JP2952091B2 - Ink droplet ejection recording method and recording head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink-jet recording head for recording a recording material such as paper, a resin sheet, cloth, or the like by using thermal energy to fly droplets, and a recording method thereof. Related to the device.

[0002]

2. Description of the Related Art An ink jet recording method for forming an image by applying a liquid or a solid recording medium (ink) which can be melted by heating to a recording material using thermal energy is capable of high-speed recording. It has the advantages of high target recording quality and low noise. Further, this method has many excellent advantages such as relatively easy recording of a color image, recording on plain paper and the like, and further, easy downsizing of the apparatus.

A recording apparatus using such an ink jet recording method generally includes a discharge port for discharging ink as flying ink droplets, an ink path communicating with the discharge port, and an ink provided in a part of the ink path. A recording head having energy generating means for applying ejection energy to the ink in the path for ejection. For example, JP-B-61-59911, JP-B-61-59912, JP-B-61-59913, and JP-B-61-59914 each use an electrothermal converter as an energy generating means and apply an electric pulse. There is disclosed a method of ejecting ink by applying the generated thermal energy to ink.

That is, according to the recording methods disclosed in the above publications, the ink subjected to the action of thermal energy undergoes a state change accompanied by a sharp increase in volume, and bubbles in the film boiling region based on this state change are produced. Mainly due to growth and contraction
Ink is ejected from an ejection port at the tip of the recording head, and the ejected ink droplets adhere to a recording medium to form an image. According to this method, the ejection ports in the recording head can be arranged at a high density, so that a high-resolution, high-quality image can be recorded at a high speed. A recording apparatus using this method includes a copier, It can be used as information output means in a printer, facsimile, or the like.

On the other hand, as an ink jet recording method which uses thermal energy but whose conditions are unknown, Japanese Patent Application Laid-Open No.
There is a method described in JP-A-4-161935. In this publication, ink in a liquid chamber is gasified (presumably due to nucleate boiling) by a cylindrical heating element, and this gas is discharged from an ink discharge port together with ink droplets. According to this method, the gas is ejected in the form of fine droplets, resulting in poor image quality. In addition, the gas ejected by the gas discharges the ink to generate a splash, a mist, or the like, and as a result, the recording paper may be stained or the inside of the apparatus may be stained.

[0006] For example, Japanese Patent Application Laid-Open No. 61-197246 discloses a thermal transfer type recording apparatus using a modification of a conventional ink jet recording method using thermal energy. That is, in this apparatus, it is one-shot ink ejection, and in addition, it is difficult to make the recording medium and the heating element completely adhere to each other. Therefore, compared to the conventional ink jet recording method using a recording head having an ejection port, ,
There is a problem that thermal efficiency tends to decrease and is not suitable for high-speed recording.

[Background Art] In order to solve the problems of the ink jet recording system as described above, the present applicant disposes air bubbles due to film boiling generated by heating ink for discharge in the vicinity of the discharge port. (Hereinafter, this method is also referred to as a continuous discharge method) in which discharge is performed by communicating with a printer (Japanese Patent Application No. 2-1128).
No. 32, Japanese Patent Application No. 2-112833, Japanese Patent Application No. 2-112
No. 834, Japanese Patent Application No. 2-114472, Japanese Patent Application No. 3-16
No. 9962).

[0008] According to the above-described communication and discharge method, the gas forming the bubble is not ejected together with the ejected ink droplets, so that the generation of splash and mist is reduced.
Background dirt on the recording medium and dirt in the apparatus can be prevented.

In addition, as a basic operation of the above-described communication discharge method, there is a case where all ink located on the discharge port side from a portion where bubbles are generated is discharged in principle as ink droplets. Therefore, the amount of ink to be ejected can be determined by the structure of the recording head, such as the distance from the ejection port to the bubble generation site. As a result, according to the above-described continuous ejection method, it is possible to perform ejection with a stable ejection amount without being significantly affected by a change in ink temperature or the like.

[0010]

However, when it is assumed that the heat generating portion and the discharge port face each other, depending on the structure of the recording head, the formed air bubbles may not efficiently communicate with the outside air to change the discharge characteristics. There was a case.

The present invention provides an ink droplet ejection recording method and a recording head which can solve the above problem in the method of communicating bubbles with the outside air, stabilize the formation of ink droplets, and achieve higher quality image formation. It is something you want to do.

According to the present invention, there is provided an ink path communicating with an ink supply source and receiving ink from the ink supply source, and a heat source for applying thermal energy to the ink in the ink path to generate bubbles by film boiling. Energy generating means, comprising a discharge port provided to face the thermal energy generating means and communicating with the outside air bubbles generated by the thermal energy generating means to discharge a part of the ink as droplets, When the distance between the thermal energy generating means and the discharge port is L and the maximum opening diameter of the discharge port is R, R / L
A recording head characterized by satisfying ≧ 0.5 is provided.

The present invention also provides an ink path communicating with an ink supply source and receiving ink supply from the ink supply source;
Thermal energy generating means for applying thermal energy to the ink in the ink path to generate bubbles by film boiling,
A discharge port provided to face the thermal energy generating means for discharging a part of the ink as a droplet, wherein a distance between the thermal energy generating means and the discharge port is L, and a maximum opening of the discharge port is provided. When the diameter is R, R / L ≧ 0.
5, a thermal energy is applied to the ink in the ink path by the thermal energy generating means, bubbles are generated by film boiling due to the thermal energy, and the bubbles are communicated with the outside air. At least a portion of the ink is ejected from the ejection port.

According to the present invention, it is possible to ensure the proper growth of the bubbles formed by the heating resistor in the communicating direction, to stabilize the state of communicating the bubbles with the outside air, and to guarantee the image quality.

