Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/17—Ink jet characterised by ink handling
  • B41J2/18—Ink recirculation systems
  • B41J2/185—Ink-collectors; Ink-catchers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/07—Ink jet characterised by jet control
  • B41J2/125—Sensors, e.g. deflection sensors

Definitions

• the invention relates firstly to a device for capturing a jet of liquid, capable of being used in a continuous ink jet print head.
• the ink is pressurized in the tank 2 upstream of an ejection nozzle. At the outlet of the nozzle, there is emission of a continuous jet 1.
• This jet is first divided into drops by a member 3 controlled by a fractionation signal. Simultaneously the drops separating from the continuous jet are electrically charged under the effect of the variable electric field established between the charging electrodes 4 and the liquid. They then pass through an electric deflection field 11, generated between two electrodes 5 or deflection plates to be deflected as a function of the individual charge of each drop.
• the ink drops are either recovered in the gutter 7, or deposited on a support 6.
• the liquid recovered in a gutter 7 flows into an umbilicus 8 leading to a recovery circuit 10 comprising a suction pump, which returns the recycled ink in the pipe 9 leading to the reservoir 2. It also relates to a process the aim of which is to recover these drops under the best conditions, that is to say:
• a first important problem associated with the recovery of the jet of drops is the difficulty of separating the liquid from gases such as entrained ambient air and the vapor of solvents.
• the impact of a drop in liquid causes gas in the wake of the drop inside the liquid.
• the bottom of the recovery gutter 7 is occupied by a liquid cluttered with small bubbles, which is aggravated by the predisposition of foaming inks. It is not permissible to recover liquid that has too much gas to recycle it.
• a plausible process, exploited for example in patent JP-A-58 96561, consists in leaving the recovered liquid to settle, but this is conceivable only in large gutters, which presents for the inks risks of drying and solidification and requires maintaining the system in a fixed orientation.
• FIG. 2 illustrates a gutter for recovering the ink unused for printing according to the art, produced using an elbow pipe 21, 22 and 25.
• Another important problem, correlated to the previous one, which one encounters when one wants to recover the unused ink properly consists in regulating the flow rate of the suction and recycling pump of the ink without sucking in excess gas.
• the patent JP-A-58 96561 already cited describes a controlled system for recovering ink not used for printing.
• the gutter is placed on the same carriage as the ink emission device.
• the detection of the ink level using the electrical conduction in the ink between two electrodes makes it possible to modify the pumping rate of the ink from the gutter and thus to adjust the level of ink resting at the bottom of the gutter.
• This system uses gravity to separate the liquid and the gas, which is disadvantageous, the dimensions of the gutter are important, the air-ink contact is important and the ink may solidify in the gutter if it is quick-drying . Furthermore, the dimensions of the gutter do not allow the head to operate in different orientations, in particular head upside down.
• US Pat. No. 4,890,119 attempts to improve the conditions for recovering the drops by a specially shaped gutter.
• the drops are collected on various orientations and flow into a bottom tank of the gutter with little entrained air; the recovery exploits gravity, which reduces the evaporation of the solvent from the ink and gives an inexpensive recovery system.
• the flow rate of the gutter which is not controlled, must be defined to avoid clogging in ink of the gutter whatever the circumstances. The absorption of gas then becomes inevitable and the flow in the recovery navel which follows the gutter becomes chaotic.
• US-A-5 739 829 attempts to improve the recovery of the jet by adjusting the depression of the ink recovery tank located behind the gutter and the umbilicus.
• a pressure sensor located near the tank records pressure fluctuations.
• the navel gradually fills with ink and the pressure fluctuations decrease.
• the amplitude of the pressure fluctuations reaches a predetermined regime, the depression is increased by an arbitrary coefficient in order to avoid an overflow of the "gutter.
• the quantity of air absorbed by the gutter is reduced by decreasing the depression
• the position of the sensor very close to the reservoir, does not however make it possible to obtain information on the state of the flow at the gutter, and the duration induced between the measurement and the effect of an adjustment in the gutter.
