JP3127663B2 - Ink jet recording apparatus and recording method - Google Patents

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 by means of the pressure of a vapor bubble generated by the heat generated by a heater to perform recording. The present invention relates to an inkjet recording apparatus.

[0002]

2. Description of the Related Art Conventionally, as one method of performing gradation recording using thermal ink jet, gradation is represented by a distribution of dots in a dot matrix, such as a dither method. Since such a method requires a large number of nozzles at high density so that the resolution does not decrease,
There is a problem that the number of driving circuits corresponding to each increases. Therefore, as a method of expressing gradation without sacrificing resolution, an attempt has been made to change the size of the ejected ink droplet itself.

As a method of changing the amount of ink droplets, as disclosed in Japanese Utility Model Laid-Open Publication No. Sho 57-144103, the amount of ejecting ink droplets is changed in accordance with 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 ink droplet ejected. As shown in FIG. 12, even when the applied voltage is increased, the applied range of the ink droplet ejection amount is small for an applied voltage equal to or higher than a certain value because the ink droplet amount hardly changes. There is a problem that it is narrow and a sufficient gradation level cannot be obtained.

[0004] For this reason, Japanese Patent Application Laid-Open No. 55-132259 discloses a method in which a plurality of heaters are provided in one flow path and the plurality of heaters are selectively driven in accordance with a gradation signal. I have. Japanese Patent Application Laid-Open No. Sho 62-261453 discloses a method in which 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. A method is described. These methods can change the ink droplets to be ejected in a wide range.However, since a signal is applied to and driven by a plurality of heaters independently, wiring and drive circuits corresponding to the number of heaters are required. There is a problem that the size is increased and the manufacturing cost is increased.

[0005] In order to solve this problem, a method of electrically connecting a plurality of heaters in series, selecting a heater that generates bubbles by applying a voltage, and changing the amount of ink droplets ejected is also conceivable. By doing so, it is possible to suppress the increase in the number of wirings and the number of drive circuits, but a high voltage is required in order to apply sufficient energy to generate bubbles in the heater far from the electrode supplying the voltage. At this time, an excessive voltage is applied to a specific heater in the vicinity of the electrode supplying the voltage, which causes a problem that the heater is deteriorated and the life of the head is shortened.

In the halftone recording method described in Japanese Patent Application 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 image. Things. Although there is an advantage that a large number of gradation levels can be obtained, this method also requires a large number of nozzles to be arranged at a high density, and has the problems that the recording head becomes large and the drive circuit becomes complicated.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and performs sufficient gradation expression by modulating the ink droplet amount in a wide range without increasing the number of drive circuits. It is an object of the present invention to provide a thermal ink jet recording apparatus capable of performing high quality gradation recording without reducing the head life.

[0008]

According to a first aspect of the present invention, there is provided a nozzle for discharging ink, a flow path communicating with the nozzle, and an ink supply port for supplying ink to the flow path. An ink jet recording apparatus having a heater provided in the flow path and ejecting ink droplets from the nozzle by the pressure of the bubble generated by the heat generated by the heater. A plurality of heaters having different threshold values for generating bubbles are provided, and the plurality of heaters are always electrically connected in parallel.

According to a second aspect of the present invention, there is provided a nozzle for discharging ink, a flow path communicating with the nozzle, an ink supply port for supplying ink to the flow path, and A plurality of heaters having different threshold values for generating bubbles with respect to the applied energy are provided, and the plurality of heaters are electrically connected in parallel at all times, and the plurality of heaters are driven by the applied energy. In a recording method 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, an applied energy for driving the plurality of heaters is controlled in accordance with a density of an image to be recorded. It is characterized in that printing with gradation is performed by changing the amount of ejected ink droplets.

[0010]

According to the present invention, a plurality of heaters for ejecting ink droplets from the nozzles are provided in one flow path, and the threshold values for generating bubbles with respect to the applied energy of the plurality of heaters are made different from each other. Further, these heaters are always electrically connected in parallel. 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. Thereby, a heater for generating 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 always connected in parallel, gradation recording can be performed without increasing the number of drive circuits and the number of wirings.

