JPH06320735A - Ink jet recording device and recording method - Google Patents

Abstract

PURPOSE:To provide a thermal ink jet recording device which modulates an ink droplet amount over a broad range to express a gradation adequately as well as performs high-quality gradation recording without an increase in the number of drive circuits and a reduction of the life of a head. CONSTITUTION:Heaters 7a, 7b having a minimum energy required for bubble generation which is different from the other, are provided in a single flow path. In addition, these heaters 7a, 7b are electrically connected side by side to a common electrode 11 and an individual electrode 12. An energy corresponding to a gradation signal for an image to be recorded is supplied to the heaters. In this case, bubbles generate only the heater which generates the bubble using a minimum energy below an applied energy level, and ink droplets 13 are ejected from a nozzle 5. Thus it is possible to change the volume of an ink droplet to be ejected selectively so that a gradation recording is made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal ink jet technique in which ink droplets are ejected from a nozzle to record by the pressure of a vapor bubble generated by heat generation of a heater, and particularly, to perform gradation recording. The present invention relates to an inkjet recording device.

[0002]

2. Description of the Related Art Conventionally, as one method of performing gradation recording by using a thermal ink jet, a gradation is expressed by a distribution of dots in a dot matrix like a dither method. In such a method, since a large number of nozzles are required at high density so that the resolution is not deteriorated,
There is a problem that the number of drive circuits corresponding to each increases. Therefore, as a method of expressing gradation without sacrificing resolution, it has been attempted to change the size of the ejected ink droplet itself.

As a method of changing the amount of ink droplets, as shown in Japanese Utility Model Laid-Open No. 57-141043, the amount of ink droplets to be ejected is changed according to the voltage value of a drive pulse applied to a heater. There is. FIG. 12 is a graph showing the relationship between the voltage value applied to the heater and the amount of ejected ink droplets. As shown in FIG. 12, even if the applied voltage increases, there is a flat area in which the ink droplet amount hardly changes for an applied voltage of a certain value or more, so the range in which the ink droplet ejection amount changes is There is a problem that it is narrow and a sufficient gradation level cannot be obtained.

For this reason, Japanese Patent Application Laid-Open No. 55-132259 discloses a method in which a plurality of heaters are provided in one channel and the plurality of heaters are selectively driven according to a gradation signal. There is. Further, in Japanese Patent Application Laid-Open No. 62-261453, a plurality of heaters are arranged in series in one flow path, a heater that generates bubbles is selected and driven, and the amount of ejected ink droplets is changed. The method is described. These methods can change the ink droplets ejected in a wide range, but since signals are independently applied to multiple heaters to drive them, wiring and drive circuits corresponding to the number of heaters are required, and There are problems such as an increase in size and an increase in manufacturing cost.

In order to solve this problem, a method of electrically connecting a plurality of heaters in series, selecting a heater that generates bubbles according to the applied voltage, and changing the amount of ink droplets to be ejected is also considered. In this way, it is possible to suppress the increase in the number of wirings and the drive circuit, but a high voltage is required in order to apply sufficient energy to the heaters far from the electrodes supplying the voltage to generate bubbles. At this time, an excessive voltage is applied to a specific heater in the vicinity of the electrode that supplies the voltage, which causes the heater to deteriorate and shortens the life of the head.

In the halftone recording method described in Japanese Patent Laid-Open No. 57-89967, a plurality of nozzles capable of forming dots having different characteristics are provided and these are selectively combined to form a halftone dot image. It is a thing. Although there is an advantage that many gradation levels can be taken, this method also has a problem that a large number of nozzles must be arranged at high density, the recording head becomes large, and the driving circuit becomes complicated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it modulates the amount of ink droplets in a wide range to perform sufficient gradation expression and does not increase the number of drive circuits. An object of the present invention is to provide a thermal ink jet recording apparatus that can perform high quality gradation recording without reducing the head life.

[0008]

The present invention is directed to a nozzle for ejecting ink, a flow path communicating with the nozzle, an ink supply port for supplying ink to the flow path, and an inside of the flow path. In an ink jet recording apparatus having a heater provided in a nozzle and ejecting an ink droplet from the nozzle by the pressure of the bubble generated by the heat generation of the heater,
It is characterized in that a plurality of heaters having different thresholds for generating bubbles with respect to applied energy are provided in one flow path, and these heaters are electrically connected in parallel to each other.

