JP2783647B2 - Liquid ejection method and recording apparatus using the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a liquid ejecting method which can be suitably used for liquid ejecting recording in which recording is performed by attaching a liquid ejected using thermal energy to a recording medium. And a recording apparatus using the method.

<Prior Art> A liquid jet recording method in which a liquid or a solid recording medium (ink) that can be melted by heating is deposited on a recording medium by using thermal energy to form an image has a high resolution,
Excellent features such as high-speed printing, high recording quality, low noise, easy recording of color images, recording on plain paper, etc., and easy downsizing of the recording head and the entire device. have.

As a recording method for discharging a recording liquid using thermal energy, many methods and apparatuses using the method are already known.

Among them, for example, JP-A-54-161935, JP-A-61-185455, and JP-A-61-249768 disclose that a recording liquid is gasified by applying heat to the recording liquid (ink). A method is described in which recording is performed by causing bubbles to be generated in a recording liquid, and then ejecting the gas or the gas forming the bubbles together with the recording liquid.

That is, Japanese Patent Application Laid-Open No. 54-161935 discloses that ink in a liquid chamber is gasified by a heating element, and the gas is ejected from an ejection port together with ink droplets.

Japanese Patent Application Laid-Open No. 61-185455 discloses that a liquid ink filled in a minute gap between a plate-shaped member having a small opening and a heating element head is heated by the heating element head, and ink generated from the small opening by bubbles generated. It is shown that an image is formed on a recording paper by flying a target and also ejecting gas forming the bubble from the small opening.

Further, Japanese Patent Application Laid-Open No. 61-249768 discloses that a bubble is formed by applying thermal energy to a liquid ink, and ink droplets are formed and fly based on the expansion force of the bubble, and at the same time, the gas forming the bubble is removed. It also describes that an image is formed by jetting into the atmosphere from a large opening.

Further, according to the above publications, clogging of an orifice and an opening can be eliminated by ejecting a gas together with a recording liquid.

Japanese Patent Application Laid-Open No. 61-197246 discloses a recording apparatus using thermal energy, in which ink supplied to a plurality of holes provided in a recording medium is heated by a recording head having a heating element.
A recording apparatus for flying ink droplets onto a recording material is shown. However, in the recording apparatus, it is difficult to bring the heating element and the recording medium into close contact with each other, and the thermal efficiency may not be improved as expected. Therefore, there are cases where high-speed recording cannot be adequately performed. In addition, although it is described that the ink is caused to fly using the pressure of the generated air bubbles, since the specific principle and the like are not described, there is no guide to solve such a problem, and no description is given.

<Problems to be solved by the invention> However, Japanese Patent Application Laid-Open Nos. Sho 54-161935 and
185455 and JP-A-61-249768 disclose that gas forming ink is ejected into the atmosphere together with the flight of ink droplets as the ink droplets fly, so that the gasified ink is used as a spray or mist of the recording liquid. As a result, there have been cases in which problems such as causing soiling of the recording paper and causing stains in the apparatus have occurred.

Further, in the recording apparatus described in JP-A-61-197246, it is difficult to bring the heating element and the recording medium into close contact with each other, and the thermal efficiency may not be better than expected. Therefore, there are cases where high-speed recording cannot be adequately performed. In addition, although it is described that the ink is caused to fly using the pressure of the generated air bubbles, the specific principle and the like are not shown, so that it is not possible to obtain a specific policy for performing good ink ejection. I could not do it.

<Purpose> The present invention has been made in view of the above-described problems, and its purpose is to stabilize the volume and speed of a droplet to be ejected, further suppress the generation of splash or mist, Prevents background dirt on the image and dirt inside the device when it is made into a device, improves discharge efficiency, prevents clogging, etc., further improves the life of the recording head, and can print high-quality images It is to propose a liquid ejection method.

<Means for Solving the Problems> According to a liquid ejecting method of the present invention for achieving the above object, an ejection port for ejecting a liquid, and a liquid communicating with the ejection port to supply the liquid to the ejection port. A liquid path, and using a head having a heater provided in the liquid path, by driving the heater to generate bubbles in the liquid and discharge the liquid, wherein the internal pressure of the bubbles is The method is characterized in that the liquid is ejected by communicating the air bubbles with the outside air under a condition of an external pressure or less.

