JP2007001243A - Inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method wherein a bubble energy efficiency in a discharge direction is maintained without decreasing even in re-discharging after pause of discharging, a refilling performance is also maintained without decreasing, and a discharge speed is always constant. <P>SOLUTION: An bubble jet type inkjet recording head to generate an air bubble with heat energy, is provided with: a heating body 1 for discharging which generates a first air bubble 8 for discharging an ink droplet; and a heating body 2 for controlling a discharge pressure which is provided between the heating body 1 for discharging and an ink supply passage 5, does not communicate with the first air bubble 8, and generates a second air bubble 9 to give the first air bubble 8 a pressure in a foaming chamber direction from an ink supply chamber direction. The heating body 1 for discharging is driven in continuous discharging, and both the heating body 1 for discharging and the heating body 2 for controlling a discharge pressure are driven in re-discharging after pause of discharging. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bubble jet ink jet recording method in which bubbles are generated in ink by thermal energy.

  Ink jet recording apparatuses that discharge ink from a recording head use an electromechanical converter such as a piezo and an electrothermal converter such as a heating element as means for generating ink ejection energy provided in the recording head. There is. Among these, the bubble jet (registered trademark) type ink jet recording head that discharges ink using the thermal energy generated by the electrothermal transducer has a simple recording head structure and has a high density of ink discharging portions that discharge ink droplets. Are widely used.

  In an ink jet recording apparatus, if ink is left without being ejected, volatile components (water, alcohols) in the ink evaporate from the ejection port, and ejection failure due to ink concentration and drying becomes a problem. It was. For this reason, the current recording apparatus is provided with means for preventing ejection failure due to evaporation of volatile components in the ink (hereinafter referred to as ink evaporation).

  As a means to reduce ink evaporation during non-recording over a long period of time, a cap that covers the ejection port in a sealed state is provided to reduce ink evaporation, and negative pressure is applied to the cap just before the start of recording to suck ink. A suction recovery operation for removing the concentrated ink from the inside of the ejection port is performed.

  However, even during the recording operation, there is a nozzle that stops ejection depending on the image. When the volatile components (water, alcohols) in the ink are evaporated from the ejection port while ejection is suspended, the ink composition changes. At this time, the ink viscosity in the vicinity of the ejection port increases, and a viscosity distribution is generated in the ejection port, the foaming chamber, and the ink supply chamber. When ejection is resumed in this state, ejection failure is observed in which the ejection speed of the first few ink drops is reduced or the ejection volume is reduced. Furthermore, in the worst case, there is a possibility of non-ejection. The ejection failure that occurs after ejection suspension due to the evaporation of these inks causes image failures such as deviations in ink droplet landing positions, variations in print dot diameter, and missing dots.

  As a means for preventing the ejection failure due to ink evaporation during the recording operation, the carriage for transporting the recording head is moved out of the recording medium at a certain timing during the recording operation, and the same driving as the ejection is performed a plurality of times. There is a method called preliminary discharge that removes the thickened ink near the discharge port.

  In recent years, image quality has been rapidly improved in ink jet recording apparatuses, and ink droplets have been made smaller accordingly. In the bubble jet method, the discharge port diameter decreases as the size of the droplet decreases, and the volume of the discharge port to the foaming chamber tends to decrease. It has been found that the evaporation rate of water per unit area increases as the outlet diameter decreases.

  Further, when the volume of the ejection port is reduced, the ratio of the thickened ink to the ejected ink is increased. Therefore, as the droplet size is reduced, the time until ejection failure occurs due to ink evaporation becomes shorter and the number of preliminary ejections must be increased. However, if the number of preliminary ejections increases, the waste of ink increases. Therefore, there is a problem that the running cost is high.