The constitution and conditions for making each of the above-mentioned inventions more excellent inventions are as follows: first, the nozzle is not blocked by the bubble at the time of the communication; and second, the nozzle is not blocked by the bubble at the time of the communication. Third, the bubble is communicated with the outside air under the condition that the internal pressure is equal to or less than the outside pressure. Third, at the time of the communication, the bubble is communicated with the outside air under the condition that the acceleration of the moving speed of the tip in the discharge direction of the bubble is not positive. Fourth, the distance between the end of the thermal energy generating means on the side of the discharge port and the end of the bubble on the side of the discharge port is la, and the end of the thermal energy generating means on the side opposite to the side of the discharge port is connected to the end of the bubble. Assuming that the distance from the end opposite to the outlet is lb, at least one of communicating bubbles generated in the ink with the outside air by the thermal energy generating means under the condition of la / lb ≧ 1. Can be mentioned.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below, but the contents of the preferred structure of the present invention for stably communicating bubbles with the outside air will be described later. The following features of the present invention are more preferable that include this configuration.In the present invention, however, the present invention can be applied to any device that does not generate a splash due to a communication system of outside air and bubbles exceeding the above-described conventional level. It is something.

FIG. 1 shows a partial structure of a recording head to which the present invention is applied. Reference numeral 5 denotes a circular ejection port;
Denotes an ink supply path, and 2 denotes a heating section of a heating resistor section having a substantially square shape. Reference numeral 1 denotes an insulating substrate having a heating resistor on the surface. The ink supply path is bent down at the heat generating portion, and the heat generating portion 2 and the discharge port 5 face each other. An orifice plate 8 forms an orifice with the ink supply path 12.

A bubble generated by the heater is communicated with outside air from a discharge port to discharge ink (FIG. 2 (a) described later).
For reference, the size may be appropriately set in consideration of conditions such as the size of the heater, the distance between the discharge port and the heater, the width, length and height of the liquid path, and the size of the discharge port.

In particular, the bubbles generated by the heater are efficiently communicated with the outside air from the ejection ports, and the size (volume) of the ejected ink droplet, which is one of the features of the present recording system, is made constant. To achieve this, among the conditions described above,
When the distance from the discharge port is L and the maximum opening diameter of the discharge term is R, it is important to satisfy R / L ≧ 0.5.

If the above relational expression is not satisfied, it is difficult to efficiently discharge the ink by causing bubbles generated by the heater to efficiently communicate with the outside air from the discharge port. That is, in this case, since the inertance (inertia resistance) between the heater and the discharge port is substantially increased, the bubble is unlikely to grow in the direction of the discharge port. Therefore, even if the bubble communicates with the outside air from the discharge port, ink is likely to remain between the discharge port and the heater. There is a problem.

In the above relational expression, a more preferable range is 0.5 ≦ R / L ≦ 5.0. In this range, it is possible to discharge the ink droplets by efficiently communicating the bubbles with the outside air from the discharge ports. Therefore, the volume of the ink droplets can be constantly stabilized without substantially remaining ink near the ejection openings. Optimally, the above condition is 0.7 ≦ R / L ≦ 3.0, which is particularly effective for continuous ejection.

The table discloses the results of the study to clarify the effects of the present invention. In the table, R is the maximum diameter of the discharge port, L
Is the distance between the heat acting surface of the thermal energy supply means and the discharge port. a is the height of the liquid path, b is the width of the liquid path, and c is the length of the liquid path. In these Examples 1 to 6, the ejection frequency was set to 4
KHz, drive pulse is 3 μsec, drive voltage of the first embodiment is 7 V, drive voltage of the second embodiment is 13.5 V, and the third to third embodiments.
The drive voltage of Example 5 was 7 V, and the drive voltage of Example 6 was 15.4 V. A multihead having an orifice density of 360 dpi was used.

The results are good in Examples 1, 2, 4, 5, and 6 which satisfy the conditions of the present invention, but in Example 3, continuous discharge could not be performed because these conditions were not satisfied.

[0024]

[Table 1]

FIGS. 2A and 2B show a preferred embodiment of the concept of the present invention, showing two examples of typical configurations of the liquid passage B, but the present invention is not limited to this. FIG.
(A) is provided with a heating resistance layer 2 on a substrate (not shown),
The recording head includes the side discharge ports 5 (plural) on the surface. E1 and E2 are conventional structures showing a selection electrode and a common electrode. D is a protective layer, and C is a common liquid chamber. In response to an electrode signal (pulse signal) corresponding to the recording signal from the electrodes E1 and E2, the heat generating portion between the electrodes E1 and E2 causes a rapid temperature rise causing film boiling in a short time (30).
0 ° C. or higher) to generate bubbles 6. As a result, in the present example, the bubble 6 communicates with the atmosphere at the end A of the discharge port 5 on the side of the heating resistance layer 2 to form a stable droplet (broken line 7). As described above, by communicating with the atmosphere (outside air) near the periphery of the ejection port 5, the liquid can be ejected according to the recording signal without splash and without generating mist-like ink droplets. Can be.

According to this recording principle, the liquid path B is not completely shut off at the growth stage of the bubble 6, so that the refill characteristics for the subsequent ink recording are excellent, and the high heat of the high temperature portion of 300 ° C. or more is also directed to the outside air side. Since the liquid is discharged, the response frequency is also excellent.

In FIG. 2B, the common liquid chamber C is not shown, but the liquid path B is a liquid path of a bent path, and the heat generating resistance section 2 is provided on the substrate surface at the bent portion. . The discharge port has a shape in which the area decreases in the discharge direction.
Facing. The discharge ports (plural) are formed in the orifice plate OP.

