FR2775625A1 - DEVICE FOR MOVING A FLUID - Google Patents

Abstract

The invention relates to a device for moving a fluid capable of being used in the field of inkjet printing. The device according to the invention comprises means for moving the fluid by means of polymers whose hydrophilic properties or hydrophobic are selectable under the action of an external constraint. Application to inkjet heads.

Description

DEVICE FOR MOVING A FLUID

  The present invention relates to a device for moving a fluid,

  device capable of being used in particular in an inkjet printer.

  In the inkjet printing technique, the major concerns are to improve the quality as well as the speed of printing. The printing technologies developed today have almost all

  as a goal to produce high quality copies as quickly as possible.

  In the case of inkjet technologies, to achieve rapid printing, the various manufacturers multiply on the surface of the heads the number of nozzles capable of ejecting drops of ink in order to print in parallel a greater number of dots on the receiver support. Nevertheless, the number of nozzles on the surface of the head is limited either because of the problems relating to heat dissipation in the methods consisting in bringing the ink to high temperature as in the technologies developed by Canon and Hewlett Packard, or because problems with dimensional instability due to vibrations caused by the use of

  piezoelectric technologies like those developed by Seiko-Epson.

  One of the technologies conventionally used for producing inkjet heads consists in bringing the ink in a channel to a high temperature for a very short time, typically 300 to 400 C. This induces a local vaporization of the ink which generates the expulsion in the form of a drop of the liquid part of

  the ink between the spray area and the surface of the inkjet head.

  This method requires thermal energy in the very volume of the jet head

  ink which must then be dissipated.

  Other techniques, for example those described in patent application WO96 / 32284, consist of bringing a fluid into contact with an annular heating element located at the periphery of the opening of a channel connecting a reservoir containing the fluid with the opening on the surface of the inkjet head. Pressure is applied to the reservoir to allow the ink to be transported through the channel and to spread over the annular heating surface of the jet head

ink.

  When the heating element of the ink jet head is brought to a temperature of about 130 C, this results in significant changes in the surface tension of the drop of ink coming into contact with the element. heating. The change in surface tension causes a reduction in the radius of curvature of the meniscus of the drop of ink, thereby allowing the drop of ink to flow freely through the channel and to form a drop of suitable size for the desired impression. Once formed, this drop is then ejected by a means which can be an electrostatic field between the ink jet head and the printing medium, for example a sheet of paper. This technique, which has the advantage of considerably lowering the temperature required for ejecting a unitary volume of ink, is therefore more suitable for the manufacture of highly integrated ink jet heads. However, although it is theoretically necessary to heat only the surface of the meniscus of the drop of ink in order to obtain the modification of the radius of curvature thereof and therefore to obtain the formation of said drop of ink, in practice it is necessary to heat the entire volume of the ink drop, which requires a much higher energy supply for the ejection of an ink drop. On the other hand, it should be noted that as the ink is heated in its volume, part of the energy supplied to obtain the drop of ink is always contained therein during ejection; this facilitates the dissipation of this energy which does not remain confined in the

inkjet head itself.

  One of the objects of the invention is to provide a fluid displacement device, for example ink, which minimizes the amount of energy to be used

  to eject a drop of this fluid.

  Such a device facilitates the ejection of a fluid from a channel and makes it possible to eject

  a fluid having a precisely determined volume.

  These objects are achieved with the present invention which relates to a device for moving a fluid, characterized in that it comprises means for moving the fluid composed of polymers whose hydrophilic or hydrophobic properties are

  selectable under the action of an external constraint.

  The invention also relates to a method for displacing a fluid, this method comprising the use of a polymer whose hydrophilic or hydrophobic properties are selectable under the action of an external stress in a

  device for moving this fluid.

  The invention also relates to a fluid jet head for printing comprising: a) at least one means for supplying fluid for printing; b) at least one channel terminated by a nozzle open to the outside; characterized in that it further comprises: c) means for displacing the fluid for printing comprising polymers whose hydrophilic or hydrophobic properties are selectable under the action

from an external constraint.

  All the embodiments which will be described later are used to displace a hydrophilic fluid. However, when the fluid to be ejected is hydrophobic, the embodiments described below are implemented using appropriate polymers. One can for example choose polymers which are in their hydrophobic state when they are not subjected to an external stress and in

  their hydrophilic state when subjected to an external stress.

