JPH07101059A - Thermal ink jet head - Google Patents

Abstract

PURPOSE:To provide a thermal ink jet head lowering the resistance of a passage while holding the capturing capacity of refuse and capable of performing stable injection at a high speed. CONSTITUTION:A plurality of heating elements 1 are formed to a heater wafer 10 composed of Si and a polyimide layer 9 is formed thereon. The pits 2 extending from the upper parts of the heating elements so as to be connected to ink passages 6, a common slit 3 and bypass pits 4 are formed to the polyimide layer 23 Nozzle passages 5, the ink passages 6 and an ink reservoir 7 are formed to a channel wafer 10 composed of Si from ODE. At the generation of an air bubble, the wall surfaces on the side of the nozzle passages 5 of the non-etched parts 11 between the nozzle passages 5 and the ink passages 6 reflect the pressure of the air bubble and energy is efficiently used. When air bubbles disappear, the pressure chambers are filled with ink from the extended part of the pits 2 by parallel movement. As a result, passage resistance is reduced and high speed driving is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal ink jet head for recording by generating bubbles in ink by heat generated from a bubble generating resistor and discharging the ink from nozzles by the generated bubbles. ,
In particular, it relates to the structure of the ink flow path of the thermal inkjet head.

[0002]

2. Description of the Related Art As a flow path structure of a conventionally known thermal ink jet head, for example, Japanese Patent Application Laid-Open No. Sho 61-61 is known.
As described in JP-A-230954, it is composed of a first Si substrate (heater substrate) and a second Si substrate (channel substrate), and a heating element is formed on the first Si substrate. There is a Si substrate on which a nozzle and an ink reservoir are formed by using ODE (anisotropic etching).

Further, in the thermal ink jet head described in JP-A-1-148560, in such a nozzle forming method, in order to surely control the length of the nozzle, the nozzle portion and the ink reservoir are respectively provided. Means are used in which they are formed as independent grooves, and the two are connected by a recess (bypass) provided in the polyimide layer of the first Si substrate. In the ink flow path of the thermal inkjet head formed in this way, since the bypass portion is narrow and bent, dust in the ink is likely to accumulate in the bypass portion and the ink supply to the nozzle is likely to be hindered. There was a problem. The dust accumulated in the bypass portion hinders the ink supply to the nozzles, deteriorates the repeated jetting characteristics of the nozzles, and causes defects such as small jetting drops or no jetting at all, resulting in poor image quality. On the other hand, it is extremely difficult to eliminate dust mixed in the head in the ink or in the manufacturing process, and it is inevitable that some dust is mixed in stochastically.

In order to solve this problem, for example, in the thermal ink jet head disclosed in Japanese Patent Laid-Open No. 5-155020, the bypass portion is formed in a slit shape, and even if dust remains in the bypass portion, other By supplying ink from the bypass portion, ink supply failure due to dust is avoided. However, since the bypass portion has a slit shape, a large amount of dust passes through the bypass portion, and a certain degree of ejection failure occurs.

Therefore, a structure has been proposed in which a plurality of ink flow paths are provided between the ink reservoir and the nozzle flow paths, and the ink flow paths function as filters. FIG. 11 is a perspective view showing a flow channel structure of a conventional thermal inkjet head, and FIG. 12 is a sectional view of the flow channel at the center of the nozzle,
FIG. 13 is a plan view of the flow channel structure. 1,
1a, 1b, 1c are heating elements, 2, 2a, 2b, 2c are pits, 3 is a common slit, 4 is a bypass pit, 5, 5
a, 5b and 5c are nozzle flow paths, 6, 6a, 6b and 6c are ink flow paths, 7 is an ink reservoir, 8 is a heater wafer, 9 is a polyimide layer, 10 is a channel wafer, 11 is an unetched portion, and 12 is It's garbage.

The heater wafer 8 has a plurality of heating elements 1
a, 1b, 1c, ... Are formed. in addition,
A polyimide layer 9 is formed. The polyimide layer 9 has pits 2a, 2b, 2c, ... Which define bubble forming regions, common slits 3 and bypass pits 4 formed above the heating elements 1a, 1b, 1c. On the other hand, the channel wafer 10 has nozzle channels 5a, 5b,
5c, ... and ink flow paths 6a, 6b, 6c ,.
And an ink reservoir 7 is formed. The bypass pit 4 provided on the heater wafer 8 connects the ink reservoir 7 and the ink flow paths 6a, 6b, 6c, ... And the common slit 3 is the nozzle flow paths 5a, 5b, 5c ,.
Are connected to the ink flow paths 6a, 6b, 6c, ... And bypass the unetched portion 11 between them.