According to another aspect of the invention, there is provided a recording apparatus including: a discharge port configured to discharge a liquid; a liquid path communicating with the discharge port and supplying the liquid to the discharge port; A head having a heater provided, a driving signal supply means for driving the heater so that the bubble communicates with the outside air under conditions other than the outside air pressure, and a cover for receiving the discharged liquid. Means for conveying the recording medium.

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

1 (a) to 1 (e) are schematic cross-sectional views for explaining liquid ejection by the liquid ejection method of the present invention.

1 (a) to 1 (e), reference numeral 1 denotes a base,
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. In addition,
The liquid path is formed by the base 1, the top plate 4, and a wall (not shown).

FIG. 1A 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, the ink generates bubbles 6 on the heater 2 due to so-called film boiling. , Suddenly starts to expand (FIG. 1 (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. 1 (c)). At this time, the outside air is in equilibrium with the inside of the bubble 6 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 forms independent droplets on the recording medium 101 such as paper. It flies toward (Fig. 1 (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. 1 (e)). Return. 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 may be fixed, and the ejection port 5 may be moved (the moving 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.

In FIG. 1 (c), when the bubble 6 communicates with the outside air, there is no movement of gas between the outside air and the inside of the bubble, or the inside pressure of the bubble is equal to the outside pressure in order for the outside air to flow into the bubble. It is necessary to communicate the bubble with the outside air at lower or lower conditions.

Therefore, in order to satisfy the above condition, in FIG. 2 (a), 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. 2 (b). That is, in FIG. 2B, t = tb (t1 ≦ t
At the time of b), the bubble may be communicated with the outside air.

When droplets are ejected under these conditions, compared to the case where bubbles are communicated with outside air and droplets are ejected (gas is ejected into the atmosphere) when the bubble internal pressure is higher than the outside air pressure, the ink mist It is possible to prevent the recording paper and the inside of the apparatus from being stained by the ink or splash. Further, since the bubble communicates 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.

In other words, communicating the bubble with the outside air under the condition that the internal pressure of the bubble is lower than the outside air pressure may cause the unstable liquid near the discharge port to be scattered, which occurred when the inside pressure of the bubble was communicated under the condition that the inside pressure of the bubble was higher than the outside air pressure. In addition, since the force that draws the unstable liquid into the liquid path is smaller than that when the pressure is equal, the discharge of the liquid and the unnecessary scattering of the liquid are prevented. Can be.

The recording head used in the present 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 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 (The distance between the discharge port and the heater, the width and height of the discharge port and the liquid path) and the like can be selected as desired, so that the bubble can be communicated with the outside air in a desired state.

As described above, the conditions for achieving the present invention more effectively include the liquid channel shape. 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 using 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.

Also, it is not possible to make the bubble communicate with the outside air 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 when the bubble does not communicate with the outside air. It is preferred.

In addition to the conditions of the present invention, the condition that the bubble is communicated 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 condition of the discharge port side of the discharge energy generating means distance l _b and the l _a of the end portion opposite to the bubble discharge port from the end opposite to the discharge port of the distance l _a between the discharge energy generating means of the discharge port-side end of the bubble from the end / l _b ≧
It is preferable that the bubble and the outside air be communicated under the condition satisfying the condition 1 or both.

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

Since it is difficult to directly measure the pressure in the bubble, the magnitude relationship between the internal pressure and the external pressure of the bubble can be determined 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.

(Method of Determining from Bubble Volume) 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 d ² V / dt ² of V It is possible to know the magnitude relationship between the internal pressure and the external pressure of the bubble. That is, d ² V / dt ²
If> 0, the internal pressure of the bubble is higher than the external pressure, d ² V / dt ²
If ≦ 0, the internal pressure of the bubble is lower than the external pressure. When described in FIG. 2 (c), the internal pressure of the bubble from the bubbling start t = t ₀ to t = t ₁ is higher than the outside pressure d ² V / dt ^2> 0, and the
the internal pressure of the bubble until the time t = t _b of from t = t ₁ until the bubble is communicated with the outside air is other than outside air pressure, the ^{d 2 V / dt 2 ≦ 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 d ² V / dt ² of V.

