The present invention relates to a liquid ejection device.
A liquid ejection device is known in which the liquid inside a liquid chamber is heated by electrifying a heat element, the liquid is foamed in the liquid chamber by the film boiling thereof caused by the heating, and droplets are ejected from an ejection port by the foam energy at this time. When printing is done with such a liquid ejection device, physical effects such as the impact due to the cavitation caused when a liquid foams, contracts, and is defoamed on the area over a heat element may be brought about on the area over the heat element. In addition, when the liquid is ejected, chemical effects such that the components of the liquid thermally decompose and adhere to be fixed to and accumulated on the surface of the heat element may be brought about on the area over the heat element because the heat element is at a high temperature. For protecting the heat element from these physical and chemical effects on the heat element, a protective layer to cover the heat element is disposed on the heat element.
Here, in a heat-affected portion that is the protective layer over the heat element in the liquid ejection device, the phenomenon such that a color material, an additive, etc. which are contained in the liquid are disassembled at a molecular level by high temperature heating and are changed to low-soluble substances to physically adsorb on an upper protective layer arises. This phenomenon is referred to as “kogation.” The adsorption of low-soluble organic and/or inorganic substances on the upper protective layer as described leads to ununiform heat conduction from the heat-affected portion to the liquid, and unstable foaming.
Japanese Patent No. 6918636 discloses the technique of providing, inside a liquid chamber, a first electrode including a heat-affected portion, and a second electrode different from the first electrode, applying a voltage across the two electrodes to generate an electric field in the liquid inside the liquid chamber, and thereby leading to the repulsion of the charged particles in the liquid to suppress kogation.
However, a better-durable liquid ejection device has been demanded in recent years, so that further suppression of generation of kogation has been required. Thus, the present invention is to further suppress generation of kogation in a liquid ejection device, and to improve the durability thereof.
The present invention is a liquid ejection device comprising:
According to the present invention, generation of kogation in a liquid ejection device can be further suppressed, and the durability of the liquid ejection device can be improved.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter examples of embodiments according to the present invention will be described using drawings. It is noted that the following description does not limit the scope of the present invention.
This embodiment describes an inkjet printing apparatus (printing apparatus) in the form of circulating a liquid such as ink through a tank and a liquid ejection device, but the inkjet printing apparatus may be in any other form. For example, one may provide two tanks on the upstream and downstream sides of the liquid ejection device to draw ink from one to the other tank, whereby flow the ink in a pressure chamber without circulating the ink.
This embodiment also describes a so-called line head having a length corresponding to the width of a recording medium. The present invention can be also applied to a so-called serial liquid discharge device with which printing is done on a recording medium while the recording medium is scanned. For example, the serial liquid discharge device has the structure of installing printing element substrates for a black and a color ink, respectively, but is not limited to this. The serial liquid discharge device may be in the form of scanning a recording medium with a line head shorter than the width of the recording medium which is produced in such a way that a plurality of printing element substrates are arranged so that ejection ports thereof overlap in the direction of the ejection port array.
The structure of the liquid ejection head 3 according to this embodiment will be described.
As shown in
As shown in
The structure of the printing element substrate 10 in this embodiment will be described.
As shown in
As shown in
As shown in
Next, the flow of the liquid in the printing element substrate 10 will be described.
Description of Printing Element Substrate, and Structure of Heat-Affected Portion
In the liquid ejection head 3, the printing element substrates 10 are each formed by layering a plurality of layers on the substrate 11 formed of silicon. In this embodiment, a heat accumulation layer 132 that is formed of a thermal oxidation film, a SiO film, a SiN film, etc. is disposed on the substrate 11. A heat element 126 is disposed on the heat accumulation layer 132 at the position opposite each of the ejection ports 13. An electrode wiring layer 131 as the wiring formed of a metal material such as Al, Al—Si, and Al—Cu is connected to the heat element 126 via a tungsten plug 128. An insulating protective layer 127 is disposed on the heat element 126. The insulating protective layer 127 is provided on the top side of the heat element 126 so as to cover the heat element 126. The insulating protective layer 127 is formed of a SiO film, a SiN film, etc. The insulating protective layer 127 is requested to be thin in view of thermal efficiency of foaming, and thus, is set to have a thickness of 150 nm.
