JPH09323417A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image of high quality by gradation due to an area of a printing dot in an ink jet printer used as output machinery such as a computer. SOLUTION: Projected parts approaching each other are provided to two places of counter electrodes 22, 23. By this constitution, since two bubbles small in vol. can be generated at the same time, the speed of the volumetric change of bubles can be enhanced as compared with a conventional method and an emitting speed in such a case that emitted ink droplets are small is increased and the vol. of emitted ink droplets can be controlled over a wide range as compared with a conventional method and an image of high quality having high gradation properties can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet head used in an inkjet printer.

[0002]

2. Description of the Related Art In recent years, inkjet printers have been widely used as output printers for home and office computers because of their quietness during recording, high-speed recording capability, and easy colorization. It started to come. Such an ink jet printer prints by making ink droplets fly and then depositing them on recording paper. Depending on the droplet generation method and the flight direction control method, there are two methods: continuous method and on-demand method. Be separated.

The continuous system is a system disclosed in, for example, US Pat. No. 30,60429, in which ink droplets are electrostatically attracted and the generated droplets are electrolyzed according to a recording signal. It controls the recording and selectively deposits small droplets on the recording paper for recording.This recording method provides a high-quality image by changing the dot area of the recorded material and expressing the density gradation. can do. However, since high voltage is required to generate small droplets and it is difficult to form multiple nozzles, it is not suitable for high-speed recording.

[0004] The on-demand system is described in, for example, US Pat.
According to the method disclosed in Japanese Patent No. 747120, an electric recording signal is added to a piezoelectric vibrating element attached to a recording head having a nozzle hole for ejecting a small droplet, and this electric recording signal is added to the piezoelectric vibrating element. Recording is performed by changing to the mechanical vibration of (1) and ejecting a small droplet from the nozzle hole according to the mechanical vibration to adhere to the recording paper. With this method, ink is ejected from the nozzle holes on-demand for recording, so unlike the continuous method, it is not necessary to collect the droplets that were not required for image recording among the ejected droplets. Therefore, a simple configuration is possible. on the other hand,
It is not suitable for high-speed recording because it is difficult to process the recording head, it is extremely difficult to miniaturize the piezo vibration element, it is difficult to make multiple nozzles, and the mechanical energy of mechanical vibration of the piezo element is used to fly small droplets. Have.

Further, Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 62-11035, and Japanese Patent Publication No. 61-59914 disclose recording methods of a system in which a heating resistor causes boiling to cause droplets to fly. ing.

As another example of the on-demand system, US Pat. No. 3,179,042 discloses that instead of utilizing mechanical vibration energy by means such as a piezoelectric vibration element,
The use of thermal energy is described. This method is characterized by higher energy conversion efficiency and easier multi-nozzle method than the method using mechanical vibration energy.

The ejection principle of the conventional on-demand type bubble jet type ink jet head will be described below.
This will be described with reference to FIGS. 14 is a vertical cross-sectional view of a nozzle of a conventional bubble-jet type inkjet head, and FIG. 15 is a cross-sectional view taken along the line BB of FIG.

In FIG. 14, 1 is a substrate of an ink jet head, 2 is a heating resistor forming an electrothermal converter patterned on the substrate 1, and 3 is a protective film for insulating and protecting the heating resistor 2. Is. Reference numeral 4 denotes a flow path wall formed on the substrate 1 for partitioning the plurality of heat generating resistors 2, 5 is an orifice member formed on the flow path wall 4 in accordance with the heat generating resistors 2, and an ink ejection port is provided at the end. The discharge port 6 is provided. The substrate 1, the flow path wall 4 and the orifice member 5 constitute a pressure chamber 7. Reference numeral 20 is an ink droplet ejected from the ejection port 6, and 40 is a recording paper to which the ink droplet 20 is attached. In FIG. 15, reference numeral 8 is an ink flow path for supplying ink to the pressure chamber 7.

The operation of the ink jet head having the above structure will be described below. First, a pulse voltage is applied to the heating resistor 2 by a signal generator (not shown). The heating resistor 2 generates heat by this pulse voltage, and the ink filled in the pressure chamber 7 is heated. The ink in the vicinity of the heating resistor 2 starts boiling due to a rapid temperature rise, and a thin bubble film is generated on the heating resistor 2. The film of this bubble absorbs the heat of the heat generating resistor 2 and the ink in the surrounding area and abruptly expands in volume, the pressure of the ink in the pressure chamber 7 rapidly increases, and the ink droplet 20 jumps out from the ejection port 6.
It flies and adheres to the recording paper 40 to form dots. The ink consumed by the dot formation is supplied from an ink tank (not shown) through the ink flow path 8 and can perform arbitrary continuous dot formation.

