Liquid injection recording method

Abstract: In a liquid injection recording method, the falling time of a voltage pulse applied to electro-­ mechanical converting means for generating energy for discharging liquid droplets to a recording medium is made longer under a high temperature environment than under a room temperature environment.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an ink jet recording method and apparatus, and more particularly of the on-demand type, by means of which it is possible to accomplish harmonious expression on a recording medium by controlling a voltage pulse applied to electro-mechanical converting means. Related Background Art An ink jet recording apparatus such as an ink jet printer supplies ink to a recording head and the ink in the recording head is discharged from a discharge port on the basis of recording information, whereby flying ink droplets going to a recording medium are formed to accomplish recording. As energy converting means for discharging the ink, there is known electro-mechanical converting means such as a piezoelectric element or electro-thermal converting means such as a heat generating resistance member in an ink discharge system utilizing heat energy. Document US 4,284,996 involves a method for driving an ink jet comprising a compression chamber for the ink, the volume of which is expanded and contracted cyclewise by means of an piezo-electric transducer to achieve printing. That is, document US 4,284,996 discloses the ejection of ink droplets from an ink chamber by means of changing the volume of the ink chamber wherein the changing of the volume is achieved by means of applying a voltage to the piezo-electric transducer. Document US 3,914,772 discloses an ink type printing device which is adapted to print characters etc. on a recording paper by means of ink droplets jetting continuously from a nozzle and deflection controlling of same by means of a high voltage generator. The output of the high voltage generator is controlled in relation to temperature changes detected by means of a heat sensitive element. Post-published document EP 0,208,484 discloses a control circuit for an ink jet head wherein two voltage pulses of equal duration but different slopes are applied to the circuit. The two pulses are combined and form a signal to a particular waveform, which is applied to a piezo-electric transducer for the ejection of a droplet of ink. The present invention is directed, above all, to an ink jet recording method and apparatus using said electro-mechanical converting means. In the ink jet recording method of this type, there is adopted a method of disposing electromechanical converting means, for example, a piezo-electric element, in the circumferential wall portion of the pressure chamber, for example, of a ink jet recording head (ink jet head), applying a voltage pulse in the direction of polarization to the piezo-electric element and abruptly reducing the volume of the pressure chamber, thereby causing ink droplets for recording to be discharged. Figure 3 of the accompanying drawings shows a longitudinal cross-section of the essential portion of a recording head used in the ink jet recording method of this type, and Figure 4 of the accompanying drawings shows an enlarged longitudinal cross-section of the electro-mechanical converting means in Figure 3. In Figures 3 and 4, a plurality of tubular liquid flow paths 2 are connected in a sub-tank 1 and a cylindrical piezo-electric vibrator 3 is provided on the outer periphery of each liquid flow path, and the end of each liquid flow path is gathered up to form an ink discharge port 4, whereby the dot forming portion of the recording head is constructed. The sub-tank 1 is connected to a main tank, not shown, through an ink supply tube 5 and connected to a suction pump and a waste liquid tank, not shown, through a suction tube 6, and is designed to maintain the level of the ink 7 therein within a predetermined range. Said cylindrical piezo-electric element 3 is secured to the peripheral surface of said liquid flow path 2 by means of an adhesive agent 8. The liquid flow path is made of a relatively hard material such as glass or a metal to propagate the vibration of the piezo-electric vibrator 3 through the liquid (ink) in the liquid flow path 2, and constitutes a nozzle at the end thereof to form a discharge port for discharging recording dots (ink droplets). A filter 9 is mounted at the entrance of the liquid flow path 2 which is adjacent to the sub-tank 1 so that by providing a predetermined flow resistance, proper balance of the pressure in the direction of discharge during the discharge of ink droplets and in the opposite direction is kept to thereby adjust the discharge state of ink. During recording, when a voltage pulse is applied to the cylindrical piezo-electric vibrator 3 to cause vibration thereof, the vibration is propagated to the liquid flow path 2, whereby the pressure of the liquid (ink) in the liquid flow path 2 is changed to permit ink droplets to be discharged from the discharge port 4 and thus, dot recording is accomplished. In the ink jet recording method of this type, by varying the magnitude of the voltage of the voltage pulse applied