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

When the top plate of the recording head is made of, for example, metal, opaque ceramic, or colored plastic, the constituent members may be replaced with transparent plastic (for example, transparent acrylic), glass, or the like. The places and the materials used for them are not limited to the places and materials described above. .

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

Further, 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 known by the following method. .

(Method for determining the volume of ink ejected) in the time until the ink droplets from the start of the foaming flies, the volume V _d of the ink from the discharge port jumped outward measures, second derivative of V _d By determining d ² V _d / dt ² ), the magnitude relationship between the internal pressure of the bubble and the external pressure can be known.
That is, if d ² V _d / dt ² > 0, the internal pressure of the bubble is higher than the external pressure, and if d ² V _d / dt ² ≦ 0, the internal pressure of the bubble is lower than the external pressure. FIG. 2 (d) shows the time change of the first derivative dV _d / dt of the volume V _d 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. there is, until the time t = t _a until bubbles from foaming start t = t ₀ is communicated with the outside air, the internal pressure of the valve is higher than the outside pressure, the ^{_{d 2 V d / dt 2>}} 0. On the other hand, FIG.
Shows the time change of the primary differential dV _d / dt of V _d when the internal pressure of the bubble is communicated with outside air communicating a bubble in the following conditions the outside air pressure. From the figure, but until t = t ₁ from the foaming start t = t ₀ is the internal pressure of the bubble is higher ^{_{d 2 V d / dt 2>}} 0 than outside pressure, than to t = t _b t = t ₁ is The internal pressure of the bubble is equal to or lower than the external pressure, and d ² V _d / dt ² ≦ 0.

By determining the second derivative d ² V _d / dt ² of V _d as described above, the magnitude relationship between the internal pressure of the bubble and the external pressure can be known.

A method of measuring the volume Vd of the ink existing outside the ejection port will be described. The shape of the droplet at each time after ejection can be measured by using a light source 31 such as a strobe, an LED, or a laser to observe the microscope 32 while illuminating the droplet ejecting 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. Although the droplet volume can be roughly estimated from this one-way measurement, it is desirable to measure it by the following method in order to obtain it more accurately.

As shown in FIG. 3, the droplet discharging method is x, and as described above, the projected shape of the droplets simultaneously discharged from two directions y and z orthogonal to the x axis and orthogonal to each other while being illuminated with the pulse light as described above. Is measured with a microscope. At this time, the measurement direction y or z in the microscope is desirably a direction parallel to the direction in which the discharge ports are arranged. With respect to the images measured in the two directions, the widths a (x) and b (x) of the droplet portion with respect to the x coordinate value are measured as shown in FIGS. 4 (a) and 4 (b). . By calculating from these values according to the following equation, the volume Vd of the droplet after a predetermined time can be obtained. It should be noted that this equation yz section is approximated by an ellipse, and can be obtained with sufficient accuracy for calculating the volume of a droplet or a bubble described below.

V _d = (π / 4) ∫a (x) · b (x) dx Further, by changing the lighting delay time of the pulse light in order from 0, a change in Vd after application of the driving pulse can be obtained. .

The measurement of the bubble volume in the liquid path can also be performed by applying the above method.

As described above, after the bubble in the liquid path is made observable, measurement is performed while illuminating the projected shape from two directions with pulsed light in the same manner as in the above-described droplet volume measurement method, and the above calculation formula is applied. Its volume can be determined.

Since the behavior of both droplets and bubbles requires a time resolution of about 0.1 μsec, an infrared LED is used as the pulse light source, a pulse width of 50 nsec is used, and an infrared camera is connected to a microscope to capture images. And from the image
(X) and b (x) may be obtained and measured by applying the above formula.

In addition to the above, the magnitude relationship between the internal pressure of the bubble and the external pressure can be known from the air flow.

(Method of Determining from Airflow (Motion of Gas)) A method of detecting an airflow (movement of gas) caused by a pressure difference between the inside and outside of the bubble at the moment of communication of the bubble will be described.

In order to know the magnitude relationship between the internal pressure of the bubble and the external pressure from the air flow, a fine tuft is provided near the discharge port, and a method of observing the movement of the tuft caused by a change in the air flow with a microscope or a discharge generated by the air flow. A method of detecting a change in the density of air near the outlet by an optical method such as a Schlieren method, a Mach-Zehnder interferometry, or a hologram method can be used.