As shown in FIG. 12, the ink flow from the ink reservoir 7 to the bypass pit 4, the ink flow path 6,
The nozzle flow path 5 is reached through the common slit 3. Of the dust 12 that has entered the ink reservoir 7, large ones are
Trapped in bypass pit 4. Bypass pit 4
The dust that is not trapped in 1 is extremely small, so that it does not clog the nozzle flow path 5 and is discharged to the outside as ink is discharged.

When large dust or air bubbles are trapped in the ink flow path 6, the fluid resistance in the ink flow path 6 becomes large, the ink supply to the nozzles becomes insufficient, and small dots or misfiring jetting defects occur. Cause of. At this time, as shown in FIG. 13, by supplying ink from a nozzle adjacent or in the vicinity through a common slit 3 connecting the channels, it is possible to supplement the ink supply to the nozzle that is short of ink. it can. As a result, the ink supply shortage can be suppressed to a level that is not noticeable as the actual image quality.

However, in the thermal ink jet head having such a structure, since the flow path structure is complicated, the flow path resistance is increased, the ink filling property is deteriorated, and the frequency for printing is decreased. There was a problem.
Further, by providing the ink flow path 6, the flow path becomes longer. Therefore, the length of the Si device that constitutes the head becomes long, and as a result, the number obtained from one Si wafer also becomes small. Therefore, if the yields are the same,
The long flow path causes an increase in the cost of one nozzle device.

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and while maintaining the ability to capture dust,
It is an object of the present invention to provide a thermal inkjet head that can reduce flow path resistance and perform high-speed and stable ejection.

[0011]

According to the present invention, there is provided a thermal ink jet head comprising a heater substrate having a bubble generating resistor and a channel substrate having a plurality of nozzle channels, ink reservoirs, and ink supply ports, wherein the channels are provided. A substrate is provided with a plurality of ink channels between a plurality of nozzle channels and an ink reservoir, and a polyimide layer is provided on the heater substrate, and the polyimide layer has at least the resistor for bubble generation. It is characterized in that a groove extending from the upper portion to the ink channel formed in the channel substrate is provided.

[0012]

According to the present invention, the function of filtering for capturing dust is obtained by the ink flow path provided in the channel substrate. Moreover, since the groove extends not only to the upper portion of the bubble generating resistor but also to the ink flow path, heat is generated in the bubble generating resistor to generate bubbles,
After that, when the bubbles contract, ink is refilled into the upper portion of the bubble generating resistor from the extended portion of the first groove other than the upper portion of the bubble generating resistor. At this time, since the ink only moves in parallel, the flow path resistance can be reduced and the printing frequency can be improved. Further, when bubbles are generated on the bubble generating resistor, the unetched portion between the nozzle flow path and the ink flow path and the end of the groove on the ink flow path side suppress the propagation of pressure due to bubble generation. Therefore, the pressure of the bubbles can be efficiently used toward the opening of the nozzle. Further, unlike the conventional case, it is not necessary to separately form the concave portion on the upper portion of the bubble generating resistor and the groove for connecting the ink flow channel and the nozzle flow channel, so that the total length can be suppressed to be short and can be obtained from one wafer. The number of nozzle devices to be used is increased, and the cost can be reduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view showing a flow channel structure in a first embodiment of an ink jet head of the present invention, FIG. 2 is a sectional view of the flow channel at the center of the nozzle, and FIG. It is a top view of a structure. Reference numerals in the drawings are the same as those in FIGS.
Is the same as.

The thermal ink jet head is constructed by bonding a channel wafer 10 and a heater wafer 8 having a polyimide layer 9 formed thereon. The heater wafer 8 is made of, for example, Si and has a plurality of heating elements 1.
a, 1b, 1c, ... And a common electrode (not shown),
Individual electrodes and the like are formed. A polyimide layer 9 is formed thereon. The polyimide layer 9 has heating elements 1a, 1
Pit 2 connected to the ink flow path 6 from the upper part of b, 1c
a, 2b, 2c, ... And each pit 2a, 2b, 2
A common slit 3 for connecting c, ... In the nozzle array direction, an ink reservoir 7, and ink flow paths 6a, 6
Bypass pit 4 for connecting b, 6c, ...
Are formed by etching, for example. on the other hand,
The channel wafer 10 is also made of, for example, Si, and has nozzle flow paths 5a, 5b, 5c, ...
The ink reservoir 7 is formed of ODE, for example.

