JP2004174849A - Recording method of inkjet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording method of an inkjet head which can hold a good printing quality even for the first gradation by making a drop stably hit which is the first to hit a recording medium without damping a discharge velocity and a discharge volume in the case of carrying out gradation recording by a multi-drop system. <P>SOLUTION: The inkjet head of the multi-drop system which carries out recording on the recording medium by sequentially discharging one or a plurality of ink drops from nozzles in accordance with gradations forms the first gradation by two drops of a first drop D1 and a second drop D2, and forms one pixel by (n+1) drops. For example, in the case of expressing one pixel in 8 gradations including 0, the second gradation is formed by three drops, and the seventh gradation is formed by eight drops. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a recording method of a multi-drop type ink jet head that sequentially discharges one or a plurality of ink droplets from a nozzle according to a gradation to record on a recording medium.
[0002]
[Prior art]
The ink jet recording method is a recording method in which ink is ejected and landed directly on a recording medium.This recording method is generally classified into a continuous method and an on-demand method according to a method of forming an ink droplet and a method of generating an ejection. You. The on-demand method is roughly classified into a bubble jet method and a piezo method according to the discharge generating means.
[0003]
As an energy generating means for generating energy for ejecting the ink, there are an energy generating means for heating a liquid by an electrothermal converting element having a heating resistor, and a means using an electromechanical converting element such as a piezo element. Here, a method of outputting a gradation by an ink jet recording apparatus includes a dither method in which one pixel of an image signal is made to correspond to one pixel of a binary recording, and this is binarized by a determined threshold value to express a gradation. Is formed on the recording medium at the same location to form one pixel, and a gradation is obtained according to the number of the landed droplets. Dithering involves a reduction in image resolution. On the other hand, the multi-drop method is excellent in that high-gradation printing can be performed by selecting an ink jet head having small droplets.
[0004]
However, in the multi-drop method, depending on a driving method for ejecting ink, only the first drop is a droplet whose ejection speed is low from the beginning, or the first drop is affected by air resistance because the droplet is small. The ejection speed decreases, and the first gradation formed by the first drop becomes unstable at the time of landing on the recording medium, and may be shifted from the landing position, resulting in deterioration of print quality.
[0005]
[Problems to be solved by the invention]
For example, when one pixel (dot) is formed by seven drops in the multi-drop method, the ejection drive voltage waveform is a voltage waveform as shown in FIG. 5, and the number of gradations is 1 drop to 7 drops and 0 (white). 8 gradations. For example, as shown in FIG. 6, in an ink jet head including an ink pressure chamber 1, an orifice plate 2, a nozzle 3, and a piezo element which is an electromechanical transducer, one pixel of ink is supplied from a nozzle 3 to a recording medium 4 by a multi-drop method. As a driving method for ejecting ink on the upper side, there is a method of applying a driving waveform shown in FIG. In FIG. 7, t1, t2, and t3 indicate driving waveforms of the first gradation, and t4, t5, and t6 indicate driving waveforms of the second gradation.
[0006]
That is, in the first drop, at t1, the piezo is deformed by applying a negative voltage, the volume of the ink pressure chamber 2 is increased, and the ink is filled. Next, at t2 and t3, the piezo is deformed so as to reduce the volume of the ink pressure chamber 2 at once, and the first drop of the ink droplet 5 is ejected as shown in FIG. Similarly, by applying a negative voltage at t4, the piezo is deformed and the volume of the ink pressure chamber 2 is increased, and at t5 and t6, the piezo is deformed so that the volume of the ink pressure chamber 2 is reduced at a stretch, and the piezo is deformed as shown in FIG. The ink droplet 6 of the second drop is ejected as shown in FIG.
[0007]
In the case of performing seven-drop ejection, this is repeated six times. However, it was found that the ejection speed and the ejection volume were significantly different between the first drop and the second drop. FIG. 8 shows, by way of example, the relationship between the ejection speed and the number of drops. There is a difference in the ejection speed between the first drop and the second to seventh drops. In this example, it can be seen that the ejection speed of the first drop is about 5 m / sec, and the ejection speed is lower than that after the second drop. In addition, when the discharge volume is normally set to 6 pl per drop, the first drop is as small as about 4 pl.
[0008]
This is due to the drive waveforms of the first drop and the second drop. First, the voltage at t1 of the first drop changes from 0V to -V1, whereas the voltage at t4 of the second drop changes at a stretch from + V1 to -V1. . By increasing the ink filling energy in this way, the ejection energy is increased.
[0009]
Therefore, only the first drop has a low ejection speed, and the ejection speed is substantially constant from the second drop to the seventh drop. Since the ejection speed and the ejection volume of the first drop are reduced in this way, when only the first drop is ejected, that is, when the ink droplet lands on the recording medium to form one gradation, a positional shift occurs. Printing failure may occur. In addition, if the ejection speed is low, the speed of the ejected ink droplets is further reduced due to the air resistance during flight, so that landing on the recording medium 4 becomes unstable and the print quality deteriorates.
[0010]
Therefore, according to the present invention, when performing gradation recording by the multi-drop method, a drop which first lands on a recording medium can be stably landed on the recording medium without attenuating the ejection speed and the ejection volume. Provided is a recording method of an ink jet head which can maintain good print quality even in a tune.
[0011]
[Means for Solving the Problems]
The present invention provides a multi-drop type inkjet head that sequentially discharges one or a plurality of ink droplets from a nozzle in accordance with a gradation and records the recording on a recording medium. With (n + 1) drops (where n is a natural number of 1 or more).
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a driving waveform when one pixel is formed by a multi-drop method in an ink jet head recording apparatus. This driving waveform is for the case where one pixel is expressed by eight gradations. The eight gradations are eight gradations obtained by adding 1 to 7 gradations and 0 (white), and the first gradation is the first drop. The second gradation is formed by combining the third drop, the third gradation is formed by combining the fourth drop, and the fourth gradation is further formed by combining the fourth drop. The fifth drop is formed by combining the sixth drop, the fifth drop is formed by combining the sixth drop, the sixth drop is formed by combining the seventh drop, and the seventh drop is further formed by the eighth drop. Are synthesized.
[0013]
That is, the first gradation is formed by two droplets of the first drop and the second drop. The reason why the first gradation is made into two droplets is due to the driving waveforms of the first drop and the second drop. Since the ejection speed and the ejection volume of the first drop have become small, the ejection speed and the ejection volume have predetermined values by including the second drop.
[0014]
When the first drop and the second drop are actually observed, as shown in FIG. 2, the first drop D1 and the second drop D2 ejected from the ink pressure chamber 1 through the nozzle 3 of the orifice plate 2 are: After the ejection, before landing on the recording medium 4, the second drop D2 catches up with the first drop D1 and lands on the recording medium 4 in a united state.
[0015]
This situation will be described specifically. FIG. 3 shows the ejection drive voltage waveform of the first gradation. When the first gradation is formed by two drops, the voltage at t1 of the first drop changes from 0 V to −V1, so that the ink filling energy is small, and after the first drop is ejected, the second drop becomes , + V1 to -V1, the ink pressure chamber 2 expands at a stretch, so that the ink filling energy increases and the ejection energy increases. Therefore, the second drop catches up with the first drop, the ejection speed and the volume can be maintained at values close to the predetermined values, and the droplet can land on the recording medium 4.
[0016]
In addition, since eight drops are formed instead of the usual seven drops for expressing eight gradations, the total amount of ink becomes larger than a predetermined total ink amount. In this case, the image quality may be degraded. In order to prevent this, the total amount of ink that lands on the recording medium 4 in the case of 8 drops as shown in FIG. 4A and the case of 7 drops as shown in FIG. It is necessary to be a quantity.
[0017]
As one method, the ejection voltage was lowered so that the total ink amount was adjusted. As an example, specifically, normally, when one pixel (one dot) is formed by seven drops, if about 6.2 pl per one drop, the total ink amount in seven drops is about 4 pl + 6 × about 6.2 pl = Approximately 41.2 pl. In addition, what is about 4 pl is the ejection amount of the first drop, which is smaller than the ejection amount after the second drop.
[0018]
On the other hand, in the case of 8 drops, the total ink amount is about 4 pl + 7 × about 6.2 pl = about 47.2 pl.
Further, the relationship between the voltage and the ejection amount is reduced by about 3 pl per 1 V. Therefore, by reducing the ejection voltage by about 1.5 V in the case of 8 drops, the total ink amount becomes 47.2 pl-4.5 pl = 42.7 pl.
[0019]
As shown in FIG. 4, in the ink ejected from the nozzle 3, the droplet ejection speed and the ejection volume decrease by lowering the voltage. However, the total ink amount of 7 drops and 8 drops can be kept substantially equal.
[0020]
Therefore, when gradation is expressed by forming one pixel by the multi-drop method, by forming the first gradation with two drops and forming one pixel with n + 1 drops, the ejection speed and the ejection volume are kept constant. It becomes possible to. As a result, the ejection speed and ejection volume of the first gradation are stably landed on the recording medium 4 without attenuating, and the print quality is not impaired even at the first gradation. Further, by lowering the droplet discharge driving voltage so that the total ink amount of n drops and (n + 1) drops forming one pixel is constant, good image quality can be maintained.
[0021]
Further, printing omission can be prevented by lowering the voltage. As a cause of the print omission, it is considered that bubbles are entangled from the orifice at the nozzle tip due to the disorder of the meniscus. By lowering the voltage, the operating range of the meniscus at the time of ejection becomes smaller, so that entrainment of bubbles is less likely to occur, and as a result, printing omission can be prevented.
[0022]
【The invention's effect】
As described above, according to the present invention, when performing the gradation recording by the multi-drop method, the ejection speed and the ejection volume of the drop which first lands on the recording medium stably land on the recording medium without attenuating. As a result, good print quality can be maintained even at the first gradation.
[Brief description of the drawings]
FIG. 1 is a diagram showing driving waveforms when one pixel is formed by a multi-drop method according to an embodiment of the present invention.
FIG. 2 is a diagram showing a discharge state of a first drop and a second drop in the embodiment.
FIG. 3 is a diagram showing an ejection drive voltage waveform of a first gradation in the embodiment.
FIG. 4 is a view for explaining the total landing ink amount in the case of 8 drops and the case of 7 drops in the multi-drop method.
FIG. 5 is a diagram showing driving waveforms when one pixel is formed by a conventional 7-drop multi-drop method.
FIG. 6 is a diagram showing a discharge state of a first drop and a second drop in the related art.
FIG. 7 is a diagram showing a conventional ejection drive voltage waveform of the first and second gradations.
FIG. 8 is a graph showing the relationship between the ejection speed and the number of drops in the multi-drop method.
[Explanation of symbols]
1: Ink pressure chamber 3: Nozzle 4: Recording media D1, D2: Drop of ink ejection

Claims (2)

In a multi-drop type ink jet head that sequentially discharges one or a plurality of ink droplets from a nozzle according to a gradation to record on a recording medium,
A recording method for an ink jet head, wherein the first gradation is formed by two drops, and one pixel is formed by (n + 1) drops (n is a natural number of 1 or more). The droplet discharge driving voltage is reduced so that the total ink amount when one pixel is formed by (n + 1) drops is substantially equal to the total ink amount when one pixel is formed by n drops. The recording method for an ink jet head according to claim 1.

Images