By these methods, if an airflow from the liquid channel 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 communicated at a higher pressure than the outside air pressure, and the bubble flows into the liquid channel. Observation of a flowing air current indicates that the bubbles communicated in a state where the internal pressure of the bubbles was lower than the external pressure.

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

5 (a) and 5 (b) show a schematic assembly perspective view and a schematic top view of one suitable recording head. FIG. 5B shows a state in which the top plate shown in FIG. 5A is not provided.

The configuration of the recording head shown in FIGS. 5A and 5B will be briefly described.

The recording head shown in FIGS. 5 (a) and 5 (b) has a wall 8 provided on a base 1 and joined so that the top plate 4 covers the wall 8, and a common liquid chamber 10 and a common liquid chamber 10 are provided. A liquid path 12 is formed. The top plate 4 is provided with a supply port 11 for supplying ink, and has a configuration in which ink can be supplied into the liquid path 12 through a common liquid chamber 10 to which the liquid path 12 communicates.

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

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

6 (a) and 6 (b) 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.
While the ink shown in FIG. 5 is ejected from the ejection port straight or substantially straight along the liquid path, the ink shown in FIG. This is the point where the supplied ink is bent along the liquid path (in the figure, the discharge port is formed just above the heater).

6 (a) and 6 (b), the same reference numerals as those shown in FIGS. 5 (a) and 5 (b) indicate the same parts.

6 (a) and 6 (b), reference numeral 16 denotes an orifice plate in which the discharge ports 5 are formed. Here, a wall 9 provided between the discharge ports 5 is also integrally formed. I have.

 Hereinafter, the present invention will be described with reference to specific examples.

Example 1 In this example, the recording head shown in FIG. 5 was used. In this embodiment, the top plate 6 is made of glass. The dimensions of the liquid path 12 and the heater 2 of the used recording head are respectively such that the liquid path 12 has a height of 20 μm, a width of 58 μm, a heater size of 28 μm in width × 18 μm in length, and a heater is provided. The position was 20 μm in length from the end of the heater 2 closest to the discharge port to the discharge port. Forty-eight liquid paths 12 were arranged at a density of 360 lines per inch.

Into this recording head, each component composed of CI food black 2 3.0% by weight, diethylene glycol 15.0% by weight, N-methyl-2-pyrrolidone 5.0% by weight, and ion-exchanged water 77.0% by weight was stirred in a container and uniformly mixed and dissolved. Thereafter, an ink having a viscosity of 2.0 cps (20 ° C.) obtained by filtration through a Teflon filter having a pore diameter of 0.45 μm was supplied to the liquid chamber 10 from the ink supply port 11 to discharge the ink.

When driving the heater 2 of the recording head, a pulse-like electric signal was applied to the heater 2. The applied pulse wave had a voltage of 9.0 V and a pulse width of 5.0 μsec, and was applied to the heater 2 at a frequency of 2 kHz.

First, when a state in which ink was ejected from the continuous 16 of the ejection ports 5 was observed using a strobe microscope, it was found that bubbles generated by heating were communicated with the outside air about 2 μsec after the start of foaming. Was confirmed.

Moreover, the volume V _d of the ink discharged from the discharge port, first derivative dV _d / dt of the volume V _d of the ink is shows a time change as shown in FIG. 6, 0.5 .mu.sec after foaming started The second derivative d ² V _d / dt ² of the volume of the bubble until the bubble communicates with the outside air about 2 μsec after was negative, and it was confirmed that the bubble internal pressure was lower than the outside air pressure.

Separately, when looking at the magnitude relationship between the internal pressure of the bubble and the external pressure from the volume V of the bubble, the relationship of d ² V / dt ² ≦ 0 is satisfied in this case as well, and the internal pressure of the bubble may be lower than the external pressure. confirmed.

In addition, the volume of the flying droplet at this time was within the range of 14 ± 1 pl with the volume of the flying droplet discharged from each discharge port 5. Furthermore, the speed of the flying droplets was uniform at about 14 m / sec, which was sufficient for performing excellent recording with the flying speed.

Then, next, when an electric signal is applied to the 16 heaters 2 so as to form a checkered pattern for each pixel, ink is ejected and adhered to the recording paper, a desired checkered pattern having no printing unevenness on the recording paper is obtained. The pattern of the pattern was drawn. When this image was magnified and observed, it was a clear image without scattering of extra ink and background contamination.

Example 2 Next, an image was formed using the recording head shown in FIG. In this example, transparent glass was used as the orifice plate 14.

In this embodiment, the discharge port 5 is a circle having a diameter of 36 μm on the surface side of the orifice plate, the length from the heater surface to the discharge port is 20 μm, and the size of the heater is 24 μm.
48 discharge ports were arranged at a density of × 24 μm and 360 discharge ports per inch.

The same ink as in Example 1 was supplied to this recording head to attempt ejection.

The heating condition of the recording head heater 12 is 7.0 V, 4.5 μsec
This was driven at 2 KHz.

First, when observing the situation where ink was ejected from 16 consecutive ejection ports 5 out of the ejection ports 5 using a strobe microscope, a valve generated by heating about 2.1 μsec after the start of foaming communicated with the outside air. Was confirmed.

Further, the primary differential dV / dt of the volume V of the bubble and the volume V of the bubble V from the start of the foaming until the bubble communicates with the outside air shows a time change as shown in FIG. The second derivative d ² V / dt ² of the bubble volume until the bubble communicates with the outside air after about 2.1 μsec later was negative, and it was confirmed that the bubble internal pressure was lower than the outside air pressure.

Also, when the volume of the flying droplet at this time was measured,
Each nozzle was within the range of 18 ± 1pl. Further, the speed of the droplet was about 10 m / sec.

Therefore, similarly to the first embodiment, when an electric signal is applied to the 16 heaters 2 to form a checkerboard pattern for each pixel, ink is ejected and adhered to the recording paper. The desired checkerboard pattern without any was drawn. When this image was magnified and observed, it was a clear image without scattering of extra ink and background contamination.

Example 3 Using the recording head used in Example 1, CI Direct Black 154 3.5% by weight Glycerin 5.0% by weight Diethylene glycol 25.0% by weight Polyethylene glycol 28.0% by weight (average molecular weight 300) 38.5% by weight of ion-exchanged water The same procedure as in Example 1 was carried out except that the inks having a viscosity of 10.5 cps (20 ° C.) obtained by stirring each compounded component in a container, uniformly mixing and dissolving, and then filtering through a Teflon filter having a pore size of 0.45 μm were used. Then, the magnitude relationship between the internal pressure of the bubble and the external pressure was measured, and the ink was ejected. As a result, it was found that in the present embodiment as well, the bubble communicates with the outside air when the bubble internal pressure is lower than the outside pressure when the bubble communicates with the outside air. The ink ejection speed was lower than that in Example 1 and was 7 m / sec, but the ejection itself was extremely stable.

[Examples 4 to 12] Recording was performed by supplying the same ink as in Example 2 using a recording head whose liquid path was bent similarly to the recording head used in Example 2.

Table 1 shows the outline of each recording head and the ejection results. or,
FIGS. 8 to 16 show schematic views of each recording head.

As can be seen from Table 1, in each case, the volume of the liquid to be discharged and the discharge speed of the liquid droplet were extremely stable, and the recording was also extremely excellent.

[Examples 13 to 15] As in the case of the recording head used in Example 1, a recording head in which the liquid path was not bent was used, and recording was performed by supplying the same ink as in Example 1.

Table 2 shows the outline of each recording head and the ejection results. or,
FIGS. 17 to 19 show schematic views of each recording head.

As can be seen from Table 2, in each case, the volume of the liquid to be discharged and the discharging speed of the liquid droplet were extremely stable, and the recording was also extremely excellent.

[Comparative Example 1] The discharge port side end face of the heater 2 is arranged at a position of 3 µm from the discharge port 5 with respect to the recording head of Fig. 5, and the bubble communicates with the outside air when the bubble internal pressure is higher than the outside air pressure. The recording head was manufactured as described above, and the recording state was evaluated.

When the inks used in Examples 1 and 2 were separately supplied to the print head and a drive was performed so that a checkerboard pattern could be printed in the same manner as in Examples 1 and 2, the ejection itself could be performed. However, continuous stable ejection was not performed. Further, when the image recorded on the recording paper was observed, it was found that the image had many fine background stains. Therefore, this phenomenon was analyzed in further detail.

First, as in the first embodiment, a bubble was formed by heating the heater 2 and the process until the droplet was ejected from the ejection port 5 was observed using a strobe microscope. The droplet was discharged by the formed bubble. However, this droplet was not a droplet as in the first embodiment, but a collection of a large number of fine droplets 21 as shown in FIG.

After a few pulses, a sufficient amount of momentum is not provided near the ejection port 5 and the remaining ink blocks the ejection port 5. At this time, since the inside of the nozzle is
As shown in FIG. 20 (b), air 22 was bubbled into the nozzle and remained without disappearing. No droplet was discharged in this state.

Further, the volume V of the bubble from when the bubble is formed until it communicates with the outside air, and the first derivative dV of the bubble volume V
/ dt shows a time change as shown in FIG. 21, the second derivative d ² V / dt ² of the volume V until the opening of the bubble after about 2.1 μsec from the start of foaming becomes positive, and the internal pressure of the bubble becomes It was confirmed that it was higher than the atmospheric pressure.

[Comparative Example 2] Using the recording head (FIG. 5) and the ink used in Example 1 above, applying a pulse of 6.0 V, 500 μsec and driving at 20 Hz to attempt ejection, droplets were continuously formed. Was observed to be discharged.

However, when the image on the recording paper was observed, it was an image with much background contamination. This phenomenon was analyzed in more detail.

When a bubble was formed by the heating of the heater 2 as in Example 1, and the process until the droplet was ejected from the ejection port 5 was observed using a strobe microscope, a number of bubbles were generated in the liquid path 12. It was observed that fine droplets were ejected in the form of mist with the ejection of the main droplets.

In addition, when the drive frequency was increased to 1 kHz, the ejection stopped immediately.

<Effect of the Invention> As described above, according to the liquid ejection method of the present invention,
When the bubble is communicated with the outside air, the pressure inside the bubble is lower than the outside air pressure, preventing the gas in the bubble from escaping, thereby preventing the recording paper from becoming dirty due to mist or splash and the inside of the device. it can. In addition, a high-quality image can be obtained by constantly stabilizing the ejection volume of the droplet.

Furthermore, since the kinetic energy of the bubble can be sufficiently transmitted to the ink, the ejection efficiency increases,
Clogging can be eliminated. The ejection speed of the droplets is also improved, so that the ejection direction of the droplets is stabilized, and the distance between the recording head and the recording paper can be increased, so that the device design becomes easy.

In addition, since there is no bubble defoaming process, the heater destruction phenomenon due to the defoaming is eliminated, and the life of the recording head is improved.

Incidentally, the liquid injection method of the present invention is a so-called on-demand type,
Although it can be applied to any of the continuous type, in particular, in the case of the on-demand type, the electrothermal converter is arranged corresponding to the sheet or liquid path holding the liquid (ink), By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding nucleate boiling, heat energy is generated in the electrothermal transducer, and the film is heated on the heat-acting surface of the recording head. As a result, air bubbles in the liquid (ink) can be formed in one-to-one correspondence with the drive signal, which is effective.

As a recording head using the liquid ejection method of the present invention,
The present invention is not limited to those described in the above embodiments, and many forms and modifications of a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus can be considered. . 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 chip-type print head of the replacement itself, which can be electrically connected to the device main body or supplied with ink from the device main body by being attached to the device main body, or provided integrally with the print head itself The present invention is also effective when a cartridge type recording head is used.

Further, in addition to the above-described recovery means for the recording head, which is provided as a configuration of the recording apparatus of the present invention, it is preferable to add auxiliary auxiliary means and the like because the effects of the present invention can be further stabilized. Things. Specific examples thereof 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. It is also effective to perform a preparatory ejection mode in which ejection is performed separately from printing, in order to perform stable printing.

Further, as the recording mode of the recording apparatus, not only the mainstream color such as black, but also the recording mode, the recording head may be integrally formed or a combination of a plurality of recording heads. The present invention is extremely effective for an apparatus having at least one of the full colors.