  Other characteristics will appear on reading the following description, in

  reference to the drawings in which: - Figure IA represents a polymer element in a hydrophilic state on which is a drop of hydrophilic fluid; - Figure lB shows a polymer element in a hydrophobic state on which there is a drop of hydrophilic fluid; Figure 2 shows a polymer element provided with means for generating external stress; - Figure 3 shows a channel for ejecting a fluid provided with the fluid displacement means according to the invention, the polymer element being in a hydrophilic state; - Figure 4 shows a channel for ejecting a fluid provided with means for displacing the fluid according to the invention, the polymer element being in a hydrophobic state; - Figure 5A shows a portion of a fluid jet head for printing provided with fluid displacement means according to the invention, the polymer element being in a hydrophilic state; Figure 5B shows a portion of a fluid jet head for printing provided with the fluid displacement means according to the invention, the polymer element being in a hydrophobic state; - Figure 6 shows a second embodiment of a fluid jet head for printing provided with fluid displacement means according to the invention; - Figure 7 shows a third embodiment of a fluid jet head for printing provided with fluid displacement means according to the invention; and - Figure 8 shows a fourth embodiment of a fluid jet head for printing provided with fluid displacement means according

the invention.

  In general, the technique used to move a fluid 10 according to the present invention consists in using a polymer element 20 whose hydrophilic or hydrophobic properties are selectable under the action of an external stress. The polymer element 20 may be in a hydrophilic state 20a or in a hydrophobic state 20b. The principle is to have an element 20 composed of such polymers in contact with the fluid 10 that we want to move. When the polymer is in its hydrophilic state 20a, as shown in Figure 1A, the fluid 10 tends to remain in contact with the polymer element. On the other hand, when the polymer is passed into its hydrophobic state 20b, as shown in FIG. 1B, the fluid 10 tends to be repelled and thus to form a drop on the surface of the polymer element. Thus, the passage of the polymer from one state to another leads to a

displacement of the fluid.

  Depending on the choice of polymer, the external stress necessary to move it from one state to another will be determined, and therefore the means for generating the external stress. When choosing thermo-reversible polymers, i.e. polymers which, when their temperature exceeds a threshold temperature called phase transition temperature, pass from a hydrophilic state to a hydrophobic state or vice versa, the external stress will be l application of thermal energy. It is preferable to choose thermoreversible polymers which have a transition temperature

  phase between 20 and 100 C, and preferably between 30 and 70 C.

  FIG. 2 represents a polymer element 20 provided with means 30 for generating the external stress, namely in this case, thermal energy. The means 30 consist of a temperature control element, for example a heating element 31 disposed under the polymer element. The heating element is constituted for example by a thin layer of polycrystalline silicon in which a current adapted to generate a quantity of thermal energy is circulated allowing the polymer to exceed its phase transition temperature to pass from a state to another. The polymer element can then return to its initial state, its temperature having decreased by simple diffusion of heat. It is also possible to provide an additional cooling system such as for example a radiator or a

Pelletier effect device.

  The thermo-reversible polymers which are used in the present device are organic polymers such as those described in patent application WO 91/15526. These are polymers which have a hydrophilic group and a hydrophobic group, the hydrophilic group being a water-soluble ionic polymerizable vinyl monomer and the hydrophobic group comprising an acrylamide or methacrylamide monomer. For example, a poly (N-alkylacrylamide), a modified polyethylene glycol or a polysilylamine will be chosen. Preferably, a polymer which passes very quickly from one state to another will be used, for example poly (N-isopropylacrylamide). To change the polymer element 20 from its hydrophilic state to its hydrophobic state, it must exceed a phase transition temperature Tg hydrophilic / hydrophobic specific to the polymer. The poly (N-isopropylacrylamide) has a temperature Tg of around 32. When this polymer is at a temperature below 32, it is hydrophilic. When it exceeds 32, it becomes hydrophobic. In addition, it is known to modify the hydrophilic / hydrophobic phase transition temperature of a polymer by various means. One can for example increase the phase transition temperature by adding a surfactant to the fluid to be transported. This technique is described in the publication Langmuir, 1995, volume 11, No. 7, pages 2493-2495. We could for example modify the temperature of

  Tg phase transition of poly (N-isopropylacrylamide) from 32 C to 90 C.

