JPH11997A - Inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head capable of reducing fluctuations in a printing position due to a change in volume of an ink droplet, having high gradation, high quality, excellent frequency response, and capable of high-speed printing. I do. SOLUTION: An opening shape of a discharge port 26 opened in a pressure chamber 7 to which ink is supplied has a closed curved profile such as a circle and a linear cut forming a part of an opening edge. The ejection is performed so that the line segment of the cut linear portion 46 is perpendicular to the main scanning direction at the time of printing, and is opposite to the center of the ejection port 26 with respect to the relative traveling direction of the recording medium. An outlet 26 is arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink-jet head used in an ink-jet printer for printing by making ink droplets small and flying.

[0002]

2. Description of the Related Art In recent years, ink jet printers have been widely used as output printers for home and office computers because of their quietness, high speed, and easy colorization during recording. Such ink-jet printers print ink by making ink droplets fly in small droplets and attaching them to recording paper, and are roughly classified into a continuous system and an on-demand system according to the method of generating droplets and the method of controlling the flight direction. You.

The continuous system is, for example, a system described in US Pat. No. 3,060,429, in which ink droplets are reduced electrostatically by suction, and the generated droplets are recorded as recording signals. Is controlled by controlling the electrolysis according to the condition, and a small droplet is selectively adhered to the recording paper for recording. In this recording method, a high-quality image can be provided by expressing the density gradation by changing the dot area of the recorded matter. However, since a high voltage is required for the generation of small droplets, it is difficult to form a multi-nozzle, and thus it is not suitable for high-speed printing.

The on-demand system is a system disclosed in, for example, US Pat. No. 3,447,120. In this method, a piezo-vibration element is attached to a recording head having a nozzle hole for discharging a small droplet, and an electric recording signal is added to the piezo-vibration element to change the vibration into mechanical vibration of the piezo-vibration element.
According to this mechanical vibration, small droplets are ejected from the nozzle holes and adhere to recording paper. In this scheme,
Since recording is performed by discharging ink from the nozzle holes on demand, it is not necessary to collect small droplets that are not required for image recording among small droplets that are ejected and fly, unlike the continuous method. Configuration is possible. However, it is not suitable for high-speed recording because the processing of the recording head is difficult and the miniaturization of the piezo-vibration element is extremely difficult, so that it is difficult to form a multi-nozzle. It has been.

Further, Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 62-11035, and Japanese Patent Publication No. 61-5991
Japanese Patent Application Laid-Open No. 4 (1999) -1995 describes a method in which boiling is caused by a heating resistor to cause droplets to fly.

As another example of the on-demand system, the system described in US Pat. No. 3,179,042 uses heat energy instead of mechanical vibration energy by means such as a piezoelectric vibrating element. It is based on
According to this method, the energy conversion efficiency is higher than that of a method using mechanical vibration energy, and it is said that a multi-nozzle can be easily formed.

FIG. 15 is a longitudinal sectional view of one nozzle of a conventional bubble jet type ink jet head, and FIG.
FIG. 5 is a view taken along line AA of FIG. 5.

In FIG. 15, 1 is a substrate of an ink jet head, 53 is a heating resistor for forming an electrothermal converter patterned on the substrate 1, and 3 is a protective film for insulating and protecting the heating resistor 53. It is. Reference numeral 4 denotes a flow path wall formed on the substrate 1 that partitions the plurality of heating resistors 53. Reference numeral 5 denotes an orifice member formed on the flow path wall 4 in accordance with the heating resistors 53. A discharge port 6 serving as an injection port is provided. A pressure chamber 7 is constituted by the substrate 1, the flow path wall 4 and the orifice member 5. 20 is an ink droplet ejected from the orifice member 5, and 40 is an ink droplet 2
0 is the recording paper to which it adheres. Further, in FIG. 16, reference numeral 8 denotes an ink flow path for supplying ink to the pressure chamber 7.

The operation of such an ink jet head is as follows. First, when a pulse voltage is applied to the heating resistor 53 by a signal generator (not shown), the heating resistor 53 generates heat by the pulse voltage and heats the ink filled in the pressure chamber 7. The ink in the vicinity of the heating resistor 53 starts boiling due to a rapid temperature rise, and a thin bubble film is generated on the heating resistor 53. The bubble film takes away the heat of the heating resistor 53 and the surrounding ink and rapidly expands in volume, and the pressure of the ink in the pressure chamber 7 sharply increases. As a result, the ink droplet 20 jumps out of the ejection port 6 and flies, and the ink droplet 20 adheres to the recording paper 40 to form a dot. The ink consumed during the dot formation is supplied from an ink tank (not shown) via the ink flow path 8, and continuous dot formation can be performed.