In the conventional thermal ink jet head, the pits 2a, 2b, 2c, ...
Only the upper part of b, 1c, ...
As shown in FIG. 2, the wall surface of the pit 2 is not formed on the ink reservoir 7 side of the heating element 1, and the flow path is directly connected to the common slit 3. The pit 2 is substantially connected to the ink flow path 6. It is connected.

Since the pit 2 is connected to the ink flow path 6, the unetched portion 11 between the nozzle flow path 5 and the ink flow path 6 can be arranged close to the heating element 1.
That is, as shown in FIG. 2, the nozzle flow path 5 formed in the channel wafer 10 has a length substantially from the nozzle opening to the ink reservoir 7 side of the heating element 1 so as to cover the bubble generation region of the heating element 1. Can be the same length. Unetched portion 11 between nozzle channel 5 and ink channel 6
Are bypassed by the pit 2 and the common slit 3.

As shown in FIG. 2, the ink flow reaches the pit 2 and the nozzle flow path 5 from the ink reservoir 7 through the bypass pit 4, the ink flow path 6, and the common slit 3. Of the dust 12 that has entered the ink reservoir 7, large dust is trapped in the bypass pit 4. The dust 12 that has passed through the bypass pit 4 enters the ink flow path 6. However, the portion of the ink flow path 6 is bent.
In addition, the cross-sectional area of this portion can be reduced, and the dust 12 can be reliably trapped. The dust that has not been trapped in the ink flow path 6 is so small that it does not clog the nozzle flow path 5 and is discharged to the outside as ink is ejected.

When large dust or air bubbles are trapped in the ink flow path 6, the fluid resistance in the ink flow path 6 becomes large, and the ink supply to the nozzles becomes insufficient, resulting in small dots and ejection failure such as misjet. Cause of. At this time, as shown in FIG. 3, it is possible to supplement the ink supply to the nozzles in which the ink is insufficient by supplying the ink from the adjacent or nearby nozzles via the common slit 3 connecting the pits 2. it can. As a result, the ink supply shortage can be suppressed to a level that is not noticeable as the actual image quality.

FIG. 4 is an explanatory view of a bubble generation process in the vicinity of the heating element 1 of the first embodiment of the thermal ink jet head of the present invention, and FIG. 5 is a bubble generation in the vicinity of the heating element 1 of the conventional thermal ink jet head. 6 is an explanatory diagram of a process of FIG. 11, those parts that are the same as those corresponding parts in FIGS. 11 to 13 and FIGS. 1 to 3 are designated by the same reference numerals, and a description thereof will be omitted. 13 is a bubble. 4 and 5 schematically show the generation process of bubbles generated on the heating element 1 with the passage of time.

In the conventional flow path structure of the thermal ink jet head, as shown in FIG. 5, the heating element 1 is surrounded by the pits 2 to regulate the shape of the generated bubble and secure a stable pressure propagation characteristic. ing. That is, the bubbles generated by the heat generation of the heating element 1 grow upward along the side wall of the pit 2. The pressure of the bubbles at that time is dispersed and acts in the direction toward the opening of the nozzle flow path 5 and the direction toward the ink reservoir 7. The pressure in the direction toward the ink reservoir 7 reaches the wall surface of the unetched portion 11 on the nozzle channel side.

In the first embodiment of the present invention, as shown in FIG. 2, the unetched portion 11 can be arranged near the end of the heating element 1 on the ink reservoir side. In such a configuration, as shown in FIG. 4, the growth direction of the bubble has a high velocity on the wall surface side of the pit 2, and the pressure direction has an inclination instead of the vertical direction. However, the wall surface on the nozzle channel 5 side of the unetched portion 11 formed when the nozzle channel 5 is formed by ODE is formed obliquely, as shown in FIG. Is converted into pressure for drop injection. At this time, as shown in FIG. 4, the pressure also escapes to the common slit 3 side, but since it reaches the side wall of the common slit 3 immediately, the pressure loss is not so great, and it is sufficiently stable as compared with the conventional case. The resulting drop discharge was obtained. In this way, the wall surface of the unetched portion 11 on the nozzle flow path 5 side functions as a pressure reflection wall that propagates the pressure of the bubble to the nozzle side.

After a bubble is generated and ink is ejected from the opening of the nozzle, the bubble disappears and the ejected ink is refilled. At this time, the ink is moved in parallel from the common slit 3 side of the pit 2 to fill the upper part of the heating element 1 with the ink. As compared with a conventional thermal ink jet head in which ink is filled so as to sneak into the pits 2 from the nozzle flow passage 5, the flow passage resistance at the time of refilling the ink is small, and refilling can be performed at high speed. it can.

