and α 1 =15°. 
     In contrast, the nature of the fluid coming from the reservoir  30  differed in these tests. 
     Specifically, the test leading to the line of ink A′ was carried out with helium coming from the reservoir  30  and the test leading to the line of ink B′ was carried out using hydrogen. 
     In both cases, the width of the lines A′ and B′ was about 58 μm; however, the line A′ obtained with helium was slightly straighter than the line B′ obtained with hydrogen. 
     The lines A′ and B′ are to be compared with the line A obtained without injecting fluid, and for the same substrate temperature of 65° C. The nozzle used to obtain the lines A′ and B′ was different from that used to obtain the line A. For this reason, the voltage of the piezoelectric actuator was adjusted to V 1 =50 V in the tests used to produce the lines of ink A′ and B′, in order to obtain, in the absence of any gas flow, an ink drop velocity of 1.3 m/s, i.e. identical to the velocity of the ink drops in the test used to produce the line of ink A. 
     An improved resolution was therefore obtained, with injection of helium or hydrogen, relative to the test leading to line A. More generally, the device  1 ′ allows similar advantages to the advantages observed with the device  1  corresponding to the first embodiment of the invention described above, to be obtained. 
     The device  1 ′ of the second embodiment moreover has additional advantages over the device  1  of the first embodiment. 
     Thus, it is particularly advantageous to implement an effect whereby drops of ink delivered from the head  10  are driven by the gas delivered from the reservoir  30 . 
     Specifically, in known inkjet printing devices, it sometimes proves to be necessary to increase the velocity of the ink drops. 
     For example, if it is desired to deposit ink on irregular target surfaces containing steps that are several hundred microns, even several millimeters, in height, the inkjet head is generally placed a relatively large distance away from the target surface. Thus, the velocity of the drops of ink is increased so that the jet of ink is not deviated by external disturbances when the head  10  is located at greater distances from the substrate  100 . 
     To increase ink-drop velocity, known inkjet printing devices increase the voltage of the piezoelectric actuator in the inkjet head  10  if it is actuated by a piezoelectric actuator (or heating power if a thermal actuator is used in this head). This is accompanied by an increase in the diameter of the drops and therefore a decrease in the resolution of the deposit of ink thus obtained. 
     The device  1 ′ of the second embodiment does not have these drawbacks. 
     The Applicant has carried out tests measuring the variation in the velocity of the drops delivered from the nozzle  101  as a function of the voltage V 1  of the piezoelectric actuator, in the absence of fluid injection, on the one hand, and with injection of fluid coming from the reservoir  30 , in this case helium, on the other hand. 
     The results are shown in  FIG. 5 . 
     A first curve C 1  shows the variation in the velocity of the drops delivered from the nozzle as a function of the voltage of the piezoelectric actuator, in the absence of fluid injection. 
     A second curve C 2  shows the variation in the velocity of the drops delivered from the nozzle as a function of the voltage of the piezoelectric actuator, with injection of helium at a flow rate of 515 ml/mn. Moreover, the position of the inkjet head  10  was adjusted so that the passage cross section of the fluid between the inkjet head  10  and its housing  23 ′ was equal to 4.7 mm 2 . 
     A third curve C 3  shows the variation in the velocity of the drops delivered from the nozzle as a function of the voltage of the piezoelectric actuator, with injection of helium at a flow rate of 1100 ml/min. The position of the inkjet head was identical to that used for the tests resulting in curves C 1  and C 2 . 
     The other test conditions were identical and as follows. 
     The ink consisted only of the solvent, namely ethylene glycol. This had no influence on the velocity of the drops of ink delivered from the nozzle  101 . 
     The ejection nozzle used had a diameter of 80 μm and said nozzle was heated to a temperature of 47° C. 
     A line was formed by depositing drops in succession every 50 μm. 
     The nozzle was moved relative to the substrate at a speed of 450 μm/s. 
     The substrate  100  used had a contact angle of 40°, measured beforehand with a drop of water, and its temperature was set to 65° C. 
     For these tests, the distance between the nozzle  101  and the substrate  100  was between 2 mm and 3 mm. This distance was larger than in the tests carried out using the first embodiment of the device because the movement of the inkjet head  10  in the conical part of the housing  23 ′ was limited. 
     As may be seen by comparing the various curves C 1  to C 3  the variation was substantially linear. In contrast, for a given voltage V 1 , it will be noted that increasing the flow rate of helium effectively allowed the velocity of the drops to be increased. 
     This characterizes the driving effect whereby the drops of ink are driven by the helium flow. 
     The tests presented above are only examples illustrating the advantages associated with the invention. In particular, the test conditions detailed are provided in order to allow the results obtained with the device  1 , |″ according to the invention to be compared with a reference (absence of gas injection) under the same conditions, without however defining limiting setpoints for the operation of this device according to the invention. 
