JPH05116312A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To avoid record irregularity in a recording method wherein a high speed printing is performed by jetting a large quantity of ink droplets in a short time by multi-nozzles. CONSTITUTION:In a droplet jet recording method, bubbles are generated by temperature rise which exceeds nuclear boiling rapidly with heat energy so as to record by jetting droplets. In this method, recording is performed on a material to be recorded by using a plurality of droplets discharged by making the bubbles burst in the outside air at a discharge outlet. Thus, image irregularity occurring at the start and end of recording will be improved and excellent images can be formed.

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 head and a recording method for recording by recording droplets flying on a recording material such as paper, resin sheet and cloth by utilizing thermal energy. Regarding the device.

[0002]

2. Description of the Related Art A liquid jet recording method in which a liquid or a solid recording medium (liquid) that can be melted by heating is attached to a recording material using thermal energy to form an image is capable of high-speed recording. It has the advantages of relatively high recording quality and low noise. Further, this method has many excellent advantages that color images can be recorded relatively easily, it can be recorded on plain paper, and that the apparatus can be easily downsized.

A recording apparatus using such a liquid jet recording method is generally provided with an ejection port for ejecting liquid as flying droplets, a liquid path communicating with this ejection port, and a part of this liquid path. There is provided a recording head having an energy generating unit that applies discharge energy for discharging the liquid in the liquid path. For example, Japanese Patent Publications No. 61-59911, No. 61-59912, No. 61-59913, and No. 61-59914 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 eject the liquid.

That is, in the recording method disclosed in each of the above publications, the liquid subjected to the action of thermal energy causes 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 portion mainly due to growth and contraction, and the ejected droplets adhere to the recording medium to form an image. According to this method, since the ejection openings in the recording head can be arranged at a high density, it is possible to record an image of high resolution and high quality at high speed. A recording apparatus using this method is a copying machine, It can be used as information output means in printers, facsimiles and the like.

[Background Art] The droplet jet recording method based on the above-mentioned recording method using thermal energy has many advantages, and images are printed in accordance with the specifications of dot matrix printers used in various printers. It is formed by various processes. However, although it has been proposed that the gradation is carried out by dot embedding and that a large number of dots are concentrated in a predetermined area to control the image density, new technical problems are being caused.

That is, in the droplet ejection using thermal energy, the volume of the droplet and the ejection speed are easily changed due to the change of the characteristic of the liquid, and it is necessary to concentrate many droplets in a minute area. , This phenomenon becomes a remarkable problem.

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

Further, the variation of the liquid droplets of the current recording head is not only changed in the long-term specification but also changed in the period of one-line printing, and it is first necessary to solve this problem before considering high image quality. It is also something that must be resolved.

When recording is performed using a plurality of liquid droplets, and when binary recording is performed at 4 KHz, four-value recording is performed.
3 = 12 KHz is required, and if it is performed at a high frequency, the temperature of the recording head will rise significantly. However, 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 high-speed processing is performed, many droplets can be recorded in a minute area with an equivalent volume, and high-speed printing can be performed in a short time by many nozzles. A droplet ejection recording method that solves the recording irregularity of the recording method to be ejected, has a high droplet ejection speed and is stable, and can achieve recording with almost no volume change of the droplet itself. It is intended to be provided.

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

[0012] The present invention achieves the above-mentioned object, in which heat energy is applied to a liquid passage communicating with a liquid supply source so as to rapidly supply nucleate boiling. In a droplet jet recording method in which bubbles are generated by exceeding a temperature rise and droplets are jetted for recording, a plurality of droplets ejected by communicating the bubbles with the outside air from an ejection port are used as a recording material. A droplet ejection recording method characterized by performing recording.