In FIG. 2B as well, when film boiling (300 ° C. or more) is caused as in FIG. 2A, bubbles 6 grow and push the ink in the thickness portion of the orifice plate OP. , To dilute the ink in that portion. Thereafter, the bubble 6 communicates with the atmosphere in the area A2 near the discharge port from the outside air side periphery A1 of the discharge port 5 to the inside. According to such a communication state, stable droplets (broken line 7) can be discharged from the center of the discharge port without splash and without generating mist. At this time, since the growth of bubbles does not block the liquid path, the liquid that does not need to go in the discharge direction can be left as an aggregate continuous with the liquid in the liquid path. It can contribute to stabilization and stabilization of the discharge speed.

In this embodiment, the stabilization region of 300 ° C. or more of the film boiling can be utilized to rapidly and surely increase the bubble growth near the discharge port. High stability and high speed recording can be achieved with the help of the characteristics.

FIG. 2 (c) is a cross-sectional view of one side of the liquid passage B in FIG. 2 (b) from the common liquid chamber C side toward the heating resistor layer 2. FIG. As can be seen from FIG. 2C, the liquid (hatched portion) in the liquid path B communicates with the droplet 7, and the air bubbles 6 near the discharge port on the central side at that time become air near the discharge port. It can be understood that the droplet 7 and the liquid in the liquid path maintain the state of communication when communicating with the liquid. 6W
Shows the shape of the bubble end in this section of the bubble.

As described above, similarly, in FIG. 2A, when the air bubbles communicate with the atmosphere, the liquid in the liquid path gradually separates the liquid droplets while communicating with the liquid droplets protruding from the discharge port. Therefore, the conventional splash can be prevented.

Preferred conditions incorporated into FIGS. 2 (a) and 2 (b) to achieve even more particularly preferable droplet formation are described below.

The first condition is that the bubble communicates with the outside air under the condition that the internal pressure of the bubble is lower than the outside pressure.

That is, making the bubble communicate with the outside air under the condition that the internal pressure of the bubble is lower than the outside air pressure scatters the unstable liquid near the discharge port, which occurs when the bubble communicates under the condition that the inside pressure of the bubble is higher than the outside air pressure. In addition, since the force that draws the unstable liquid into the liquid path is smaller than that in the case where the pressure is equal, even more stable discharge of the liquid and prevention of scattering of the unnecessary liquid can be achieved. Can be planned.

In addition to the above conditions, the second condition for communicating the bubble with the outside air under the condition that the first derivative of the moving speed of the tip of the bubble in the direction of the discharge port becomes negative, or the discharge port of the discharge energy generating means. Distance l from the side end to the bubble outlet end
a and a distance lb from the end of the ejection energy generating means opposite to the discharge port to the end of the bubble opposite to the discharge port satisfies la / lb ≧ 1, or both of them. It is more preferable that the bubble be communicated with the outside air under certain conditions.

Next, one configuration of a recording head suitably used in the present invention will be described.

FIGS. 3A and 3B show a schematic perspective view and a schematic top view of one suitable recording head. (B) is a state in which the top plate shown in (a) is not provided. The configuration of the recording head shown in FIGS.

In the recording heads shown in FIGS. 1A and 1B, a wall 8 is provided on the base 1 and the wall 8 is joined by the top plate 4 so as to cover the common liquid chamber 10 and the liquid path 12. Is formed. A supply port 11 for supplying ink to the top plate 4
Is provided, and the ink can be supplied into the liquid path 12 through the common liquid chamber 10 to which the liquid path 12 communicates.

A heater 2 is provided on the base 1,
Each liquid path is provided corresponding to each of the heaters 2. The heater 2 has a heating resistor layer and electrodes (both not shown) electrically connected to the heating resistor layer, and the heater 2 is energized in accordance with a recording signal by these electrodes. By this energization, the heater 2 generates thermal energy and can apply thermal energy to the ink supplied in the liquid path. With this heat energy, bubbles can be generated in the ink according to the recording signal.

Another configuration of the recording head suitably used in the present invention will be described.

FIGS. 4A and 4B are a schematic sectional view and a schematic plan view of the recording head, respectively. The difference between this recording head and the recording head shown in FIG. 4 is that the ink supplied in the liquid path is ejected straight or substantially straight from the discharge port along the liquid path. On the other hand, what is shown in FIG. 4 is that the supplied ink is bent along the liquid path (in the figure, the discharge port is formed immediately above the heater). In FIGS. 4A and 4B, the same reference numerals as those in FIGS. 4A and 4B indicate the same components. In FIGS. 4A and 4B, reference numeral 16 denotes an orifice plate in which the discharge ports 5 are formed, and here, a wall 9 provided between the discharge ports 5 is also integrally formed.

FIGS. 5 (a) to 5 (e) are explanatory views of a first specific example of a liquid ejecting method and apparatus to which the present invention is applied, which is an invention which pays attention to temporal changes in the internal pressure and volume of a bubble. is there. The present invention is summarized as follows: 1) In a liquid ejecting method in which a bubble is generated by heating ink and at least a part of the ink is ejected by the bubble to perform recording, a condition that the internal pressure of the bubble is equal to or less than an external pressure. Wherein the bubbles are communicated with outside air. 2)
A recording head having a discharge port for discharging ink at least partly by heating the ink by the discharge energy generating means to generate at least a part of the ink by the ink, and generating the air bubble under the condition that the internal pressure of the air bubble is equal to or less than the external pressure. A recording apparatus, comprising: a driving circuit for driving the ejection energy generating means so as to communicate with outside air; and a platen provided at a position where the ejection port and the recording medium face each other.

The first embodiment of the present invention stabilizes the volume and speed of the ejected liquid droplets, suppresses the generation of splashes and mist as causes that cannot sufficiently cope with high-speed printing, and realizes background contamination on an image and a device. In this case, dirt in the apparatus is prevented, ejection efficiency is improved, clogging and the like are prevented, the life of the recording head is improved, and high-quality images can be printed.

