JP3048055B2 - Liquid jet recording head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid jet recording head.

2. Description of the Related Art Non-impact recording methods have recently attracted attention in that the generation of noise during recording is extremely small to a negligible level. Among them, the so-called ink jet recording method, which can perform high-speed recording and can perform recording on so-called plain paper without requiring a special fixing process, is an extremely powerful recording method. Some have been proposed and commercialized with improvements, while others are still being put to practical use.

In such an ink jet recording method, recording is performed by flying droplets of a recording liquid called so-called ink and attaching the droplets to a recording member. The control method for controlling the flying direction of the generated recording liquid droplet is roughly classified into several types.

First, the first method is disclosed in, for example, US Pat. No. 3,060,429 (Tele type method),
Recording liquid droplets are generated by electrostatic attraction, and the generated recording liquid droplets are subjected to electric field control according to a recording signal, and recording is performed by selectively adhering the recording liquid droplets onto a recording member. It is.

More specifically, in more detail, an electric field is applied between the nozzle and the accelerating electrode to discharge a uniformly charged droplet of the recording liquid from the nozzle, and the discharged droplet of the recording liquid is converted into a recording signal. In accordance with this, recording is performed by causing the droplets to fly between the xy deflection electrodes configured so as to be electrically controllable and selectively adhering small droplets onto the recording member by a change in the intensity of the electric field.

The second method is described, for example, in US Pat. No. 3,596,275,
The method disclosed in US Pat. No. 3,298,030 and the like (S
Weet method), in which droplets of a recording medium whose charge amount is controlled are generated by a continuous vibration generation method, and the generated droplets whose charge amount is controlled are subjected to a uniform electric field. The recording is performed on the recording member by flying between the deflection electrodes.

More specifically, a charging electrode configured to apply the signal is separated by a predetermined distance in front of an orifice (ejection port) of a nozzle, which is a part of a recording head provided with a piezoelectric vibrating element. The piezoelectric vibrating element is mechanically vibrated by applying an electric signal of a constant frequency to the piezoelectric vibrating element, and a droplet of the recording liquid is discharged from the discharge port. At this time, a charge is electrostatically induced in the recording liquid droplet discharged by the charging electrode, and the droplet is charged with a charge amount according to the recording signal. When the droplet of the recording liquid whose charge amount is controlled flies between the deflection electrodes to which a constant electric field is uniformly applied, the droplet is deflected according to the added charge amount and carries a recording signal. Only the recording material can be deposited on the recording member.

The third method is a method (Hertz method) disclosed in, for example, US Pat. No. 3,416,153, in which an electric field is applied between a nozzle and a ring-shaped charging electrode, and a continuous vibration generation method is used. This is a method in which small droplets are generated and atomized for recording. That is, in this method, the atomization state of the small droplet is controlled by modulating the electric field intensity applied between the nozzle and the charging electrode in accordance with the recording signal, and the image is recorded with the gradation of the recorded image.

The fourth system is, for example, a system (Stemme system) disclosed in US Pat. No. 3,747,120, and this system is fundamentally different from the above three systems in principle.

That is, in each of the three methods, the droplet of the recording liquid discharged from the nozzle is electrically controlled during the flight, and the droplet carrying the recording signal is selectively attached to the recording member. On the other hand, according to the Stemme method, recording is performed by ejecting a small droplet of recording liquid from an ejection port in accordance with a recording signal.

That is, in the Stemme method, the piezoelectric vibrating element attached to the recording head having the ejection port for ejecting the recording liquid includes:
Applying an electrical recording signal, converting the electrical recording signal into mechanical vibration of a piezo-vibrating element, and ejecting a droplet of the recording liquid from the ejection port in accordance with the mechanical vibration to cause the droplet to fly and adhere to the recording member. Is to record.

Each of these four conventional methods has its own features, but on the other hand, there are points that can be solved.