     The gas delivered from the reservoir may comprise an additive allowing the contact angle between the ink deposited on the substrate  100  and this substrate to be modified. For this purpose, the additive must be tailored to the substrate in question. For example, the additive may be hexadecanethiol for a substrate made of gold or comprising a superficial layer made of gold. 
     Thus, the contact properties between the ink and the substrate are modified. More precisely, the resolution of the deposit of ink obtained increases when the contact angle between the ink and the substrate increases. 
     The gas may also comprise an additive the function of which is to modify the properties of the particles contained in the ink after it has been deposited on the target surface and the solvent has evaporated. 
     The advantage of adding such an additive is explained below using an example. 
     With known devices, it is possible to deposit silver (or copper) nanoparticles on a surface using an ink containing silver (or copper) nanoparticles suspended in a solvent in order to produce, for example, a conductive line. Silver and copper oxidize in air. They can be protected from this oxidation by functionalizing them with a thiol. With these known devices, two operations must be carried out in succession. In a first operation the ink is deposited on the substrate, and in a second operation the nanoparticles contained in the ink are functionalized, after evaporation of the solvent. 
     In the context of the invention, adding an additive such as a thiol to the gas coming from the reservoir  30  allows a result of the same nature to be obtained in a single operation. 
     The process is thus much simpler to implement. 
     The embodiments of the invention presented above are given by way of example. Other variants may be envisioned. 
     In particular, the embodiments presented above comprise only one outlet orifice  21 ,  21 ′ around the inkjet head  10 . However, it could be envisioned to provide a plurality of outlet orifices around the head. 
     In particular, a plurality of inkjet heads, with one or a plurality of orifices could also be envisioned. 
     Finally, the device  1 , |″ according to the invention provides, by injecting a suitable gas into the volume located between the supporting member  20 ,  20 ′ and the target surface  100 , many advantages relative to known devices. 
     One advantage is that it is possible to print ink on cooler target surfaces i.e. on target surfaces at lower temperatures. For example, the results shown in  FIG. 2  demonstrate a temperature saving of 25° C. to 30° C. for similar or even better resolution, with injection of a suitable gas. 
     It is thus possible to print on substrates made of polymers that cannot withstand high temperatures, while maintaining the resolution of the deposit obtained. 
     It is also possible to print materials, diluted in the solvent of the ink, that cannot withstand high temperatures, such as inks comprising biological compounds. 
     Moreover, this substrate temperature saving limits the cost of manufacturing and using the device. 
     In particular, in the field of nanotechnologies or microtechnologies, manufacture of the substrate carrier is made easier and the precision of its alignment is increased because thermal expansion of the latter is limited. 
     In addition, the lifetime of surface treatments liable to be produced on the substrate is increased. Specifically, when it is desired to deposit ink on an area smaller than the diameter of a drop, a hydrophobic region is defined around this area by photolithography and the hydrophobic zone is functionalized, for example with octadecyltrichlorosilane if the substrate is made of silicon. The deposited drops are then confined to the area inside the hydrophobic zone. However, the lifetime of this hydrophobic treatment is highly dependent on the operating temperature of the substrate. The higher the temperature of the substrate, the shorter the lifetime of the treatment. 
     Another advantage relates to the increase in resolution of the deposit thus obtained. 
     Specifically, the device  1 , V allows the resolution of a line of ink deposited on a target surface to be substantially increased relative to known devices. The reader may refer, for example, to the results shown in  FIG. 2 . 
     Moreover, it is possible to choose nozzles having larger diameters than known nozzles, in order to prevent problems with blockages, without decreasing resolution. 
     In addition, in the particular case of the device |′, the effect whereby the drops of ink are driven, generated by the velocity of the gas delivered from the reservoir  30 , makes it possible to decrease the voltage of the piezoelectric actuator and/or to obtain smaller drops for higher drop velocities and/or to work with larger distances between the supporting member  20 ′ and the target surface  100 , without decreasing resolution. 
     In particular, this makes it possible to print ink on target surfaces comprising geometric patterns with relatively large heights. This is for example the case if it is desired to produce a conductive track between a holder and an electronic chip. 
     The use of such inks, having high boiling points, decreases the risk of blockage of the nozzles during phases in which the inkjet printing device is stopped and restarted. 
     Working under an atmosphere saturated with such a gas, such as helium or hydrogen, moreover isolates the ink from external environmental conditions and in particular from the moisture contained in ambient air. Thus, the reproducibility of the conditions under which ink is deposited on the target surface is improved. 
     Lastly, it should be noted that the tests presented above were carried out with either helium or hydrogen. The gases have a very low molar mass and the inventors consider them to be particularly advantageous. 
     However, the use of other gases, such as neon, fluorine, methane, ethane and even nitrogen (N 2 ) could be envisioned.