Before explaining FIG. 5, the principle of liquid ejection will be described with reference to FIG. The liquid path is formed by the base 1, the top plate 4, and a wall (not shown).

FIG. 6A shows an initial state, in which the liquid path is filled with ink 3. Ink 3 First, when a current is instantaneously applied to a heater (for example, an electrothermal converter) 2 to rapidly heat the ink 3 in the vicinity of the heater in a pulsed manner, a bubble 6 is generated on the heater 2 by so-called film boiling. , Suddenly starts expanding (FIG. 6 (b)). Further, the bubble 6 continues to expand, grows mainly toward the discharge port 5 having a small inertia resistance, and finally passes through the discharge port 5, and the outside air communicates with the bubble 6 (FIG. 6C). At this time, the outside air is bubble 6
It is in equilibrium with the inside or flows into the bubble 6.

By this moment, the ink 3 pushed out from the discharge port 5 continues to fly further forward due to the momentum given by the expansion of the bubble 6, and finally becomes independent droplets for recording on paper or the like. Fly toward the medium 101.
(FIG. 6 (d)). Further, the gap formed at the tip of the ejection port 5 side is supplied with the ink 3 rightward in the drawing by the surface tension of the rear ink 3 and the wetting of the member forming the liquid path (FIG. 6).
(E)) Return to the initial state. The recording medium 101 is conveyed along the platen to a position facing the discharge port 5 by a platen, a roller, a belt, or any combination thereof. Alternatively, the recording medium 101 is fixed,
The ejection port 5 may be moved (the recording head is moved), or a combination of them may be used. The point is that the ejection port 5 and the recording medium can be relatively moved so that the desired ejection port can face a desired position of the recording medium.

Now, in FIG. 6 (c), when the bubble 6 communicates with the outside air, it is checked whether gas moves between the outside air and the inside of the bubble.
In order for the outside air to flow into the bubble, it is preferable that the bubble communicates with the outside air under the condition that the internal pressure of the bubble is equal to or lower than the atmospheric pressure.

Therefore, in order to satisfy the above condition,
In FIG. 5A, the bubble and the outside air may be communicated at the time t ≧ t1. Actually, ink is ejected as the bubble grows, and the graph of the relationship between the internal pressure or volume of the bubble and time is as shown in FIG. 5B. That is, in FIG. 5B, t = tb (t1
At the time of ≦ tb), the bubble may be communicated with the outside air.

When droplets are ejected under these conditions, compared to the case where the bubbles are communicated with the outside air and the droplets are ejected under the condition that the internal pressure of the bubble is higher than the outside air pressure (gas is ejected into the atmosphere),
As described above, it is possible to prevent recording paper and the inside of the apparatus from being stained by ink mist or splash. Further, since the bubble is communicated with the outside air after the volume of the bubble increases, sufficient kinetic energy can be transmitted to the ink, and the effect of increasing the ejection speed can be obtained. In addition, it is more desirable to make the bubble communicate with the outside air under the condition that the internal pressure of the bubble is lower than the outside air pressure, since the above effect can be made more remarkable.

That is, the communication of the bubble with the outside air under the condition that the internal pressure of the bubble is lower than the outside air pressure scatters the unstable liquid near the discharge port, which occurs when the communication of the bubble under the condition that the inside pressure of the bubble is higher than the outside air pressure. In addition, since the force that draws the unstable liquid into the liquid path is smaller than that in the case where the pressure is equal, even more stable discharge of the liquid and prevention of scattering of the unnecessary liquid can be achieved. Can be planned.

The recording head used in the first embodiment of the present invention is provided at a position where the position of the heater 2 is close to the direction of the discharge port 5. This is the simplest method to allow the bubbles to communicate with the outside air. However, simply bringing the heater close to the discharge port cannot satisfy the above-described conditions of the present invention. Therefore, in order to satisfy the above conditions of the present invention, the amount of thermal energy generated by the heater (the configuration of the heater, the forming material, the driving conditions, the area, the heat capacity of the substrate on which the heater is provided, etc.), the physical properties of the ink, and the components of the recording head By selecting the size (distance between the discharge port and the heater, width and height of the discharge port and the liquid path) as desired, the bubble can be communicated with the outside air in a desired state.

Second Specific Example As a condition for achieving the invention more effectively, the liquid channel shape can be mentioned as described above. Although the width of the liquid path shape is almost determined by the shape of the thermal energy generating element to be used, the specific relationship is only an empirical rule. In the present invention, it has been found that the shape of the liquid path greatly affects the growth of bubbles, and is effective for the above conditions in the liquid path.

That is, it has been found that the communication state of the bubbles can be changed by utilizing the height of the liquid path. It is preferable that the height H of the liquid path be lower than the width W of the liquid path (H <W) in order to be less susceptible to other influences such as the environment and to achieve further stabilization.

Further, when the bubble has a maximum volume of 70% or more, more preferably 80% or more of the maximum volume of the bubble which would be reached if the bubble does not communicate with the outside air, the bubble communicates with the outside air. Is preferred.

Next, a method for measuring the relationship between the internal pressure of the bubble and the external pressure will be described.

Since it is difficult to directly measure the pressure in the bubble, the magnitude relationship between the internal pressure of the bubble and the external pressure can be known by the following method or by appropriately combining those methods. First, a method of measuring the temporal change of the volume of the bubble or the volume of the ink outside the ejection port to determine the magnitude relationship between the internal pressure and the external pressure of the bubble will be described.