That is, in the first to third methods, the direct energy of the generation of the droplet of the recording liquid is electric energy,
Droplet deflection control is also electric field control. Therefore, the first method is simple in structure, but requires a high voltage to generate small droplets, and is not suitable for high-speed printing because it is difficult to use a multi-nozzle recording head.

The second method enables multi-nozzle recording heads and is suitable for high-speed recording. However, the method is complicated in structure, and the electrical control of small droplets of recording liquid is difficult and difficult. Are liable to occur.

The third method has a feature that an image having excellent gradation can be recorded by atomizing a recording liquid droplet, but on the other hand, it is difficult to control the atomization state, and fogging occurs in the recorded image. In addition, there are problems such as the fact that it is difficult to use a multi-nozzle recording head, and it is not suitable for high-speed recording.

The fourth scheme has relatively many advantages over the first to third schemes. That is, in order to perform recording by discharging the recording liquid from the discharge port of the nozzle on demand (on-demand), it is simple in terms of the configuration. It is not necessary to collect small droplets that are not required for recording an image, and there is no need to use a conductive recording liquid as in the first and second methods, and the recording liquid material Has a great advantage such as a large degree of freedom. However, on the other hand, it is difficult to form a multi-nozzle recording head because there are problems in processing the recording head and it is extremely difficult to reduce the size of the piezoelectric vibrating element having a desired resonance number. However, since the recording liquid droplets are ejected and fly by the mechanical energy of mechanical vibration of the piezo-vibration element, it is not suitable for high-speed recording.

Further, Japanese Patent Application Laid-Open No. 48-9622 (the aforementioned U.S. Pat.
No. 120) describes, as a modification, the use of thermal energy instead of the mechanical vibration energy by means such as the piezo-vibration element.

That is, the above-mentioned publication describes a so-called bubble jet liquid jet recording apparatus which uses a heating coil for directly heating a liquid as a pressure increasing means instead of a piezo vibrating element in order to generate a vapor which causes a pressure increase. I have.

However, the above publication discloses that a heating coil serving as a pressure increasing means is energized to directly evaporate the liquid ink in a bag-shaped ink chamber (liquid chamber) having only one opening through which the liquid ink can enter and exit. However, there is no suggestion as to how to heat the liquid when the liquid is continuously and repeatedly discharged. In addition, since the position where the heating coil is provided is provided at the deepest part of the bag-shaped liquid chamber far from the supply path of the liquid ink, in addition to being complicated in terms of the head structure, continuous It is not suitable for repeated use.

Moreover, according to the technical contents described in the above-mentioned publication, it is not possible to quickly form a preparation state for the next liquid discharge after performing the liquid discharge with the generated heat which is practically important.

As described above, the conventional method has advantages and disadvantages in terms of configuration, high-speed recording, multi-nozzle recording head, generation of satellite dots and occurrence of fogging of a recorded image, etc. There was a restriction that only the application was possible.

As described above, many of the conventional recording apparatuses have many problems in terms of structure, high-speed recording above 4 KHz, processing, and high density exceeding 16 lines / mm. In addition, JP
No. -87960, by changing the area of the heating element,
Although the recording dots are made uniform, ejection stability is not always obtained by changing the area.