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

Further, the constitutions and conditions for making the above inventions more excellent inventions are as follows: firstly, the liquid passage is not blocked by the bubbles during the communication; and secondly, during the communication. Means to communicate the bubble with the outside air under the condition that the internal pressure of the bubble is equal to or lower than the outside atmospheric pressure. Thirdly, at the time of the communication, the bubble is removed under the condition that the acceleration of the moving speed of the tip portion in the discharge direction of the bubble is not positive. Fourthly, it is communicated with the outside air, or fourthly, the distance la between the discharge-side end of the plane heating portion and the discharge-side end of the bubble is equal to the end of the discharge energy generating means opposite to the discharge side. Distance lb from the end opposite to the bubble discharge part
On the other hand, there can be mentioned at least one of making bubbles generated in the liquid by the discharge energy generating means communicate with the outside air from the discharge part under the condition of la / lb ≧ 1. In order to solve the problems of the inkjet recording method as described above, the present applicant discharges air bubbles caused by film boiling generated by heating a liquid for discharging by communicating with the outside air near the discharge port. A liquid jet recording method (hereinafter, this method is also referred to as a continuous discharge method) was proposed (Japanese Patent Application No. 2-112832 and Japanese Patent Application No. 2-112).
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 bubbles does not jet together with the discharged droplets, so that the generation of splash or mist is reduced, and scumming on the recording medium is prevented. It is possible to prevent dirt inside the device.

Further, as a basic operation of the above-mentioned continuous discharge method, there is a principle that all the liquid on the discharge port side of the portion where bubbles are generated is discharged as liquid drops.
Therefore, 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 generating portion. As a result, according to the above-mentioned continuous discharge method, it becomes possible to perform stable discharge of the discharge amount without being affected by the change of the liquid temperature.

[0017]

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

A multi-valued image forming method by a so-called multi-droplet method is used in which one pixel is formed by repeating at least one or more steps of discharging the liquid by communicating the air bubbles generated by the heater with the outside air from the discharge port, (A) and (C) show the conventional state when the recording head is moved from the recording start S to the recording end E, and the image of the embodiment of the present invention is shown in (B). In the conventional (A) and (C), the image of D1 first becomes gradually larger (D1 <D2 <D3 <D4
<D5, Da <DA, Db <DB), and at the end portion, the image forming position is also displaced.

On the other hand, the present invention, as will be described later,
Since it is a method of communicating bubbles to the atmosphere, it is not affected by such a problem of thermal energy. Therefore, an image formed by being collected by a plurality of droplets can be recorded in an appropriate state.

2 (a) and 2 (b) show preferred forms of the concept of the present invention, and show two examples of typical constitutions of the liquid passage B, but the present invention is not limited thereto. Figure 2
(A) has a heating resistance layer 2 on a substrate (not shown),
The print head is provided with the side ejection ports 5 (plurality) on that 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 the electrode signal (pulse signal) corresponding to the recording signal from the electrodes E1 and E2, the heating portion between the electrodes E1 and E2 causes a rapid temperature rise that causes film boiling (30).
And generate bubbles 6. As a result, in this example, the bubble 6 communicates with the atmosphere at the end portion A of the ejection port 5 on the heating resistance layer 2 side to form a stable droplet (broken line 7). In this way, by communicating with the atmosphere (outside air) in the vicinity of the periphery of the ejection port 5, the liquid can be ejected according to the recording signal without splashing or generating mist-like ink droplets. You can

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

Although the common liquid chamber C is not shown in FIG. 2B, the liquid passage B is a bent liquid passage, and the heating resistor portion 2 is provided on the substrate surface of the bent portion. .. The discharge port has a shape that reduces the area in the discharge direction,
Is facing. The discharge ports (plurality) are formed in the orifice plate OP.

In FIG. 2 (b) as well, when film boiling (300 ° C. or higher) is caused as in the case of FIG. 2 (a), the bubbles 6 grow and push the ink in the thickness portion of the orifice plate OP. , Dilute the ink in that part. After this, the bubbles 6 communicate with the atmosphere from the outside air side peripheral edge A1 of the discharge port 5 to the inside discharge port vicinity region A2. According to such a communication state, stable droplets (broken line 7) can be ejected from the central portion of the ejection port without splashing and generating mist. At this time, since the growth of the bubbles does not block the liquid path, it is possible to leave the liquid that does not need to go in the discharge direction as an aggregate that is continuous with the liquid in the liquid path. It can contribute to stabilization and stabilization of discharge speed.

In the present embodiment, the refilling of the liquid path in the non-interrupted state can be performed because the bubble growth can be rapidly and rapidly made near the discharge port rapidly and reliably by utilizing the stabilization region of film boiling of 300 ° C. or higher. High stability and high speed recording can be achieved with the help of the performance.