A plurality of heaters having different thresholds for generating bubbles with respect to applied energy can be realized by changing the resistance value of the heater, the area of the heater, and the like. When the resistance value of the heater is changed, the current flowing through each heater is different, and the generated Joule heat is different. Also, even if the resistance value is the same, if the area of the heater 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 the resistance value and the area can be changed. In this way, heaters having different thresholds for generating bubbles with respect to the applied energy are electrically connected in parallel at all times, and by selecting the applied energy such as the voltage of the voltage pulse or the pulse width, the steam bubbles can be formed. Since the bubble is generated only from the heater that generates sufficient Joule heat to generate, the volume of the bubble, that is, the volume of the ejected ink droplet can be selectively changed.

Further, since the plurality of heaters are electrically connected in parallel at all times, no excessive voltage is applied to the specific heater, and no current is concentrated on the specific heater. There is no problem that the specific heater deteriorates to shorten the life of the head and that a desired gradation level cannot be obtained.

[0013]

FIG. 1 is a sectional view of a thermal ink jet head in a plane direction of a first embodiment of an ink jet recording apparatus of the present invention, FIG. 2 is a front view seen from a nozzle side, and FIG. 3 is an ink flow path of each nozzle. It is sectional drawing of a direction. FIG. 1 is a sectional view taken along line AA ′ in FIG. 3, and FIG. 2 is a sectional view taken along line BB ′. 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, 6
Is an ink flow path, 7a and 7b are heaters, 8 is a thick 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, an SiO ₂ film as a heat storage layer is formed on a polished Si substrate, and poly-Si serving as a heater is deposited thereon.
Perform patterning. Further, Al as a wiring is vapor-deposited and patterned so that heaters in the same flow path are connected in parallel with each other. In addition, a heater substrate 2 is formed by depositing polyimide, SiN _x , Ta, or the like, which serves as a protective layer for the heater and wiring, and patterning. On the other hand, an ink flow path 6, an ink chamber 3, and an ink supply port 4 are formed on another 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 adhered, and separated into one print head by dicing. At this time, the ink flow path 6 is opened, and the nozzle 5 is formed.

This thermal ink jet head has a polyimide layer 8 on the bottom surface of an ink flow path 6 communicating with a nozzle 5.
Heaters 7a and 7b are provided in a pit 9 which is a concave portion of each of the above, and each ink flow path is partitioned by a channel partition wall 10. The ink passes through the ink chamber 3 from the ink supply port 4 and is guided to each ink flow path 6. The heaters 7a and 7b are electrically connected in parallel by the common electrode 11 and the individual electrodes 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 such that the minimum energies for generating bubbles are different from each other. 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 resistance values of the two heaters are the same, by making the heating areas different, the input energy per unit area differs when the same energy is input, resulting in a difference in the maximum temperature of the heater surface. Therefore, two heaters 7
Since the minimum energy required to reach the temperature at which bubbles are generated differs between a and 7b, the heater 7a having a smaller heating area generates bubbles with smaller energy.

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

FIG. 4 is a graph showing the relationship between the applied energy and the amount of ejected ink droplets in the ink jet head of the present invention. The minimum energy for generating a bubble in the heater 7a is E1, and the minimum energy for generating a bubble in the heater 7b is E2. The two heaters
Since the applied energy required to generate bubbles differs from one another, when energy within a range smaller than the threshold value E2 is applied, bubbles are generated only from one of the heaters 7a, and ink droplets are ejected. As in the case of the conventional example described above, the dependency with the flat portion 16a is shown. When energy exceeding this threshold E2 is applied, 2
Since bubbles are generated from the two heaters 7a and 7b, the amount of ink drops temporarily increases and again has the flat portion 16b. Thus, the energy ranges 15a corresponding to the two flat portions,
By applying binary energy within 15b, 2
Two different ejection ink droplet amounts VOL1 and VOL2 can be obtained, and gradation expression can be performed.

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

The ink droplet volumes VOL1 and VOL2 are, as in the conventional example, the size of the heater and the position in the flow path, and other parameters such as the flow path width, the flow path length, and the pit depth. Determined by size. A conventional head design method can be used to determine the flow path structure for obtaining the required ink droplet amount. Therefore, the ink droplet volumes VOL1, VO
L2 can be freely set to a value required to obtain 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 a heater having a smaller energy required for generating bubbles is provided at a position closer to the nozzle. This is because the distance from the heater that first generates the bubble to the nozzle is shortened to minimize the loss due to the flow path resistance of the momentum of the ink moving due to the generated bubble when the amount of the ink droplet is small. This is because the ink drop speed is not reduced. In this way, it is possible to minimize the difference in velocity between the two heaters and the large ink droplet ejected when a bubble is generated.