When dust 12 or the like is trapped in the ink flow path 6, the ink is supplied from the adjacent or nearby ink flow path 6 via the common slit 3. Even in such a case, since the ink flow path is bent only once at a right angle from the common slit 3, the flow path resistance is small and high-speed refilling can be performed.

FIG. 6 is a graph showing the characteristics of the thermal ink jet head according to the first embodiment of the present invention. As the operating frequency of the thermal inkjet head rises, ink filling cannot catch up, and thus defects such as stripes appear in the printed image. In the first embodiment of the present invention, since the pit 2 is connected to the common slit 3, the flow path resistance is small and the ink supply property to the upper portion of the heating element 1 is improved. Therefore, as can be seen from FIG. 6, compared with the conventional thermal inkjet head,
The frequency at which defects appear is high. As a result, the thermal inkjet head of the present invention enables high-speed printing.

FIG. 7 is a plan view showing a second embodiment of the thermal ink jet head of the present invention. In the figure, the same parts as those in FIG. 2 and FIG. In the thermal inkjet head shown in the above-mentioned first embodiment, since the heating element 1 and the common slit 3 are close to each other, the occurrence of crosstalk between the nozzles cannot be avoided. In order to avoid this, the nozzle can be divided into a plurality of blocks, the common slit 3 is provided for each block, and the flow path can be blocked between the blocks. For example, in FIG. 7, a block is formed by four nozzles, and the common slit 3 is divided and arranged for each block. The other configuration is the same as that of the first embodiment.

FIG. 8 is an explanatory diagram of the ink ejection state of the thermal ink jet head in the second embodiment of the present invention, and FIG. 9 is an explanatory diagram of the ink ejection state of the conventional thermal ink jet head. Here, it is assumed that four nozzles are set as one block and nozzles in one block are simultaneously driven, and each block is sequentially driven. 8,
In FIG. 9, nozzles # 1 to # 4 constitute one block,
The nozzle # 5 is assumed to belong to the adjacent block. Nozzles adjacent to the next block of each block are most likely to become unstable due to interference with adjacent nozzles belonging to the next block, and image defects are likely to occur. This state is shown in Figure 9.
Is shown in. In the example shown in FIG. 9, the nozzles # 3 and # 4 are affected by the interference with the nozzle # 5 belonging to the next block.

Therefore, since the common slit 3 is divided and installed for each block as in the above-described second embodiment, the ink flow between the blocks does not occur.
No interference with adjacent nozzles belonging to the next block,
Crosstalk between blocks can be suppressed, and FIG.
It is possible to obtain a normal injection state as shown in. In FIG. 8 and FIG. 9, there is a difference in the height direction between the common slit 3 and the nozzle flow path 5, but it is shown here as a plane.

When the adjacent nozzles in the block are driven almost simultaneously, the phenomenon of crosstalk also appears. In order to avoid this, the printing order of each nozzle in the block may be interlaced. That is, the nozzles in the block are not driven at the same time, and the adjacent nozzles are sequentially driven so as not to be sequentially driven. By such driving, the driving between the adjacent nozzles can be temporally separated, crosstalk can be avoided, and normal injection can be performed.

In the second embodiment described above, other operations, for example, the process of bubble generation and ink refill after disappearance are almost the same. As for the characteristics, as shown in FIG. 6, the operating frequency can be improved as compared with the conventional thermal inkjet head.

FIG. 10 is a plan view showing a third embodiment of the thermal ink jet head of the present invention. Reference numerals in the figure are the same as those in FIGS. 2 and 3. In this third embodiment,
Each pit 2 is connected to the ink flow path 6 without using a common slit. In the above-mentioned first and second embodiments, even when a certain flow path is blocked by the dust 12, it is guaranteed that the ink will be replenished through the common slit 3. Due to the improvement, when there is no dust, the common slit 3 becomes unnecessary.
In that case, the thermal inkjet head having the structure shown in FIG. 10 can be used. In this case, the filter function of the ink flow path 6 is not necessary, but by providing the ink flow path 6 and providing the unetched portion 11 between the nozzle flow path 5 and the ink flow path 6, The pressure of the bubble is reflected by the wall surface on the nozzle flow path 5 side, and the energy at the time of generating the bubble can be efficiently used. Further, since the pits 2 extend to the ink flow path 6, the flow path resistance can be reduced and the ink can be refilled at high speed after the bubbles disappear.