  Electrically conductive organic polymers can be chosen, for example polymethylethiophene, which under the action of an electric current as an external stress changes from the hydrophilic state to the hydrophobic state or vice versa. The means for generating the external stress are in this case means for applying a

  electric current to the polymer element.

  Depending on the choice of polymer, other external constraints can be used such as for example, a change in pH, a change in ionic strength or even a pressure. For each polymer, a person skilled in the art who knows the constraint necessary for passing the polymer from the hydrophilic state to

  the hydrophobic state, will determine the appropriate means to generate said constraint.

  It is known that in the case of the polymers which interest us, the change

  hydrophilic / hydrophobic state causes a variation in the volume of the polymer.

  However, it is preferable to get rid of these volume variations. However, it is known to control the variations in volume of the polymers which can go from a hydrophilic state to a hydrophobic state. To this end, known techniques such as those

  described in Polymer Communications, "Synthesis of fast response, temperature-

  sensitive poly (N-isopropylacrylamide) gel "can be used.

  In the embodiments which will be described, the polymers used are

thermo-reversible polymers.

  FIGS. 3 and 4 show a channel 40 filled with a fluid 10. In order to move the fluid 10 out of the channel 40, means 20, 30 of the fluid 10 are provided along the internal wall of the channel 40, near the end 40a of the canal. The displacement means comprise a polymer element 20 whose hydrophilic or hydrophobic properties are selectable under the action of thermal energy. The polymer element 20 may be in a hydrophilic state 20a or in a hydrophobic state 20b. Said displacement means also include temperature control means which are heating means 31 of the polymer element 20. The heating means 31 are identical to those described

  in Figure 2. The polymer element 20 is covered with the heating means.

  The polymer element can then be heated to exceed a threshold temperature which is the phase transition temperature of the polymer. In the device shown in Figure 3, the polymer element 20 is shown in its hydrophilic state 20a. The fluid 10 is uniformly distributed throughout the channel 40. FIG. 4 shows the polymer element 20 in its hydrophobic state 20b. In this case, the fluid 10 which is at the height of the hydrophobic polymer element 20b tends to be repelled by this element, an empty volume 50 is thus created inside the channel 40. The volume of fluid which between the polymer element 20 and the end 40a of the channel constitutes an independent volume of fluid which is displaced out of the channel. In order to prevent the return of the fluid in the fluid supply means, the supply means can be kept under pressure by

  any means known to those skilled in the art.

  According to a preferred embodiment of the invention, the fluid to be displaced by the device according to the invention is a fluid for printing, for example a printing ink, or a thermopolymer which makes it possible to obtain a printing in three

  dimensions in stereolithography processes.

  Figures SA and 5B show a portion of a fluid jet head for printing 60 on a support 800 which comprises means 700 for supplying the fluid for printing, a channel 400 for moving the fluid 100 outward. In particular, when the fluid is ink 100, the fluid displacement device according to the invention is an ink jet head. The channel 400 ends with a nozzle 400a open to the outside. The periphery of the nozzle 400a is provided with a polymer element 200. The polymer element 200 can be in a hydrophilic state 200a or in a hydrophobic state 200b. Such an element is provided to create a drop of ink and thus facilitate the ejection of the ink 100. Preferably, the polymer element is a very thin layer. The temperature control means are heating means 310 such as those described above. Said means of

  heating 310 are provided under the polymer element 200.

  Figure 5A shows the ink jet head portion when the polymer element is in its hydrophilic state 200a. The ink supply means 700 always being kept under pressure to prevent the ink from returning to the supply means 700, the ink tends to come and stay in contact with the polymer element 200a. When the polymer element goes into its hydrophobic state 200b as shown in FIG. 5B, the ink tends to move away from the polymer element 200b. Since the ink supply means is kept under pressure, the ink cannot return to the supply means 700 and a drop of ink is formed. The ink drop 100 can then be ejected by any means known to those skilled in the art. We can for example foresee the application of a field

  electrostatic as described in patent application WO 96/32284.

  In a variant of this embodiment, provision is made to arrange the polymer element not at the periphery of the nozzle, but along the internal wall of the channel 400, near the nozzle 400a. The polymer element is preferably annular in shape. In this embodiment, it is also possible to provide an element at the periphery which facilitates the ejection of the ink. In the case where the fluid is hydrophilic,

  the element will, for example, be a hydrophobic polymer element.