The volume relationship V between the internal pressure and the external pressure of the bubble is determined by measuring the volume V of the bubble from the time when the ink starts foaming until the bubble communicates with the outside air, and calculating the second derivative d2V / dt2 of V. You can know.
That is, if d2V / dt2> 0, the internal pressure of the bubble is higher than the external pressure, and if d2V / dt2 ≦ 0, the internal pressure of the bubble is lower than the external pressure. 5C, the internal pressure of the bubble is higher than the external pressure from the start of foaming t = t0 to t = t1, d2V / dt2> 0, and the time t until the bubble communicates with the outside air from t = t1. Until = tb, the internal pressure of the bubble is equal to or lower than the external pressure, and d2V / dt2 ≦ 0. As described above, the magnitude relation between the internal pressure of the bubble and the external pressure can be known by obtaining the second derivative d2V / dt2 of V.

In this case, it is necessary that the bubbles be visible from outside the recording head. In order to observe the bubble from outside the recording head, it is preferable that a part of the recording head is formed of a transparent member so that bubble bubbling and growth can be observed from outside the recording head.
When the constituent members of the recording head are non-transparent, for example, the top plate or the like of the recording head may be replaced with a transparent member. At this time, it is desirable that the hardness, the elasticity, and the like of the replaced member and the replaced member are selected as equal as possible.

When the top plate of the recording head is made of, for example, metal, opaque ceramic or colored plastic, it may be replaced with a transparent plastic (for example, transparent acrylic), glass, or the like. Of course, the replacement place and the material used for it are not limited to the place and the material described above.

However, at this time, in order to avoid the difference in the foaming characteristics due to the difference in the physical properties of the members, it is desirable to select a material having physical properties such as wettability to ink as close as possible to the original member. Whether or not the foaming state is the same as that of the original member can be confirmed by discharging and checking whether or not the discharge speed and the discharge volume are the same as the original state. The above operation is unnecessary when the member is made of a transparent member in advance.

Even if the constituent members of the recording head are not replaced with other members, or if the constituent members of the recording head cannot be replaced with other members, the magnitude relationship between the internal pressure and the external pressure of the bubble can be determined by the following method. be able to.

Another method is to measure the volume Vd of the ink ejected outside the ejection port from the start of bubbling until the ink droplet flies, and to calculate the second derivative d2V of Vd.
By calculating d / dt2, the magnitude relationship between the internal pressure of the bubble and the external pressure can be known. That is, d2Vd / dt
If 2> 0, the internal pressure of the bubble is higher than the external pressure and d2
If Vd / dt2 ≦ 0, the internal pressure of the bubble is equal to or lower than the external pressure. FIG. 5D shows a time change of the first derivative dVd / dt of the volume Vd of the ink ejected from the ejection port when the bubble is communicated in a state where the internal pressure of the bubble is higher than the external pressure. From the foaming start t = t0 to the time t = ta until the bubble communicates with the outside air, the internal pressure of the bubble is higher than the outside pressure, and d2Vd / dt2> 0. On the other hand, FIG. 5B shows the primary differential dVd / Vd when the bubble is communicated with the outside air while the internal pressure of the bubble is equal to or lower than the outside pressure.
It shows a time change of dt. As shown in the figure, from the start of foaming t = t0 to t = t1, the internal pressure of the bubble is higher than the external pressure and d2Vd / dt2> 0, but from t = t1 to t = tb, the internal pressure of the bubble is lower than the external pressure. Yes d2V
d / dt2 ≦ 0.

As described above, the second derivative of Vd, d2Vd / d
By obtaining t2, the magnitude relationship between the internal pressure of the bubble and the external pressure can be known.

The volume V of the ink existing outside the ejection port
A method for measuring d will be described. The shape of the droplet at each time after the ejection can be measured by observing with a microscope a light source such as a strobe, an LED, or a laser while illuminating the droplet protruding from the ejection port with pulsed light.
That is, by causing a recording head that continuously ejects at a constant frequency to emit pulse light in synchronization with the driving pulse and with a predetermined delay time, the head emits light in one direction after a predetermined time from the ejection. The projected shape of the droplet viewed from above can be measured. At this time, the measurement can be performed more accurately if the pulse width of the pulse light is as small as possible within a range where a sufficient light amount for measurement can be secured.

When an airflow from the liquid path side to the outside is observed at the moment when the bubble communicates with the outside air by these methods, it indicates that the bubble has been communicated with the internal pressure being higher than the external pressure. Observation of the airflow flowing into the interior indicates that the bubbles communicated in a state where the internal pressure of the bubbles was lower than the external pressure.

As another condition, as shown in FIG. 7, a condition in which the first differential value of the moving speed of the tip of the bubble in the discharge port direction is negative is such that the bubble communicates with the outside air, or as shown in FIG. As described above, the distance la from the discharge port side end of the discharge energy generating means to the bubble discharge port side end and the end opposite to the bubble discharge port from the end opposite to the discharge port of the discharge energy generating means. It is more preferable that the bubble communicates with the outside air under the condition that the distance lb to the portion satisfies la / lb ≧ 1 or both conditions.

FIGS. 6A to 6F are explanatory views of a second specific example of the liquid ejecting method and apparatus to which the present invention is applied, and the invention paying attention to the growth state of bubbles. The present invention can be summarized as follows: 3) a discharge port for discharging ink, a liquid path communicating with the discharge port, and a bubble formed in the liquid path to be used for discharging the supplied ink. A recording head having discharge energy generating means for generating thermal energy is used, and the distance la between the discharge port side end of the discharge energy generating means and the discharge port side end of the bubble is opposite to the discharge port of the discharge energy generating means. The distance lb between the end on the opposite side and the end on the opposite side of the bubble discharge port is la / l
A liquid ejecting method, wherein a bubble generated in the ink by the ejection energy generating means is communicated with outside air from an ejection port under a condition of b ≧ 1. 4) A discharge port for discharging ink, a liquid path communicating with the discharge port, and discharge for generating thermal energy used to discharge the supplied ink by forming bubbles in the liquid path. A recording head having an energy generating means, and a distance l between an end of the ejection energy generating means on the side of the ejection port and an end of the bubble on the side of the ejection port.
a represents a distance lb between an end of the discharge energy generation means opposite to the discharge port and an end of the discharge energy generation means opposite to the discharge port of the bubble under a condition of la / lb ≧ 1. A driving circuit for supplying a signal to the discharge energy generating means for causing bubbles generated in the ink to communicate with the outside air from a discharge port, and a platen capable of moving a recording medium along with the discharged liquid for adhering the liquid. A recording apparatus comprising: Becomes

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 6A to 6F are schematic cross-sectional views for explaining liquid ejection by the liquid ejection method of the present invention.