FIG. 2C is a cross-sectional view of one side of the liquid passage B of FIG. 2B from the common liquid chamber C side toward the heat generating resistance layer 2. As can be seen from FIG. 2C, the liquid in the liquid path B (hatched portion) is in communication with the droplet 7, and the bubbles 6 near the central discharge port at that time are in the atmosphere near the discharge port. It will be understood that the droplet 7 and the liquid in the liquid passage are kept in communication with each other when communicating with the liquid. 6W
Shows the shape of the bubble end in this cross section of the bubble.

As described above, also in FIG. 2A, when the air bubbles communicate with the atmosphere, the liquid in the liquid passage communicates with the liquid droplets protruding from the discharge port, and the liquid droplets are gradually separated. Since it goes, it can prevent the conventional splash.

The conditions which are incorporated into FIGS. 2 (a) and 2 (b) and which are preferable conditions and achieve even more particularly preferable droplet formation are listed below.

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

That is, communicating the bubble with the outside air under the condition that the internal pressure of the bubble is lower than the external pressure means that the unstable liquid near the discharge port, which is generated when the internal pressure of the bubble is communicated with the internal pressure higher than the external pressure, is scattered. In addition, since the force that draws the unstable liquid into the liquid passage works slightly more than in the case where the pressure is equal, the discharge of the liquid is more stable and the unnecessary liquid is prevented from scattering. 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 differential value 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 edge to the bubble outlet side edge
a and a distance lb between the end on the side opposite to the ejection port of the ejection energy generating means and the end on the side opposite to the ejection port of the bubble satisfy the third condition of la / lb ≧ 1, or both of them. It is more preferable to make the bubbles communicate with the outside air under the conditions.

Next, one structure of the recording head preferably used in the present invention will be described.

FIGS. 3A and 3B are a schematic assembly perspective view and a schematic top view of one suitable recording head. Note that (b) is a state in which the top plate shown in (a) is not provided. The configuration of the recording head shown in (a) and (b) will be briefly described.

In the recording heads shown in (a) and (b), a wall 8 is provided on the substrate 1, the ceiling plate 4 is joined to cover the wall 8, and the common liquid chamber 10 and the liquid passage 12 are provided. 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 passage 12 through the common liquid chamber 10 communicating with the liquid passage 12.

A heater 2 is provided on the base 1,
Each liquid path is provided corresponding to each heater 2. The heater 2 has a heating resistance layer and an electrode (not shown) electrically connected to the heating resistance layer, and the electrode is energized according to a recording signal. By this energization, the heater 2 generates thermal energy, and the thermal energy can be applied to the ink supplied into 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 preferably used in the present invention will be described.

FIG. 4A and FIG. 4B show 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 passage is ejected straight or substantially straight from the ejection port along the liquid passage. 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 ejection port is formed immediately above the heater). In FIGS. 4A and 4B, the same reference numerals as those shown in FIGS. 4A and 4B indicate the same components. In FIGS. 4A and 4B, reference numeral 16 is an orifice plate in which the discharge ports 5 are formed, and here, the wall 9 provided between the discharge ports 5 is also integrally formed.

FIGS. 5 (a) to 5 (e) are explanatory views of a novel first specific example of a liquid ejecting method and apparatus to which the present invention is applied, which is an invention focusing on the time change of the internal pressure and volume of the bubble. is there. The present invention can be summarized as follows: 1) In a liquid ejecting method in which ink is heated to generate bubbles, and at least a part of the ink is ejected by the bubbles to perform recording, a condition that the internal pressure of the bubbles is equal to or lower than the external atmospheric pressure A method for ejecting liquid, characterized in that the bubbles are communicated with the outside air. 2)
A recording head having an ejection port for heating at least one part of the ink by the ink by heating the ink by the ejection energy generating means and the bubble under the condition that the internal pressure of the bubble is equal to or less than the external pressure. A recording apparatus comprising: a drive circuit for driving the ejection energy generating means so as to communicate with the 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 invention stabilizes the volume and speed of the ejected liquid droplets, suppresses the generation of splashes and mists, which are the cause of insufficient support for high-speed recording, and is used as a background stain on an image or as a device. In this case, the inside of the device is prevented from becoming dirty, the ejection efficiency is improved, clogging is prevented, the life of the recording head is improved, and high-quality images can be printed.