  FIG. 6 shows another embodiment of the ink jet head 60 according to the invention. A first polymer element 200 is provided at the periphery of the nozzle 400a and a second polymer element 201 is provided along the internal wall of the channel 400. The polymer element 201 is preferably of annular shape. Heating means 310 and 311 are provided for heating the polymer elements 200 and 201 respectively. In this embodiment, the volume of the drop to be ejected can be determined. The polymer elements 200 and 201 are initially in a hydrophilic state. When an ink volume desired to form a drop is obtained, the polymer element 201 is heated and goes into its hydrophobic state. This volume of ink is moved out of the channel 400. The polymer element 200 is then passed into its hydrophobic state in order to facilitate the ejection of the drop of ink. Since the polymer element 201 is kept in

  its hydrophobic state, the drop of ink cannot return to channel 400.

  According to another embodiment shown in FIG. 7, the heating means, not shown, are provided for heating, not directly the polymer element, but the ink 100 in the ink supply means 700. A polymer element 200 is provided at the periphery of the nozzle 400a. To prevent the drop of ink which forms at the periphery of the nozzle 400a from spreading over the entire external surface of the ink jet head 60, the materials of the external surface of the jet head are provided ink are hydrophobic. The ink will not have so

  tendency to spread beyond the polymer element 200.

  The ink 100 is heated to a temperature T which is higher than the phase transition temperature Tg of the polymer element 200. When the ink 100 leaves

  the nozzle 400a at temperature T, it is in contact with the polymer element 200.

  The heat of the ink is transferred to the polymer element 200 which exceeds its phase transition temperature Tg. The polymer element 200 then passes into its hydrophobic state 200b. The ink wetting angle 100 becomes large, thereby creating an ink drop 100. The ink drop 100 can then be ejected in the same manner as that described in the embodiment shown in FIG. When the heating means is not activated, the ink 100 has a temperature o0 lower than the phase transition temperature of the polymer element 200 which is thus in its hydrophilic state 200a. In this case, the ink cannot form a drop on the surface of the ink jet head, and therefore there is no ejection. In addition, in order to prevent the ink jet head from becoming blocked by the ink drying at the opening of the channel, the pressure maintained in the

  supply means to return the ink to the supply means.

  Advantageously, an annular polymer element 201 is provided inside the channel 400 so as to control the ejection of ink 100. FIG. 8 shows this other embodiment. Heating means 311 such as those described in FIG. 2 are provided for heating the polymer element 201. The polymer element 201 covers the entire surface of the heating means 311, so that the entire surface of the heating element polymer 201 changes state. The phase transition temperature Tg 'of the polymers used in the polymer element 201 must be higher than the phase transition temperature Tg of the polymers used in the polymer element 200 and higher than the temperature T of the ink. When one does not want to eject ink 100, the polymer element 201 is kept in its hydrophobic state

  by bringing it to a temperature higher than Tg 'using the heating means 311.

  The ink 100 present in the channel 400 is then no longer able to flow to the surface of the ink jet head, making any ejection impossible. When it is desired to eject the ink 100, the polymer element 201 is first of all maintained in its hydrophilic state by not activating the heating means 311. The ink 100 can therefore flow freely until the ink jet head surface. The temperature T of the ink being higher than the phase transition temperature Tg of the polymer element 200, it follows that on contact with the ink, this polymer element 200 will pass from the state hydrophilic in the hydrophobic state and thus allow the formation of a drop of ink on the surface of the head. The polymer element 201 can then be brought into its hydrophobic state by activating the heating means 311 which stops the flow of ink in the channel 400 and therefore makes it possible to precisely select the volume of ink to be ejected. When the drop thus formed has been ejected, the polymer element

  which is no longer in contact with the heated ink, returns to its hydrophilic state.

  In order to be able to start the ejection cycle of an ink drop again, the heating means 311 is deactivated, which allows the polymer element 201 to return to its hydrophilic state and therefore allow the ink 100 to flow freely into the

  channel 400 to the surface of the ink jet head.