Further, a nozzle for ejecting ink,
A flow path communicating with the nozzle, an ink supply port for supplying ink to the flow path, and a plurality of heaters provided in the flow path and having different thresholds for generating bubbles in response to applied energy are provided. However, these heaters are electrically connected in parallel to each other for each flow path, and in a recording method in an inkjet recording apparatus that ejects ink droplets from the nozzles by the pressure of the bubbles generated by the heat generation of the heaters, It is characterized in that the applied energy for driving the plurality of heaters is controlled according to the density of the image to be recorded, and the amount of ink droplets ejected from the nozzle is changed to perform gradation recording.

[0010]

According to the present invention, a plurality of heaters for ejecting ink droplets from the nozzles are provided in one flow passage, and the threshold values for generating bubbles are different from each other with respect to the applied energy of the plurality of heaters. Further, the plurality of heaters are electrically connected in parallel with each other. An applied energy corresponding to a gradation signal of an image to be recorded is supplied from a common drive circuit to the plurality of heaters connected in parallel. As a result, a heater that generates a vapor bubble can be added according to the applied energy, and the volume of the bubble, that is, the volume of the ejected ink droplet can be selectively changed. Since the heaters are connected in parallel, gradation recording can be performed without increasing the number of drive circuits and wiring.

A plurality of heaters having different thresholds for generating bubbles with respect to applied energy can be realized by differentiating the resistance value of the heater and the area of the heater. When the resistance value of the heater is changed, the current flowing through each heater is different and the Joule heat generated is different. Further, even if the resistance value is the same, if the heater area is changed, the amount of heat generated per unit area changes, the temperature rise on the heater surface changes, and the threshold value for generating bubbles differs. Both resistance and area can be changed.
In this way, by connecting heaters with different thresholds for generating bubbles to the applied energy in parallel and selecting the applied energy such as the voltage of the voltage pulse or the pulse width, it is possible to generate vapor bubbles. Since bubbles are generated only from the heater that generates sufficient Joule heat, the volume of bubbles, that is, the volume of ejected ink droplets can be selectively changed.

Further, since the plurality of heaters are connected in parallel, an excessive voltage is not applied to the specific heater, and the current is not concentrated on the specific heater. Does not cause a problem that the head life is shortened and a desired gradation level cannot be obtained.

[0013]

FIG. 1 is a sectional view of a thermal ink jet head in a plane direction in a first embodiment of an ink jet recording apparatus of the present invention, FIG. 2 is a front view seen from the nozzle side, and FIG. 3 is an ink flow path of each nozzle. It is sectional drawing of a direction. A sectional view taken along the line AA 'in FIG. 3 is shown in FIG. 1, and a plane BB' is shown in FIG. In the figure, 1 is a channel substrate, 2 is a heater substrate, 3 is an ink chamber, 4 is an ink supply port, 5 is a nozzle, and 6
Is an ink flow path, 7a and 7b are heaters, 8 is a thick film resin layer, 9 is a pit, 10 is a channel partition, 11 is a common electrode, 12 is an individual electrode, 13 is an ink droplet, and 14 is a recording paper.

In this thermal ink jet head, a SiO ₂ film as a heat storage layer is formed on a polished Si substrate, and a poly-Si film serving as a heater is deposited on the SiO ₂ film.
Pattern. Further, Al to be wiring is vapor-deposited and patterned so that the heaters in the same flow path are connected in parallel with each other. Further, the heater substrate 2 is formed by depositing and patterning polyimide, SiN _x , Ta, or the like, which serves as a protective layer for the heater and the wiring. On the other hand, the ink channel 6, the ink chamber 3, and the ink supply port 4 are formed on the other polished Si substrate by anisotropic etching to form the channel substrate 1. The two heater substrates 2 and the channel substrate 1 are aligned and bonded to each other, and separated into one print head by dicing. At this time, the ink flow path 6 is opened and the nozzle 5 is formed.

In this thermal ink jet head, the polyimide layer 8 on the bottom surface of the ink flow path 6 communicating with the nozzle 5 is used.
Heaters 7a and 7b are provided in pits 9 which are recesses, and each ink flow path is partitioned by a channel partition wall 10. Ink is guided from the ink supply port 4 through the ink chamber 3 to each ink flow path 6. The heaters 7a and 7b are electrically connected in parallel by the common electrode 11 and the individual electrode 12, and are driven by one drive circuit (not shown).

The heaters provided in the ink flow path 6 and electrically connected in parallel are configured to have different minimum energies for generating bubbles. In the first embodiment, as shown in FIG. 1, the number of heaters in one flow path is two, and the areas of the two heaters are different from each other. Here, the area of the heater 7a is smaller than the area of the heater 7b. If the two heaters have the same resistance value, different heating areas cause different input energy per unit area when the same energy is input, resulting in a difference in the maximum temperature rise of the heater surface. Therefore, two heaters 7
Since the minimum energy required to reach the temperature at which bubbles occur is different between a and 7b, the heater 7a having a smaller heating area produces bubbles with smaller energy.