Japanese Patent Publication No. 61-59912 describes an example in which a single nozzle is collected and a multi-nozzle is formed.However, this method has a limit of several nozzles / mm at the maximum, and high-definition image quality cannot be obtained. . Further, Japanese Patent Application Laid-Open No. 55-27281 discloses a method in which a groove is formed in a substrate by fine cutting to form a nozzle, but this method also employs 10 nozzles as described in the specification. / mm is the limit.
In order to aim for higher definition images, it is necessary to increase the density of the heat generating part, in other words, the arrangement of the nozzles to 16 nozzles / mm or more, and the most effective nozzle forming method to achieve this is:
As disclosed in Japanese Patent Publication No. 62-59672, a flow path and a nozzle are formed by providing a flow path wall with a photosensitive resin on a heating element substrate and joining the flow path wall with a lid substrate. However, the relationship between the shape of the nozzle formed by the forming method described in JP-B-62-59672 and the ink droplet ejection characteristics is not shown at all, and in particular, 16 nozzles / m
When the diameter is more than m, the nozzle becomes extremely fine.Thus, although the nozzle shape is greatly related to the ink droplet ejection characteristics, this point is not described at all or even suggested. , 16 lines / m
When manufacturing a high-density head of m or more, it was completely unknown what nozzle shape would provide stable ejection characteristics. In the so-called bubble jet method, in which a liquid is directly heated and discharged in order to generate a vapor that causes a pressure rise, advanced thin film technologies such as sputtering, vapor deposition, and etching are used to form a heating element and a flow path. Processing accuracy is required and greatly affects ink ejection. In other words, there is a drawback that stable ejection cannot be performed due to variations in the nozzle shape. Also, the size of the nozzle is a major factor in the size of the ink droplet,
Depending on the shape of the nozzle, it has a drawback that the nozzle becomes mist-like, the flying speed is significantly reduced, and the ejection direction is largely different from the intended direction.

Further, in the case of a multi-nozzle arrayed at a high density of 16 nozzles / mm or more, since the adjacent nozzles are very close, ink droplets ejected from a plurality of adjacent nozzles, or ink columns, When they are ejected almost simultaneously, merging and merging can often occur. This is because the size of the ink droplet to be ejected is generally larger than the diameter of the orifice. Another reason is that the condition for ejecting the ink droplet is not always preferable (unstable ejection condition, for example, splash, Or, it occurs when the ink droplets (pillars) are in asymmetric ejection. These are largely due to the shape and symmetry of the nozzle. Therefore, the nozzle shape, which has not been a problem in the multi-inkjet having a low density, is an extremely large problem in terms of the ink droplet ejection characteristics in the multi-inkjet having a higher density aiming at a copier or the like.

In addition, the high frequency responsiveness of the bubble jet method depends on the above-described ink droplet ejection characteristics, that is, driving at a high speed condition (for example, 4 KHz) despite being greatly changed by the shape of the nozzle. The relationship between the nozzle shape and the ejection stability in the case of (above) is not described in the prior art, and it is not clear how to shape the nozzle.

An object of the present invention is to solve the above-mentioned disadvantages, and an object of the present invention is to provide a liquid jet recording head that is excellent in ink droplet ejection stability, ejection efficiency, and ejection frequency. .

It is another object of the present invention to improve the ink droplet ejection performance of a multi-nozzle type head arranged at a higher density (for example, arranged at a high density of 16 nozzles / mm or more).

Still another object of the present invention is to improve the ink droplet ejection performance of a multi-nozzle head that is driven at a higher speed (for example, above 4 kHz).

Configuration In order to achieve the above object, the present invention has a thermal energy generating means for applying thermal energy to a recording liquid in a liquid chamber, and the thermal energy action causes bubbles in a thermal energy action section in the recording liquid. A liquid jet recording head for performing recording by causing the recording liquid to fly as droplets from an ejection orifice with an acting force accompanying an increase in the volume of the bubble and attaching the recording liquid to a recording surface, and a response frequency of 4 kHz or more. In a liquid jet recording head that performs high-density printing of 16 lines / mm or more, when the lateral length a and the vertical length b of the orifice do not substantially match, the ratio is allowed. The value is 0.6 ≦ a / b ≦ 1.4.

In addition, such a relational expression has a high density of 16 lines / mm or more,
It is suitable to be applied to copiers and the like that require high-definition quality. In addition, in order to form a high-definition image like a copier, the number of dots to be printed on the paper surface is inevitably increased because the pixel diameter is small. Takes a lot of time. Therefore, it is preferable to drive the head at a high driving frequency, and from that point of view, the above-described relational expression of the present invention drives at a high frequency (for example, 4 kHz).
Above).

First, the principle of ink ejection by bubble jet will be described with reference to FIG. In the figure, 21 is a lid substrate, 22
Is a heating element substrate, 27 is a selection (independent) electrode, 28 is a common electrode,
29 is a heating element, 30 is ink, 31 is a bubble, and 32 is a flying ink droplet.

