JPH0586342B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an inkjet recording device, and more particularly to an inkjet recording device that uses an electromechanical converter as an energy generator for generating energy for forming flying droplets. [Prior Art] The inkjet recording method has been attracting attention because it can record on so-called plain paper without using any special means such as fixing, and because the noise during recording is so small that it can be ignored. As one such recording method, there is a known recording method in which a mechanical displacement of the converter is applied to the recording liquid using an electromechanical converter to cause droplets to fly from an ejection orifice and perform recording. It is being The converter is usually made of ceramics containing lead zirconate titanate as a main component and subjected to polarization treatment. Here, polarization processing refers to applying a large direct current electric field to a material using a polarization signal to transform the material into a crystalline structure without macroscopic central symmetry. As a result, the material exhibits piezoelectricity and generates strain (mechanical displacement) when a voltage is applied. An inkjet recording device for achieving the recording method described above is usually filled with a recording liquid.
It is bonded to a member constituting an energy action chamber communicating with the discharge orifice using an adhesive material such as a polymeric material (for example, adhesive) or a low melting point alloy. By the way, in such a configuration, the thermal expansion coefficient of the electrical/mechanical converter itself and the thermal expansion coefficients of the members constituting the adhesive material energy action chamber are generally different, so the environmental temperature in which the device is placed, An external mechanical force may be applied to the electrical/mechanical converter depending on the temperature of the recording liquid or the like. In particular, if the device is left in a high or low environmental temperature for a long period of time, an external force is applied to the electrical/mechanical converter during that time, and external stress may remain inside the converter. As a result, the amount of mechanical displacement of the converter may be reduced. An inkjet recording device in which the amount of displacement of the electromechanical transducer is reduced has a droplet ejection performance, that is, the droplet ejection speed and the size of the ejected droplets, which reduces the print density and makes it difficult to record images. The quality of images may deteriorate or highly accurate image recording may not be possible. To give a specific example, when the apparatus constructed as described above was left in a -30°C temperature environment for one month, the droplet ejection speed decreased to about 80% of the initial ejection speed. Also, an inkjet recording device that had been left at an environmental temperature of 60°C was moved to an environmental temperature of -30°C and left there for 4 hours, and then moved to an environmental temperature of 60°C and left there for 4 hours. When 1 unit is taken as 1 unit, the ejection speed of the droplet was measured after repeating this for 6 units, that is, after applying thermal shock 12 times. As a result, in conventional inkjet recording apparatuses, the ejection speed decreased to about 65% of the initial ejection speed due to the thermal shock described above. Furthermore, when recording was performed using each device in which the droplet ejection speed was reduced, it was observed that the recording density decreased as the ejection speed decreased, and the image quality deteriorated. [Purpose] The present invention causes deterioration in the quality of recorded images.
It is an object of the present invention to provide an inkjet recording device that can prevent a decrease in the amount of mechanical displacement due to changes over time in an electromechanical converter and can record high-quality images regardless of the environment in which the device is placed. An object of the present invention is to provide an inkjet recording device that performs recording using an electromechanical converter polarized by a polarization signal to generate energy for ejecting ink. , applies a drive signal when recording an image,
This is achieved by providing a drive means for applying a repolarization signal having the same polarity as the polarization signal in order to strengthen the polarization of the converter and having a larger energy than the drive signal when an image is not recorded. [Example] The present invention will be explained using a preferred example. FIG. 1 is a schematic cross-sectional view of the recording head of the inkjet recording apparatus used in this example. 1st
The figure shows an example in which a cylindrical piezoelectric element is used as the electromechanical transducer 11 polarized by a polarization signal to generate energy for ejecting droplets from an orifice. Further, in FIG. 1, 12 is a liquid flow path forming member in which an orifice is formed (hereinafter referred to as a nozzle), 13 is an adhesive for joining the converter 11 and the nozzle 12, and 14 is the converter 11.