A protective layer is disposed on the insulating protective layer 127. The protective layer is made up of a lower protective layer 125, an upper protective layer 124, and an adhesive protective layer 123, and protects the surface of the heat element 126 from chemical and physical impacts following the heat generation of the heat element 126.
In this embodiment, the lower protective layer 125 is formed of tantalum (Ta), the upper protective layer 124 is formed of iridium (Ir), and the adhesive protective layer 123 is formed of tantalum (Ta). When other than iridium, the upper protective layer 124 is desirably a platinum group element such as platinum (Pt) and ruthenium (Ru).
The protective layer formed of these materials has electroconductivity. A liquid-resistant protective layer 122 for liquid resistance and improvement in adhesiveness to the ejection port formation member 12 is formed on the adhesive protective layer 123. The liquid-resistant protective layer 122 is formed of SiCN.
When the liquid is ejected, the top face of the upper protective layer 124 is in contact with the liquid and is under a severe environment such that the temperature of the liquid on the top face of the upper protective layer 124 rises instantly so that the liquid foams, and then is defoamed there to cavitate. Therefore, in this embodiment, the upper protective layer 124 formed of a highly reliable iridium material having high corrosion resistance is formed at the position corresponding to the heat element 126 and is in contact with the liquid.
In this embodiment, the structure of circulating the ink in a liquid channel such that the liquid is fed from the feeding port 17a and collected into the collection port 17b in the pressure chamber 23 is employed. That is, the liquid is fed to the pressure chamber 23 that is the first channel from the feeding port 17a that constitutes the second channel, and the liquid in the pressure chamber 23 that is the first channel is collected from the collection port 17b that constitutes the third channel. On the heat element 126, the liquid flows from the feeding port 17a (upstream side) toward the direction of the collection port 17b (downstream side) during printing.
Desirably, an ink-resistant protective film 130 formed of TiO, TaO, etc. is formed for protecting the substrate 11 and the heat accumulation layer 132 that are in the channel from the feeding port 17a (upstream side) to the collection port 17b (downstream side) from dissolving in the ink.
In the liquid ejection head 3 according to this embodiment, the kogation suppression process for suppressing kogation that accumulates on the upper protective layer 124 on the heat element 126 during printing is carried out. That is, the kogation suppression process is carried out when the heat element 126 generates heat for ejecting the liquid from the ejection port 13. Part of the upper protective layer 124 covers the surface of the heat element 126 on the first layer side (ejection port formation member 12 side), and functions as a first electrode 133 exposed to the pressure chamber 23 that is the first channel. The substrate 11 that is the second layer is provided with a second electrode 129 exposed to the pressure chamber 23 that is the first channel at a position different from the first electrode 133. The second electrode 129 is disposed on the opposite side of the heat element 126 across the collection port 17b. That is, on the plan view shown in
Formation of an electric field through the liquid leads to repulsion of particles of a pigment or the like which are charged with a negative potential in the liquid for the surface of the upper protective layer 124 on the heat element 126. Then, the abundance of the particles of a pigment or the like in the vicinity of the surface of the upper protective layer 124 which are charged with a negative potential is reduced, and whereby the kogation accumulating on the upper protective layer 124 on the heat element 126 during printing is suppressed. Kogation is the phenomenon such that a color material, an additive, etc. which are contained in a liquid are disassembled at a molecular level by high temperature heating and are changed to low-soluble substances to physically adsorb on the upper protective layer 124. Therefore, when the upper protective layer 124 is heated at a high temperature, to reduce the abundance of a color material (pigment) and an additive in the vicinity of the surface of the upper protective layer 124 on the additive heat element 126 which causes kogation leads to kogation suppression. Generation of kogation depends on the characteristics of the color material (pigment) and the additive. Therefore, preferably, the control unit 900 applies a different voltage according to the used liquid to the first electrode 133 and the second electrode 129. This optimizes the kogation suppression effect by the voltage application according to this embodiment and allows electric power consumption to be suppressed.