  In order to solve the above problems, inventions that suppress an increase in ink viscosity due to ink evaporation from the ejection port are disclosed in Patent Documents 1 and 2 and the like. In Patent Document 1, an evaporation suppression groove is provided near the discharge port, and evaporation from the discharge port is suppressed by increasing the humidity of the atmosphere around the discharge port by moisture or alcohol vapor evaporated from the ink. In Patent Document 2, the narrowed portion where the nozzle diameter becomes the minimum is the inflection point, the nozzle diameter from the foaming chamber side toward the inflection point is tapered in the discharge direction, and the nozzle in the discharge direction is bordered by the inflection point. The diameter is tapered. The increase in ink viscosity near the discharge port can be reduced by the effect of increasing the opening area of the discharge port.

  Since these inventions can suppress an increase in ink viscosity due to ink evaporation from the discharge port, there is an effect of prolonging the time until a discharge failure occurs due to ink evaporation. However, when the ink viscosity near the ejection port increases, there is no effect of suppressing ejection failure.

  Here, the shape of bubbles generated in the ink by the discharge heating element will be described with reference to FIG.

  (A) The figure is a bubble shape at the time of continuous discharge. At this time, the ink viscosity in the discharge port, the foaming chamber, and the ink supply chamber is uniform, and thus the bubbles extend in both the discharge direction and the ink supply chamber direction. FIG. 2B shows a bubble shape when the ejection is resumed after the volatile component in the ink is evaporated from the ejection port during the ejection stop and the ink viscosity distribution is generated in the ejection port, the foaming chamber, and the ink supply chamber. At this time, the viscosity resistance on the ejection port side is high as viewed from the foaming chamber, and the viscosity resistance on the ink supply chamber side is low. Since the bubbles extend in the direction of the ink supply chamber having a low viscosity resistance while avoiding the discharge direction having a high viscosity resistance, the bubbles are smaller in the discharge direction and larger in the direction of the ink supply chamber than the bubble shape in the continuous discharge in FIG. Become. When the bubble shape is as shown in FIG. 2B, the efficiency of the bubble energy serving as the ejection force is lowered, and the ink droplet ejection speed is lowered.

As an example of an invention for improving the energy efficiency in the ejection direction of bubbles generated in the ink by the ejection heating element and improving the speed until the ink is refilled to the ejection port, that is, the refill performance, as an example, Patent Document There are three and four. In Patent Document 3, a restricting portion that restricts displacement to the movable member and the ink supply port side is formed between the heating element and the ink supply port to prevent the foaming pressure from escaping to the ink supply port side. In Patent Document 4, a movable member that is provided on the ink supply path side of the bubble generation region and moves as the bubble grows, and a restriction unit that restricts the movement range of the movable member on the ink supply path side and the discharge port side across the movable member. The discharge pressure is directed toward the discharge port.
Japanese Patent Laid-Open No. 11-005307 JP 2004-042399 A JP 2003-127399 A JP 2003-175606 A

  In Patent Documents 3 and 4, since the movable member moves each time the heating element is driven, there is a problem that the life of the recording head is short. In these inventions, the refill performance is improved as compared with the conventional invention characterized in that a movable member is provided in the flow path, but a conventional ink jet recording head in which no structure is provided in the flow path. Compared with, refill performance is poor.

  The present invention has been made in view of the above circumstances, and even when re-ejection after ejection suspension, the foam energy efficiency in the ejection direction is not lowered, and the ejection speed is not degraded without reducing the refill performance. An object of the present invention is to provide an ink jet recording method in which is always constant.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided an ejection heating element for generating ejection energy for ejecting ink droplets, and the ejection heating element is arranged to generate a first bubble in the ink. An ink jet recording head comprising: a foaming chamber; an ink supply chamber for supplying ink to the foaming chamber; an ink supply path for guiding ink to the ink supply chamber; and an ink discharge port for discharging ink droplets. An ejection pressure control heating element is provided between the ejection heating element and the ink supply path, and the ejection heating element is driven during continuous ejection, and the ejection heating element and the ejection pressure control during re-ejection after ejection suspension. It is characterized in that both of the heating elements for driving are driven.

  According to a second aspect of the present invention, in the first aspect of the invention, the foaming energy of the discharge pressure control heating element is controlled to increase as the discharge pause time increases.