• the present invention makes it possible to control the operating point of the flow of the ink while being much simpler than current implementations. Its purpose is to reduce the complexity of the reprocessing of the ink in the circuit and can make it possible to eliminate the recovery pump.
• a first object of the present invention is to reduce the number of mechanical and electrical components of the liquid jet recovery control function.
• a second object is to establish a liquid recovery device substantially eliminating the introduction of air into the product to be recovered, which then makes it possible to simplify the ink treatment and reduce the loss of volatile components of the ink.
• a third object is to propose methods of processing the information of a sensor supplying the parameters providing information on the point of operation of the flow of the liquid during recovery of the jet.
• a fourth object is a process aimed at reducing, from the information provided by the sensor, the level of recovery flow rate and minimizing the consumption of solvent.
• a fifth object is an adaptive recovery process depending on the type of ink (viscosity, density, type of solvent), the position of the jet (orientation and head-machine elevation), the printing rate.
• the device for recovering one or more jets of liquid comprises a gutter for receiving the jets or jets and a discharge hole, the gutter has at least one impact wall connecting directly at the evacuation hole, a liquid filling rate sensor being disposed in the evacuation hole, and means for acting on a flow of the liquid in a recovery circuit situated after the evacuation hole ensuring a servo-control of flow rate based on measurements given by the sensor.
• a gutter where the ink stays before being recovered, but a gutter arranged so as to be traversed quickly by the ink droplets and to form these droplets in a coherent flow that does not include gas.
• the ink immediately enters the evacuation hole without having lost too much of its kinetic energy of projection, and without having undergone a flow break thanks to the arrangement in direct connection of the gutter and the evacuation hole.
• the flow of ink thus remains continuous up to the discharge hole even if it changes direction with, for example, a curved impact wall.
• this double characteristic allows the drops to re-form into a coherent sheet which does not carry much gas with it. This is obtained if the impact wall makes an angle which remains less than a limit, determined by experience, with the jet of liquid.
• the maximum limit can go up to 20 ° depending on the applications and preferably 10 °.
• the evacuation hole is furnished with a sensor of its content; it will usually be an electrical resistance sensor whose length is preferably of the order of the diameter of the discharge hole: the ink is rather conductive, but the resistance of the emulsion which it forms with gases increases with the proportion of entrained gas.
• the position of the sensor very close to the gutter makes it possible both to react immediately to a deregulation of the flow consecutive to a variation in the rate of arrival of the drops and to better understand the conditions for the formation of the evacuation flow, by knowing the degree of filling of the evacuation hole at the inlet.
• This sensor may include, at its ends, a pair of electrodes housed either in the discharge hole or at the ends of the hole, in order to measure the resistance of the fluid in the hole. Later, it is described more precisely that the device can also include a physical resistance or of fluid content in the ink circuit.
• a particular arrangement comprises two electrodes housed at the inlet and outlet ends of the discharge hole, and a third housed in the discharge hole.
• the method according to the invention comprises regular measurements of a filling rate of the liquid recovery duct, and a flow control on the recovery duct to find a set filling rate; this rate advantageously corresponds to a single-phase flow.
• An advantageous variant makes it possible to detect the main flow modes of the gutter, including a continuous spectrum annular flow mode, a spectrum bubble flow mode formed by peaks of bubble frequencies, and a mode of Monophasic spectrum flow formed by a single modulation frequency peak.
• FIG. 1 illustrates a printer in general
• FIG. 2 illustrates the flow of ink in a gutter of known type
• Figures 3, 3A, 4, 4A and 4B show various embodiments of a gutter according to the invention, Figure 4B being a section along the line 4B-4B of Figure 4A," Figure 5 illustrates the transitional period of recovery control, 1 Figures 6 to 8 illustrate some phenomena used to achieve recovery control, “and Figures 9 to 12 show some electrical circuits for measuring the resistance of a vein of ink.
• the drops 30 entering the gutter 31 touch an impact wall 32 established on its internal surface with an angle of incidence ⁇ which is such that the drops
• the meniscus 40 is established, its shape varies as a function of the difference in flow rates. arrival of the collected drops and the suction pump, the extension of this variation is located approximately in a drainage hole.
• the gutter 31 of the recovery device has a section varying monotonically decreasing from the inlet to the umbilicus 39.
• the cavity 35 is established between a flat insulating support 37 and a concave recess 38 conductor which carries the oblique impact wall 32 and on which the sheet 33 is formed.
• the evacuation hole 36 can be made either in the flat support 37 or in the impact wall.
• the liquid continues to run in the discharge hole 36.
• the determination of the minimum deceleration distance of the sheet 33 is evaluated using experience for a range of inks linked to the application. An angle ⁇ of about 10 ° or less between the impact wall 32 and the direction of the drops gives good results of tablecloth flow stability.
• the angle ⁇ is determined experimentally by varying the angle formed between the jet and the impact wall. Thus, the maximum angle ⁇ ma ⁇ acceptable for an ink and a speed is determined. Then just choose ⁇ ⁇ ma ⁇ .
• the kinetic energy of the liquid allows it to easily cross the gutter 31 and even to remove a recovery pump if the return circuit to the printer is simple. Otherwise, the volume flow q of the pump is controlled as a function of the value of the resistance provided by the above-mentioned sensor.
• the discharge hole 36 can extend the axis of the funnel constituting the gutter or cut this axis by being oblique or perpendicular thereto.
• the funnel of the gutter 31 may have sections of different shape, although it is desired that the wall 32 is concave to form a channel where the drops converge to form the sheet 33.
• the cavity of the gutter 31 of FIG. 4 has the shape of a cylinder cut by a plane, that is to say a cylindrical tab.
• the evacuation hole 36 opens out inside this cavity.
• the axis of the funnel may be parallel to the direction of the drops 30 or be inclined; depending on the case ( Figures 3 and 4), all the faces of the gutter 31 or some of them only have an angle ⁇ ⁇ max suitable for recovery, which allows the recovery of several jets in the same gutter (figure 3A).
• the drops 30 of the different jets unite in respective layers 33 which merge before arriving at the evacuation hole 36.
• the removal of the ink accumulation reservoir which is traditionally shaped at bottom of the gutter and under which the drainage hole opens, here directly connected to the impact wall 32.
• the new arrangement leads to better filling of the evacuation hole, by exploiting the kinetic energy of the sheet 33, and with better recovery quality by reducing the proportion of air bubbles, thanks to the consistency of this sheet 33.
• the evaluation of the resistance Rc of the evacuation hole is essentially made along the axis of the hole, but the invention makes it possible to use other forms of electrodes 52 and 53, for example on generators other than the hole evacuation ( Figures 4A and 4B).
• the cavity 35 is merged with the evacuation hole 36.
• the sensor measures the overall dimensions of the cavity 35.
• the average value of the resistance R c is reduced as well as its fluctuations between an upper envelope e s and a lower envelope e ⁇ . .
• the sensor swallows less and less air and the flow is less and less two-phase.
• the bubbles are becoming increasingly scarce and disappear, the resistance becomes stable and single-phase flow, which corresponds to the PI point of the curve where one upper shell e s the value of the resistance R c almost joins the lower envelope ei.
• the ink profile is then defined by a meniscus (40 in FIG. 4) at the entrance to the evacuation hole 36. At most, there remain variations in resistance linked to the rate of pumping and variations in flow in the umbilicus.
• the meniscus 40 leaves the hole 36 towards the cavity 35, and the resistance R ⁇ inside the hole 36 then takes a minimum value corresponding to that which has been calculated above, this which is observed at point P2 of the curve.
• the minimum value C min result of the measurement of our device, is used to calculate from the previous formula the value of the volume resistivity p of the ink, the dimensional parameters rec »0r ec being known from construction, or deduced experimentally during measurements made beforehand using a liquid with known resistivity. It so happens that the information obtained Rci n also allows us to obtain from our sensor the resistivity of the ink used.
• the desired operating point can be defined in several ways. 1 °