The distance L1 between the heat element 126 and the feeding port 17a, and the distance L2 between the heat element 126 and the collection port 17b are equal. In relation to liquid refilling after the foaming, the liquid is refilled from the feeding port 17a and the collection port 17b, and the liquid refiling time is short so that high-speed driving can be performed.
The detailed experiments by the inventor of the present invention revealed that the potential relationship between the first electrode 133, the second electrode 129, and the substrate 11 affects kogation suppression. The details of the experiments are as follows.
In these experiments, examination was made using an ink containing a solid content including a magenta pigment, wax, and latex, and being with a negative zeta potential.
In these experiments, a predetermined voltage was applied to the first electrode 133 and the second electrode 219 by the use of an external power supply. In these experiments, the voltage was applied from the outside of the liquid ejection head 3 by the use of the control unit 900 as the external power supply, as the voltage application unit, whereas a member configured to apply the voltage to the electrode 113 and the second electrode 219 may be provided in the substrate 11.
The graph of
The ejection velocity gradually reduced just after the ejection was started. When the number of ejections reached 0.5×108, the ejection velocity was found to be lower than the initial ejection velocity by approximately 2 m/s. At this time point, it was visually confirmed that much kogation accumulated on the surface of the upper protective layer 124 on the heat element 126. After the number of ejections reached 1×108, the kogation further accumulated, and the ejection velocity also reduced.
The graph of
Further, when the voltage was applied so that the potential difference between the first electrode 133 and the second electrode 129 was at least 2.5 V to form a larger electric field across the electrodes, iridium itself, which was used as the material of the first electrode 133, eluted into the ink by an electrochemical reaction. Therefore, the method of applying the voltage in which the potential of the first electrode 133 was at 0 V as a conventional method could not lead to formation of a sufficient electric field across the electrodes, and continuous ejection of the ink led to accumulation of kogation on the surface of the upper protective layer 124 on the heat element 126, and the reduction in ejection velocity.
The graph of
The kogation suppression process of example 1 was such that the substrate 11 was used to be with the ground potential, and the voltage was applied so that the first electrode 133 of the upper protective layer 124 was at a negative potential (−2 V) by the use of the external power supply that allowed a negative voltage to be applied. The second electrode 129 was set to be a floating electrode.
The ink was ejected under the same ejection conditions as comparative examples 1 and 2. No large reduction in ejection velocity was found, and the reduction in velocity fell within 0.5 m/s even when the number of ejections exceeded 5×108.
In addition, when the surface of the upper protective layer 124 on the heat element 126 was observed with an optical microscope at this time point, kogation as found in comparative examples 1 and 2 did not adhere thereto.
The graph of
The kogation suppression process of example 2 was such that the substrate 11 was used to be with the ground potential, and the voltage was applied so that the first electrode 133 of the upper protective layer was at a negative potential by the use of the external power supply that allowed a negative voltage to be applied. In addition, the substrate 11 was used to be with the ground potential, and a positive voltage was applied to the second electrode 129 by the use of another external power supply. At this time, the potential of the first electrode 133 was set to be −1 V, the potential of the second electrode 129 was set to be 1 V, and the potential difference between the first electrode 133 and the second electrode 129 was 2 V.
Compared to example 1, the potential of the first electrode 133 was changed from −2 V to −1 V. At this time, the voltage applied across the heat element 126 and the first electrode 133 became lower, and whereby the film thickness of the insulating protective layer 127 could be designed thinner, which allowed the liquid to be ejected with lower energy.
The ink was ejected under the same ejection conditions as comparative examples 1 and 2. No large reduction in ejection velocity was found, and the reduction in velocity fell within 0.5 m/s as in example 1 even when the number of ejections exceeded 5×108.
In addition, when the surface of the upper protective layer 124 on the heat element 126 was observed with an optical microscope at this time point, kogation as found in comparative examples 1 and 2 did not adhere thereto.
The graph of
In this example, the voltage was applied to the first electrode 133 and the second electrode 129 by the use of the external power supply in the same manner as in example 2. At this time, the potential of the first electrode 133 was set to be −0.5 V, the potential of the second electrode 129 was set to be 1 V, and the potential difference between the first electrode 133 and the second electrode 129 was 1.5 V.