Before describing FIG. 5, the principle of liquid ejection will be described with reference to FIG. The liquid passage 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 passed through a heater (for example, an electrothermal converter) 2 to rapidly heat the ink 3 near the heater in a pulsed manner, the ink causes bubbles 6 to be generated on the heater 2 due to so-called film boiling. Then, it rapidly expands (FIG. 6 (b)). Further, the bubble 6 continues to expand and grows mainly on the side of the ejection port 5 having a small inertial resistance, and finally passes through the ejection port 5 to communicate the outside air with the bubble 6 (FIG. 6C). At this time, the outside air is a bubble 6
It is in equilibrium with the inside or flows into the bubble 6.

The ink 3 pushed out from the ejection port 5 continues to fly further forward by this moment due to the momentum given by the expansion of the bubble 6, and finally becomes an independent droplet to be recorded on paper or the like. Fly toward the medium 101.
(FIG.6 (d)). Further, in the gap formed at the tip of the ejection port 5 side, the ink 3 is supplied rightward in the drawing due to the surface tension of the ink 3 behind 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 ejection 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 may be moved), or they may be combined. The point is that the ejection port 5 and the recording medium can be moved relative to each other so that the desired ejection port can face the desired position of the recording medium.

Now, in FIG. 6C, when the bubble 6 communicates with the outside air, is there a movement of gas between the outside air and the inside of the bubble?
In order for the outside air to flow into the bubble, it is preferable to communicate the bubble 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 with each other at the time of t ≧ t1. In reality, since the ink is ejected as the bubble grows, a graph of the relationship between the bubble internal pressure or volume and time is as shown in FIG. That is, in FIG. 5B, t = tb (t1
The bubble may be communicated with the outside air at a time of ≤tb).

Compared with the case where the droplet is discharged under this condition, the bubble is communicated with the outside air and the droplet is discharged under the condition that the internal pressure of the bubble is higher than the external pressure (gas is ejected into the atmosphere).
As described above, it is possible to prevent stains on the recording paper and the apparatus due to the mist and splash of the ink. Further, since the bubble is made to communicate with the outside air after the volume of the bubble is increased, sufficient kinetic energy can be transmitted to the ink, and the effect of increasing the ejection speed can be obtained. Further, it is more desirable to communicate the bubble with the outside air under the condition that the internal pressure of the bubble is lower than the outside pressure because 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 atmospheric pressure means that the unstable liquid near the discharge port, which is generated when the internal pressure of the bubble is communicated with the internal pressure of the bubble higher than the atmospheric pressure, is scattered. In addition, since the force that draws the unstable liquid into the liquid passage works slightly more than in the case where the pressure is equal, the discharge of the liquid is more stable and the unnecessary liquid is prevented from scattering. Can be planned.

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

As a condition for more effectively achieving the invention of the second embodiment, the shape of the liquid passage can be mentioned as described above. The width of the liquid path is almost determined by the shape of the thermal energy generating element used, but the specific relationship is only an empirical rule. In the present invention, it has been found that the shape of the liquid path has a great influence on the growth of bubbles and is effective for the above conditions in the liquid path.

That is, it was found that the communication state of bubbles can be changed by utilizing the height of the liquid passage. It is preferable that the height H of the liquid passage is lower than the width W of the liquid passage (H <W) in order to reduce the influence of other factors such as the environment and to achieve further stabilization.

Further, when the bubble does not communicate with the outside air, the bubble communicates with the outside air when it reaches the maximum volume of the bubble or 70% or more of the maximum volume of the bubble, more preferably 80% or more. Is preferred.