Since the two heaters are connected in parallel, an excessive voltage is not applied to a specific heater, and since the resistance values are the same, current does not concentrate on one heater. As in the case of connecting in series, there is no problem that the specific heater deteriorates, the head life is shortened, and the desired gradation level cannot be obtained.

FIG. 4 is a graph showing the relationship between the applied energy and the ejected ink droplet amount in the ink jet head of the present invention. Let E1 be the lowest energy that causes bubbles in the heater 7a, and E2 be the lowest energy that causes bubbles in the heater 7b. The two heaters are
Since the applied energies required to generate bubbles are different from each other, when energy in a range smaller than the threshold value E2 is applied, bubbles are generated only from one heater 7a and ink droplets are ejected, which will be described with reference to FIG. Similar to the conventional example described above, the dependence having the flat portion 16a is shown. If energy exceeding the threshold value E2 is applied, 2
Since bubbles are generated from the two heaters 7a and 7b, the amount of ink droplets once increases and has the flat portion 16b again. Thus, the energy ranges 15a corresponding to the two flat portions,
By applying binary energy in 15b,
It is possible to obtain three different ejected ink droplet amounts VOL1 and VOL2, and it is possible to perform gradation expression.

The applied energy depends on the pulse voltage, pulse width and the like. Therefore, to change the applied energy, at least one of these factors may be changed.

The ink droplet volumes VOL1 and VOL2 are the same as in the conventional example, such as the size of the heater and the position in the flow path, and other flow paths such as flow path width, flow path length, and pit depth. It depends on the size. A conventional design method for a head can be used to determine the flow channel structure for obtaining the required ink droplet amount. Therefore, the ink drop volumes VOL1, VO
L2 can be freely set to a value required for obtaining good image quality, and a sufficient gradation level can be obtained.

In this embodiment, a plurality of heaters are arranged in the direction of the flow path, and heaters that require less energy to generate bubbles are placed closer to the nozzle. This is because by shortening the distance from the heater that initially generates bubbles to the nozzles, when the amount of ink drops is small, the loss of momentum of the ink that moves due to the generated bubbles due to the flow path resistance is minimized, and ejection is performed. This is because the ink drop speed is not lowered. In this way, it is possible to minimize the difference in velocity between a large ink droplet ejected when bubbles are generated from the two heaters.

FIG. 5 is a cross-sectional view in the plane direction showing the second embodiment of the ink jet recording apparatus of the present invention. As shown in FIG. 5, the heater 7b, which requires a large amount of energy to generate bubbles, may be arranged near the nozzle. Also in this embodiment, the size of the heater is changed in order to change the energy for generating bubbles.

In this case, when energy in a range exceeding the threshold value E2 is applied, bubbles are first generated from the heater far from the nozzle, and the ink starts moving toward the nozzle,
Since bubbles are sequentially generated from the heater toward the nozzle, the ink is sequentially pushed out from the depth of the ink flow path, and the ejected ink droplet becomes large. Therefore, the difference between the ink droplet amount when the ink droplets are ejected by one heater and the ink droplet amount when the ink droplets are ejected by the two heaters in sequence increases, and the gradation difference becomes larger. You can get a large image of. At this time, the timing at which bubbles are generated from each heater can be adjusted by changing the voltage change when the heater is driven so as not to change stepwise but to have an inclination.

As described above, since the recording heads having different characteristics can be obtained by disposing the plurality of heaters, the disposition of the heaters may be determined according to the application. That is, for a color printer that has many image images that require gradation expression, it is preferable to arrange the heater so that the closer the nozzle is to the heater, the smaller the minimum energy required to generate bubbles. As a result, the difference between the small ink drop and the large ink drop velocity can be reduced, the landing positions of the ink drops can be made uniform, and high image quality can be obtained even in the halftone.
Also, for monochrome printers that output many characters and the like with a single ink drop volume and have few gradation representations, arrange the heater so that the closer the heater is to the nozzle, the greater the minimum energy required to generate bubbles. A clear image can be obtained by increasing the amount difference and increasing the gradation difference.

FIG. 6 is a sectional view in the plane direction showing a third embodiment of the ink jet recording apparatus of the present invention. In the third embodiment, as shown in FIG. 6, the shape of the two heaters,
The size and film thickness were the same, and only the resistance value of the heater was changed. More specifically, the material of the heater is poly-
The impurity concentration in Si was changed to change the resistivity.