  The invention according to claim 3 is characterized in that, in the invention according to claim 1, control is performed so that the foaming energy of the discharge pressure control heating element increases as the relative humidity of the discharge environment decreases.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the foaming energy of the discharge pressure control heating element is controlled by changing at least one of a drive voltage and a pulse width. Features.

  According to a fifth aspect of the present invention, in the first aspect of the present invention, the difference between the foaming start timing (hereinafter referred to as foaming timing) of bubbles generated from the discharge heating element and the discharge pressure control heating element is the discharge Control is performed by changing at least one of a difference in driving start timing (hereinafter referred to as driving timing) between the heating element and the discharge pressure controlling heating element or a driving voltage of the discharge pressure controlling heating element.

  According to the present invention, the first bubble is not communicated with the first bubble in the direction of the ink supply chamber between the discharge heating element for generating the first bubble for discharging the ink droplet and the ink supply path. Is provided with a discharge pressure control heating element that generates a second bubble that gives pressure in the direction of the foaming chamber, drives the discharge heating element during continuous discharge, and controls the discharge heat generator and discharge pressure during re-discharge after discharge suspension. Since both the heating elements for driving are driven, it is possible to prevent the energy of the first bubbles from escaping in the direction of the ink supply chamber even during re-ejection after ejection suspension, It is transmitted in the discharge direction without lowering energy efficiency. Therefore, it is possible to prevent a drop in the ink droplet discharge speed due to a decrease in energy efficiency in the bubble discharge direction, and to keep the ink droplet discharge speed constant.

  The best mode for carrying out the present invention will be described below.

  FIG. 1 is a cross-sectional view of an ink jet recording head showing the configuration of the present invention.

  Reference numeral 1 denotes an ejection heating element for generating ejection energy for ejecting ink droplets, and reference numeral 2 denotes an ejection pressure control heating element, which is a first for applying pressure to the first bubbles 8 generated from the ejection heating element 1. 2 bubbles 9 are generated. Reference numeral 7 denotes an ink discharge port, 3 denotes a discharge heating element, a foaming chamber in which a first bubble 8 is generated, and 4 denotes an ink supply chamber. The discharge pressure control heating element 2 is provided between the discharge heating element 1 and the ink supply path 5 and has a desired distance from the discharge heating element 1.

  The principle of the embodiment of the present invention will be described below.

  As described above, the volatile component in the ink evaporates from the ejection port when ejection is stopped, and the ink viscosity near the ejection port increases. At this time, an ink viscosity distribution is generated in the ejection port, the foaming chamber, and the ink supply chamber, the viscosity resistance on the ejection port side is high as viewed from the foaming chamber, and the viscosity resistance on the ink supply chamber side is low. When only the discharge heating element 1 is driven at the time of re-discharge after the discharge stop as in the case of continuous discharge, the first bubbles 8 generated from the discharge heat generating element 1 are (a) as shown in FIG. ) Compared to the bubble shape at the time of continuous discharge in the figure, the shape is small in the discharge direction with high viscosity resistance and large in the direction of the ink supply chamber with low viscosity resistance. Since the bubble growth in the ejection direction is reduced, the bubble energy efficiency that is the ejection force of the ink droplets is lowered, and thus the ink droplet ejection speed is lowered.

  In the present invention, as means for making the ink droplet ejection speed at the time of re-ejection after ejection suspension equal to the ink droplet ejection speed at the time of continuous ejection, heat for ejection pressure control is provided between the ejection heating element 1 and the ink supply path 5. The body 2 is provided, and both the discharge heating element 1 and the discharge pressure control heating element 2 are driven at the time of re-discharge after discharge stop. The pressure in the discharge direction generated when the second bubble 9 is generated by the discharge pressure control heating element 2 prevents the pressure of the first bubble 8 generated by the discharge heating element 1 from escaping in the ink supply path direction. However, the bubble energy efficiency can be improved by transmitting in the discharge direction.

  Here, in order to give the pressure to the first bubble 8 generated when the second bubble 9 is generated, it is important that the first bubble 8 and the second bubble 9 do not communicate with each other. . In the present invention, as means for preventing the first bubble 8 and the second bubble 9 from communicating with each other, the control of the foaming energy of the second bubble 9 or the difference in the foaming timing between the first bubble 8 and the second bubble 9 is used. At least one of the controls is performed.

  First, a method for controlling foaming energy will be described.

The energy E supplied to the heating element can be expressed as Pw · V ² where R is the resistance of the heating element, V is the driving voltage, and Pw is the pulse width. This supply energy E becomes thermal energy for heating the ink, and a part thereof becomes foaming energy. In order to control the foaming energy, the supply energy may be controlled. However, since the resistance R of the heating element is determined by the shape of the heating element, it is controlled by changing at least one of the driving voltage V or the pulse width Pw. When the drive voltage is increased (the pulse width is shortened) while keeping the value of Pw · V ² constant from the drive conditions in the normal recording operation, the time until the ink rises to approximately 315 ° C. at which film boiling occurs Becomes shorter.

  At this time, since the amount of ink heated by the heating element is reduced, the foaming energy is reduced and the generated bubbles are reduced. Conversely, when the drive voltage is lowered (the pulse width is lengthened), the time until the ink rises to approximately 315 ° C. at which film boiling occurs is lengthened. At this time, since the amount of ink heated by the heating element increases, the foaming energy increases, and the generated bubbles increase. However, care must be taken because the foaming timing is advanced when the drive voltage is increased, and the foaming timing is delayed when the drive voltage is decreased (FIG. 3).

If the drive voltage and pulse width are changed while keeping the value of Pw · V ² constant, the supplied energy can be kept constant, so that the heating element can be prevented from being damaged by air blown or cavitation. The invention is not limited to this, and the value of Pw · V ² may not be kept constant, and either the drive voltage V or the pulse width Pw may be changed.

Even if the drive voltage is changed while keeping the pulse width constant from the drive conditions in the normal recording operation, the same effect as when the drive voltage and pulse width are changed while keeping the value of Pw · V ² constant is obtained. can get. However, if the time for the ink to reach approximately 315 ° C. becomes longer than the pulse width, it does not foam, so the drive voltage when changing the drive voltage while keeping the pulse width constant is 0.85 times or more the drive voltage in the recording operation.

  Further, when the pulse width is changed while the driving voltage is kept constant, the foaming energy does not change because the time until the ink reaches approximately 315 ° C. does not change even if the pulse width is increased. If the pulse width is shortened, the effect as in the case of changing the drive voltage cannot be obtained, but the foaming energy is slightly reduced. However, if the pulse width is shorter than the time when the ink reaches approximately 315 ° C., foaming does not occur. Therefore, when the pulse width is changed while the drive voltage is kept constant, the pulse width is 0.8 to 1. Set to 0 times.

  In the present invention, the driving conditions of the discharge heating element 1 (drive conditions in the recording operation) are made constant, and the foaming energy of the discharge pressure control heating element 2 is controlled. The above explanation is the control of foaming energy when the shape of the discharge heating element 1 and the discharge pressure control heating element 2 are the same. When the two heating elements are different in shape, the discharge R is considered in consideration of the resistance R of the heating element. It is obvious that the foaming energy of the heating element 1 and the discharge pressure control heating element 2 may be controlled.

  Next, control of foaming timing will be described.

  The bubble growth starts at the moment when the ink reaches approximately 315 ° C. after the energy is supplied to the heating element (the heating element is driven). Therefore, the foaming timing is the time until the ink reaches approximately 315 ° C. by shifting the driving timing of the discharge heating element 1 and the discharge pressure control heating element 2 or by changing the drive voltage of the discharge pressure control heating element 2. It can be controlled by changing the time. The pressure at which the bubbles generated by the heating element push the ink outward is greatest at the moment of foaming, then decreases as the bubbles grow, and is minimal at the time of maximum foaming. Therefore, in order to apply the pressure in the direction of the foaming chamber generated when the second bubble 9 is generated to the first bubble 8, the second bubble 9 is generated between the moment when the second bubble is generated and the maximum bubble formation of the second bubble. The timing may be controlled so that one bubble is generated.

  By controlling the foaming timing, the first bubble 8 and the second bubble 9 can be prevented from communicating with each other, and the pressure applied to the first bubble 8 can also be controlled.

  In the present invention, the foaming energy is controlled by the discharge pause time and the relative humidity of the discharge environment. The relationship between the ejection pause time and the relative humidity of the ejection environment and the ink droplet ejection speed during re-ejection after ejection pause will be described with reference to FIGS.

  FIG. 4 shows the dependency of the ink droplet ejection speed upon re-ejection after ejection suspension on the ejection pause time. The longer the ejection stop time, the greater the amount of ink evaporated from the ink ejection port 7, so the ink viscosity near the ejection port increases. Therefore, the longer the ejection pause time, the smaller the expansion of the first bubbles 8 generated by the ejection heating element 1 in the ejection direction, and the greater the elongation in the direction of the ink supply path 5. Therefore, the longer the ejection suspension time, the lower the bubble energy efficiency and the slower the ink droplet ejection speed.

  FIG. 5 shows the relative humidity dependence of the ink droplet ejection speed when re-ejection after ejection suspension. The amount of evaporation per unit time increases as the relative humidity of the discharge environment decreases, and decreases as it increases. Therefore, as the relative humidity of the discharge environment is lower, the ink viscosity in the vicinity of the discharge port is increased, and the first bubble 8 generated by the discharge heating element 1 is less elongated in the discharge direction, and is directed toward the ink supply path 5. Elongation increases. Therefore, the lower the relative humidity of the discharge environment, the lower the bubble energy efficiency and the slower the ink droplet discharge speed.

  Therefore, in the present invention, the second bubble 9 becomes the first bubble 8 by increasing the foaming energy of the discharge pressure control heating element 2 as the discharge pause time is longer and the relative humidity of the discharge environment is lower. The pressure given to is increased. As a result, the ink droplet ejection speed can be kept constant regardless of the ejection pause time and the relative humidity of the ejection environment.

  The foaming energy (drive voltage, pulse width) and the drive timing of the discharge pressure control heating element 2 with respect to the discharge pause time and the relative humidity of the discharge environment are tabulated in advance, and the drive voltage and pulse width are determined using this table. It ’s fine. The evaporation rate of the ink volatile component per unit area increases as the discharge port diameter decreases, and as the nozzle plate thickness decreases, the ratio of the evaporated ink to one drop increases. Therefore, as a matter of course, the foaming energy with respect to the discharge pause time and the relative humidity of the discharge environment and the drive timing of the discharge pressure control heating element 2 differ depending on the structure of the printer head, and a table must be created for each print head structure. . The relative humidity of the discharge environment is monitored by a humidity sensor (not shown) mounted on the carriage.

  In this embodiment, a recording head having a discharge port diameter of 30 μm, a nozzle plate thickness of 60 μm, a foaming chamber height of 20 μm, and a discharge heating element size of 40 μm × 40 μm was used. The discharge pressure control heating element 2 had the same shape as the discharge heating element 1, and the distance between the centers of the two heating elements was 55 μm.

  After continuous ejection for a time sufficient for the ejection to stabilize, ejection was paused for several tens of seconds, and the ink droplets and bubbles ejected first when ejection was resumed were observed using a microscope.

  First, the discharge pressure control heating element 2 was not driven, but only the discharge heating element 1 was driven, and ink droplets and bubbles were observed in the conventional recording method. At this time, the first bubbles 8 generated by the ejection heating element 1 were larger in the ink supply path direction and smaller in the ejection direction than bubbles during continuous ejection. Further, the ink droplet ejection speed was 0.6 times that during continuous ejection.

  Next, the ejection heating element 1 and the ejection pressure control heating element 2 were driven by the recording method of the present invention, and the ink droplets and the first and second bubbles were observed. The drive timing of the discharge pressure control heating element 2 is the same as that of the discharge heating element 1. The driving voltage was set to 1.2 times the driving voltage of the discharge heating element 1, and the pulse width was set so that the supplied energy was the same as that of the discharge heating element 1.

  At this time, the first bubble 8 and the second bubble 9 generated by the discharge heating element 1 do not communicate with each other, and the first bubble 8 extends in the ink supply path direction and the discharge direction during continuous discharge. In addition, the ink droplet ejection speeds were about the same. In this way, by applying pressure in the direction of the foaming chamber to the first bubble 8 by the foaming pressure of the second bubble 9, the bubble shape at the time of re-discharge after discharge stop is made equal to the bubble shape at the time of continuous discharge, and the discharge is performed. It is possible to prevent a drop in ink droplet ejection speed during re-ejection after a pause.

  In the present embodiment, an example of energy control based on the discharge pause time is shown. At rests 0, 20, and 40 seconds, the driving voltage and the pulse width were changed while keeping the supplied energy constant, and the ink droplets and the first and second bubbles were observed. The driving timing of the discharge heating element 1 was the same as that of the discharge pressure control heating element 2, and the relative humidity of the discharge environment was 40%. The drive voltage of the discharge heating element 1 is Vu and the pulse width is Pwu. The experimental results in this example are shown in Table 1.

  In this embodiment, an example of energy control by relative humidity is shown. At a relative humidity of 100, 60, and 30% in the discharge environment, the drive voltage and pulse width were changed while keeping the supplied energy constant, and the ink droplets and the first and second bubbles were observed. The drive timing of the discharge heating element 1 was the same as that of the discharge pressure control heating element 2, and the rest time was 30 seconds. The experimental results in this example are shown in Table 2.

1 is a cross-sectional view showing an embodiment of an ink jet recording head according to the present invention. The shape of bubbles generated in the ink from the discharge heating element, (a) is the shape of bubbles during continuous discharge, and (b) is the shape of bubbles during re-discharge after discharge stop. It is a characteristic view of the drive voltage applied to the heat generating body and the foaming start time in the embodiment of the present invention. FIG. 10 is a diagram illustrating the ejection pause time dependence of the ink droplet ejection speed when a recording operation is performed by a conventional recording method. It is a figure showing the relative humidity dependence of the ink droplet ejection speed when a recording operation is performed by a conventional recording method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating element for discharge 2 Heating element for discharge pressure control 3 Foaming chamber 4 Ink supply chamber 5 Ink supply path 6 Nozzle plate 7 Ink discharge port 8 First bubble 9 Second bubble

Claims (5)

An ejection heating element that generates ejection energy for ejecting ink droplets, a foaming chamber in which the ejection heating element is arranged and generating first bubbles in the ink, and an ink for supplying ink to the foaming chamber In an inkjet recording head having a supply chamber, an ink supply path that guides ink to the ink supply chamber, and an ink discharge port that discharges ink droplets.
An ejection pressure control heating element is provided between the ejection heating element and the ink supply path, and the ejection heating element is driven during continuous ejection, and the ejection heating element and the ejection pressure during re-ejection after ejection suspension. An ink jet recording method, wherein both of the control heating elements are driven.   2. The ink jet recording method according to claim 1, wherein control is performed such that the foaming energy of the discharge pressure control heating element increases as the discharge pause time increases.   2. The ink jet recording method according to claim 1, wherein the foaming energy of the discharge pressure control heating element is controlled to increase as the relative humidity of the discharge environment decreases.   The ink jet recording method according to claim 1, wherein the foaming energy of the discharge pressure controlling heating element is controlled by changing at least one of a driving voltage and a pulse width.   The difference between the foaming start timing (hereinafter referred to as foaming timing) of bubbles generated from the discharge heating element and the discharge pressure control heating element is the drive start timing (hereinafter referred to as the discharge pressure control heating element). 2. The ink jet recording method according to claim 1, wherein control is performed by changing at least one of a difference in driving timing) and a driving voltage of the discharge pressure control heating element.

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