The following method has conventionally been proposed as a method for reproducing the gradation in such a conventional ink jet head.

In the first method, one pixel is constituted by a matrix composed of, for example, 4 × 4 dots without changing the dot diameter.
This matrix expresses the gradation by using the dither method. In the second method, a plurality of inks having different coloring densities are used, and the gradation is reproduced by a difference in the densities.

However, in the first method, for example, 1
When the pixels are configured in a 4 × 4 matrix, it is possible to reproduce the gradation of 17 gradations.
By making 4 = 16 times, the resolution becomes 1/16, and there is a limit in obtaining high image quality such as a photographic image. Further, since the print speed is also reduced to 1/16, the number of gradations cannot be increased.

Further, in the second method, the resolution is not reduced because the gradation can be expressed by one dot, but the same number of inks and the same number of inks do not mix with each other by the number of gradations. A head must be prepared. In addition, since a plurality of print heads are controlled, there is a problem that the configuration of the heads themselves becomes complicated, resulting in a significant increase in cost.

Therefore, as a third method, the amount of the ink ejected from the ink jet head is controlled so that the size of the dot diameter to be printed can be changed.
Some reproduce the gradation. In this method, the resolution does not decrease, and it is not necessary to prepare a plurality of types of heads, so that the structure of the ink jet printer can be simplified.

A control method in the case of printing with multiple gradations by a conventional ink jet head is as follows.

FIG. 17 is a graph showing the gradation control of the dot diameter in the conventional ink jet. The horizontal axis represents the heating time, and the vertical axis represents the applied power and the bubble volume for determining the dot diameter.

When a power of 0.4 W is applied to the ink jet head, the heating time until the start of boiling becomes 7 μs and E ₁
= 0.4 × 7 = 2.8 μJ of heat energy is given.
Then bubble up bubble volume grows as B ₁ represents a 200 pl. Similarly, when a power of 0.23 W is applied to the head, the heating time until the start of boiling becomes 22 μs and E
A thermal energy of ₂ = 0.23 × 22 = 5.06 μJ is given, and the bubble at that time grows like B ₂ , and the maximum bubble volume becomes 400 pl. As described above, the time until the start of boiling is determined by the applied electric power, whereby the heated volume of the ink changes, and the larger the heated volume, the larger the maximum growth bubble volume. That is, larger bubbles can be formed by slow heating. When the boiling starts, the current between the electrodes is cut off by the bubble. Therefore, even if the voltage is controlled to be cut immediately, the maximum growth bubble volume is not affected. In this way, changing the bubble volume,
The gradation of the dot diameter can be controlled by changing the amount of ink to be ejected.

[0018]

However, when the dot diameter gradation control is performed by changing the amount of ink to be ejected, the speed at the time of ejection greatly changes according to the amount of ink. . FIG. 18 is a graph showing a change in the speed of ink droplets depending on the amount of ink discharged, and shows the relationship between the volume of ejected ink and the speed when a conventional inkjet head prints in multiple gradations.

As can be seen from FIG. 18, when the amount of ink to be ejected is changed, a time difference occurs until the ejected ink reaches the recording paper due to an increase or decrease in speed, and as a result, variations in the printing position for each density are caused. This has been a problem and has hindered the achievement of high image quality. For this reason, there is naturally a limit in obtaining a large width from the minimum dot diameter to the maximum dot diameter that can be printed.

It is an object of the present invention to provide an ink jet head capable of reducing fluctuation of a printing position due to a change in volume of an ink droplet, having high gradation, high quality, excellent frequency response, and capable of high-speed printing. With the goal.

[0021]

According to the present invention, there is provided a pressure chamber which forms a chamber to which ink for printing is supplied, has a discharge port for partially discharging the ink, and a discharge chamber disposed in the pressure chamber. Energy generating means for generating energy for discharging ink from the outlet, and a part of the ink in the pressure chamber is evaporated by the energy generating means,
An ink jet head that discharges ink from a discharge port by generated bubbles, wherein the opening shape of the discharge port has a closed curved profile such as a circle and a linear cut that forms a part of the opening edge. The discharge ports are arranged so that the line segment of the linear cut portion is perpendicular to the main scanning direction during printing.

According to this configuration, it is possible to adjust the printing position at the time of reaching the recording paper for each amount of the ejected ink liquid without performing special control, and to reduce the printing position deviation. Can be.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to the first aspect of the present invention provides a pressure chamber in which a chamber for supplying ink for printing is formed and a discharge port for discharging ink is partially opened, and a pressure chamber is provided in the pressure chamber. And an energy generating means for generating energy for discharging ink from the discharge ports, wherein the energy generating means evaporates a part of the ink in the pressure chamber and discharges the ink from the discharge ports by the generated bubbles. The head has a discharge port opening shape with a closed curved profile such as a circle and a linear cut that forms a part of the opening edge, and the line segment of this linear cut portion is printed. The ejection ports are arranged so as to be perpendicular to the main scanning direction at the time, and without special control, each time the amount of ink liquid ejected reaches the recording paper An effect that it is possible to adjust the shape location.

According to a second aspect of the present invention, the line segment of the linear cut portion of the ejection port is located on the opposite side of the center of the ejection port with respect to the relative traveling direction of the recording medium. This has the effect that the printing position shift in the main scanning direction due to the speed difference of the flying ink droplets can be adjusted without special control.

An embodiment of the present invention will be described below with reference to FIGS. FIGS. 1A and 1B are diagrams showing an outlet shape of a nozzle of an inkjet head according to an embodiment of the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a perspective view.

In FIG. 1A, reference numeral 45 denotes an ink blocking member provided in accordance with the traveling direction of the ink jet head; 26, a discharge port provided on the ink blocking member 45 for discharging ink droplets; This is a straight line portion showing the straight line portion of the discharge port 26. In the present embodiment, the discharge port 26
Is provided in the direction perpendicular to the traveling direction of the inkjet head and on the traveling direction side.

FIG. 2 is a longitudinal sectional view of one nozzle of the ink jet head according to the embodiment of the present invention, and FIG. 3 is a view taken along line AA of FIG.

In FIGS. 2 and 3, reference numeral 21 denotes a substrate of the ink jet head, and reference numerals 22 and 23 denote counter electrodes which are formed on the substrate 21 and generate energy at high density. 28 is a protective film for insulating and protecting the opposing electrodes 22 and 23. Reference numeral 24 denotes a flow path wall formed on the substrate 21 that partitions the plurality of opposing electrodes 22 and 23, and 25 denotes an opposing electrode 2
An orifice member formed on the flow path wall 24 according to 2 and 23, and a discharge port 26 is provided at the end. Substrate 2
The pressure chamber 27 is constituted by the members 1, the channel wall 24 and the orifice member 25. Reference numeral 29 denotes an ink channel for supplying ink to the pressure chamber 27. 42 is a counter electrode 22, 23
Drive device for applying a voltage to drive device 43, drive device 4
Reference numeral 44 denotes a signal generator for sending a print signal to the reference numeral 2 and a thermistor 44 for measuring the environmental temperature. Reference numeral 20 denotes an ink droplet ejected from the orifice member 25, and reference numeral 40 denotes a recording paper to which the ink droplet 20 adheres.

FIG. 4 is an exploded perspective view of the ink jet head according to the embodiment of the present invention.

In FIG. 4, reference numeral 31 denotes a common ink chamber for supplying ink to the pressure chamber 27.
1, the channel wall 24 and the orifice member 25.

FIG. 5 is a view showing an ink jet head incorporated in an ink cartridge according to the embodiment of the present invention. Numeral 32 denotes an ink cartridge to which the ink jet head 30 is attached, and numeral 36 denotes an ink filter.

FIG. 6 is a partially cutaway perspective view of the ink cartridge of FIG. In FIG. 6, reference numeral 33 denotes an ink tank provided in the ink cartridge 32, reference numeral 34 denotes an ink filter for removing dirt and dust contained in the ink in the ink tank 33, and reference numeral 35 denotes an ink introduction for guiding the ink to the common ink chamber 31. It is a groove.

FIG. 7 is a partially cutaway perspective view of an ink jet printer to which the ink cartridge of FIG. 5 is attached.

In FIG. 7, reference numeral 37 denotes a carriage for fixing the ink cartridge 32; 38, a guide shaft for guiding the carriage 37 which reciprocates serially;
It is a pickup roller that sends 0.

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

First, the signal generator 43 receives necessary dot area and print position information from a signal from a computer or the like, and uses the information as a print signal as a drive device 42.
Tell The drive unit 42 corrects the print signal based on the environmental temperature obtained from the thermistor 44, and applies a voltage to each of the opposed electrodes 22 and 23 corresponding to a required nozzle. The voltage applied at this time is an AC voltage to prevent the electrodes from being worn.

When a potential difference is generated between the opposing electrodes 22 and 23 by the application of the voltage, lines of electric force are generated in the ink having a predetermined volume resistivity, and current flows along the lines of electric force. The energized ink self-heats by I ² × R (I: current, R: resistance of the ink), and finally, micro bubbles in the ink become foam nuclei to generate bubbles (not shown). It expands rapidly due to evaporation from the surrounding ink. As a result, the pressure of the ink in the pressure chamber 27 sharply increases, and the ink blocking member 45
The ink droplet 20 that has passed through is ejected. This ink drop 20
Flies and adheres to the recording paper 40 to form dots.

The volume of the ink droplet 20 changes depending on the volume of the generated bubble, and similarly, the area of the formed dot also changes. The amount of conductive ink consumed by the ejection of the ink droplet 20 is supplied from the ink tank 33 to the pressure chamber 27 through the ink flow path 29, and returns to the initial state.

By repeating the above operation, the carriage 3 is controlled in accordance with a print signal sent from a computer or the like.
7, the ink cartridge 32 reciprocates along the guide shaft 38, the signal generator 43 sends a signal to the drive device 42 in accordance with the position of the carriage 37, and the drive device 42 A drive voltage is applied between 23 to continuously generate ink droplets 20,
Recording paper 40 fed by pickup roller 39
, And printing on the recording paper 40 by dots can be performed.

Next, ejection of ink droplets in the present embodiment will be described with reference to FIGS.

FIGS. 8 to 11 are longitudinal sectional views of the nozzle showing the ejection state of the ink droplets. FIGS. 8 and 9 show the case where the amount of the ejected ink droplet is large, and FIGS. Show.

In FIG. 8, reference numeral 50 indicates the ink in the discharging process, and arrow b indicates the flow of the ink. Bubbles occur,
When the pressure of the ink in the pressure chamber 27 increases, the ink 50 is pushed out from the ejection port 26 as shown in FIG. At this time, the flow velocity of the ink 50 rapidly decreases near the linear portion 46 due to the fluid resistance of the wall surface. For this reason, the ink 50 when exiting the ejection port 26 has a shape as shown by a curve c in the drawing.
It has a velocity distribution that decreases as it approaches the straight line portion 46. Therefore, the ejected ink droplet 51 is ejected in the direction opposite to the straight line portion 46 as shown by the arrow d in FIG.

When the amount of the ejected ink droplets is small, the fluid resistance is almost proportional to the square of the flow velocity, so that the speed drop by the linear portion 46 is small, and the speed distribution is as shown by a curve e in FIG. Therefore, as shown by the arrow f in FIG. 11, the ink droplet 52 is ejected substantially perpendicularly to the cross section of the ejection port. As the discharge speed increases, the discharge angle indicated by θ in FIG. 9 decreases. The discharge angle θ and the discharge speed change depending on the length of the linear portion 46.

FIG. 12 is a graph showing the relationship between the ejection direction of the ink jet head and the length of the ejection port linear portion in the embodiment of the present invention. As can be seen from FIG. Can adjust the magnitude of the ejection angle θ.

FIG. 13 is a conceptual diagram showing the ink droplet ejection direction of the ink jet head according to the embodiment of the present invention, in which the ink droplets 51 and 52 of different amounts are printed when they adhere to the recording paper 40. It shows the position.

In FIG. 13, the arrow h indicates the carriage 37.
Indicates the direction of movement. The ink droplet 51 shown in FIG.
Is discharged in the direction opposite to the straight line portion 46 because the discharge speed is high. On the other hand, since the ink droplet 52 shown in FIG. 11 has a low speed, it is ejected almost vertically and adheres to the recording paper 40.

FIG. 14 is a plan view showing a printing position of ink droplets ejected by the ink jet head according to the embodiment of the present invention. When ink droplets 51 and 52 are ejected at the same time, they adhere to the recording paper 40. Shows what became the print dot.

In FIG. 14, a straight line j indicates the position of the ink discharge port 26 at the start of the discharge, and a straight line k indicates the discharge port accompanying the movement of the carriage 37 when the ink droplet 51 of FIG. The line 26 indicates the position of the ink droplets 51 and 52 in FIG.

As can be seen from FIG. 13, the ink droplet 51 reaches the recording paper 40 when the ejection port 26 is at the position of the straight line k, but the ejection direction is shifted in the direction opposite to the traveling direction, and It adheres to the recording paper 40. On the other hand, since the ink droplet 52 has a smaller ejection amount and a lower ejection speed than the ink droplet 51, it takes longer to arrive at the recording paper 40 than the ink droplet 51, and as a result, the ink droplet 52 adheres to the recording paper 40 near the straight line l. I do. If there is no ink blocking member 45, the ink drop 5
1 is attached to the recording paper 40 at the position of the straight line k,
And the printing position of the ink droplet 52 is greatly shifted.
By disposing the linear portion 46 of the discharge port 26 on the traveling direction side, it is possible to reduce such a shift in the printing position due to the magnitude of the discharge amount.

As described above, according to the present embodiment, the linear portion 46 of the ink blocking member 45 is arranged perpendicular to the traveling direction of the head and on the traveling direction side without any special control. It is possible to correct the printing position at the time of reaching the recording paper for each amount of the ejected ink liquid, and to reduce the printing position deviation. For this reason, the width from the minimum dot diameter to the maximum dot diameter that can be printed can be widened, and high-quality printing with high gradation can be obtained. Therefore, by controlling the volume of the ejected ink droplets to various sizes, a high-quality image having high gradation can be obtained.

[0051]

According to the first aspect of the present invention, it is possible to adjust the printing position at the time of reaching the recording paper for each amount of the ink liquid ejected without performing special control, and it is possible to reduce the printing position deviation. Therefore, the width from the minimum dot diameter to the maximum dot diameter that can be printed can be widened, and high-quality printing with high gradation can be obtained.

According to the second aspect of the present invention, the printing position shift in the main scanning direction due to the speed difference of the flying ink droplets can be surely adjusted without requiring any special control. The quality can be further improved.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating an outlet shape of a nozzle of an inkjet head according to an embodiment of the present invention, wherein FIG. 1A is a plan view and FIG.

FIG. 2 is a vertical sectional view of a nozzle of the inkjet head according to the embodiment of the present invention.

FIG. 3 is a view taken along line AA of FIG. 2;

FIG. 4 is an exploded perspective view of the inkjet head according to the embodiment of the invention.

FIG. 5 is a diagram illustrating the incorporation of an inkjet head into an ink cartridge according to an embodiment of the present invention.

FIG. 6 is a partially cutaway perspective view of the ink cartridge of FIG. 5;

FIG. 7 is a partially cutaway perspective view of an ink jet printer to which the ink cartridge of FIG. 5 is attached.

FIG. 8 is a longitudinal sectional view showing an ejection state when the amount of ejected ink droplets of the inkjet head according to the embodiment of the present invention is large.

FIG. 9 is a longitudinal sectional view showing an ejection state when the amount of ejected ink droplets of the inkjet head according to the embodiment of the present invention is large.

FIG. 10 is a longitudinal sectional view showing an ejection state when the amount of ejected ink droplets of the inkjet head according to the embodiment of the present invention is small.

FIG. 11 is a longitudinal sectional view showing an ejection state when the amount of ejected ink droplets of the inkjet head according to the embodiment of the present invention is small.

FIG. 12 is a graph showing the relationship between the ejection direction of an inkjet head and the length of an ejection port linear portion in the embodiment of the present invention.

FIG. 13 is a conceptual diagram showing the ejection direction of ink droplets of the inkjet head according to the embodiment of the present invention.

FIG. 14 is a plan view showing a printing position of an ink droplet ejected by the inkjet head according to the embodiment of the present invention.

FIG. 15 is a longitudinal sectional view of a nozzle of a conventional bubble jet type ink jet head.

FIG. 16 is a view taken along line AA of FIG. 15;

FIG. 17 is a graph showing gradation control of dot diameter in a conventional inkjet head.

FIG. 18 is a graph showing a change in the speed of an ink droplet depending on an ink ejection amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Counter electrode 3 Protective film 4 Flow path wall 5 Orifice member 6 Discharge port 7 Pressure chamber 8 Ink flow path 20 Ink droplet 21 Substrate 22, 23 Counter electrode 24 Flow path wall 25 Orifice member 26 Discharge port 27 Pressure chamber 28 Protection Film 29 Ink flow path 30 Inkjet head 31 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 45 Ink shut-off member 46 Linear part 50 Ink 51, 52 Ink drop

Claims (2)

[Claims] A pressure chamber which forms a chamber to which ink for printing is supplied and has a discharge port for partially discharging the ink, and a pressure chamber disposed in the pressure chamber for discharging the ink from the discharge port. And an energy generating means for generating energy, wherein the energy generating means evaporates a part of the ink in the pressure chamber and discharges the ink from the discharge port by generated bubbles. , Shall have a closed curved profile such as a circle and a linear cut forming a part of the opening edge, and the line segment of this linear cut portion is perpendicular to the main scanning direction at the time of printing. An ink jet head characterized in that discharge ports are arranged in the ink jet head. 2. A printing apparatus according to claim 1, wherein the line segment of the linear cut portion of the ejection port is located on the opposite side of the center of the ejection port with respect to the direction of relative movement of the recording medium. The inkjet head according to the above.