to the piezo-electric vibrator 3 for the formation of ink droplets, the diameter of dots on a recording medium (paper or the like) can be controlled to accomplish harmonious expression. In this case, the greater is made the voltage value of the voltage pulse, the greater dot diameter can be obtained and the wider harmony range can be obtained. Now, the formation of ink droplets is subject to the influence of the environmental conditions, particularly, temperature. That is, when the ink jet recording apparatus is placed under a high temperature, the viscosity of ink becomes lower than under the normal room temperature environment and thus, the ink droplet formation conditions change. However, in the conventional ink jet recording method, if the voltage value is increased to increase the dot diameter with the viscosity of ink being reduced under a high temperature, the vibration of the meniscus surface during the discharge of ink droplets becomes vehement to cause bubbles to be produced in the liquid flow path 2 and thereby cause unstability of discharge, or cause the occurrence of the phenomenon that small-diametered ink droplets of low discharge speed are re-discharged after the discharge of original ink droplets, thereby degrading the quality of recording, and this has led to the problem that the range of variation in the voltage of the voltage pulse is limited by the state of discharge in a high temperature environment and the harmony range cannot be sufficiently widened. SUMMARY OF THE INVENTION It is an object of the invention to provide an ink jet recording method and/or apparatus which is capable of reducing disadvantages in printing caused by viscosity changes of the ink due to temperature changes. This object can be achieved by means of an ink jet recording method comprising the steps of: providing a recording head including an energy generating element which is an electromechanical converting means and is associated with a discharge port at which an ink meniscus forms, said energy generating element being capable of generating energy that discharges ink through said discharge port when a voltage pulse drives said energy generating element; driving said energy generating element using a first voltage pulse when the ambient temperature is a predetermined temperature; and driving said energy generating element using a second voltage pulse when the ambient temperature is higher than said predetermined temperature, wherein the first and second voltage pulses have different waveforms and the falling time of the second voltage pulse is longer than that of the first voltage pulse so that the second voltage pulse provides gentler restoration of the ink meniscus after ink discharge than the first voltage pulse. Furthermore, this object can be achieved by an ink jet recording apparatus comprising: a recording head having an energy generating element which is an electro-mechanical converting means and is associated with a discharge port at which an ink meniscus forms, said energy generating element being capable of generating energy that discharges ink through said discharge port; driving voltage control means for supplying a first voltage pulse to said energy generating element when the ambient temperature is a predetermined temperature and a second voltage pulse when the ambient temperature is higher than said predetermined temperature, wherein the first and second voltage pulses have different waveforms and the falling time of the second voltage pulse is longer than that of the first voltage pulse so that the second voltage pulse provides gentler restoration of the ink meniscus after ink discharge than the first voltage pulse. According to the invention, the falling time of the second voltage pulse applied to electro-mechanical converting means such as a piezo-electric vibrator under a high temperature environment for the formation of ink droplets is longer than that of the first voltage pulse applied under a room temperature environment, and therefore, even if the viscosity of ink is reduced under high temperatures, the restoration of meniscus is gentle and inconveniences such as the introduction of bubbles and the re-discharge of small-diametered ink droplets after the discharge of original ink droplets are eliminated and thus, recording of high quality and of a wide harmony range can be accomplished. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing the wave form of a voltage/pulse applied to a piezo-electric element (electro-mechanical converting means) in the method of the present invention. Figure 2 is a diagram of a circuit for driving the piezo-electric vibration of an ink jet recording head suitable for carrying out the method of the present invention. Figure 3 is a longitudinal cross-sectional view of the essential portion of a recording head used in the ink jet recording method. Figure 4 is an enlarged longitudinal cross-sectional view of the electro-mechanical converting means in Figure 3. DESCRIPTION OF THE PREFERRED EMBODIMENT The method of the present invention will hereinafter be described specifically with reference to Figure 1 and Table 1. The present invention will be described with respect to a case where a recording head of the previously described construction is used. Figure 1 illustrates the wave form of a voltage pulse applied to a piezo-electric vibrator (electro-mechanical converting means) in the present invention. In Figure 1, the solid line shows a voltage pulse applied under a room temperature environment (25°C), and the broken line shows a voltage pulse applied at 40°C which is a high temperature environment. It is to be noted that the temperatures regarded as a high temperature environment refer to temperatures higher than the standard temperature (or the room temperature). Also, the ordinate represents the voltage V and the abscissa represents time t. Under the high temperature environment, the viscosity of ink is generally lower than at the room temperature and therefore, if the same voltage pulse as that at the room temperature is applied, the vibration of meniscus will become vehement and bubbles will be introduced into the liquid flow path to make the discharge unstable, or the phenomenon that small-diametered ink droplets of low discharge speed are re-discharged after the discharge of original ink droplets will occur to readily degrade the quality of recording. So, in the method of the present invention, as shown in Figure 1, where a voltage pulse of the falling characteristic as indicated by the solid line is to be applied under the room temperature environment, when the environmental temperature rises, for example, to 40°, a voltage pulse of a long falling time as indicated by the broken line has been applied. By such a method, even when the viscosity of ink became low under the high temperature environment, the restoration of meniscus could be maintained in a gentle state and the disadvantage as noted above could be eliminated and thus, stable recording of excellent quality and of a wide harmony range could be accomplished. Table 1 shows the result of the test of the stability of ink discharge at the room temperature (25°C) and a high temperature (40°C). Table 1 shows the evaluation of the stability of discharge when the 10-90% falling time was changed from the ordinary 90 µs to long 130 µs and the 3KHz discharge speed was changed to 10 m/s - 16 m/s. In Table 1, the marks ○ show the fact that discharge continued for five minutes or longer, and the marks x show the fact that the introduction of bubbles or the phenomenon of small-diametered ink droplets of low discharge speed being re-discharged after the discharge of original ink droplets occurred. The discharge speed changed depending on the magnitude of the applied voltage, and the discharge speed has been changed from 10 m/s to 16 m/s as the applied voltage is increased. As is apparent from Table 1, even if the applied voltage has been in a voltage range (10 m/s - 16 m/s) in which discharge is stable when the falling time (10 - 90%) of the voltage pulse is 90 µs at the room temperature of 25°C, when the environmental temperature has reached 40°C, the vibration of meniscus has become more vehement due to the reduction in the viscosity of ink than at 25°C, and discharge has become unstable for a voltage of discharge speed 12 m/s or higher. In contrast, when under a high temperature environment of 40°C, the falling time (10-90%) was extended to 130 µs, discharge could be accomplished stably up to a voltage of 16 m/s, and the stability of discharge equal to that when a voltage pulse of falling time 90 µs was applied at 25°C could be obtained. It could be easily accomplished in the designing of the circuit to change the falling time of the voltage pulse in conformity with such an environmental temperature. Figure 2 shows an example of a drive circuit for applying the voltage pulse to the piezo-electric vibrator of a ink jet recording head. In Figure 2, an image signal Si is produced from a control unit, not shown, in response to image information, and the voltage value of the voltage pulse is determined by the value of VH (head voltage) in the figure. Thus, in the circuit shown, the falling time of the voltage pulse in determined by the electrostatic capacity of the piezo-electric vibrator 3 and a falling resistor R1 or R2. In the circuit shown, design has been made such that one of two kinds of falling resistors can be selected and the falling time is set by operating a change-over switch 10. The setting of this falling time is not limited to the two stages shown, but could be accomplished in a multi-stage fashion of three stages or more or in the continuous stageless fashion. The operation of the change-over switch 10 has been controlled by the detection of a temperature sensor, not shown, through a control unit, not shown. In the test of Table 1, two resistors R1 and R2 whose falling times (10-90%) are 90 µs and 130 µs, respectively, have been prepared and use has been made of the drive circuit as shown in Figure 2 designed such that the falling resistors are changed over at two stages with 35°C as the boundary, and at each temperature, the most desirable falling time has been empirically found from the stability of discharge and the ink droplet formation frequency, and as required, the number of the falling resistors has been increased and could be changed over at three or more stages or continuously in accordance with temperature. According to the ink jet recording method described above, when a high temperature environment has been encountered, the falling time of the voltage pulse applied to the piezo-electric vibrator 3 has been made longer than the falling time of the ordinary voltage pulse applied under the room temperature environment, whereby the restoration of meniscus in the discharge port has become gentle, and even if the viscosity of ink was reduced by the rise of the environmental temperature, the vibration of meniscus could be prevented from becoming vehement. It has therefore been possible to obtain a ink jet recording apparatus in which there is no introduction of bubbles in a wide voltage range and there is no small-diametered ink droplet of low discharge speed re-discharged after the discharge of original ink droplets and stable discharge of ink droplets can always be maintained and which is of wide harmony range and of high quality of printing. Also, generally, the longer is the falling time of the voltage pulse, the lower is the ink droplet formation frequency, but in the ink jet recording method according to the present invention, the falling time is lengthened only when the viscosity of ink is reduced under high temperatures and therefore, the reduction in the ink droplet formation frequency caused by the falling time being lengthened is offset by the control for increasing the ink droplet formation frequency with the reduction in the viscosity of ink, whereby stable and good ink discharge could always be maintained. As is apparent from the foregoing description, according to the present invention, there is provided a ink jet recording method and apparatus by means of which, even under a high temperature environment, it is possible to ensure ink droplet discharge as stable as that under a room temperature environment and by means of which recording of wide harmony range can be accomplished.

Claims: An ink jet recording method comprising the steps of: providing a recording head including an energy generating element ( 3 ) which is an electro-mechanical converting means and is associated with a discharge port ( 4 ) at which an ink meniscus forms, said energy generating element ( 3 ) being capable of generating energy that discharges ink ( 7 ) through said discharge port ( 4 ) when a voltage pulse drives said energy generating element ( 3 ); driving said energy generating element ( 3 ) using a first voltage pulse when the ambient temperature is a predetermined temperature; and driving said energy generating element ( 3 ) using a second voltage pulse when the ambient temperature is higher than said predetermined temperature, wherein the first and second voltage pulses have different waveforms and the falling time of the second voltage pulse is longer than that of the first voltage pulse so that the second voltage pulse provides gentler restoration of the ink meniscus after ink discharge than the first voltage pulse. An ink jet recording method according to claim 1, wherein the falling time of said voltage pulse is set to multiple steps in conformity with the ambient temperature. An ink jet recording method according to claim 1, wherein the falling time of said voltage pulse is continuously variable in conformity with the ambient temperature. An ink jet recording method according to one of the claims 1 to 3, wherein said electro-mechanical converting means is a piezoelectric element. An ink jet recording apparatus comprising: a recording head having an energy generating element ( 3 ) which is an electro-mechanical converting means and is associated with a discharge port ( 4 ) at which an ink meniscus forms, said energy generating element ( 3 ) being capable of generating energy that discharges ink ( 7 ) through said discharge port ( 4 ); driving voltage control means ( Fig. 2 ) for supplying a first voltage pulse to said energy generating element ( 3 ) when the ambient temperature is a predetermined temperature and a second voltage pulse when the ambient temperature is higher than said predetermined temperature, wherein the first and second voltage pulses have different waveforms and the falling time of the second voltage pulse is longer than that of the first voltage pulse so that the second voltage pulse provides gentler restoration of the ink meniscus after ink discharge than the first voltage pulse. An ink jet recording apparatus according to claim 5, wherein the falling time of said voltage pulse is set to multiple steps in conformity with the ambient temperature. An ink jet recording apparatus according to claim 5, wherein the falling time of said voltage pulse is continuously variable in conformity with the ambient temperature. An ink jet recording apparatus according to one of the claims 5 to 7, wherein said ambient temperature is detected by a sensor. An ink jet recording apparatus according to one of the claims 5 to 8, wherein said driving voltage control means is a driving signal generator for driving said energy generating element ( 3 ).

Inventors: HIROSAWA TOSHIAKI, SHIMODA JUNJI, TANABE SAKIKO, HIROSAWA, TOSHIAKI, SHIMODA, JUNJI, TANABE, SAKIKO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1987
Main classification: B41J2
IPC codes: B41J2