Next, a control method when a conventional ink jet head is printed with multiple gradations will be described. FIG. 16 is a graph showing the gradation control of the dot diameter. In FIG. 16, the horizontal axis represents the heating time, and the vertical axis represents the applied power and the bubble volume that determines the dot diameter. When 0.4 W of electric power is applied to the head, the heating time until boiling starts is 7 μs, and E1 = 0.4
Energy of × 7 = 2.8 μJ is given. The bubble at that time grows like B1, and the maximum bubble volume is 200.
pl. Similarly, when 0.23 w of electric power is applied to the head, the heating time until the start of boiling becomes 22 μs and E2 =
Energy of 0.23 × 22 = 5.06 μJ is given, and the bubble at that time grows like B2, and the maximum bubble volume becomes 400 pl.

In this way, the time until the start of boiling is determined by the applied power, and the heated volume of the ink changes accordingly. The larger the heated volume, the larger the maximum growth bubble volume. That is, the slower the heating, the larger bubbles can be formed. When boiling starts, the current between the electrodes is interrupted by the bubbles, so controlling the voltage to cut off immediately does not affect the maximum growth bubble volume. By changing the bubble volume and the amount of ink to be ejected in this way, it is possible to control the gradation of the dot diameter.

FIG. 17 is a graph showing the relationship between the volume and speed of ink droplets discharged from a conventional ink jet head. As shown in the figure, if the ink ejection amount is reduced by using small bubbles, the ejection speed is reduced due to pressure loss such as fluid resistance of the nozzle. This decrease in speed causes variations in the printing position of the ejected ink and causes instability in ejection. Therefore, there is a limit to reducing the print dot diameter.

[0013]

In the above conventional structure, as shown in FIG. 17, when the amount of ejected ink is reduced, the speed of ejected ink is reduced accordingly, and therefore the ejected ink amount is reduced. There is a large difference in speed from the case of a large number, which causes variations in printing positions. Further, if the ejection speed is low, it is easily affected by the surface tension of the ink and the like, which may cause ejection instability, and as a result, there is a limit to reducing the print dot diameter. Therefore, by changing the volume of the ink droplets 20 to change the area of the dots adhering to the recording paper 40 and expressing the density change of the printed matter, the density gradation of the printed material is low and the gradation of the continuous method is high. The print quality is lower than that of an inkjet printer.

The present invention solves the above-mentioned problems of the prior art. By reducing the speed fluctuation with respect to the volume change of the ink droplet, the gradation is high, the quality is high, the frequency response is excellent, and the high speed printing is performed. It is an object of the present invention to provide an inkjet head capable of performing the above.

[0015]

In order to solve this problem, the present invention provides a pressure chamber filled with conductive ink, an ink flow path for supplying ink to the pressure chamber, and a pressure chamber of the pressure chamber. A discharge port that discharges ink provided in part,
In the pressure chamber, a pair of opposing electrodes provided in the pressure chamber corresponding to the discharge port, an energy generating unit provided in the pressure chamber, and an energy applying unit supplying energy to the electrode are provided. An ink jet head for ejecting ink from the ejection port by bubbles generated by evaporating a part of ink, characterized in that a plurality of bubbles are generated on a surface facing the electrode when a voltage is applied. Is.

With this, by reducing the velocity fluctuation with respect to the volume change of the ink droplet, it is possible to obtain an ink jet head having high gradation, high quality, excellent frequency response and capable of high-speed printing.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An ink jet head according to claims 1 and 2 of the present invention comprises a pressure chamber filled with conductive ink, an ink flow path for supplying ink to the pressure chamber, and the pressure. An ejection port for ejecting ink, which is provided in a part of the chamber, a pair of opposing electrodes provided in the pressure chamber corresponding to the ejection port, energy generating means provided in the pressure chamber, and the electrode And an energy applying unit for supplying energy to the inkjet head, the inkjet head ejecting the ink from the ejection port by the bubbles generated by evaporating a part of the ink in the pressure chamber, and applying a voltage to the opposing surfaces of the electrodes. It is characterized in that a protrusion or the like that sometimes generates a plurality of bubbles is formed.

As a result, the growth rate of a small volume of bubbles can be improved as compared with the conventional case, and stable printing can be performed even when the ejected ink droplets are small. Further, since the bubble having a large volume has the same growth rate as that of the conventional one, the difference in the ejection speed due to the size of the bubble becomes small, and the print position deviation can be reduced. Therefore, the volume of the ejected ink droplet can be controlled to various sizes, and high-quality printing with high gradation can be obtained.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4. 1 is a vertical sectional view of a nozzle of an inkjet head according to an embodiment of the present invention, FIG.
2 is a sectional view taken along the line AA of FIG.

In FIG. 1 and FIG. 2, reference numeral 21 is a substrate of an ink jet head, and 22 and 23 are counter electrodes which are patterned on the substrate 21 and generate energy at high density. Reference numeral 28 is a protective film for insulating and protecting the counter electrodes 22 and 23. 24 is a plurality of counter electrodes 22, 2
A channel wall formed on the substrate 21 for partitioning 3 is an orifice member formed on the channel wall 24 corresponding to the counter electrodes 22 and 23, and a discharge port 26 is provided at the end.
The substrate 21, the flow path wall 24, and the orifice member 25 form a pressure chamber 27. An ink flow path 29 supplies ink to the pressure chamber 27. 42 is the counter electrode 2
A drive device for applying a voltage to 2 and 23, a signal generator 43 for sending a print signal to the drive device 42, and a thermistor 44 for measuring the environmental temperature. Further, 20 is an ink droplet ejected from the ejection port 26, and 40 is a recording paper to which the ink droplet 20 is attached.

Referring to FIG. 3 which is an exploded perspective view of the ink jet head according to the embodiment of the present invention, reference numeral 30 denotes a common ink chamber for supplying ink to the pressure chamber 27, which includes the substrate 21, the flow path wall 24, and It is formed of the orifice member 25.

FIG. 4 is an assembly diagram of the ink jet head in the embodiment of the present invention, in which reference numeral 32 denotes the ink cartridge to which the substrate 21 is attached.

FIG. 5 is an exploded perspective view of the ink cartridge 32. In FIG. 5, 33 is an ink tank provided in the ink cartridge 32, and 34 is dust and dirt contained in the ink in the ink tank 33. The ink filter 35 is an ink introduction groove for guiding the ink to the common ink chamber 30.

FIG. 6 is an exploded perspective view of an ink jet printer equipped with an ink cartridge incorporating an ink jet head. In the figure, 37 is a carriage for fixing the ink cartridge 32, and 38 is a guide for guiding the carriage 37 that reciprocates serially. A shaft and 39 are pickup rollers for feeding the recording paper 40.

The operation of the ink jet head constructed as above and its peripheral portion will be described below.

First, the signal generator 43 receives information on the required dot area and print position from a signal from a computer or the like, and transmits this to the drive device 42 as a print signal. The drive device 42 corrects this print signal according to the ambient temperature obtained from the thermistor 44, and applies a voltage to each of the counter electrodes 22 and 23 corresponding to the required nozzle. The voltage applied at this time is an AC voltage in order to prevent electrode wear. When a potential difference occurs between the counter electrodes 22 and 23 due to this voltage application, an electric force line B is generated in the ink having a predetermined volume resistivity, and a current flows along the electric force line B. The energized ink is I ² × R (I:
Electric current, R: Ink resistance)
Finally, minute bubbles in the ink become foam nuclei to generate bubbles (not shown), and the bubbles rapidly expand due to evaporation from the surrounding ink that has become high temperature. As a result, the pressure chamber 27
The pressure of the ink inside rapidly increases, and the ink droplet 20 jumps out from the ink ejection port 26 and flies and adheres to the recording paper 40 to form a dot. The volume of the ink drop 20 changes depending on the volume of the bubble generated, and the area of dots formed in the same manner also changes. The conductive ink consumed by the ejection of the ink droplets 20 is transferred from the ink tank 33 to the ink flow path 2.
It is supplied to the pressure chamber 27 through 9 and returns to the initial state.

By repeating the above operation, the ink cartridge 32, which is inserted from the cartridge insertion port and attached to the carriage 37, reciprocates along the guide shaft 38 in response to a print signal sent from a computer or the like. , The signal generator 43 sends a signal to the drive device 42 in accordance with the position of the carriage 37, the drive device 42 applies a drive voltage between the opposing electrodes 22 and 23, and the ink droplets 20 are continuously generated. It adheres to the recording paper 40 sent by the pick-up roller 39, which enables printing with dots on the recording paper 40.

As the ink is printed, the ink is introduced from the ink tank 33 through the ink filter 34 into the ink introducing groove 3.
5 to enter the common ink chamber 30, and further is supplied from the common ink chamber 30 to the pressure chamber 27 through the ink flow path 29, which enables continuous printing.

Next, the bubble growth in the ink jet head of this embodiment will be described in detail with reference to FIGS. 7 to 9. 7 to 9 are plan views showing the opposing electrodes 22 and 23 of the ink jet head of this embodiment and the growth state of bubbles. FIG. 7 shows immediately before the occurrence of bubbles, FIG. 8 shows immediately after the occurrence of bubbles, and FIG. FIG. 9 shows a certain point in the middle of bubble growth when a sufficient amount of heat is applied.

In FIG. 7, 51 and 52 are counter electrodes 22.
Among them, the protrusions protruding toward the counter electrode 23 side, and 53 and 54 are the protrusions of the counter electrode 23 similarly. The protrusions 51 and 52 of the counter electrode 22 have the same shape, and the center-to-center distance is 40 μm.
m, the entire width of the counter electrode 22 is 60 μm. In this embodiment, the counter electrodes 22 and 23 have the same shape. Further, the counter electrodes 22 and 23 face each other, and the protrusion 5
The spacing is closest between 1 and 53 and 52 and 54. In this embodiment, the distance is 1.5 μm.

The counter electrode 22 having the above shape,
When a voltage is applied from the drive device 42 to 23, a potential difference is generated between the counter electrodes 22 and 23, and a current flows along the line of electric force B generated in the ink having a predetermined volume resistivity. Self-heating. As shown in FIG. 7, at this time, the lines of electric force become the closest between the protrusions 51 and 53 and 52 and 54 that are closest to each other, and more current flows. Since the amount of heat generated is proportional to the square of the current as described above, the ink has the highest temperature between the protrusions 51 and 53 and 52 and 54, and one bubble is generated in each ink. In FIG. 8, C and D indicate the two bubbles that have occurred. The generated bubble grows due to the heat of the surrounding ink, and its volume change is due to the pressure chamber 27 before the bubble is generated.
It depends on the amount of heat applied to the ink inside. When a sufficient amount of heat is applied and the bubbles C and D grow larger than the distance between them, the two bubbles overlap to form one bubble E, as shown in FIG. The bubbles after becoming one have the same volume change as the bubbles generated by a single bubble.

Next, the principle of dot diameter gradation in the ink jet head of the present embodiment will be described with reference to FIGS. 10 and 11 are plan views showing the growth state of the counter electrodes 22 and 23 and the bubbles in the ink jet head of the present embodiment. FIG. 12 shows the time variation of the bubble volume generated, and FIG. 13 shows the same ejected ink droplet. It is a graph showing the speed of 20.

As described in the prior art, by changing the electric power applied to the ink jet head, a small volume of bubbles can be generated by applying high power for a short time, and a large volume of bubbles can be generated by applying low power for a long time. Obtainable.

In FIG. 10, a power of 0.6 W is applied, and immediately after the start of boiling, two bubbles C and D are generated between the counter electrodes 22 and 23. At this time, the time from the application of power to the generation of bubbles is 4 μs. Each of the bubbles C and D grows up to a maximum volume of 25 pl, but even when they have the maximum volume, the radii are 18 μm, and the bubbles shrink and disappear without any contact with each other.

In FIG. 12, C is the volume change of the bubble indicated by C in FIG. 10, C + D is the sum of the volumes of the two bubbles C and D in FIG. 10, and B1 is the conventional bubble of the same volume. Shows the change in volume. As shown in FIG. 12, by generating two bubbles C and D at the same time, the growth rate of the total volume of them is about twice as fast as the conventional one. As a result, the ejection speed of the ejected ink droplet 20 is improved.

Further, in FIG. 11, the counter electrodes 22 and 23 have 0.
Power of 2W is applied, and the time until bubble generation is 18
μs. In this case, as shown in FIG. 11, the two generated bubbles coalesce into one bubble indicated by E in FIG. 11 during the growth, and the bubble E grows to a maximum volume of 150 pl. The volume of the ejected ink droplet 20 changes with such a change in the volume of the bubble, and the diameter of the dot attached to the recording paper 40 can be controlled.

In the portion where the volume of the ink droplet 20 is small, the growth rate of the bubble volume is higher than that of the conventional one as shown in FIG. 12, so the velocity of the ink droplet 20 is improved.

As described above, according to the ink jet head of this embodiment, the counter electrodes 22 and 23 have the two protrusions 51, 52, 53 and 54, respectively, which are opposed to each other. Since two bubbles having a small volume can be generated at the same time, the volume change rate of the bubbles can be improved as compared with the conventional case, and the ejection speed when the ejected ink droplet 20 is small is improved, thereby printing a smaller area. Dots can be formed. Further, since the bubble having a large volume has the same growth rate as that of the conventional one, the difference in the ejection speed due to the size of the bubble becomes small, and the print position deviation can be reduced. Therefore, by controlling the volume of the ejected ink droplets 20 to various sizes, it is possible to obtain a high-quality image having high gradation.

[0039]

As described above, according to the present invention, it is possible to simultaneously generate two bubbles having a small volume.
It is possible to improve the speed of bubble volume change compared to the past, to improve the ejection speed when the ejected ink droplet is small, to form a print dot of a smaller area, and to compare the ejection speed difference depending on the ejected ink droplet volume. Can be reduced, and the print position deviation can be reduced. Therefore, the volume of ejected ink droplets can be controlled in a wider range than in the past, and by controlling the volume of ejected ink droplets to various sizes, a high-quality image having high gradation can be obtained. . Further, it is possible to provide a high-speed, small-sized, inexpensive printer as compared with other printers capable of obtaining high-quality images such as the continuous recording method.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a nozzle of an inkjet head according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is an exploded perspective view of an inkjet head according to an embodiment of the present invention.

FIG. 4 is a diagram showing how the inkjet head according to the embodiment of the present invention is incorporated into an ink cartridge.

FIG. 5 is an exploded perspective view of the ink cartridge according to the embodiment of the present invention.

6 is an exploded perspective view of an inkjet printer having an ink cartridge incorporating the inkjet head of FIG. 5 attached thereto.

FIG. 7 is a plan view showing a counter electrode and a bubble growing state of the inkjet head according to the embodiment of the present invention.

FIG. 8 is a plan view showing a counter electrode and a bubble growth state of the inkjet head according to the embodiment of the present invention.

FIG. 9 is a plan view showing a counter electrode and a bubble growing state of the inkjet head according to the embodiment of the present invention.

FIG. 10 is a plan view showing a counter electrode and a bubble growing state of the inkjet head in the embodiment of the present invention.

FIG. 11 is a plan view showing a counter electrode and a bubble growing state of the inkjet head according to the embodiment of the present invention.

FIG. 12 is a graph showing a change over time in bubble volume generated by the inkjet head according to the embodiment of the present invention.

FIG. 13 is a graph showing the velocity of ink droplets ejected from the inkjet head according to the embodiment of the present invention.

FIG. 14 is a vertical cross-sectional view of a nozzle of a conventional bubble-jet type inkjet head.

15 is a sectional view taken along line BB of FIG.

FIG. 16 is a graph showing gradation control of bubble diameter of a conventional inkjet head.

FIG. 17 is a graph showing the relationship between the volume and speed of ink droplets discharged from a conventional inkjet head.

[Explanation of symbols]

 1 Substrate 2 Heat-generating resistor 3 Protective film 4 Channel wall 5 Orifice member 6 Discharge port 7 Pressure chamber 8 Ink flow channel 20 Ink droplet 21 Substrate 22,23 Counter electrode 24 Flow channel wall 25 Orifice member 26 Discharge port 27 Pressure chamber 28 Protective film 29 Ink flow path 30 Common ink chamber 32 Ink cartridge 33 Ink tank 34 Ink filter 35 Ink introduction groove 37 Carriage 38 Guide shaft 39 Pickup roller 40 Recording paper 42 Drive device 43 Signal generator 44 Thermistor 51-54 Protrusion of counter electrode Department

Claims (3)

[Claims] 1. A pressure chamber filled with conductive ink, an ink flow path for supplying ink to the pressure chamber, and an ejection port for ejecting ink provided in a part of the pressure chamber.
A pair of opposing electrodes provided in the pressure chamber according to the ejection port and an energy applying unit for supplying energy to the electrodes are provided, and the bubbles are generated by vaporizing a part of ink in the pressure chamber. An inkjet head for ejecting ink from an ejection port, characterized in that a plurality of bubbles are generated on the surfaces of the electrodes facing each other when a voltage is applied. 2. A pressure chamber filled with conductive ink, an ink flow path for supplying ink to the pressure chamber, and an ejection port for ejecting ink provided in a part of the pressure chamber.
A pair of opposing electrodes provided in the pressure chamber according to the ejection port and an energy applying unit for supplying energy to the electrodes are provided, and the bubbles are generated by vaporizing a part of ink in the pressure chamber. An inkjet head for ejecting ink from an ejection port, characterized in that projections for generating a plurality of bubbles when a voltage is applied are formed on the surfaces of the electrodes facing each other. 3. The ink jet head according to claim 2, wherein the protrusions are formed in two places and have the same shape.