6A to 6F, 1 is a substrate, 2 is a heater, 3 is ink, 4 is a top plate, 5 is a discharge port, 6 is a bubble, 7 is a droplet, and 101 is a recording medium. It is. The liquid path is formed by the base 1, the top plate 4, and a wall (not shown).

FIG. 6A shows an initial state, in which the liquid path is filled with ink 3. Ink 3 First, an electric current is instantaneously passed as a signal from a drive circuit to a heater (for example, an electrothermal converter) 2 so that the ink
When the ink is heated rapidly, bubbles 6 are generated on the heater 2 by so-called film boiling, and the ink starts to expand rapidly (FIG. 6B). Further, the bubble 6 continues to expand (FIG. 6).
(C)) Mainly grows toward the ejection port 5 side having a small inertia resistance, and finally passes through the ejection port 5, and the outside air communicates with the bubble 6 (FIG. 6D). At this time, the distance la from the discharge port side end of the heater 2 as the discharge energy generating means to the discharge port side end of the bubble 6 is equal to the distance from the end opposite to the discharge port of the heater 2 to the discharge port of the bubble 6. The outside air and the bubble 6 communicate with each other under the condition of la / lb ≧ 1 with respect to the distance lb to the opposite end.

Up to this moment, the ink 3 pushed out from the discharge port 5 continues to fly further forward due to the momentum given by the expansion of the bubble 6, and finally becomes an independent droplet 7.
And flies toward the recording medium 101 such as paper (FIG. 6E). Further, the gap formed at the tip of the ejection port 5 side is supplied with the ink 3 rightward in the drawing by the surface tension of the rear ink 3 and the wetting of the member forming the liquid path (FIG. 6).
(F)) Return to the initial state. The recording medium 101 is conveyed to a position facing the discharge port 5 by a platen, a roller, a belt, or any combination thereof along with a platen. Alternatively, the recording medium 101 is fixed, and the ejection port 5 is moved (the recording head is moved).
Alternatively, they may be combined with each other. The point is that the ejection port 5 and the recording medium can be relatively moved so that the desired ejection port can face a desired position of the recording medium.

When the liquid is ejected according to the recording principle described above, the volume of the liquid pushed out from the ejection port is always constant because the bubble communicates with the outside air.
It is possible to obtain a high-quality recorded image without unevenness in the recording density.

Further, since the bubble is communicated with the outside air under the condition of la / lb ≧ 1 as described above, the kinetic energy of the bubble can be effectively transmitted to the ink, and the ejection port ratio is improved.

Further, when the liquid is discharged under the above conditions,
Compared with the case where the liquid (ink) is ejected under the condition of la / lb <1, the time until the new ink is filled in the gap formed near the ejection port after the ejection of the liquid can be shortened, and furthermore. High-speed recording becomes possible. In the second embodiment, the method of measuring the distances la and lb between the end of the bubble and the end of the heater when the bubble communicates with the outside air may be, for example, in the case of the recording head shown in FIG. There is a method in which the top plate 4 is formed of a transparent glass plate, the recording head is irradiated from above the top plate 4 with a light source capable of emitting pulses, such as a strobe, a laser, or an LED, and observed with a microscope.

Specifically, the pulse light source is turned on and off in synchronization with the driving pulse applied to the heater, and the phenomenon from the start of bubble foaming to the ejection of the liquid is observed using a microscope and a camera as described above. lb can be determined.

Although the width of the liquid path shape is substantially determined by the shape of the thermal energy generating element to be used, the specific relationship is only an empirical rule. In the second specific example, it was found that the shape of the liquid path greatly affected the growth of bubbles, and was effective for the above conditions of the heat energy generating element in the liquid path.

That is, by using the height component of the liquid path, the growth of bubbles is set to la / lb ≧ 1, preferably la / lb ≧ 2, more preferably la / lb ≧ 4 (see FIG. 8). ,
It has been found that the liquid passage height H should be at least lower than the liquid passage width W (H <W) in order to be less affected by the environment and other influences and to perform the operation in a more stable state. This can reduce the influence of the inner wall of the liquid jet by reducing the influence of the inner wall of the liquid jet, and further increase the jet direction and speed since the communication state of the air bubble with the atmosphere can be performed by the air bubble whose growth rate at the interface of the ceiling of the liquid path is increased. Can be stable. In the second specific example, the relationship between the width W and the height H was further pursued. When H ≧ 0.8 W, the characteristic change was small and stable injection was performed even when performing high-speed injection for a long time. It was suitable for recording.

If H ≧ 0.65 W, it is possible to obtain high-precision impact performance even if each recording jet carrying recording information is performed while giving a considerable change.

In addition to the above conditions, it is more preferable that the bubble communicates with the outside air under the condition that the first derivative of the moving speed of the tip of the bubble in the discharge port direction becomes negative.