FIG. 5 is a sectional view in the plane direction showing a second embodiment of the ink jet recording apparatus of the present invention. As shown in FIG. 5, a heater 7b that requires a large amount of energy to generate bubbles can 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, a bubble is first generated from a heater far from the nozzle, and the ink starts moving in the nozzle direction.
Since bubbles are sequentially generated from the heater toward the nozzles, the ink is sequentially pushed out from the back of the ink flow path, and the ejected ink droplets become large. Therefore, the difference between the amount of ink droplets when one heater ejects ink droplets and the amount of ink droplets when two heaters sequentially generate bubbles increases the difference in tone. Image can be obtained. At this time, the timing at which bubbles are generated from each heater can be adjusted by, for example, changing the voltage change at the time of driving the heaters so as to have a slope without changing the voltage stepwise.

As described above, it is possible to obtain recording heads having different characteristics depending on the arrangement of a plurality of heaters. Therefore, the arrangement of the heaters may be determined according to the application. That is, in a color printer having many image images requiring gradation expression, it is preferable to arrange the heater closer to the nozzle so that the minimum energy required to generate bubbles is smaller. As a result, the difference between the small ink droplet speed and the large ink droplet speed is reduced, the landing positions of the ink droplets are aligned, and high image quality can be obtained even in the case of halftone.
Also, in a monochrome printer that outputs a large amount of characters and the like with a single ink droplet amount and has a small gradation expression, a heater closer to the nozzle should be arranged so that the minimum energy required to generate bubbles increases. By increasing the difference in the amount and the gradation difference, a clear image can be obtained.

FIG. 6 is a plan sectional view showing a third embodiment of the ink jet recording apparatus of the present invention. In the third embodiment, as shown in FIG.
The size and the film thickness were equal, and only the resistance value of the heater was changed. More specifically, the material of the heater, poly-
The resistivity was varied by changing the impurity concentration in Si.

FIG. 7 is a graph showing the relationship between the impurity concentration in poly-Si at room temperature and the volume resistivity of poly-Si. 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 is used as a method for imparting impurities, and the impurity concentration is changed by changing the time of implantation (ion implantation) in the two heater regions, and the resistance is changed by changing the resistivity. Was.

In FIG. 6, for example, the impurity concentration of the heater 7a can be made higher than that of the heater 7b, the resistivity can be made small, and the resistance value can be made small. 2
Since the two heaters are electrically connected in parallel,
The same voltage is applied, but the heater 7a having a small resistance value
The current flows more in 7b than in 7b. The heater 7a has a smaller minimum voltage or pulse width to reach the energy required to generate a bubble, and it is possible to select a heater in which a bubble is generated by a voltage and a pulse width as in the first embodiment. And the amount of ink drops can be changed.

Also in this embodiment, since two heaters are connected in parallel, no excessive voltage is applied to a specific heater. Further, by selecting a voltage and a pulse width for generating a bubble, it is only necessary to adopt a configuration having a boundary which can be switched so that a bubble is generated from only one heater or both heaters. The difference between the resistance values of the two heaters does not need to be large. Therefore, since the current does not concentrate on the specific heater, the problem that the specific heater is deteriorated, the head life is shortened, and the desired gradation level cannot be obtained as in the first embodiment. Does not happen.

FIG. 8 is a plan sectional view showing a fourth embodiment of the ink jet recording apparatus of the present invention. In this embodiment, the resistance value is changed by changing the shape of the heater. In FIG. 6, the length of the heater having the same volume resistivity is changed, the heater 7a is shorter than the heater 7b, and the resistance value is reduced. Since the two heaters are electrically connected in parallel, the same voltage is applied, but a larger current flows through the heater 7a having a smaller resistance than the heater 7b. The minimum voltage or pulse width that reaches the energy required to generate a bubble is
The value a is smaller, and a heater in which bubbles are generated can be selected according to the voltage and pulse width as in the first embodiment, and the amount of ink droplets can be changed. Also in the case of this embodiment, as in the third embodiment, the change in the resistance value does not need to be large, so that the specific heater does not deteriorate.

In FIG. 8, the common electrode 11 extends on the nozzle side in the nozzle arrangement direction. By arranging the common electrode 11 in this manner, the common electrode 11 can be connected to all 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 flow channel direction, it is also possible to arrange them in parallel with the flow channel direction. Also in the case of such a configuration, each heater is formed by changing the minimum energy required to generate bubbles as in the first to fourth embodiments. Thus, by controlling the voltage, the pulse width, and the like, the heater can be selected, and the amount of ink can be changed. Also in this embodiment, the common electrode 11 is connected to all the heaters.

