JP3495863B2 - Ink jet head and ink jet device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet head and an inkjet device for forming an image by ejecting ink onto a recording medium.

[0002]

2. Description of the Related Art An image recording apparatus for information communication equipment such as printers, plotters, copiers, word processors and facsimiles.
In recent years, a recording method using an inkjet recording head (hereinafter, also referred to as an inkjet head) has been evaluated and widely used. In particular, a method using bubble pressure generated by an electrothermal converter or the like, that is, a bubble jet method (Japanese Patent Laid-Open No. 61-599).
Nos. 11 to 4) are characterized in that the device can be downsized and the image density can be easily increased.

The structure of the liquid flow path in the conventional ink jet head is shown in FIGS. 9 and 10.

In FIGS. 9 and 10, reference numeral 8 is a discharge port, 16 is a liquid flow path, 17 is a common liquid chamber, and 14 is a discharge energy generating element as a discharge pressure generating means. The inkjet head shown in FIG. 9 has a liquid flow path having a constant height. In the head having such a configuration, by applying a voltage to the ejection energy generating element 14, it is possible to generate bubbles to eject the ink in the liquid flow path 16 from the ejection port 8 and from the common liquid chamber 17 side. Ink can be refilled in each liquid channel 16 to prepare for the next ink ejection.

Generally, the front-to-back ratio of the pressure at the time of bubble generation is adjusted by the size of the discharge energy generating element, the position in the liquid flow path, the area of the discharge port, the liquid flow path height, the liquid flow path length and the like. It In the case of the liquid flow path having the configuration shown in FIG. 9, it is difficult to secure the backward resistance while shortening the ink refill time after bubbling and ejection. Therefore, the liquid flow path 1 after the ink refill is performed.
It was difficult to increase the printing speed as a result of the ink vibration in 6 being difficult to subside and the ejection interval having to be set longer.

Reference numeral 31 in FIG. 10 is a resistance element added to the rear of the liquid flow path 16 of the ink jet head shown in FIG. As a result of suppressing the vibration as one of the effects of providing the resistance element 31 behind the liquid flow path 16 as described above, printing can be performed at a higher drive frequency than in the case of FIG.

[0007]

However, due to its structure, there is a stagnation portion around the resistance element where the ink does not move much even when the ink is refilled, and residual bubbles in the ink generated during foaming and defoaming are stagnation. Bubbles may be accumulated by staying in the area and repeating ejection. in this case,
It is necessary to take measures such as enlarging the suction mechanism of the inkjet device because the bubbles may not be ejected when bubbled during foaming, or the bubbles may become difficult to come off even after a long-term standing by the inkjet device. .

Furthermore, the recent demands for ink jet recording systems are high-speed printing, high-definition images, large-format continuous printing, and downsizing and cost reduction of the recording apparatus, low running cost, and high printing cost. It is becoming more reliable and reliable.

As an ink jet head structure for meeting at least one or more of these requirements, there is a conventional 6 in order to increase the bandwidth of one scan of the head.
4 or 128 nozzles or more, such as 256, 512,
Furthermore, the number of nozzles such as 1024 nozzles has been greatly increased, and 6 from the current 360 or 400 dpi.
It is conceivable to increase the nozzle density from 00 to 1200 dpi and increase the drive frequency as a recording method.

This requirement is completely opposite to the suppression of the accumulation of bubbles in the liquid flow path or the liquid chamber, and the increase in the number of nozzles and the increase in the density lead to the temperature rise of the head itself.
The accumulation of bubbles is promoted, and the increase in the frequency increases the number of discharges per unit time, which promotes the accumulation of bubbles.

Further, in order to further increase the speed of printing, and to reduce the number of suction operations in order to maximize the use of ink contained in the head, it is necessary to reduce the number of suction operations. However, it is necessary to suppress the accumulation of air bubbles during printing as much as possible because it cannot be applied in the middle of one band.