FIG. 7 is a graph showing the relationship between the impurity concentration in poly-Si and the volume resistivity of poly-Si at room temperature. As shown in FIG. 7, when the impurity concentration in poly-Si is increased, the volume resistivity decreases.

In this embodiment, phosphorus is used as an impurity,
Ion implantation (ion implantation method) is used as a method of giving impurities, and the impurity concentration is changed by changing the implantation (ion implantation method) time in two heater regions, and the resistivity is changed to change the resistance value. It was

In FIG. 6, for example, the heater 7a can be made to have a higher impurity concentration and a lower resistivity than the heater 7b, so that the resistance value can be reduced. Two
Since the two heaters are electrically connected in parallel,
The same voltage is applied, but the heater 7a has a small resistance value.
In this case, more current flows than 7b. The minimum voltage or pulse width to reach the energy required to generate bubbles is smaller in the heater 7a, and it is possible to select the heater in which bubbles are generated by the voltage and pulse width as in the first embodiment. It is possible to change the ink drop amount.

Also in this embodiment, since the two heaters are connected in parallel, an excessive voltage is not applied to the specific heater. Further, it is sufficient to have a boundary that can be switched so that bubbles are generated from only one heater or both heaters by selecting the voltage and pulse width for generating bubbles. It is not necessary to increase the difference in resistance between the two heaters. Therefore, since the current does not concentrate on the specific heater, as in the first embodiment, the specific heater is deteriorated to shorten the life of the head and the desired gradation level cannot be obtained. It won't happen.

FIG. 8 is a sectional view in the plane direction showing a fourth embodiment of the ink jet recording apparatus of the present invention. In this embodiment, the shape of the heater is changed to change the resistance value. In FIG. 6, the length of the heater having the same volume resistivity is changed, the heater 7a is made shorter than the heater 7b, and the resistance value is made smaller. Since the two heaters are electrically connected in parallel, the same voltage is applied, but more current flows through the heater 7a having a smaller resistance value than 7b. The minimum voltage or pulse width to reach the energy required to generate bubbles is the heater 7
As a becomes smaller, a heater that generates bubbles can be selected with a voltage and a pulse width as in the first embodiment, and the ink droplet amount can be changed. In the case of this embodiment as well, as in the case of the third embodiment, the change in the resistance value does not have to be large, and therefore the specific heater does not deteriorate.

Further, in FIG. 8, the common electrode 11 is extended to the nozzle side in the nozzle arrangement direction. By disposing the common electrode 11 in this manner, the common electrode 11 can be connected to all the heaters.

FIG. 9 is a sectional view in the plane direction showing a fifth embodiment of the ink jet recording apparatus of the present invention. As shown in FIG. 9, instead of arranging a plurality of heaters in the channel direction, it is possible to dispose them in parallel to the channel direction. Even in the case of such a configuration, each heater is formed by changing the minimum energy required to generate bubbles as in the above-described first to fourth embodiments. Thus, the heater can be selected and the amount of ink can be changed by controlling the voltage, the pulse width, and the like. Also in this embodiment, the common electrode 11 is connected to all the heaters.

The heater connection method is not limited to the one described above, and for example, by using multilayer wiring, a print head corresponding to a higher density pitch can be manufactured.

As a means for making the minimum energy for generating bubbles different among a plurality of heaters, the surface condition of the heater can be made different, in addition to the above-mentioned method. Further, the resistance value can be made different by changing the film thickness and shape of the heater. Furthermore, it is needless to say that various methods can be combined, and at least one of the minimum voltage value, the pulse width, and the current at which bubbles are generated among a plurality of heaters are different from each other.

The present invention can be applied not only to the side shooter type print head as described above but also to a roof shooter type print head. Figure 1
0 is a sectional view showing a sixth embodiment of the ink jet recording apparatus of the present invention, and FIG. 11 is a plan view of the same. In the figure,
The same parts as those in FIGS. 1 to 3 are designated by the same reference numerals and the description thereof will be omitted. Reference numeral 21 is a nozzle plate, and 22 is a thick film resin layer. The nozzle plate 21 is provided with openings serving as the nozzles 5. Heaters 7a and 7b are provided below the nozzle 5. An ink flow path is between the heater substrate 2 and the nozzle plate 21. The thick resin layer 2 is formed around each nozzle 5.
2 are arranged to separate the adjacent nozzles.

Also in this embodiment, the heaters 7a, 7a
b has a different minimum energy for generating bubbles. As described above, for example, by changing the voltage value or the pulse width, it is possible to generate bubbles from only one heater or both heaters. When bubbles are generated only from one of the heaters, a small amount of ink droplets are ejected from the nozzle 5 upward in the drawing. Similarly, when bubbles are generated from both heaters, a large amount of ink droplets are ejected upward from the nozzle 5. In this way, a gradation image can be recorded.

Although the heaters are arranged in parallel in FIG. 11, the heaters may be arranged concentrically. In this case, since the position of the bubble generated on each heater is aligned with the center of the circle, the trajectory of the ink droplet is determined,
High image quality can be obtained. Further, as a means for making the minimum energy for generating bubbles different among a plurality of heaters, various means can be used as in the case of the side shooter type head. Furthermore, the method of selectively driving each heater and the method of wiring are also the same.

In each of the above-described embodiments, the case where the number of heaters arranged in one ink flow path and electrically connected in parallel is two has been described, but the number is not limited to two.
It is also possible to arrange three or more to obtain a larger number of gradations.

[0039]

As is apparent from the above description, according to the present invention, a plurality of heaters having different minimum energies for generating bubbles are provided in one flow path, and the plurality of heaters are electrically connected to each other. High-quality gradation expression is achieved by controlling the heater driven by at least one of the voltage value pulse width of the voltage pulse to be applied and the current by connecting in parallel to be able to. At this time, even if a large number of heaters are connected in parallel and the number of gradations that can be expressed is increased, the plurality of heaters are driven by a common drive circuit, and therefore the number of drive circuits does not increase. In addition, the amount of ink droplets ejected depends on the shape of the heater,
It can be set in a wide range depending on the number and the flow path shape. Further, since excessive voltage and current are not concentrated on a specific heater, there is an effect that the heater is not deteriorated and the head life is not shortened.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in a plane direction of a thermal inkjet head in a first embodiment of an inkjet recording device of the present invention.

FIG. 2 is a front view of the thermal inkjet head of FIG. 1 viewed from the nozzle side.

3 is a cross-sectional view of each nozzle of the thermal inkjet head of FIG. 1 in the ink flow path direction.

FIG. 4 is a graph showing the relationship between applied energy and the amount of ejected ink droplets in the inkjet head of the present invention.

FIG. 5 is a cross-sectional view in the plane direction of a thermal inkjet head in a second embodiment of the inkjet recording apparatus of the present invention.

FIG. 6 is a cross-sectional view in the plane direction of a thermal inkjet head in a third embodiment of the inkjet recording apparatus of the present invention.

FIG. 7 is a graph showing the relationship between the impurity concentration in poly-Si and the volume resistivity of poly-Si at room temperature.

FIG. 8 is a cross-sectional view in the plane direction of a thermal inkjet head in a fourth embodiment of the inkjet recording apparatus of the present invention.

FIG. 9 is a cross-sectional view in the plane direction of a thermal inkjet head in a fifth embodiment of the inkjet recording apparatus of the present invention.

FIG. 10 is a sectional view of a thermal inkjet head in a sixth embodiment of the inkjet recording apparatus of the present invention.

11 is a cross-sectional view of the thermal inkjet head shown in FIG. 10 in a plane direction.

FIG. 12 is a graph showing the relationship between the voltage value applied to the heater and the amount of ink droplets ejected.

[Explanation of symbols]

1 channel substrate, 2 heater substrate, 3 ink chamber,
4 ink supply ports, 5 nozzles, 6 ink flow paths, 7 heaters, 8 thick film resin layers, 9 pits, 10 channel partition walls, 11 common electrodes, 12 individual electrodes, 13 ink droplets, 14 recording paper, 21 nozzle plates, 22 Thick film resin layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location B41M 5/00 A 8808-2H B41J 3/04 103 X

Claims (2)

[Claims] 1. A nozzle for ejecting ink, a flow path communicating with the nozzle, an ink supply port for supplying ink to the flow path, and a heater provided in the flow path. In an ink jet recording apparatus that ejects ink droplets from the nozzles by the pressure of the bubbles generated by the heat generated by the heater, a plurality of heaters having different thresholds for generating bubbles with respect to the applied energy in one flow path are provided. An ink jet recording apparatus provided with these heaters electrically connected in parallel with each other. 2. A nozzle for ejecting ink, a flow path communicating with the nozzle, an ink supply port for supplying ink to the flow path, and an applied energy provided in the flow path with respect to applied energy. A plurality of heaters having different thresholds for generating bubbles are provided, and these heaters are electrically connected in parallel to each other, and ink droplets are ejected from the nozzles by the pressure of the bubbles generated by the heat generation of the heaters. In the recording method in the inkjet recording apparatus, the applied energy for driving the plurality of heaters is controlled according to the density of the image to be recorded, and the amount of ink droplets ejected from the nozzle is changed to perform gradation recording. A recording method in an inkjet recording apparatus, comprising: