JP3118038B2 - 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 head for recording by flying droplets on a recording material such as paper, a resin sheet, and cloth using thermal energy, and a recording method thereof. Related to the device.

[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.

[0005]

2. Description of the Related Art The above-described droplet jet recording method using a recording method using thermal energy has many advantages, and follows the specifications of a dot matrix printer used in various printers to process images in various ways. Is formed. 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 practical level of image processing and the recording head itself is about 400 DPI, recording interruption processing is performed to reduce the recording speed or to promote fixing of a recording medium in which droplets are absorbed. As a result, the above problem is not a major problem as a result. However, in pursuit of high image quality, the number of droplets that can be used at present is increased, and at the same time, the volume per droplet is reduced. If it can be made minute and stable, it will be the biggest problem.

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.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned state of the art, the present invention provides an epoch-making method of ejecting droplets. Compared to the recording method in which many droplets are ejected in a short time by the multi-nozzle, the droplet ejection speed is high and stable, and recording is performed with almost no change in volume of the droplet itself. It is an object of the present invention to provide a droplet ejection recording method that can be achieved and to eliminate problems to be solved in the future.

The present invention particularly provides a droplet ejection recording method which is optimal 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 thermal energy to a liquid in a liquid passage which is connected to a liquid supply source and receives the supply of the liquid from the liquid supply source. To generate air bubbles.
A step of letting the air bubbles communicate with the outside air under the condition that the internal pressure is equal to or lower than the outside air pressure , and discharging a part of the liquid as droplets from the discharge port, wherein the amount of liquid discharged per process is 30 pl
The following is a droplet ejection recording method, wherein one pixel is formed by repeating the above steps at least once.

According to the present invention, even when a droplet having a volume of 30 pl or less is used, the volume of the droplet is kept constant even if the volume of the droplet is minute by merely setting the configuration of the ejection portion of the recording head to a desired range of 30 pl or less. High-speed recording, multiple driving, etc.
It enables many complex recording schemes. If the present invention is to be performed by the conventional method, it is not possible to obtain even stable ejection of the droplet itself, and it is not possible to obtain the effects of the present invention.

According to the present invention, by setting the liquid to be discharged by communicating the bubbles with the outside air in this range, the discharge speed of the droplets can be improved, and the structure that can reliably communicate the bubbles with the outside air can be easily achieved. In addition to that, despite the use of thermal energy, the advantage of its responsiveness remains the same, and thermal instability elements are eliminated during recording. It can be provided.

[0014] The constitution 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 air bubbles at the time of the communication;
Be in communication with the outside air to the air bubbles under the conditions acceleration of the moving speed of the ejection direction distal end portion of said bubble is not positive, or the discharge port-side end portion of the energy generating means for generating <br/> the heat energy to the third And the distance between the end of the energy generating means opposite to the discharge port and the end of the energy generation means opposite to the discharge port is lb.
At least one of communicating air bubbles generated in the liquid by the above energy generating means with the outside air under the condition of / 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, also referred to as a continuous discharge method) has been proposed (Japanese Patent Application No. 2-1128).
No. 32, Japanese Patent Application No. 2-112833, Japanese Patent Application No. 2-112
No. 834, Japanese Patent Application No. 2-114472, Japanese Patent Application No. 3-16
No. 9962).

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]

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

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

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

A multi-value image forming method by a so-called multi-droplet method is used in which a step of discharging bubbles by causing bubbles generated by a heater to communicate with outside air from a discharge port is repeated at least once or more to form one pixel. In the case of forming a full-color image, it is necessary to set the volume of the discharged liquid per one process to 30 pl or less.

The extent to which the volume of the liquid to be ejected should be within the above range is determined by the resolution, the number of gradations, the liquid density, the recording material, etc. necessary for obtaining a full-color image. . For example, when an image having a recording density of 400 dots / inch and four gradations per dot (1 shot to 3 shots) is to be obtained by using a commonly used aqueous liquid and coated paper, It is desirable that the volume of the liquid to be discharged at one time is approximately 5 to 15 pl. In order to further increase the number of gradations and obtain, for example, an image of eight values (1 shot to 7 shots), it is preferably 3 to 10 pl.
Further, in order to obtain an image having a four-level gradation per dot at a recording viewing rate of 300 dots / inch, the liquid volume to be ejected at one time is preferably 7 to 25 pl, and in order to obtain an eight-level image. Is preferably 4 to 15 pl.

If the liquid ejection volume per process exceeds 30 pl, for example, yellow, magenta and cyan liquids
When the recording medium is hit into the pixels, the liquid on the recording medium dries slowly and causes deterioration of recording quality such as blurring of an image. This is particularly noticeable when the recording medium is plain paper. Even if these drawbacks are solved by any means, if the ejection volume is large, the refill time will be long, which is disadvantageous especially when performing multi-value recording.

(Embodiment 1) The nozzle has a width of 30 μm and a height of 1.
8μ, length 200μ, width 2 at 15μ from discharge port
It has a heater of 2μ, length 30μ, and 48 nozzles 40
Four recording heads (FIG. 1) provided at a recording density of 0 dots / inch were supplied with black liquid as I. Food rack 2 3.0% by weight Diethylene glycol 15.0% by weight N-methyl-2-pyrrolidone 5.0% by weight Ion-exchanged water 77.0% by weight as yellow liquid C.I. I. Direct Yellow 86 3.0% by weight Diethylene glycol 15.0% by weight N-methyl-2-pyrrolidone 5.0% by weight Ion-exchanged water 77.0% by weight as magenta liquid as C.I. I. Acid Red 35 3.0% by weight Diethylene glycol 15.0% by weight N-methyl-2-pyrrolidone 5.0% by weight Ion-exchanged water 77.0% by weight as a cyan liquid, C.I. I. Direct Blue 119 3.0% by weight Diethylene glycol 15.0% by weight N-methyl-2-pyrrolidone 5.0% by weight Deionized water 77.0% by weight was supplied, and a color image was formed on coated paper.

The driving conditions of the recording head were as follows: the driving voltage was 12 V, the pulse width was 3 μs, and the frequency of one liquid ejection was 8 KHz for each color. Under these conditions, a maximum of three shots per pixel were controlled and a color image was formed by quaternary recording. As a result, the obtained color image was of high quality without blurring of printing. When the volume of the liquid discharged by one discharge was measured, it was about 11 pl.

(Embodiment 2) In a recording head having the same shape as that of Embodiment 1, the width of the nozzle was reduced to 24 μm,
The liquid used in Example 1 was supplied to a recording head having a heater having a width of 20 μm and a length of 26 μm at a position 12 μm from the discharge port, and further reducing the density to 300 dots / inch.
0V, pulse width 3μs, frequency of one liquid discharge is 12K
Hz, a color image was formed. In this embodiment, a control is performed so that up to seven shots per pixel are performed, and a color image is formed by octal recording. As a result, a higher quality image than in the first embodiment can be obtained without blurring.
In this embodiment, the volume of the liquid discharged by one discharge is 5 to 6 pl.

(Embodiment 3) The height of the liquid path is 13 μm, the length of the liquid path is 70 μm, the width is 36 μm, the distance between the discharge port and the heater is 25 μm, and the diameter of the circular discharge port is 36 μm. The liquid used in Example 1 was supplied to a recording head (FIG. 2) having a heater having a 24 μ square heater just below the outlet and having 64 nozzles arranged at a density of 400 dots / inch.

When quaternary recording was performed in the same manner as in Example 1 except that the driving voltage was 11.5 V, the pulse width was 3 μs, and the frequency of liquid discharge per time was 6 KHz, it was slightly blurred compared to Example 1. An image that does not cause a practical problem was obtained. The volume of the liquid discharged by one discharge was about 27 pl.

(Embodiment 4) The height of the liquid path is 10 μm, the length of the liquid path is 58 μm, the width is 27 μm, the distance between the discharge port and the heater is 20 μm, and the diameter of the circular discharge port is 27 μm. The liquid used in Example 1 was supplied to a recording head (FIG. 2) having a heater having a size of 18 μ square just below the outlet and arranged with 64 nozzles at a density of 400 dots / inch.

When quaternary recording was performed in the same manner as in Example 1 except that the driving voltage was 8 V, the pulse width was 3 μs, and the frequency of liquid discharge per operation was 12 KHz, a high-quality image without bleeding could be obtained. . The volume of the liquid discharged by one discharge was about 9 pl.

As described above, according to the present invention, the liquid re-supply speed in the communication state of the bubbles to the outside air can be set in a desired range by setting the ejection amount of the liquid droplets to 30 pl or less. While the volume of the liquid to be ejected is extremely stabilized by the effect of the characteristics, a large number of multivalued images can be formed by the landing performance, and a recording method that can withstand high-speed processing can be realized.

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 characteristic for the subsequent ink recording is 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 as well, when film boiling (300 ° C. or higher) occurs 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 among the film boiling can be utilized to rapidly and surely cause the bubble growth near the discharge port. High stability and high speed recording can be achieved with the help of the characteristics.

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

As described above, in FIG. 2A, similarly, when the bubble communicates with the atmosphere, the liquid in the liquid path gradually separates the liquid droplet while communicating with the liquid droplet 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 particularly preferable droplet formation are listed below.

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

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

In addition to the above conditions, the second condition for communicating the bubble with the outside air under the condition that the first derivative of the moving speed of the tip of the bubble in the 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 assembly 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. 5A and 5B, a wall 8 is provided on the base 1, and the wall 8 is joined so that the top plate 4 covers the same. 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 a 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. 5A to 5E 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 temporal changes in the internal pressure and volume of a bubble. is there. The present invention is summarized as follows: 1) In a liquid ejecting method in which a bubble is generated by heating ink and at least a part of the ink is ejected by the bubble to perform recording, a condition that the internal pressure of the bubble is equal to or less than an external pressure. Wherein the bubbles are communicated with outside air. 2)
A recording head having a discharge port for discharging ink at least partly by heating the ink by the discharge energy generating means to generate at least a part of the ink by the ink, and generating the air bubble under the condition that the internal pressure of the air bubble is equal to or less than the external pressure. A recording apparatus, comprising: a driving circuit for driving the ejection energy generating means so as to communicate with outside air; and a platen provided at a position where the ejection port and the recording medium face each other.

The first embodiment of the present invention stabilizes the volume and speed of the ejected liquid droplets, suppresses the occurrence of splashes and mist as causes that cannot sufficiently cope with high-speed recording, 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 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.
For the outside air flows into the bubble, the outside pressure of the bubble
Preferably, the bubble communicates with the outside air under conditions 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 ejected under these conditions, the droplets are ejected by causing the bubbles to communicate with the outside air when the internal pressure of the bubble is higher than the outside pressure (gas is ejected into the atmosphere).
As described above, it is possible to prevent recording paper and the inside of the apparatus from being stained by ink mist or splash. Further, since the bubble is communicated with the outside air after the volume of the bubble increases, sufficient kinetic energy can be transmitted to the ink, and the effect of increasing the ejection speed can be obtained. In addition, it is more desirable to make the bubble communicate with the outside air under the condition that the internal pressure of the bubble is lower than the outside air pressure, since the above effect can be made more remarkable.

That is, 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 shape of the liquid passage 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.

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

In this case, it is necessary that the bubbles are visible from outside the recording head. In order to observe the bubble from outside the recording head, it is preferable that a part of the recording head is formed of a transparent member so that bubble bubbling and growth can be observed from outside the recording head. When the 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 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 a material having physical properties such as wettability with ink as close as possible to the original member. Whether or not the foaming state is the same as that of the original member can be confirmed by discharging and checking whether or not the discharge speed and the discharge volume are the same as the original state. 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 the ink that has protruded outside the ejection port from the start of bubbling to the time when 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.

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

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

FIGS. 6A to 6F are explanatory views of a second specific example of the liquid ejecting method and apparatus to which the present invention is applied. 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 the ejection of liquid by the liquid ejecting 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.

Up to this moment, the ink 3 pushed out from the discharge port 5 continues to fly further forward due to the momentum given by the expansion of the bubble 6, and finally becomes independent droplets 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 discharged according to the recording principle described above, the volume of the liquid pushed out from the discharge port is always constant because the bubble communicates with the outside air.
It is possible to obtain a high-quality recorded image without unevenness in the recording density.

Further, since the bubble communicates with the outside air under the condition of la / lb ≧ 1, 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 applied 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 substantially determined by the shape of the thermal energy generating element to be used, the specific relationship is only an empirical rule. In the second specific example, it was found that the shape of the liquid path greatly affected the growth of bubbles, and was effective for the above conditions of the heat energy generating element in the liquid path.

That is, by 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.

Further, if H ≧ 0.65W, 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. Is a recording device.

This third embodiment of the present invention solves the above-mentioned object and 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 at the discharge port end in the discharge port direction 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. 7A and 7B show the third embodiment of the invention based on the principle of FIG. 6, and show the first derivative of the moving speed of the tip of the bubble in the direction of the discharge port. In the negative condition, the generated bubble is communicated with the outside air to discharge 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 recording paper from being stained by ink mist or splash and the inside of the apparatus.

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

Further, since there is no defoaming process of 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 ejecting method of the present invention is not limited to the one described in the above embodiment, but has a length corresponding to the maximum recording medium width that can be recorded by the recording apparatus. Many forms and variations of a full-line type recording head are possible. Further, the full-line type recording head may be either a configuration that satisfies the length by combining a plurality of recording heads or a configuration as a single recording head that is integrally formed. The invention can exhibit the above-mentioned effects more effectively.

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

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

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

Next, a method for obtaining the moving speed of the tip of the bubble in the direction of the discharge port 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 constituent members may be replaced with transparent plastic (for example, transparent acrylic) or glass. Of course, the replacement place and the material used for it are not limited to the above place and material.

[0103]

As described above, the recording head and the recording method of the present invention use a method in which bubbles are communicated with the outside air to discharge ink droplets, and the amount of liquid discharged per process is 3 times.
0 pl or less, and the above-described process is repeated at least once to form one pixel. Therefore, when a droplet is ejected, the formation of bubbles in an environment or the like does not require a complicated configuration. Even if it changes, a proper droplet discharge is achieved, the image quality is stabilized, and a high-quality recorded image without image disturbance can be obtained.

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

[Brief description of the drawings]

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

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

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

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

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

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

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

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

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

[Explanation of symbols]

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

Continuation of front page (56) References JP-A-54-161935 (JP, A) JP-A-61-185455 (JP, A) JP-A-61-249768 (JP, A) JP-A-2-299854 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41J 2/05

Claims (4)

(57) [Claims] 1. A method for applying heat energy to a liquid in a liquid passage that is connected to a liquid supply source and receives the supply of the liquid from the liquid supply source, generates bubbles by film boiling due to the heat energy, and generates an internal pressure of the bubbles. the amount of liquid but which has a step of ejecting a part of the liquid from the discharge port by the bubble is communicated <br/> outside air communication with the following conditions outside pressure as droplets, and discharges to the process per injection A droplet ejection recording method of forming a pixel at 30 pl or less by repeating the above steps at least once or more. 2. The droplet jet recording method according to claim 1, wherein the liquid path is not blocked by the bubble during the communication. Wherein when said communication is droplet jetting according to claim 1 or claim 2 in which to communicate ambient air communicating the bubble with the conditions acceleration of the moving speed of the ejection direction distal end portion of said bubble is not positive Recording method. 4. A distance between the end of the energy generating means for generating thermal energy on the side of the discharge port and the end of the bubble on the side of the discharge port is la, and the end of the energy generating means on the side opposite to the discharge port is connected to the bubble. The air bubbles generated in the liquid by the energy generating means are communicated with the outside air under the condition of la / lb ≧ 1, assuming that the distance from the end opposite to the discharge port is lb. Item 6. A droplet jet recording method according to any one of Items 3 .