Next, a method of 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 and the external atmospheric pressure of the bubble can be known by the method shown below or by appropriately combining these methods. First, a method of knowing the magnitude relationship between the internal pressure of the bubble and the external atmospheric pressure by measuring the time change of the volume of the bubble or the volume of the ink outside the ejection port 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 determining the second derivative d2V / dt2 of V. 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 equal to or lower than the external pressure. Explaining with reference to FIG. 5C, the internal pressure of the bubble is higher than the external pressure and becomes d2V / dt2> 0 from the start t = t0 to the time t = t1, and the time t from the time t = t1 until the bubble communicates with the external air. The internal pressure of the bubble is equal to or lower than the external atmospheric pressure up to tb, and d2V / dt2 ≦ 0. As described above, the magnitude relationship between the internal pressure of the bubble and the external atmospheric pressure can be known by obtaining the second derivative d2V / dt2 of V.

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

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

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 the one whose physical properties such as wettability to ink are as close as possible to the original member. Whether or not the foamed state is equivalent to 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. If it is made of a transparent member in advance, such an operation is unnecessary.

Even if the constituent members of the recording head are not replaced with other members, or even 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 to the outside from the ejection port during the time from the start of foaming until the ink droplet is ejected, and the second derivative d2V of Vd is measured.
By determining d / dt2, it is possible to know the magnitude relationship between the internal pressure of the bubble and the external pressure. 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 bubbles are communicated with each other in a state where the inner pressure of the bubble is higher than the outer pressure. From the start of foaming t = t0 until the time t = ta until the bubble communicates with the outside air, the internal pressure of the bubble is higher than the outside air pressure, and d2Vd / dt2> 0. On the other hand, FIG. 5B shows the first derivative dVd / of Vd when the bubble is communicated with the outside air in a state where the inside pressure of the bubble is equal to or lower than the outside pressure.
It shows the change over time in dt. From 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 is d2Vd / dt2> 0, but the internal pressure of the bubble is below the external pressure from t = t1 to t = tb. Yes d2V
d / dt2 ≦ 0.

As described above, the second derivative of Vd d2Vd / d
By obtaining t2, it is possible to know the magnitude relationship between the internal pressure of the bubble and the external atmospheric pressure.

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

According to these methods, if an air flow from the liquid passage side to the outside is observed at the moment when the bubble communicates with the outside air, it indicates that the internal pressure of the bubble is higher than the outside air pressure, and the liquid passage communicates. If the airflow flowing into the interior is observed, it indicates that the bubbles communicate with each other at a lower internal pressure than the external pressure.

As another condition, as shown in FIG. 7, the condition that the bubble and the outside air are communicated with each other under the condition that the first derivative value of the moving speed of the tip of the bubble in the discharge port direction is negative, or as shown in FIG. As described above, the distance la from the end on the ejection port side of the ejection energy generating means to the end on the side on the ejection port side of the bubble and the end on the side opposite to the ejection port of the ejection energy generating device from the end on the side opposite to the ejection port of the bubble It is more preferable that the bubble and the outside air are communicated with each other under the condition that the distance lb with the section satisfies la / lb ≧ 1, or both conditions.

FIGS. 6A to 6F are explanatory views of a new second specific example of the liquid ejecting method and apparatus to which the present invention is applied, and the invention focuses on the growth state of bubbles. The present invention can be summarized as follows: 3) An ejection port for ejecting ink, a liquid channel communicating with the ejection port, and a bubble formed in the liquid channel to be used for ejecting 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 portion of the discharge energy generating means and the discharge port side end portion of the bubble is opposite to that of the discharge energy generating means. La / l with respect to the distance lb between the side end and the end opposite to the bubble discharge port
A liquid ejecting method characterized in that, under the condition of b ≧ 1, bubbles generated in the ink by the ejection energy generating means are communicated with the outside air from the ejection port. 4) An ejection port for ejecting ink, a liquid path communicating with the ejection port, and an ejection for generating thermal energy used for ejecting 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 portion of the ejection energy generating means on the ejection port side and an end portion of the bubble on the ejection port side.
The ejection energy generating means is such that a / la ≧ 1 with respect to the distance lb between the end of the ejection energy generating means on the side opposite to the ejection port and the end of the bubble on the side opposite to the ejection port. A drive circuit for giving a signal to the ejection energy generating means for communicating the bubble generated in the ink with the outside air from the ejection port, and a platen for advancing a recording medium for adhering the ejected liquid. A recording device having: Becomes

The present invention will be described in detail below with reference to the drawings.

6 (a) to 6 (f) are schematic sectional views for explaining the ejection of the liquid by the liquid ejecting method of the present invention.

In FIGS. 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, 101 is a recording medium. Is. The liquid passage 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, the heater (for example, an electrothermal converter) 2 is instantaneously supplied with a current as a signal from a drive circuit, and the ink 3 near the heater is pulsed.
When ink is rapidly heated, bubbles 6 are generated on the heater 2 due to so-called film boiling in the ink, and the ink rapidly expands (FIG. 6B). Bubble 6 continues to expand (Fig. 6
(C)) Mainly grows toward the discharge port 5 side with a small inertial resistance, and finally passes through the discharge port 5 and the outside air communicates with the bubble 6 (FIG. 6 (d)). At this time, the distance la from the discharge port side end of the heater 2 which is the discharge energy generating means to the discharge port side end of the bubble 6 is from the end opposite to the discharge port of the heater 2 from the discharge port of the bubble 6. The outside air communicates with the bubble 6 under the condition of la / lb ≧ 1 with respect to the distance lb to the opposite end.

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

When the liquid is ejected according to the above-described recording principle, the volume of the liquid pushed out from the ejection port because the bubble communicates with the outside air is always constant.
It is possible to obtain a high-quality recorded image with uniform 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 opening ratio is improved.

Furthermore, when the liquid is discharged under the above conditions,
Compared with the case of ejecting a liquid (ink) under the condition of la / lb <1, it is possible to shorten the time until the new ink is filled in the voids formed in the vicinity of the ejection port after ejecting the liquid. High-speed recording is possible. In the second embodiment of the invention, as a method for 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, for example, in the case of the recording head shown in FIG. There is a method in which the top plate 4 is made of a transparent glass plate, and the recording head is irradiated from above the top plate 4 with a pulsed light source such as a strobe, a laser, an LED, or the like and observed by a microscope.

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

The width of the liquid path is almost determined by the shape of the thermal energy generating element used, but the specific relationship is only an empirical rule. In the second embodiment of the invention, it was found that the shape of the liquid path greatly affects the growth of bubbles and is effective for the above conditions of the thermal energy generating element in the liquid path.

That is, by utilizing the height component of the liquid path, the bubble growth is set to la / lb ≧ 1, preferably la / lb ≧ 2, and more preferably la / lb ≧ 4 (see FIG. 8). ,
It has been found that it is preferable to make the liquid path height H lower than at least the liquid path width W (H <W) in order to make the operation in a more stable state unlikely to be affected by other factors such as the environment. This makes it possible for the bubbles to communicate with the atmosphere in the bubbles that have increased the growth rate at the interface of the ceiling of the liquid channel, so that the influence of the inner wall of the liquid jet can be reduced, and the jet direction and velocity can be further improved. Can be stable. In the second embodiment of the invention, when the relationship between the width W and the height H is further pursued, when H ≧ 0.8 W, the characteristic change is small even if high-speed injection is performed for a long time, and stable injection is performed. And was suitable for recording.

Further, if H ≧ 0.65 W, it is optimal because a highly accurate landing performance can be obtained even if each recording jet carrying recording information is carried out with a considerable change.

In addition to the above conditions, it is more preferable to communicate the bubble with the outside air under the condition that the first-order differential value of the moving speed of the tip of the bubble in the discharge port direction is negative.

FIGS. 7 (a) and 7 (b) are explanatory views of a new third specific example of the liquid ejecting method and apparatus to which the present invention is applied, which is an invention focusing on the time change of the internal pressure and volume of the bubble. is there. The present invention can be summarized as follows: 5) An ejection port for ejecting ink, a liquid channel communicating with the ejection port, and a bubble formed in the liquid channel to be used for ejecting the supplied ink. Using a recording head equipped with a discharge energy generating means for generating thermal energy, under the condition that the first differential value of the moving speed of the generated bubble toward the discharge port end is negative,
A method for ejecting droplets, characterized in that the bubbles generated by the ejection energy generating means are communicated with the outside air from an ejection port. 6) An ejection port for ejecting ink, a liquid path communicating with the ejection port, and an ejection for generating thermal energy used for ejecting the supplied ink by forming bubbles in the liquid path. A recording head provided with an energy generating unit, and the bubble is generated by the discharge energy generating unit under the condition that the first-order differential value of the moving speed of the bubble generated by the discharge energy generating unit at the tip in the discharge port direction is negative. A drive circuit for giving a signal to the ejection energy generating means for communicating the bubble with the outside air from the ejection port, and a platen along which the recording medium can be placed so as to attach the ejected liquid. Recording device. Is.