FIGS. 7A and 7B are explanatory views of a third specific example of a liquid ejecting method and apparatus to which the present invention is applied. The present invention focuses on the time variation of the internal pressure and volume of a bubble. is there. The present invention is summarized as follows: 5) a discharge port for discharging ink, a liquid path communicating with the discharge port, and a bubble formed in the liquid path to be used for discharging the supplied ink. Using a recording head having an ejection energy generating means for generating thermal energy, under the condition that the first derivative of the moving speed of the tip of the generated bubble toward the ejection port is negative,
A method for ejecting liquid droplets, comprising: causing the bubbles generated by the discharge energy generating means to communicate with outside air from a discharge port. 6) A discharge port for discharging ink, a liquid path communicating with the discharge port, and discharge for generating thermal energy used to discharge the supplied ink by forming bubbles in the liquid path. A recording head having an energy generating means, and the bubble is generated by the discharging energy generating means under a condition that the first derivative of the moving speed of the bubble generated by the discharging energy generating means toward the discharge port is negative. A drive circuit for supplying a signal to the discharge energy generating means for communicating the bubble generated from the discharge port with the outside air, and a platen capable of moving a recording medium along the discharge liquid to adhere the liquid. Recording device. It is.

The third embodiment of the present invention solves the above-mentioned object and the effects of the first embodiment of the present invention by another means. When the bubble communicates with the outside air, the ink in the vicinity of the communicating portion discharges the ink. Because of excessive acceleration
It is recognized that separation from main ink droplets is a main technical problem. According to this separation, the ink in the vicinity scatters in the form of splash or mist becomes remarkable and scatters.Moreover, in a high-density discharge port arrangement, a discharge failure due to ink adhesion to the discharge port surface is caused. However, the origin of the third specific example is that the cause was clarified to be due to acceleration.

Further analysis on this point has revealed that the above-mentioned problem occurs when the outside air and the bubble communicate with each other when the primary differential value of the moving speed of the tip of the bubble in the discharge port direction is positive. .

The amount of displacement from the start of bubbling until the bubble communicates with the outside air from the end of the heater in the direction of the discharge port from the end of the heater in the direction of the discharge port is measured, and the first derivative and the second derivative of the displacement are measured. FIG. 8 shows the result of calculating the (first-order differential value of the moving speed). According to FIG. 7, the above problem occurs only in FIG.
In the case of the curve A shown in each of (a) and (b), it was confirmed that the first derivative of the moving speed of the tip of the bubble in the discharge port direction was positive.

Curves B shown in FIGS. 7A and 7B show the third embodiment of the invention based on the principle of FIG. 6, and show the first derivative of the moving speed of the tip of the bubble in the discharge port direction. Under negative conditions, the generated bubbles are communicated with the outside air to discharge droplets, so that the volume of the droplets is always stabilized, and a high-quality recorded image can be obtained. Therefore, it is possible to prevent the recording paper from being stained by ink mist or splash and the inside of the apparatus.

Further, since the kinetic energy of the bubble can be sufficiently transmitted to the ink, the ejection efficiency can be increased and clogging can be eliminated. In addition, since the ejection speed of the droplets is improved, the ejection direction of the droplets is stabilized, and the distance between the recording head and the recording paper can be increased.

Further, since there is no defoaming process of generated bubbles, a heater destruction phenomenon due to defoaming is eliminated, and the life of the recording head is improved.

The liquid ejecting method of the present invention can be applied to any of a so-called on-demand type and a continuous type. In particular, in the case of the on-demand type, a liquid (ink) is held. By applying at least one drive signal corresponding to recorded information and providing a rapid temperature rise exceeding nucleate boiling to an electrothermal transducer arranged corresponding to a sheet or a liquid path, This is effective because heat energy is generated in the liquid and the film is boiled on the heat-acting surface of the recording head. As a result, bubbles in the liquid (ink) can be formed in one-to-one correspondence with the drive signal.

The recording head using the liquid jetting method of the present invention is not limited to the one described in the above embodiment, but has a length corresponding to the maximum recording medium width that can be recorded by the recording apparatus. Many forms and variations of a full-line type recording head are possible. Further, the full-line type recording head may be either a configuration that satisfies the length by combining a plurality of recording heads or a configuration as a single recording head that is integrally formed. The invention can exhibit the above-mentioned effects more effectively.

In addition, the print head is replaceable with a print head of a replaceable chip type, which can be electrically connected to the main body of the apparatus or supplied with ink from the main body of the apparatus, or is integrated with the print head itself. The present invention is also effective when a cartridge-type recording head provided in a fixed manner is used.

Further, in addition to the above-described recovery means for the recording head provided as a configuration of the recording apparatus of the present invention, the addition of preliminary auxiliary means and the like further stabilizes the effect of the present invention. It is preferable because it can be performed. Specific examples include a cleaning unit, an electrothermal converter, a separate heating element, a preheating unit using a combination thereof, and the like for the recording head. Also,
Performing a preliminary ejection mode in which ejection is performed separately from printing is also effective for performing stable printing.

Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, and may be a single recording head or a combination of plural recording heads. The present invention is also very effective for an apparatus provided with at least one of full colors by color mixture.

Next, a method for obtaining the moving speed of the tip of the bubble in the discharge port direction and the first derivative of the moving speed for implementing the present invention will be described below.

At each time after the start of bubbling, the position of the tip of the bubble in the direction of the discharge port is determined by illuminating the bubble generated in the nozzle from the top plate surface or the side surface of the recording head with pulse light such as strobe light, LED, or laser. Can be used to observe. Specifically, as shown in time series in a schematic cross-sectional view in each of FIGS. 9A and 9B, a heater unit at a tip end of a bubble discharge port from the start of foaming until the bubble communicates with the outside air. Of the displacement xb-n from the end of the discharge port can be measured. By calculating the first derivative dxb-n / dt of the displacement amount based on the measurement result, the moving speed v of the tip of the bubble in the discharge port direction is obtained.
x is required. Next, the first derivative dvx /
dt (second derivative of displacement amount d2xb-n / d2t) can be obtained.