Claims (21)

  1 - Device for moving a fluid (10) characterized in that it comprises means for moving the fluid (10) composed of polymers whose hydrophilic or hydrophobic properties are selectable under the action of an external constraint. 2 - Device according to claim 1 wherein the fluid displacement means (10) comprise, on the one hand, at least one polymer element (20) whose hydrophilic or hydrophobic properties are selectable under the action of a constraint exterior, and secondly, means (30) for generating said external constraint.   3 - Device according to one of the preceding claims wherein the fluid (10) is moved in a channel (40).   4 - Device according to claim 3 wherein the polymer element (20) is   provided on the inner wall of the channel (40).   5 - Device according to claim 4 characterized in that the polymer whose hydrophilic or hydrophobic properties are selectable under the action of a   external stress is a thermo-reversible polymer.   6 - Device according to claim 5 wherein the means (30) for generating said   external constraint are means of temperature control.   7 - Device according to claim 6 wherein the temperature control means comprise a resistor (31) in contact with the element   polymer (20), said resistor being supplied by an electrical circuit.   8 - Device according to claim 4 wherein the polymer whose hydrophilic or hydrophobic properties are selectable under the action of a stress   exterior is an electrically conductive organic polymer.   9 - Device according to claim 8 wherein the means (30) for generating said   external stress are means for applying an electric current.   - Device according to one of the preceding claims, characterized in that it   further comprises: 1) at least one fluid supply means;   2) at least one fluid receiver.   11 - Fluid jet head for printing (60) comprising a) at least one means (700) for supplying fluid for printing; b) at least one channel (400) terminated by a nozzle (400a) open towards the outside; characterized in that it further comprises: 1! c) means for displacing the printing fluid (100) comprising polymers whose hydrophilic or hydrophobic properties are selectable   under the action of an external constraint.   12 - jet head for printing fluid (60) according to claim 11 wherein said means for moving the printing fluid (100) comprise, on the one hand, at least one polymer element (200) whose hydrophilic properties or hydrophobic are selectable under the action of a constraint   external, and secondly, means for generating said external stress.   13 - fluid jet head for printing (60) according to claim 12 wherein a polymer element is disposed either at the periphery of the opening of the nozzle (400a), or along the inner wall of the channel (400 ), or on the outskirts of   the opening of the nozzle (400a) and along the internal wall of the channel (400).   14 - Fluid jet head according to claim 13 wherein in the case where a polymer element is provided along the internal wall of the channel (400), an element is provided at the periphery of the nozzle (400a) in a facilitating state ejecting the fluid (100).   - fluid jet head for printing (60) according to claim 13 wherein the polymer element (201) provided along the internal wall of the channel (400) is   disposed near the opening of the nozzle (400a).   16 - Fluid jet head for printing (60) according to one of claims 11 to 15   in which the polymer whose hydrophilic or hydrophobic properties are   selectable under the action of an external constraint is a thermo-polymer reversible.   17 - head for printing fluid jet (60) according to claim 16 wherein   the means for generating the external stress are means for controlling temperature.   18 - fluid jet head for printing (60) according to claim 17 wherein the temperature control means comprise resistors supplied by an electric circuit, each polymer element being in contact with a resistance.   19 - head for printing fluid (60) according to claim 17 wherein the temperature control means are provided for controlling the temperature of the fluid for printing (100) in the supply means (700) in fluid for printing (100).   20 - head for printing fluid jet (60) according to claim 19 wherein in the case where a polymer element is provided at the periphery of the opening of the nozzle (400a) and along the inner wall of the channel (400), the temperature control means include a resistor (311) in contact with   the polymer element provided along the inner wall of the channel (400).   21 - Fluid jet head for printing (60) according to one of claims 11 to 15   wherein the polymer is an electrically conductive organic polymer. 22 - head for printing fluid jet (60) according to claim 21 wherein the means for generating the external stress are means for applying an electric current.   23 - Fluid jet head according to any one of claims 11 to 22 in which the fluid is ink.   24 - Use of a polymer whose hydrophilic or hydrophobic properties are selectable under the action of an external stress in a jet head of   fluid for printing according to one of claims 11 to 23.   - Use of a polymer whose hydrophilic or hydrophobic properties are selectable under the action of an external constraint in a   displacement of a fluid according to one of claims 1 to 10.   26 - Printing process using polymers whose hydrophilic properties or   hydrophobic are selectable under the action of an external constraint.