Compared to example 1, the potential of the first electrode 133 was changed from −2 V to −0.5 V. At this time, the voltage across the heat element 126 and the first electrode 133 became lower, and whereby the film thickness of the insulating protective layer 127 could be designed thinner, which allowed the liquid to be ejected with lower energy.
The ink was ejected under the same ejection conditions as in comparative examples 1 and 2. The ejection velocity reduced more than in example 1 at the time point, but the reduction in velocity fell within 1.5 m/s when the number of ejections reached 5×108.
In addition, when the surface of the upper protective layer 124 on the heat element 126 was observed with an optical microscope at this time point, kogation as found in comparative examples 1 and 2 did not adhere thereto.
Impurities derived from the pigment deposited on the first electrode 133 according to an ink when the potential difference between the first electrode 133 and the second electrode 129 became large. It was confirmed that setting a potential difference small as in example 3 was also useful for the durability of a heater.
The graph of
In example 4, the potential of the first electrode 133 was set to be −0.2 V, the potential of the second electrode 129 was set to be 1.8 V, and the potential difference between the first electrode 133 and the second electrode 129 was 2 V by the use of the external power supply in the same manner as in example 2.
The voltage applied across the heat element 126 and the first electrode 133 further became lower than in example 2, and whereby the film thickness of the insulating protective layer 127 could be designed thinner, which allowed the liquid to be ejected with lower energy.
The ink was ejected under the same ejection conditions as comparative examples 1 and 2, and example 1. No large reduction in ejection velocity was found, and the reduction in velocity fell within 1 m/s even when the number of ejections exceeded 5×108. In addition, when the surface of the upper protective layer 124 on the heat element 126 was observed with an optical microscope at this time point, kogation as found in comparative examples 1 and 2 did not adhere thereto as in example 1.
The evaluation results of the foregoing ejection durability are shown in table 1.
As shown in table 1, it was found that the case where the potential of the first electrode 133 was set to be negative compared to the substrate 11 led to improved ejection durability among the cases under the same condition that the potential difference between the first electrode 133 and the second electrode 129 was 2 V.
As described above, setting the potential of the first electrode 133 to be negative led to improved ejection durability. The foregoing example is just one example, and the potential difference between the first electrode 133 and the second electrode 129, and the potential of each of the electrodes can be determined according to a liquid, etc., and are not limited to the foregoing example.
When applied so that the first electrode 133 is with a negative potential and the second electrode 129 is with a positive potential, preferably, the voltage is applied so that the potential difference between the first electrode 133 and the second electrode 129 is smaller than 2.5 V. Also in this case, preferably, the voltage is applied so that the potential of the first electrode 133 is at least −2 V and not more than −0.1 V, and the potential of the second electrode 129 is at least 0.1 V and not more than 2.4 V. Also in this case, preferably, the voltage is applied so that the potential of the first electrode 133 is at least −0.5 V and not more than −0.1 V, and the potential of the second electrode 129 is at least 1 V and not more than 2.4 V.
When applied so that the first electrode 133 is with a negative potential, preferably, the voltage is applied so that the potential difference between the first electrode 133 and the substrate 11 that is the second layer is smaller than 2.5 V. Also in this case, preferably, the voltage is applied so that the potential of the first electrode 133 is at least −2 V and not more than −0.1 V.
To verify the mechanism of the improvement in ejection durability by setting the potential of the first electrode 133 to be negative, a simple model was created to check the electric field distribution when the voltage was applied to each of the electrodes.
It was found that the electric field distribution did not concentrate on the first electrode 133 because there was the collection port 17b between the first electrode 133 and the second electrode 129, and the potential of the substrate 11 in the collection port 17b and the potential of the first electrode 133 were equal.
In contrast,
As described above, the experiments, and the verification through the simulation clarified that the kogation suppression process by the method of applying a voltage according to the present invention led to improved ejection durability. Employing the present invention allows a better-durable liquid ejection device to be obtained.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2022-209851, filed on Dec. 27, 2022, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2022-209851 | Dec 2022 | JP | national |