[Brief description of the drawings]

1 (a) to 1 (e) are schematic cross-sectional views for explaining a discharge state of the present invention, and FIGS. 2 (a) to 2 (e) show the internal pressure and volume of a bubble. A diagram for explaining a time change,
FIG. 3 is a schematic diagram for explaining a method of measuring a droplet volume,
4 (a) to 4 (c) are schematic explanatory views of the liquid to be ejected viewed from above and from the side, respectively, and FIG. 5 illustrates a recording head used in an embodiment of the present invention. FIG. 6, FIG. 6 is a diagram for explaining a recording head used in another embodiment of the present invention, FIG. 7 is a diagram for explaining a temporal change in the volume of a bubble, FIG. 8 (a) and FIG. FIG. 8A is a schematic perspective view for explaining a recording head according to an embodiment of the present invention, and FIGS.
FIGS. 16 and 17 (b) to 19 are schematic views for explaining the recording head according to the embodiment of the present invention, and FIGS.
FIG. 21B is a schematic cross-sectional view for explaining a comparative example, and FIG.
The figure is a diagram for explaining the time change of the bubble volume in the comparative example. DESCRIPTION OF SYMBOLS 1 ... Board, 2 ... Heater 3 ... Ink, 4 ... Top plate 5 ... Discharge port, 7 ... Droplet 8 ... Wall, 10 ... Liquid chamber 11 ... Ink supply port, 12 ... Liquid path

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshihisa Takizawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masashi Miyagawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Nao Yaegashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Katsuhiro Shirota 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. ( 72) Inventor Norio Okuma 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Akira Akira 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo Canon Inc. (56) References JP-A-62-33648 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/05

Claims (16)

(57) [Claims] A head having a discharge port for discharging a liquid, a liquid path communicating with the discharge port and supplying the liquid to the discharge port, and a heater provided in the liquid path. A method for ejecting a liquid by generating bubbles in the liquid by driving the heater using the heater, wherein the liquid is ejected by communicating the bubbles with the outside air under the condition that the internal pressure of the bubbles is equal to or less than the external pressure. A liquid discharging method. 2. A head having a discharge port for discharging a liquid, a liquid path communicating with the discharge port and supplying liquid to the discharge port, and a heater provided in the liquid path. A driving signal supply unit for driving the heater so that the bubble communicates with the outside air under the condition that the internal pressure of the bubble is equal to or less than the outside air pressure, and a unit that conveys a recording medium that receives the discharged liquid. A liquid discharge device characterized by the above-mentioned. 3. The liquid discharge method according to claim 1, wherein the discharge port and the heater are arranged at positions facing each other. 4. The liquid discharge apparatus according to claim 2, wherein the discharge port and the heater are arranged at positions facing each other. 5. The method according to claim 1, wherein the liquid is ink. 6. The liquid discharging apparatus according to claim 2, wherein said liquid is ink. 7. The liquid discharging method according to claim 1, wherein the height of the liquid path is smaller than the width of the liquid path. 8. The liquid discharging apparatus according to claim 2, wherein a height of the liquid path is smaller than a width of the liquid path. 9. The liquid discharging method according to claim 1, wherein the bubbles are communicated with the outside air under the condition that the internal pressure of the bubbles is lower than the outside pressure. 10. The liquid ejecting apparatus according to claim 2, wherein the bubble communicates with the outside air under a condition that the inside pressure of the bubble is lower than the outside pressure. 11. The liquid discharging method according to claim 1, wherein the communication of the bubble with the outside air is performed under a condition that a first derivative of a moving speed of the bubble in the direction of the discharge port becomes negative. 12. The liquid discharging apparatus according to claim 2, wherein the communication of the bubble with the outside air is performed under a condition that a first-order differential value of a moving speed of the bubble in the direction of the discharge port becomes negative. 13. The communication of the bubble with the outside air is performed under the condition that the second derivative (d ² V / dt ² ) of the volume (V) of the bubble is d ² V / dt ² ≦ 0. 2. The liquid discharging method according to 1. 14. The communication of the bubble with the outside air is performed under the condition that the second derivative (d ² V / dt ² ) of the volume (V) of the bubble is d ² V / dt ² ≦ 0. 3. The liquid ejection device according to 2. 15. A liquid discharging method according to claim 1, wherein said bubbles are bubbles generated by film boiling. 16. The liquid discharging apparatus according to claim 2, wherein said bubbles are bubbles generated by film boiling.