(A) is a steady state, in which the surface tension of the ink 30 and the external pressure are in an equilibrium state at the orifice surface.

3B shows a state in which the heater 29 is heated until the surface temperature of the heater 29 sharply rises and the adjacent ink layer is heated until a boiling phenomenon occurs, and minute bubbles 31 are scattered.

(C) shows a state in which the heater 29 rapidly vaporizes the adjacent ink layer on the entire surface, instantaneously vaporizes and forms a boiling film, and the bubbles 31 grow. At this time, the pressure in the nozzle rises by an amount corresponding to the growth of the bubble, the balance with the external pressure on the orifice surface is lost, and the ink column starts to grow from the orifice.

(D) is a state in which the bubble has grown to the maximum, and the ink 30 corresponding to the volume of the bubble is pushed out from the orifice surface. At this time, no current is flowing through the heater 29, and the surface temperature of the heater 29 is decreasing. The maximum value of the volume of the bubble 31 is slightly delayed from the timing of applying the electric pulse.

(E) shows a state where the bubble 31 is cooled by ink or the like and starts to contract. At the front end of the ink column, the ink moves forward while maintaining the pushed speed, and at the rear end, the ink flows backward from the orifice surface into the nozzle due to a decrease in the nozzle internal pressure due to the contraction of the bubble, and the ink column is constricted. .

(F) is a state in which the bubble 31 further contracts, the ink comes into contact with the heater surface, and the heater surface is cooled more rapidly. At the orifice surface, the external pressure is higher than the internal pressure of the nozzle, so that the meniscus largely enters the nozzle. The tip of the ink column becomes a droplet and moves in the direction of the recording paper.
Flying at a speed of 10m / sec.

(G) is a process in which the ink is supplied (refilled) to the orifice again by capillary action and returns to the state of (a).
The bubbles have completely disappeared.

FIG. 1 is a perspective view for explaining an embodiment of a recording head according to the present invention, FIG. 2 is a view of the recording head in FIG. 1 viewed from the orifice side, and FIG. FIG. 4A is a diagram showing a cover substrate, FIG. 4B is a diagram showing a heating element strip, and FIG. 4 is a rear view of the cover substrate of FIG. 3A. In the figure, 23 is an ink supply port, 24 is an orifice, 25 is a groove (flow path), and 26 is a region for forming a liquid chamber. The cover substrate 21 has a groove 25 forming an ink flow path and a portion 26 forming a common liquid chamber. On the heating element substrate 22, a heating element (heater) 29, a selection (independent) electrode 27 for driving the heating element 29, and a common electrode 28 are formed. The lid substrate 21 and the heating element substrate 22 are bonded as shown in FIG. 1, and an orifice 24 is formed by the groove 25. The groove 25 is formed by etching the base (eg, glass) of the lid substrate. Therefore, the horizontal / vertical ratio of the orifice 24 is
It can be set freely by adjusting the etching rate and / or etching time of.

As a result of various experiments, the present inventors have found that when the horizontal diameter a and the vertical diameter b of the orifice in FIG. 2 satisfy the relationship of 0.5 ≦ a / b ≦ 1.5, the ink is more stably formed than the orifice. I found that a drop was ejected.

The present inventors conducted an experiment using a recording head having the configuration shown in FIG. 1 at a drive voltage of 25 V, a current value of 0.2 A, and a frequency of 4.8 KHz while changing the orifice diameter. The results shown in Table 1 were obtained. Obtained.

Here, the diameter of the orifice means the maximum diameter in the horizontal and vertical directions.

In addition, Table 2 below shows an example of the results of trial production and evaluation of various heads by the present inventors. The number of nozzles in the prototype head unit was 256 in all cases. The liquid used was not ink but a vehicle whose physical properties were substantially the same as those of the ink. This is because a transparent liquid is needed to observe the bubbles.