The third embodiment of the invention solves the above-described object effect of the first embodiment of the invention by another means, and the ink in the vicinity of the communicating portion ejects the ink when the bubble and the outside air communicate with each other. Due to excessive acceleration,
The main technical issue is to separate the ink from the main ink droplets. According to this separation, the ink in the vicinity thereof is splattered in the form of a splash or becomes a mist, which is remarkable, and further, in a high-density ejection port arrangement, ejection failure due to adhesion of ink to the ejection port surface is caused. However, the origin of the invention of the third embodiment is that the cause is 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 primary differential value of the moving speed of the tip of the bubble in the discharge port direction is positive. ..

From the start of foaming until the bubble communicates with the outside air, the displacement amount of the tip of the bubble in the outlet direction from the end of the heater portion in the outlet direction is measured, and the first derivative value of the displacement amount, 2
Fig. 8 shows the result of obtaining the secondary differential value (first differential value of the moving speed).
It was shown to. From the figure, the above problem occurs in FIG.
In the case of the curve A shown in each of (a) and (b), it was confirmed that the first-order differential value of the moving speed of the tip of the bubble in the ejection port direction is positive.

Curves B shown in FIGS. 7 (a) and 7 (b) show the third specific example of the invention based on the principle of FIG. 6, and the first-order differential value of the moving speed of the tip of the bubble in the discharge port direction. In the negative condition, the generated bubble is made to communicate with the outside air to eject the droplet, so that the volume of the droplet is always stabilized and a high quality recorded image can be obtained. Therefore, it is possible to prevent the background stain of the recording paper and the stain inside the apparatus due to the ink mist or the splash.

Furthermore, since the kinetic energy of the bubbles can be sufficiently transmitted to the ink, the ejection efficiency is increased and clogging can be eliminated. Further, since the droplet ejection speed is improved, the droplet ejection direction is stabilized, and the distance between the recording head and the recording paper can be increased, which facilitates the device design.

Furthermore, since there is no defoaming process of bubbles that have occurred, 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 both the so-called on-demand type and the continuous type. Particularly, in the case of the on-demand type, the liquid (ink) is retained. By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding nucleate boiling to the electrothermal converter arranged corresponding to the sheet or liquid path, the electrothermal converter This is effective because heat energy is generated to cause film boiling on the heat acting surface of the recording head, and as a result, bubbles can be formed in the liquid (ink) in a one-to-one correspondence with this drive signal.

The recording head using the liquid ejecting method of the present invention is not limited to the one described in the above embodiment, and has a length corresponding to the maximum width of the recording medium which can be recorded by the recording apparatus. Many forms and modifications such as a full line type recording head are possible. Further, the full-line type recording head may be configured to satisfy the length by combining a plurality of recording heads or configured as one recording head integrally formed, but in any case, The invention can exhibit the above-mentioned effects more effectively.

In addition, by being attached to the apparatus main body, it can be electrically connected to the apparatus main body and can be supplied with ink from the apparatus main body by a replaceable chip type recording head or the recording head itself. The present invention is also effective when a cartridge-type recording head that is specially provided is used.

Further, in addition to the recovery means for the recording head as described above, which is provided as the structure of the recording apparatus of the present invention, it is possible to further stabilize the effect of the present invention by adding preliminary auxiliary means or the like. It is preferable because it is possible. Specific examples thereof include cleaning means for the recording head, an electrothermal converter or a heating element other than this, or a preheating means using a combination thereof. Also,
It is also effective to perform stable recording by performing a preliminary discharge mode in which discharge different from recording is performed.

Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but the recording head may be integrally formed or a plurality of combinations may be used. The present invention is also extremely effective for a device provided with at least one of full color by color mixing.

Next, in carrying out the present invention, 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 will be described below.

The position of the tip of the bubble in the discharge port direction at each time after the start of bubbling is determined by illuminating the bubble generated in the nozzle from the top plate surface or side surface of the recording head with pulsed light from a strobe, LED, laser, etc. Can be used and observed. Specifically, as shown in time series as schematic cross-sectional views in FIGS. 9A and 9B, respectively, a heater portion at the tip of the bubble in the discharge port direction from the start of foaming until the bubble communicates with the outside air. It is possible to measure the change over time in the displacement amount xb-n from the end portion of the discharge port. Based on the measurement result, the first-order differential dxb-n / dt of the displacement amount is calculated to obtain the moving speed v of the tip of the bubble in the discharge port direction.
x is required. Next, the first derivative dvx / of the moving speed
dt (second derivative of displacement amount d2xb-n / d2t) can be obtained.

In this case, it is necessary that the bubble be visible from the outside of the recording head. In order to observe the bubbles from the outside of the recording head, it is desirable that a part of the recording head is formed of a transparent member and that bubble formation and growth of the bubbles can be observed from the outside of the recording head. When the constituent members of the recording head are non-transparent, for example,
The top plate of the recording head may be replaced with a transparent member.
At this time, it is desirable that the hardness of the member to be replaced and the elasticity of the member to be replaced be the same as much 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 (transparent acrylic, for example), glass, or the like. Of course, the replacement place and the material used therefor are not limited to the above-mentioned place and material.

[0092]

As described above, according to the recording method of the present invention, heat energy is applied to the liquid passage communicating with the liquid supply source to receive the liquid supply from the liquid supply source to cause nucleate boiling. In a droplet jet recording method in which a bubble is generated by a temperature rise that exceeds abruptly and a droplet is ejected for recording, a plurality of droplets ejected by communicating the bubble with the outside air from the ejection port are used for recording. Since this is a droplet jet recording method for recording on a material, it is possible to improve image unevenness at the start and end of recording and form a good image.

[Brief description of drawings]

1 (A), (B), and (C) are explanatory views for explaining the method and effect of the present invention.

2 (a), (b), and (c) are schematic diagrams illustrating a state in which the ink bubbles of the present invention communicate 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 views 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 bubble internal pressure and volume with time.

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

7 (a) and 7 (b) are explanatory views of another novel specific example of the liquid ejection method and device to which the present invention is applied.

FIG. 8 is a graph illustrating changes in the ratio la / lb on the leading end side and the trailing end side of bubbles.

9 (a) and 9 (b) are diagrams showing changes in the tip of a bubble per unit time, respectively. FIG. 9 (a) is a cross-sectional top view on the left side,
Side sectional views are shown at the same time on the right side.

[Explanation of symbols]

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

Claims (5)

[Claims] 1. A liquid which is supplied with heat energy from a liquid supply source to a liquid passage communicating with the liquid supply source so as to generate bubbles by a temperature rise abruptly exceeding nucleate boiling. A droplet ejection recording method for ejecting droplets for recording, characterized in that recording is performed on a recording material by using a plurality of droplets ejected by communicating the bubbles with the outside air from an ejection port. Jet recording method. 2. The droplet jet recording method according to claim 1, wherein the liquid path is not blocked by the bubbles during the communication. 3. The droplet jet recording method according to claim 1, wherein at the time of the communication, the bubble is communicated with the outside air under the condition that the internal pressure of the bubble is equal to or lower than the outside atmospheric pressure. 4. The liquid according to claim 1, wherein during the communication, the bubbles are communicated with the outside air under the condition that the acceleration of the moving speed of the tip of the bubbles in the discharge direction is not positive. Drop ejection recording method. 5. The end portion of the planar heat generating portion on the side of the discharge portion and the end portion on the side of the discharge portion of the bubble where the distance la is opposite to the discharge portion of the discharge energy generating means and the discharge portion of the bubble. 5. The bubbles generated in the liquid by the discharge energy generating means are made to communicate with the outside air from the discharge part under the condition of la / lb ≧ 1 with respect to the distance lb from the end on the opposite side. The droplet jet recording method according to any one of claims.