Japanese Unexamined Patent Publication (Kokai) No. 5-69546 discloses a structure of a liquid flow path having a region where a cross-sectional area perpendicular to the liquid flow path increases from the discharge energy generating element toward the discharge port. However, although the effect of adjusting the ejection direction of ink droplets, which is called microdrop that occurs during defoaming after foaming that ejects ink, is sufficiently exerted, the effect of suppressing the accumulation of residual bubbles during printing is sufficient. Was not.

[0013]

Therefore, the present invention adopts a liquid flow path structure which has a backward resistance component but does not allow air bubbles during printing to stay, and by this structure, air bubbles are positively added to the ink. At the same time, it is possible to prevent bubbles from accumulating by discharging from the discharge port, reduce the load on the suction mechanism of the main body by preventing the accumulation of bubbles, and reduce the number of times of suction to suppress the decrease in printing speed and enable printing. (EN) An inkjet head and an inkjet device having higher reliability by increasing the number of sheets to achieve high-speed printing and reducing defects during printing.

As a result of diligent study of the above problems, the present inventors have suppressed the accumulation of residual bubbles in the positional relationship between the region where the liquid flow passage cross-sectional area increases and the discharge energy generating means, and the liquid flow passage shape. I found a way to do it. That is, the present invention provides an ejection port for ejecting ink, a liquid channel communicating with the ejection port, an ejection provided in the liquid channel, and used for ejecting ink from the ejection port. An ink jet head including a discharge pressure generating means for generating a pressure, wherein a ceiling part facing the discharge pressure generating means and forming the liquid flow path is formed from a bottom surface part forming the liquid flow path. It is composed of three regions I, II and III in order from the ejection port side according to the height.
And III are parallel to the bottom portion forming the liquid flow path, the region I has a higher liquid flow path height than the region III, and the region II is the liquid from the region III toward the region I. The connecting portion between the region II and the region III has the slope formed by a curve in which the flow path height increases.
Smoothly connected so that there is no sudden change in liquid flow path height
With that, the region II is formed in a range of distances L1~L2 from the reference point is the intersection of the discharge port forming surface and the ceiling portion, a bottom portion constituting the liquid flow path, the bottom surface portion The discharge pressure generating means is provided in the range of the distances LH1 to LH2 from the projection point of the reference point to, and the relationship between the ceiling part and the bottom part forming the liquid flow path is expressed by

It is characterized in that LH2 <L2 is satisfied.

[0016]

[0017]

The discharge port forming surface may be a surface of the member having the discharge port on the liquid flow path side.

The height of the liquid flow path may be the height of the central portion of a plane orthogonal to the length direction of the liquid flow path.

[0020]

[0021]

[0022]

[0023]

[0024]

Further, the present invention is an ink jet device, characterized by comprising means for mounting the above ink jet head.

With the above-described structure, in the present invention, the number of times of suction is increased without imposing a load on the suction mechanism of the ink jet device in order to prevent residual bubbles during printing from accumulating in the liquid flow path. It is possible to reduce the number of printable sheets while suppressing the decrease in printing speed,
It is also possible to reduce defects during printing,
A more reliable inkjet head and inkjet device can be realized.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment of Inkjet Device ) First, the inkjet device of the present invention will be described.

FIG. 4 is a schematic perspective view showing an embodiment of a recording apparatus as an ink jet apparatus of the present invention. In FIG. 4, reference numeral 1 is an inkjet head, and 2 is a carriage that fixes the inkjet head 1 on the apparatus and enables electrical connection when the head is fixed on the apparatus. Reference numeral 3 is a recording medium such as paper on which recording is performed, and is conveyed by a conveying roller 4 in a direction orthogonal to the scanning direction (arrow A direction) of the inkjet head 1. Reference numerals 5 and 6 denote shafts for the carriage 2 to scan, and the rotation of the shaft 5 causes the carriage 2 to move.