• the minimum resistance R cm in of the ink is evaluated, obtained for a discharge hole 36 filled with ink completely as a function of its dimensions and of the resistivity of the ink known or measured by elsewhere.
• Figure 7 shows the evolution of the ratio ⁇ i / i as a function of the suction depression ⁇ p: for a very large depression, we are in a regime where air is mainly entrained and the amplitude variation is moderate , then a strongly two-phase turbulent regime is established when the depression is reduced, which leads to an increase in ⁇ i / i; then, the bubbles are becoming increasingly rare and the ratio ⁇ i / i decreases constantly, before reaching its minimum value when the regime without bubbles is obtained.
• a measurement of i (t) when the bubble-free regime is reached ( ⁇ i / i ⁇ O) allows us to obtain R C i n and from there R C f, the resistance value corresponding to an operating point of the device not far from the bubble-free regime.
• the servo-control method consists in reducing the depression by following the frequency of the bubbles Fb, correlated to the position of the lateral peaks; when these peaks have disappeared, the value of i (t) can be recorded to deduce the resistance R C min from it. It is important to measure the passage of bubbles appropriately by assigning a sufficient frequency to the signal Vmode. When a bubble is entrained, its speed is that of the fluid and its time transit time in the sensor can be around 2 or 3 ms for a low bubble frequency.
• the maximum bubble frequency is approximately related to the flow of incoming liquid divided by section of the hole 36 and divided by the length of the hole 36.
• the maximum frequency is of the order of a kilohertz. It follows that the frequency of the carrier V m ⁇ e can be from 5 to 10 kHz.
• a first of these consists in placing the dipole formed by the ink stream in a loop containing a voltage generator 50 and an ammeter 51 and deducing therefrom R c (represented by the resistance of the ink stream 49), what figure 9 represents, from the known voltage and the measured current.
• the electrodes 52 and 53 on either side of the resistor R c can be placed at the impact wall 32 of the gutter 31 and at the entrance to the umbilicus 39, and more generally at the ends of the evacuation hole 36.
• the ammeter 51 informs the control device of the printer 48, which regulates the suction vacuum and the suctioned flow, that is to say the flow in the recovery circuit.
• the resistance of the ink stream 49 is in series with a resistance 54, and a voltmeter 55 is placed between the common terminal between the two resistors and the ground. From the voltage of the generator 50 and the voltage measured by the voltmeter 55, a ratio is deduced making it possible to obtain R c from the known value of the resistor 54. In this design, the role of the electrodes 52 or 53 at the terminals resistor 49 can be exchanged by placing one or the other on the ground.
• FIG. 11 Another design is shown in FIG. 11, where the resistor 54 is replaced by a resistor 56 formed by a full section of ink from the navel 39, between two electrodes 57 and 58 respectively connected to the generator 50 and to the voltmeter 55.
• the fluid content resistor 56 can also be placed elsewhere in the ink circuit, in particular in the pressure circuit where there are no bubbles. This measurement then makes it possible to know the resistivity of the ink.
• the precious advantage of this embodiment is that one does not have to take into account variations or uncertainties in the resistivity of the ink.
• the voltmeter 55 disposed between the electrodes 53 and 59 makes it possible to measure the voltage at the additional electrode 59 and, from there, calculate the filling rate of the ink stream between the electrodes 52, 59 and 53 comprising in particular the meniscus 40; the measurement of the flow in the gutter thus overcomes the resistivity of the ink.
• the control device 48 is informed by the voltmeter 55 or the ammeter 51 in the previous examples; in all the variants of the invention where it exists, it is sensitive to an electrical measurement of the content of a portion of the recovery circuit just behind the gutter 31, and it regulates the depression in the recovery circuit in one of the ways mentioned above (in connection with Figures 6 to 8 in particular).

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• Ink Jet (AREA)
• Particle Formation And Scattering Control In Inkjet Printers (AREA)

Applications Claiming Priority (3)

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• 2001
  • 2001-06-12 FR FR0107659A patent/FR2825650B1/fr not_active Expired - Lifetime
• 2002
  • 2002-06-11 WO PCT/FR2002/001989 patent/WO2002100645A1/fr not_active Application Discontinuation
  • 2002-06-11 EP EP02755071A patent/EP1395435A1/de not_active Withdrawn

Non-Patent Citations (1)

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