Balance adjustment of energy in the droplet ejection direction and energy in the liquid supply direction when driving the
Alternatively, it is a filter that prevents impurities from entering the nozzle and adjusts the flow rate of liquid supply. The recording head shown in FIG. 1 is installed with the filter 14 side of the recording head immersed in the liquid in the sub-tank 21, as shown in the schematic cross-sectional view of the area surrounding the recording head of the inkjet recording apparatus in FIG. ing. Further, 22 is a supply tube for supplying liquid into the sub-tank 21 connected to a main tank (not shown), and 23 is a suction tube for adjusting the liquid level in the sub-tank 21. FIG. 3 is a circuit diagram showing an example of a drive circuit for driving the converter 11 of the inkjet recording apparatus. In FIG. 3, 31 is a converter, 32 is a power input terminal for driving the converter 31, 33 is a pulse input changeover switch, 3
4 is a resistor for changing the voltage applied to the converter 32, and 35 is an ejection pulse trigger input terminal for inputting a pulse for ejecting droplets. What is shown in FIG. 4 is a waveform diagram showing an example of the waveform of the input pulse inputted to the electromechanical converter, where a is a trigger waveform diagram of the ejection pulse, and b is a trigger waveform diagram of the repolarization pulse. FIG. 5 is a waveform diagram showing an example of the voltage waveform of the voltage input to each electrical/mechanical converter, in which a is a voltage waveform diagram of an ejection pulse, and b is a voltage waveform diagram of a repolarization pulse. In the present invention, a repolarization signal having the same polarity as the polarization signal (here, a drive signal during image recording) is sent to the electromechanical transducer in the direction in which the electromechanical transducer is polarized at any time during non-image recording. By applying a signal of the same polarity as the inkjet recording device, the performance of the inkjet recording device is always maintained. An example of how voltage is applied to the electromechanical converter during image recording and repolarization in the present invention will be explained using FIGS. 3 to 5. Usually, the trigger input terminal 3 for the ejection pulse shown in Figure 3
A discharge signal is input to the converter 5, and a desired voltage is applied to the converter 31, thereby causing the converter 31 to undergo mechanical displacement. During repolarization, a repolarization signal is input to the repolarization pulse trigger input terminal 36. As a result, a voltage having the same polarity as that during recording is applied to the converter 31. Note that the voltage input to the converter 31 can be easily changed by changing the voltage input to the terminal 32 or the resistance 34. In this example, as a recording head configured as shown in FIG.
After bonding PZT (leadzirco-titanate) as a mechanical converter, a filter 14 was attached to the liquid inflow side of the nozzle 12. This recording head is then connected to a filter 14 as shown in FIG.
An inkjet recording device was created by immersing the inkjet side into the subtank 21. After measuring the initial ejection speed of droplets and the initial dot diameter on paper of the inkjet recording device (hereinafter abbreviated as the device) prepared as described above, it was left in a temperature environment of -30° C. for one month. Thereafter, the apparatus was returned to room temperature, and the ejection speed of the droplets and the diameter of the dots on the paper caused by the ejected droplets were measured in the same manner as when the initial ejection speed and the initial diameter of the dots on the paper were measured. next,
A means for applying the DC voltage of the present invention in a direction that strengthens the polarization of the converter was activated, and a DC power source was applied to the electromechanical converter in a direction that strengthens the polarization of the converter (repolarization pulse was applied). ) and the droplet ejection speed and dot diameter on paper were measured. The results are shown in Table 1 for the droplet ejection speed and Table 2 for the dot diameter on paper.