In this case, it is necessary that the bubbles can be seen from outside the recording head. In order to observe the bubble from outside the recording head, it is preferable that a part of the recording head is formed of a transparent member so that bubble bubbling and growth can be observed from outside the recording head.
When the constituent members of the recording head are non-transparent, for example, the top plate or the like of the recording head may be replaced with a transparent member. At this time, it is desirable that the hardness, the elasticity, and the like of the replaced member and the replaced member are selected as equal as possible.

When the top plate of the recording head is made of, for example, metal, opaque ceramic, or colored plastic, the components may be replaced with transparent plastic (for example, transparent acrylic), glass, or the like. Of course, the replacement place and the material used for it are not limited to the above place and material.

However, at this time, in order to avoid a difference in the foaming characteristics due to a difference in the physical properties of the members, it is desirable to select a material having physical properties such as ink wettability as close as possible to the original member. Whether or not the foaming state is the same as that of the original member can be confirmed by discharging and checking whether or not the discharge speed and the discharge volume are the same as the original state. The above operation is unnecessary when the member is made of a transparent member in advance.

[0098]

As described above, according to the recording head and the ink droplet ejection recording method of the present invention, the thermal energy generating means and the ejection port are connected by a method in which bubbles are communicated with the outside air to eject ink as droplets. The relationship between the distance L and the maximum opening diameter R of the discharge port satisfies R / L ≧ 0.5, so that a complicated structure is not required and proper ink discharge can be performed even if bubbles change due to the environment or the like. To stabilize the image quality and obtain a high-quality recorded image without image disturbance.

Further, the effect is further stabilized by the preferable structure of the outside air communication system, and since there is no defoaming process of generated bubbles, the resistance destruction phenomenon due to defoaming is eliminated, and the life of the recording head is improved. I do.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram for explaining the present invention.

FIGS. 2A, 2B, and 2C are schematic diagrams illustrating a state in which the ink bubble of the present invention communicates with the atmosphere or the outside air.

FIG. 3 is a diagram illustrating a recording head used in an embodiment of the present invention.

FIG. 4 is a diagram illustrating a recording head used in another embodiment of the present invention.

5 (a) to 5 (e) are explanatory diagrams of a new specific example of a liquid ejecting method and apparatus to which the present invention is applied, and are diagrams for sequentially explaining changes in the internal pressure and volume of a bubble over time.

FIGS. 6A to 6F are explanatory views of another novel specific example of the liquid ejecting method and apparatus to which the present invention is applied, and are schematic cross-sectional views for explaining liquid ejection. .

FIGS. 7A and 7B are explanatory diagrams of another novel specific example of the liquid ejecting method and apparatus to which the present invention is applied.

FIG. 8 is a graph illustrating a change in the ratio la / lb between the front end side and the rear end side of a bubble.

FIGS. 9A and 9B are diagrams showing changes per unit time of the tip of a bubble, respectively, and FIG.
The right side sectional views are shown at the same time.

[Explanation of symbols]

 2 Heat generation resistance layer 5 Discharge port 6 Bubbles 7 Droplet 6W End (bubbles) A Communication part B Liquid path C Common liquid chamber OP Orifice plate

Claims (8)

(57) [Claims] An ink supply source connected to an ink supply source.
An ink path that receives ink supply from the ink path;
Thermal energy generating means for applying thermal energy to the ink to generate bubbles by film boiling , and the thermal energy
The heat energy generating means is provided so as to face the generating means.
Therefore, the generated air bubbles are communicated with the outside air, and
And a discharge port for discharging a part as droplets, the
The distance between the thermal energy generating means and said discharge port L, and the maximum opening diameter of the <br/> discharge port when the R, R / L ≧ 0.5
A recording head characterized by satisfying the following. 2. The method according to claim 1, wherein 0.5 ≦ R / L ≦ 5.0.
2. The recording head according to 1. 3. The method according to claim 1, wherein 0.7 ≦ R / L ≦ 3.0.
3. The recording head according to 2. 4. An ink supply source which communicates with an ink supply source.
An ink path that receives ink supply from the ink path;
Thermal energy generating means for applying thermal energy to the ink to generate bubbles by film boiling , and the thermal energy
A part of the ink is provided as a droplet and is provided to face the generating means.
And a discharge port for discharging the heat energy.
The distance between the generating means and said discharge port L, and the maximum opening diameter of the discharge port when the R, using a recording head that satisfies the R / L ≧ 0.5, the Lee by the thermal energy generating means
Applying heat energy to the ink in ink channel, the heat energy
To generate air bubbles by film boiling.
Communicates with ink droplets for causing at least a portion of the ink in the vicinity of the discharge port discharged from the discharge port
Injection recording method. 5. The ink droplet ejection recording method according to claim 4, wherein said ink path is not blocked by said air bubbles during said communication. Wherein when said communication is drop ejection recording method according to claim 4 or claim 5 internal pressure of the bubble is one which communicate ambient air communicating the bubble with the following conditions outside pressure. 7. When the communication, the ink according to any one of claims 4 to 6 under conditions acceleration of the moving speed of the ejection direction distal end portion of said bubble is not positive is intended to communicate with the outside air and the air bubbles Drop ejection recording method. 8. An end of the thermal energy generating means on a discharge port side.
The distance between the air port and the end of the bubble discharge port is la,
End of the energy generation means opposite to the discharge port and the bubble discharge port
When the lb the distance between the end portion opposite to the, la / l
b by the thermal energy generating means in b ≧ 1 becomes conditions
Drop ejection recording method according to any one claims 4 to 7 to communicate ambient air communicating the occurrence air bubbles in the ink.