FIG. 5 shows a control circuit 1 of the ink jet device.
It is a block diagram which shows the structure of 00. In FIG. 5, 1
Reference numeral 08 is an interface for inputting a recording signal, 101 is an MPU, 102 is a ROM for storing a control program executed by the MPU 101, 103 is a DRAM for storing the recording signal and various data such as recording data supplied to the inkjet head 1. is there. Reference numeral 104 denotes a gate array (GA) that controls the supply of print data to the inkjet head 1, and the interface 108, MP
It also controls the data transfer of U101, RAM103 and the like. 1
Reference numeral 10 is a carriage motor for scanning a carriage on which the inkjet head 1 is mounted, and 109 is a transport motor for transporting a recording medium. 105 is a head driver for driving the inkjet head 1, 106,
Reference numeral 107 denotes a motor driver for driving the carry motor 109 and the carriage motor 110, respectively. The operation of the control circuit will be described. The interface 108
When a recording signal is input to the gate array 104 and MPU10
The recording signal is converted into the recording data for printing between 1 and 1. The motor drivers 106 and 107 are driven, and the inkjet head 1 is driven according to the recording data sent to the head driver 105 to perform recording.

Next, the ink jet head will be described. FIG. 6 is an example of its appearance. 7 is an ink tank for storing ink, 8 is a plurality of ejection ports for ejecting ink, 9 is an ink supply member, 10 is a PWB connected to a heating element (not shown), 11 is on the apparatus side and on the carriage. A contact pad 12 that is electrically connected is a base plate on which the above components are mounted.

Further, the details of the ink discharge area will be described. FIG. 7 is an enlarged cross-sectional view including an ink flow path for ejecting ink and a configuration necessary for ejection. 1 in FIG.
Reference numeral 3 denotes a substrate (hereinafter also referred to as a heater board) on which a plurality of heating elements 14 for foaming and ejecting ink are formed, and electrically connected to the PWB 10 by wires 15. Reference numeral 20 is a top plate for forming a plurality of ejection openings 8 and ink flow paths 16 for ejecting ink, and for forming a common liquid chamber 17 which is in common communication with the plurality of ink flow paths 16.

A filter 19 is provided at the end of the ink supply path 18 that connects the inside of the ink tank 7 which is the ink storage portion with the common liquid chamber 17 inside the recording head on the ink tank side. Here, the ink path from the ink tank 7 to the ejection portion formed by the top plate 20 is as shown by an arrow F in the drawing that passes through the ink supply path 18 and the common liquid chamber 17.

Reference Embodiment 1 FIG. 1 is a schematic cross-sectional view showing the structure of a liquid flow path in one reference embodiment of the inkjet head of the present invention which can be mounted on the above-mentioned inkjet device. In the figure, 8 is a discharge port, 13 is a heater board, 14 is a discharge energy generating element, 16 is a liquid flow path, and 17 is a common liquid chamber.

When the region from the discharge port to the liquid chamber is divided into three regions as shown in FIG. 1, the point where the liquid flow channel ceiling in the first region I intersects with the discharge port of the orifice plate on the opposite surface is the discharge port reference. A position 32 is defined as a region I from the ejection port reference position 32 to a distance L1, a range II is a range from the distance L1 to the distance L2, and a region III is a range from the distance L2 to the distance L3.

In FIG. 1, a ceiling parallel to the surface on which the ejection energy generating elements are arranged is formed from the ejection port reference position 32 to the distance L1, and in a region II from the distance L1 to the distance L2, the ejection port is a linear straight line. A linear ceiling that increases toward the top is formed, and in a region III from the distance L2 to the distance L3, a ceiling parallel to the arrangement surface of the ejection energy generating element is formed.

The height of the liquid channel ceiling in the region I is a parallel line segment that does not increase or decrease in FIG. 1, but there is no reason to be restricted by this, and the object of the present invention is achieved. If so, any shape can be adopted.

Similarly, the shape of the region III is also a parallel line segment, but as long as it does not decrease in the ejection direction,
Any shape can be selected as long as the object of the present invention can be achieved.

The discharge energy generating element 14 is located between the projection point 32a of the discharge port reference position 32 and LH1 and LH2, and in FIG. 1, L1 <LH1 and L2 <LH2.
The relationship between L1 and LH1 is not specified, and as in the case of FIG. 1, the protrusion from the rear end L2 of the ejection energy generating element is on the ink flow path from the projection point 32a of the ejection port reference position 32 of the ejection energy generating element. If the distance to the end on the flow side, that is, within 20% of LH2, and more preferably within 10%, the object of the present invention can be sufficiently achieved.

Next, foaming and ink ejection by the ejection energy generating element will be described.

FIGS. 8A to 8D are schematic sectional views for explaining the passage of time immediately before the start of ejection.

FIG. 8A shows a state before foaming,
An ink meniscus M exists in the ejection port 8.
FIG. 8B shows a state in which the bubble B starts to grow substantially symmetrically from the vicinity of the center of the ejection energy generating element 14 in the ejection direction immediately after bubbling by the ejection energy generating element 14. FIG. 8C shows a state in which the bubble B further grows and the ink starts to fly as droplets from the ejection port 8. Since the ceiling rises in the region II as it moves forward in the ejection direction, the bubble B that has begun to grow in a substantially symmetrical shape is larger on the ejection energy generating element 14 in the front as shown in FIG. 8B. Grows flat. At this time,
Ink on the ejection port 8 side of the ejection energy generation element 14 is ejected from the ejection port 8 as flying droplets from the ejection port 8. As shown in FIG. 8D, the flying droplets are separated from the ejection port 8, and the meniscus M of the ink recedes to the side opposite to the ejection port 8 in the liquid flow path 16 and the air bubbles are contracted. Ink is refilled from the liquid chamber 17 side into the liquid flow path 16 in the front, and again returns to the state before bubbling as shown in FIG. 8A.

In the liquid flow path having such a shape, as shown in FIG.
Unlike the liquid flow path in which the conventional fluid resistance element shown in FIG. 0 is arranged, there is no region where residual bubbles accumulated in the liquid flow path due to repeated foaming / defoaming at each ink ejection are fixed, so during refilling , And is located in front of the ejection energy generating element, and is ejected from the ejection port together with the flying droplets at the ejection timing. As a result, it is possible to prevent air bubbles from accumulating in the liquid flow path and to suppress adverse effects on printing such as non-ejection of bubbles to the utmost.

Reference Embodiment 2 FIG. 2 is a schematic sectional view showing the structure of the liquid flow path in the second reference embodiment of the ink jet head of the present invention.

A region I from the discharge port reference position 32 to the distance L1 has a ceiling portion composed of a horizontal portion toward the discharge port 8 and a liquid flow path height decreasing portion connected thereto, and from the distance L1. The area II up to the distance L2 is a linear straight line which has a non-zero inclination and is constant and has a liquid flow path height increasing portion (straight line) toward the discharge port and a portion (straight line) parallel to the arrangement surface of the discharge energy generating element. The area III from the distance L2 to the distance L3 has a ceiling part of a shape in which
It has a ceiling portion formed in a portion parallel to the arrangement surface of the discharge energy generating element.

The discharge energy generating element is located between the reference position of the discharge port and LH1 and LH2, and is L in FIG.
1 <LH1 and L2 <LH2. The relationship between L1 and LH1 is not specified, and the protrusion from the rear end L2 of the ejection energy generating element on the ink flow path from the projection point 32a of the ejection port reference position 32 of the ejection energy generating element as in the case of FIG. Distance to the flow side end, that is, 20 of LH2
If it is within%, more preferably within 10%, the object of the present invention can be sufficiently achieved.

( Embodiment of Inkjet Head ) FIG. 3 is a schematic sectional view showing the structure of a liquid flow path in an embodiment of the inkjet head of the present invention.

An area I from the discharge port reference position 32 to the distance L1 has a horizontal ceiling portion toward the discharge port and has a distance L.
A region II from 1 to the distance L2 has a ceiling portion formed by a curve increasing toward the ejection port, and a region III from the distance L2 to the distance L3 is a portion parallel to the arrangement surface of the ejection energy generating element. It has a ceiling part formed by.

In the case of FIG. 3, the connecting portions of the regions II and III are smoothly connected so that the liquid flow path height does not change suddenly, and the boundaries between the regions II and III are the respective regions. Let the rear end be the intersection point when linear approximation is performed.

The discharge energy generating element is located between the discharge port reference position 32 and LH1 and LH2, but in FIG. 3, L1 <LH1 and L2> LH2, as shown in FIGS. 1 and 2. The rear end of the discharge energy generating element is L2
Unlike the case where the ejection energy generating element protrudes, the rear end of the ejection energy generating element is included in the region II, which is effective in suppressing the accumulation of residual bubbles during ejection.

[0051]

As described above, according to the present invention,
Since the residual air bubbles during printing are not accumulated in the liquid flow path, it is possible to reduce the number of times of suction without imposing a load on the suction mechanism of the inkjet device. Since it is also possible to increase the number of defects and reduce defects during printing, it is possible to realize a more reliable inkjet head and apparatus.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a liquid flow path in a first reference mode of an inkjet head of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of a liquid flow path in a second reference mode of the inkjet head of the present invention.

FIG. 3 is a schematic cross-sectional view showing the structure of a liquid flow path in a third embodiment of the inkjet head of the present invention.

FIG. 4 is a schematic perspective view showing an example of an inkjet device of the present invention.

5 is a block diagram showing a configuration of a control circuit of the inkjet device shown in FIG.

6 is a schematic perspective view showing an example of an inkjet head that can be mounted on the inkjet device shown in FIG.

FIG. 7 is a schematic cross-sectional view showing, in an enlarged manner, an example around the ink ejection of the inkjet head according to the present invention.

8A to 8D are schematic cross-sectional views of a liquid flow path showing the behavior of ink in the liquid flow path of the inkjet head of the present invention with time.

FIG. 9 is a schematic cross-sectional view showing the structure of a liquid flow path in an example of a conventional inkjet head.

FIG. 10 is a schematic cross-sectional view showing the structure of a liquid flow path in another example of the conventional inkjet head.

[Explanation of symbols]

1 inkjet head 2 carriage 3 Recording medium 4 Conveyor rollers 5,6 shaft 7 ink tank 8 outlets 9 Ink supply member 10 PWB 11 compact pad 12 base plate 13 heater board 14 Discharge energy generation element 15 wires 16 ink flow path 17 Common liquid chamber 18 ink supply path 19 filters 20 Top plate 21 Discharge port forming surface 22 Orifice 23 Liquid flow path 24 Tapered part 31 Liquid resistance element 32 Discharge port reference position 100 control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-191028 (JP, A) JP-A-1-195050 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 2/05

Claims (4)

(57) [Claims] 1. A discharge port for discharging ink, a liquid flow path communicating with the discharge port, and a discharge pressure provided in the liquid flow path and used for discharging ink from the discharge port. In the inkjet head including a discharge pressure generating unit that generates a liquid flow path, a ceiling portion that faces the discharge pressure generating unit and that forms the liquid flow path is higher than a bottom portion that forms the liquid flow path. According to the size, three regions I and I are sequentially provided from the ejection port side.
I and region III, said regions I and II
I is parallel to a bottom surface portion that constitutes the liquid flow path, the region I has a higher liquid flow path height than the region III, and the region II is the liquid flow from the region III toward the region I. The connecting portion between the region II and the region III is smoothly connected so that the liquid flow path height does not change abruptly, and has a slope formed by a curve in which the path height increases. The region II is formed in a range of distances L1 to L2 from a reference point which is an intersection of the ceiling portion and the discharge port forming surface, and the bottom surface portion forming the liquid flow path is the reference to the bottom surface portion. The discharge pressure generating means is provided in a range of distances LH1 to LH2 from the projection point of the point, and the relationship between the ceiling portion and the bottom portion forming the liquid flow path satisfies the expression LH2 <L2. And inkjet head. 2. The ink jet head according to claim 1, wherein the ejection port forming surface is a surface of the member having the ejection port on the liquid flow path side. 3. The ink jet head according to claim 1, wherein the height of the liquid flow path is a height of a central portion in a plane orthogonal to a length direction of the liquid flow path. 4. An ink jet device comprising means for mounting the ink jet head according to claim 1. Description: