JP3082974B2 - Droplet ejection recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet jet recording method for performing recording by causing droplets to fly on a recording material such as paper, a resin sheet, and cloth using thermal energy.

[0002]

2. Description of the Related Art A liquid jet recording method for forming an image by attaching a liquid or a solid recording medium (liquid) which can be melted by heating to a recording material using thermal energy can perform high-speed recording. It has the advantages of relatively high 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 a liquid jet recording method is generally provided with a discharge port for discharging liquid as flying droplets, a liquid path communicating with the discharge port, and a part of the liquid path. A recording head having energy generating means for applying discharge energy for discharge to the liquid in the liquid path. 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. A method is disclosed in which thermal energy generated by this is applied to a liquid to discharge the liquid.

That is, in the recording methods disclosed in the above publications, the liquid 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. The liquid is ejected from the ejection port at the tip of the recording head mainly due to growth and contraction of the recording head, and the ejected droplets adhere to the 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.

[Background Art] The droplet ejection recording method based on the above-described recording method using thermal energy has many advantages, and images are formed according to the specifications of dot matrix printers used in various printers. It is formed by various processes. However, it has been proposed to control the image density by arranging the gradation by dot implantation or to control the image density by concentrating a large number of dots in a predetermined area, but this has caused new technical problems.

That is, the droplet ejection using thermal energy tends to cause a change in the volume of the droplet and a change in the ejection speed due to a change in the characteristics of the liquid, and the more droplets need to be concentrated in a minute area. However, this phenomenon becomes a significant problem.

At present, since the image processing and the practical level of the recording head itself are not sufficient, the recording speed is reduced, or the recording is interrupted to promote the fixing of the recording medium in which the liquid droplets are absorbed. Therefore, the above problem is not a major problem as a result, but in pursuit of high image quality, it is possible to increase the number of droplets that can be achieved at the same time, and at the same time, to make the volume per droplet minute and stable. If it can be done, it will be the biggest challenge.

In addition, the variation in the current recording head droplets varies not only in the long-term specification but also in the period of one-line printing, and it is first necessary to solve this problem before considering high image quality. It also has to be resolved.

When recording is performed using a plurality of liquid droplets, when binary recording is performed at 4 KHz, quaternary recording is performed.
3 = 12 KHz, and if the operation is performed at a high frequency, the temperature of the recording head is significantly increased. Of course, a large temperature distribution is formed depending on the degree of use, and the dispersion of droplets becomes extremely large.

SUMMARY OF THE INVENTION According to the present invention, even if the above-described high-speed processing is performed, many droplets can be recorded in a minute area with the same volume, and high-speed printing can be performed by using multiple nozzles in a short time. A droplet ejection recording method that solves the recording unevenness of the recording method to be ejected, has a high and stable droplet discharge speed, and can achieve recording with almost no change in volume of the droplet itself. It is intended to provide.

The present invention provides a droplet ejection recording method which is particularly suitable for multi-droplet color recording, in which liquids of a plurality of colors are respectively formed by a plurality of droplets.

The present invention achieves the above object and provides a liquid
Communication with a body source to receive a supply of liquid from the source
Nucleate boiling by applying thermal energy to the liquid in
A sudden rise in temperature causes bubbles to form,
By ejecting droplets, dots are formed on the recording material and recording is performed.
In the droplet ejection recording method, the internal pressure of the bubble is
The air bubbles are allowed to communicate with the outside air from the discharge port under the pressure
While discharging the droplets, the generation and communication of the bubbles are
So that the dots formed by the ejected droplets overlap
The liquid droplets are continuously discharged repeatedly and continuously.
Recording on the recording material using a plurality of droplets
And a droplet ejection recording method.

According to the present invention, it is possible to improve image unevenness at the start of recording and at the end of recording, and to form a good image.

Further, the constitutions and conditions for making each of the above-mentioned inventions more excellent inventions are as follows: first, the liquid path is not blocked by the bubbles at the time of the communication; Third, the bubble is communicated with the outside air under the condition that the internal pressure of the bubble is equal to or less than the outside air pressure. Thirdly, at the time of the communication, the bubble is discharged under the condition that the acceleration of the moving speed of the tip of the bubble in the discharge direction is not positive. Fourth, the distance la between the discharge-portion-side end of the flat heat-generating portion and the discharge-portion-side end of the bubble is the end opposite to the discharge portion of the discharge energy generating means. Distance lb from the end opposite to the bubble discharge section
On the other hand, at least one of communicating bubbles generated in the liquid by the discharge energy generating means with the outside air from the discharge section under the condition of la / lb ≧ 1 can be mentioned. In order to solve the problems of the ink jet recording method as described above, the present applicant performs discharge by communicating bubbles due to film boiling generated by heating the liquid for discharge to outside air near the discharge port. A liquid jet recording method (hereinafter, this method is also referred to as a continuous discharge method) has been proposed (Japanese Patent Application Nos. 2-112832 and 2-112).
No. 833, Japanese Patent Application No. 2-112834, Japanese Patent Application No. 2-11
No. 4472, Japanese Patent Application No. 3-169962).

According to the above-mentioned continuous discharge method, the gas forming the bubble is not ejected together with the ejected liquid droplets. Dirt in the device can be prevented.

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

[0017]

FIG. 1 illustrates an image recorded by the recording method of the present invention and a conventional recording problem.

The step of discharging bubbles by causing bubbles generated by the heater to communicate with the outside air from the discharge port is illustrated.
So that the dots that are formed overlap
Continuously repeat at least once to form one pixel
(A) and (C) show conventional examples in which a recording head is moved from a recording start S to a recording end E using a multivalued image forming method based on a so-called multi-droplet method.
(B) shows an image of the embodiment of the present invention. In (A) and (C) showing the related art, the dot of D1 first gradually increases (D1 <D2 <D3 <D4 <D5, D1).
a <DA, Db <DB), and at the end, the image forming position is also shifted.

In contrast, the present invention, as described below,
Since the air bubbles are communicated with the atmosphere, they are not affected by such a problem of heat energy. Therefore, an image formed collectively by a plurality of droplets can be recorded in an appropriate state.

FIGS. 2 (a) and 2 (b) 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 of 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, when film boiling (300 ° C. or more) is caused as in FIG. 2A, bubbles 6 grow and push 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 the present embodiment, the stabilization region of 300 ° C. or more is particularly used in the film boiling, and the bubble growth can be rapidly and rapidly and surely made in the vicinity of 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. 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, in FIG. 2A, similarly, when the 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.

The preferred conditions incorporated into FIGS. 2 (a) and 2 (b) to achieve even more preferable droplet formation are as follows.

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 discharge port direction is 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. 3A and 3B, a wall 8 is provided on a substrate 1, and the top plate 4 is joined so as to cover the wall 8, and a common liquid chamber 10 and a liquid path 12 are formed. 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. 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: 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 a cause that cannot sufficiently cope with high-speed printing, and implements 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 the 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.

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 eventually becomes independent liquid droplets to be recorded 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 conditions,
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 discharged under these conditions, the bubble is communicated with the outside air under the condition that the bubble internal pressure is higher than the outside air pressure, and droplets are discharged (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, 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.

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 Embodiment 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.

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 inside 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 relation V between the internal pressure and the external pressure of the bubble is determined by measuring the volume V of the bubble during the time from the start of the foaming of the ink 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 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 components 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 constituent members 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 place and the material described above.

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 one 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. Such operation is unnecessary if 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 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. 5 (b) shows the first derivative dVd /
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.

If 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 other conditions, as shown in FIG. 7, a condition in which the primary differential value of the moving speed of the tip of the bubble in the discharge port direction becomes negative is a condition in which the bubble communicates with the outside air, or a condition 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. 6 (a) to 6 (f) are explanatory views of a second specific example of the liquid ejecting method and apparatus to which the present invention is applied. The present invention focuses on the bubble growth state. 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 and the ink 3 near the heater is pulsed.
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.

By this moment, the ink 3 pushed out from the ejection 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.

Since the bubble communicates 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 illuminated 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 by a microscope.

Specifically, the pulse light source is turned on and off in synchronization with the drive pulse given to the heater, and the phenomenon from the start of bubble bubbling to the ejection of the liquid is observed using a microscope and a camera as described above. , Lb can be obtained.

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 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 utilizing 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.

When H ≧ 0.65 W, even if each recording jet carrying recording information is performed while giving a considerable change, highly accurate landing performance can be obtained, which is optimal.

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. 7 (a) and 7 (b) 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 temporal changes in 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 of this point has revealed that the above-mentioned problem occurs when the outside air and the bubble communicate with each other when the first derivative 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 outlet of the heater in the direction of the outlet is measured.
FIG. 8 shows the result of calculating the second derivative (first derivative of the moving speed).
It was shown to. 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. 7 (a) and 7 (b) show a 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 direction of the discharge port. 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 is 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 the generated bubbles, the 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, the 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 exchangeable with a print head of a chip type which is electrically connected to the main body of the apparatus and can be 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 printing mode of the printing apparatus is not limited to the printing mode of only the mainstream color such as black, and may be a single-color printing head or a combination of a plurality of printing 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 in implementing the present invention will be described below.

The position of the tip of the bubble in the direction of the discharge port at each time after the start of bubbling 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 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 components 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.

[0092]

As described above, the recording method of the present invention is described.
Is a source for receiving a supply of liquid from a liquid source.
Gives thermal energy to the liquid in the fluid path
Bubbles are generated by a temperature rise that rapidly exceeds nucleate boiling
To form dots on the recording material by jetting droplets
In the droplet jet recording method for performing recording, the internal pressure of the bubble
The air bubbles are communicated with the outside air from the discharge port under the condition of the outside air pressure or less.
To discharge the droplets, and to generate and communicate with the bubbles.
The dots formed by the ejected droplets overlap
Droplets are continuously ejected continuously and continuously as described above.
Recording is performed on the recording material using a plurality of the ejected droplets.
Since it is a droplet ejection recording method characterized by
It is possible to improve unevenness at the start of discharge and at the end of continuous discharge, and to form a good recorded image.

[Brief description of the drawings]

FIGS. 1A, 1B, and 1C are explanatory diagrams for explaining a method and effects of 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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/05 B41J 2/205

Claims (4)

(57) [Claims] 1. A method for applying heat energy to a liquid in a liquid passage connected to a liquid supply source to receive a supply of the liquid from the liquid supply source to generate bubbles due to a temperature rise that rapidly exceeds nucleate boiling. By ejecting droplets , dots are formed on the recording material
In the droplet jet recording method of forming and performing recording, the bubble is discharged from an ejection port under the condition that the internal pressure of the bubble is equal to or less than the external pressure.
The droplets are discharged in communication with outside air,
The formation and communication of the ejected droplets
Continuous discharge of droplets by repeating continuously so that dots overlap
And recording on the recording material using a plurality of the continuously ejected droplets. 2. The droplet ejection recording method according to claim 1, wherein the liquid path is not blocked by the bubble during the communication. Wherein when said communication is a droplet according to any acceleration of the moving speed of the ejection direction distal end portion of said bubble is not positive condition of claim 1 or 2 in which to communicate ambient air communicating the bubble Injection recording method. 4. The means for providing thermal energy as
The discharge port side end of the electrothermal transducer provided in the liquid path
The distance la from the discharge port side end is equal to the discharge of the electrothermal transducer.
With respect to a distance lb between the end opposite to the mouth and the end opposite to the discharge port of the bubble, the discharge energy generating means causes the communication of the bubble under the condition of la / lb ≧ 1 .
The droplet ejection recording method according to claim 1 .