Further, in the embodiment of the present invention, the orifice is rectangular, but the present invention is of course also effective in shapes such as a circle, an ellipse, and a rhombus.

Another embodiment will be described with reference to FIGS. 6 (a) to 6 (f).

In the figure, 8 is a flow path, 9 is a liquid chamber, 10 is a heating element substrate (silicon, alumina, glass, etc.), 11 is a heating element, 12 is a dry film, 13 is a photomask, 15 is an orifice, and 16 is a lid substrate. , 17 and 18 are lead electrodes, and 19 is a tapered portion.
(A) On a heating element substrate 10, a heating element 11 and lead electrodes 17 and 18 are formed by a technique such as a CVD method.
(B) After that, the heating element substrate 10 is covered with the dry film 12, and (c) the photomask 13 for forming the flow path 8 and the liquid chamber 9 is aligned with the heating element substrate 10; Thus, a substrate having the heating element 11 and the flow path 8 is obtained. A tapered portion 19 is provided at the tip of the flow channel 8.
(E) Further, the lid substrate 16 is adhered to the heating element substrate 10 shown in (d) to form a recording head. (F) is Z- of (e).
In the sectional view taken along the line Z ', CC' of FIG. 7E is cut by dicing or the like to form an orifice 15, thereby completing the recording head. As the dry film 12, a commercially available ordinary film can be used. When the flow path 8 is formed in the dry film 12, the horizontal / vertical ratio of the orifice 15 can be easily set by adjusting the width of the flow path 8 of the mask pattern and / or the thickness of the dry film 12. That is, the horizontal length can be adjusted by the mask pattern width, and the vertical length can be adjusted by the dry film thickness, so that the present invention can be easily realized. In the embodiment of the present invention, an example using a solid dry film has been described, but a liquid film can also be used.

Incidentally, as the manufacturing process and material of the recording head, those described in JP-A-61-249766 may be employed.

Effects As is apparent from the above description, according to the present invention, it is possible to provide a high-density and high-integration inkjet recording head having excellent ejection stability due to the relationship between the horizontal diameter and the vertical diameter of the orifice. Can be.

[Brief description of the drawings]

FIG. 1 is a perspective view for explaining one embodiment of a liquid jet recording head according to the present invention, FIG. 2 is a view of the recording head in FIG. 1 viewed from the orifice side, and FIG. 4A is a diagram showing a cover substrate, FIG. 4B is a diagram showing a heating element substrate, FIG. 4 is a rear view of the cover substrate of the recording head, and FIG. 5 is a diagram showing bubble jet ink of the recording head. FIG. 6 is a diagram for explaining the principle of ejection and bubble generation / dissipation. FIG. 6 is a diagram showing a manufacturing process of another embodiment of the present invention. 8 ... flow path, 9 ... liquid chamber, 10, 22 ... heating element substrate, 11, 29
... Heating element (heater), 12 ... Dry film, 13 ...
Photomask, 15, 24 Orifice, 16, 21 Cover substrate, 17, 27 Independent electrode, 18, 28 Common electrode, 19 Tapered part, 23 Ink supply port.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoaki Nakano 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (56) References JP-A-55-132253 (JP, A) JP-A Sho 60-208252 (JP, A) JP-A-63-42868 (JP, A) JP-A-56-46769 (JP, A) JP-A-60-208248 (JP, A)

Claims (1)

(57) [Claims] 1. A thermal energy generating means for applying thermal energy to a recording liquid in a liquid chamber, wherein the thermal energy action causes bubbles to be generated in a thermal energy action section in the recording liquid, and the volume of the bubbles is increased. A liquid jet recording head that flies the recording liquid as droplets from an ejection orifice with an acting force accompanying the increase and adheres to a recording surface to perform recording, and has a response frequency of 4 kHz or more and a frequency of 16 lines / mm or more. In a liquid jet recording head for performing high-density printing, when the lateral length a and the vertical length b of the orifice do not substantially match, the allowable value of the ratio is 0.67 ≦ a / b. ≦ 1.4. A liquid-jet recording head.