As a method of connecting the heater, not only the above-mentioned method but also, for example, a print head corresponding to a higher density pitch can be manufactured by using a multilayer wiring.

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

The present invention can be applied not only to the above-described side shooter type print head but also to a roof shooter type print head. FIG.
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,
1 to 3 are denoted by the same reference numerals, and description thereof will be omitted. 21 is a nozzle plate and 22 is a thick resin layer. The nozzle plate 21 has an opening serving as the nozzle 5. Heaters 7a and 7b are provided below the nozzle 5. The space between the heater substrate 2 and the nozzle plate 21 forms an ink flow path. Around the nozzles 5, a thick resin layer 2
2 are arranged to separate between adjacent nozzles.

Also in this embodiment, the heaters 7a, 7
b is configured so that the minimum energies for generating bubbles are different from each other. As described above, for example, by changing the voltage value and the pulse width, bubbles can be generated from only one heater or both heaters. When a bubble is generated from only one of the heaters, a small amount of ink is 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 nozzles 5. Thus, a gradation image can be recorded.

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

In each of the above embodiments, the case where the number of heaters arranged in one ink channel and electrically connected in parallel is two has been described. However, the number of heaters is not limited to two.
By arranging three or more, a larger number of gradations can be obtained.

[0039]

As is apparent from the above description, according to the present invention, a plurality of heaters having different thresholds for generating bubbles with respect to applied energy are provided in one flow path. A plurality of heaters are always electrically connected in parallel, and the voltage pulse width of the applied voltage pulse,
By controlling the heater driven by at least one of the currents to control the amount of ink droplets, high-quality gradation expression can be performed. At this time, even if many heaters are connected in parallel to increase the number of gradations that can be expressed,
Since a plurality of heaters are driven by a common drive circuit, the number of drive circuits does not increase. Further, the amount of ink droplets to be ejected can be set in a wide range depending on the shape, number, and flow path shape of the heater. Furthermore, since an excessive voltage or current does not concentrate on a specific heater, there is an effect that the heater is not deteriorated and the life of the head is not shortened.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of a thermal inkjet head in a first embodiment of an inkjet recording apparatus of the present invention.

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

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

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

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

FIG. 6 is a sectional view of a thermal ink jet head in a plane direction in a third embodiment of the ink jet 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 sectional view of a thermal ink jet head in a plane direction in a fourth embodiment of the ink jet recording apparatus of the present invention.

FIG. 9 is a sectional view of a thermal ink jet head in a plane direction in a fifth embodiment of the ink jet 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 a relationship between a voltage value applied to a heater and an amount of ejected ink droplets.

[Explanation of symbols]

1 channel board, 2 heater board, 3 ink chamber,
Reference Signs List 4 ink supply port, 5 nozzle, 6 ink flow path, 7 heater, 8 thick resin layer, 9 pit, 10 channel partition, 11 common electrode, 12 individual electrode, 13 ink droplet, 14 recording paper, 21 nozzle plate, 22 Thick film resin layer.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-8395 (JP, A) JP-A-1-235652 (JP, A) JP-A-63-160853 (JP, A) JP-A-3-3 240545 (JP, A) JP-A-62-201255 (JP, A) JP-A-3-146349 (JP, A) JP-A-5-261925 (JP, A) JP-A-5-261924 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/05 B41J 2/175 B41J 2/205

Claims (2)

(57) [Claims] A nozzle for discharging 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 bubble generated by the heat generated by the heater, a plurality of heaters having different thresholds for generating bubbles with respect to applied energy in one flow path are provided. An ink jet recording apparatus, wherein the plurality of heaters are electrically connected in parallel at all times. 2. A nozzle for discharging ink, a flow path communicating with the nozzle, an ink supply port for supplying ink to the flow path, and an ink supply port provided in the flow path. A plurality of heaters having different thresholds for generating bubbles, wherein the plurality of heaters are electrically connected in parallel at all times, and the plurality of heaters are driven by applied energy and generated by the heater heat generation. In a recording method in an ink jet recording apparatus that ejects ink droplets from the nozzles by the pressure of a bubble, the amount of ink droplets ejected from the nozzles is controlled by controlling applied energy for driving the plurality of heaters according to the density of an image to be recorded. A recording method in an ink jet recording apparatus, wherein the recording is performed by changing gradation.