In each of the above embodiments, the bypass pit has a slit shape. However, the bypass pit is not limited to this and may be an individual bypass pit corresponding to each nozzle. Further, in the individual bypass pit, only the lower portion of the unetched portion between the ink reservoir 7 and the ink flow path 6 is made to communicate, or the ink reservoir 7 side or the ink flow path 6 side may be formed in a slit shape. it can. In the third embodiment, it is also possible to cut the unetched portion between the ink reservoir 7 and the ink flow path 6 and use no bypass pit.

Further, in each of the above-described embodiments, one ink flow path 6 is provided corresponding to each nozzle, but the cross-sectional area of the ink flow path 6 is narrow in order to exert the effect of the filter. Better. As described above, since the ink flow path 6 is formed by ODE, it is possible to easily create a flow path having a narrow cross-sectional area with high accuracy simply by reducing the opening size of the mask during ODE. Therefore, for each nozzle, 2
It is possible to form more than one ink flow path 6 such as three or three to form a fine filter.

When a plurality of ink flow paths 6 correspond to one nozzle in this way, it is possible to deal with dust to some extent without using a common slit as in the third embodiment. An inkjet head can be created. That is, even if dust is trapped in a certain ink flow path 6, ink is supplied from the other ink flow path 6, so that some ejection failure can be avoided.

[0034]

As is apparent from the above description, according to the present invention, it is possible to prevent the nozzles from being clogged by the ink flow path portion and to extend the pits so as to be connected to the ink flow path. By making it exist, the flow path resistance can be reduced, and as a result, the operating frequency can be improved and a printer having a high recording speed can be obtained. In addition, by connecting the pits and the ink flow paths, the total flow path length can be shortened, and the device can be miniaturized. As a result, a large number of wafers can be obtained per wafer, so that the cost can be reduced. it can. Furthermore, when connecting the pit and the ink flow path, the unetched part of the nozzle flow path and the ink flow path can be arranged in the vicinity of the end of the heating element on the ink reservoir side. There is an effect that the energy of bubbles generated on the heating element can be efficiently used.

[Brief description of drawings]

FIG. 1 is a perspective view showing a flow path configuration in a first embodiment of an inkjet head of the present invention.

FIG. 2 is a cross-sectional view of the flow path at the center of the nozzle in the first embodiment of the inkjet head of the present invention.

FIG. 3 is a plan view of the flow path configuration in the first embodiment of the inkjet head of the present invention.

FIG. 4 is an explanatory diagram of a bubble generation process in the vicinity of the heating element 1 of the first embodiment of the thermal inkjet head of the present invention.

FIG. 5 is an explanatory diagram of a bubble generation process in the vicinity of the heating element 1 of the conventional thermal inkjet head.

FIG. 6 is a graph showing characteristics of the thermal inkjet head according to the first embodiment of the present invention.

FIG. 7 is a plan view showing a second embodiment of the thermal inkjet head of the present invention.

FIG. 8 is an explanatory diagram of an ink ejection state of a thermal inkjet head according to a second embodiment of the present invention.

FIG. 9 is an explanatory diagram of an ink ejection state of a conventional thermal inkjet head.

FIG. 10 is a plan view showing a third embodiment of the thermal inkjet head of the present invention.

FIG. 11 is a perspective view showing a flow path configuration of a conventional thermal inkjet head.

FIG. 12 is a sectional view of a flow path at the center of a nozzle in a conventional thermal inkjet head.

FIG. 13 is a plan view of a flow channel configuration in a conventional thermal inkjet head.

[Explanation of symbols]

1, 1a, 1b, 1c heating element, 2, 2a, 2b, 2c
Pit, 3 common slit, 4 bypass pit,
5, 5a, 5b, 5c Nozzle channel, 6, 6a, 6b,
6c ink flow path, 7 ink reservoir, 8 heater wafer, 9 polyimide layer, 10 channel wafer, 1
1 unetched part, 12 dust, 13 bubbles.

Claims (1)

[Claims] 1. A thermal inkjet head comprising a heater substrate having a bubble generating resistor and a channel substrate having a plurality of nozzle channels, an ink reservoir and an ink supply port, wherein the channel substrate has a plurality of nozzle channels. A plurality of ink flow paths between the ink reservoir and the ink reservoir, and a polyimide layer on the heater substrate,
The thermal inkjet head is characterized in that the polyimide layer is provided with at least a groove extending from an upper portion of the bubble generating resistor until it is connected to the ink flow path formed in the channel substrate.