【table】

[Table] Note that the droplet ejection speed and dot diameter on paper are the values when a rectangular voltage of 70V is input. In addition, as a repolarization pulse, the input voltage
A rectangular voltage of 90V and a pulse width of 1 minute was input. As can be seen from Tables 1 and 2, the droplet ejection speed of the device left in a -30°C temperature environment for one month has decreased significantly compared to the initial stage, and the dot diameter on paper has decreased significantly. Similarly, the value has become significantly smaller than the initial value. When an image was actually recorded using the apparatus in this state, only an image with reduced image density was obtained, and the recording was clearly inferior to the initial image. On the contrary,
In the apparatus of the present invention to which the repolarization pulse was applied, there was almost no change in the initial droplet ejection speed and dot diameter on paper, and the recorded images were also comparable to those of the initial apparatus. As another example of the present invention, a repolarization pulse was applied while the device was left in a -30°C temperature environment and compared with the initial state. In this case as well, the recorded image was I was able to obtain something that was completely comparable to the others. The pulse width of the repolarization pulse is preferably greater than the pulse width of the ejection pulse, but in order to obtain a sufficient repolarization effect, it is more preferably 10 seconds or more, and optimally 10 seconds in consideration of the time when the device is not in use. It is best to set it to 1 minute. It is preferable to use a voltage that has the same polarity as the voltage applied when printing the repolarization pulse, and the upper limit should be set in consideration of the time during which the repolarization pulse is applied to prevent damage to the electromechanical transducer. Of course, it is set so that it does not exist. The repolarization pulse does not necessarily need to consist of one pulse, and a plurality of short pulses may be input in succession. In this case, the repolarization pulse referred to in the present invention may be considered as a collection of a plurality of short pulses. or,
It goes without saying that the voltage waveform does not have to take the shape shown in FIG. 5b. Although it is necessary that the repolarization pulse be applied when the apparatus is not recording an image, it may be applied at any time as long as the conditions are met. For example, the user of the apparatus may apply a repolarization pulse at any time during non-image recording using means such as a switch, relay, or switching circuit. Alternatively, when powering on the device,
During a droplet ejection recovery operation, if the device is equipped with an ink temperature compensation mechanism such as a heater, when the compensation mechanism is activated, a repolarization pulse may be applied for a desired time by, for example, the above-mentioned means. good. The latter case is preferable in that it always avoids erroneous operations by the user and recording of defective images. <Effects> As explained in detail above, according to the present invention, in an inkjet recording device using an electromechanical converter, stable image recording can be performed at all times regardless of the temperature environment in which the device is placed. An inkjet recording device is provided.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a recording head of an inkjet recording device, FIG. 2 is a schematic cross-sectional view of the inkjet recording device, and FIG. 3 is a circuit diagram showing an example of a drive circuit for an electromechanical converter. Fig. 4 is a waveform diagram showing an example of the waveform of the input pulse, a is a waveform diagram of the ejection pulse, b is a waveform diagram of the repolarization pulse, and Fig. 5 is an example of the waveform of the voltage input to the electromechanical converter. In the voltage waveform diagram showing a, a is a voltage waveform diagram during image recording, and b is a voltage waveform diagram during repolarization. 11...Electrical/mechanical converter (converter), 12...
...Liquid flow path forming member (nozzle), 13...Adhesive,
14...Filter, 21...Subtank, 22
... Supply tube, 23 ... Suction tube.

Claims (1)

[Scope of Claims] 1. In an inkjet recording device that performs recording using an electro-mechanical converter polarized by a polarization signal to generate energy for ejecting ink, the electro-mechanical converter includes: On the other hand, the drive means applies a drive signal during image recording, and applies a repolarization signal having the same polarity as the polarization signal and having greater energy than the drive signal and intensifying the polarization of the converter during non-image recording. An inkjet recording device characterized by: 2. The inkjet recording apparatus according to claim 1, wherein the repolarization signal has a longer signal energization time than the drive signal. 3. The inkjet recording apparatus according to claim 1, wherein the repolarization signal has a higher voltage than the drive signal. 4. The inkjet recording apparatus according to claim 1, wherein the non-image recording time is an ink ejection recovery operation. 5. The inkjet recording apparatus according to claim 1, wherein the time of non-image recording is the time of ink temperature compensation operation.