JPH0410941A - Droplet jet method and recorder equipped with same method - Google Patents

Abstract

PURPOSE:To prevent scumming on an image and stain in a device and also to prevent clogging by making a bubble, which is generated by discharge energy generating means under a condition that a first order differential value of the travel speed at an end in the direction of a discharge opening is minus, communicate with the outside air through the discharge opening. CONSTITUTION:When an ink 3 close to a heater 2 is rapidly heated in a manner of pulsation by charging the heater 2 (an electrothermal conversion body, for example) with a current instantaneously at a state that a flow passage is filled with the ink 3, a bubble 6 due to film boiling is generated on the heater 2. The bubble 6 further swells growing toward a discharge opening 5 and goes over the discharge opening 5 finally so as to communicate with the outside air. In this case, the bubble communicates with the outside air under a condition that a first differential value of the travel speed at an end in the direction of the discharge opening of the bubble is minus. Accordingly, since the ink close to the communicating section is not accelerated excessively, it coalesces with a main ink drop to be discharged without becoming splash and mist, so that scumming and stain in a device can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention is a liquid jet method that can be suitably used for droplet jet recording in which recording is performed by making the ejected liquid adhere to a recording medium using thermal energy. The present invention relates to a method and a recording device using the method.

<Prior art> The liquid jet recording method, in which an image is formed by depositing a liquid or a solid recording medium (ink) that can be melted by heat onto a recording medium using thermal energy, is capable of high-resolution, high-speed printing. It has excellent features such as high recording quality, low noise, easy color image recording, ability to record on plain paper, etc., and easy miniaturization of the recording head and the entire device. It has special features.

As a recording method using a liquid ejection method in which recording liquid is ejected using thermal energy, many methods and devices using the same are already known.

Among them, for example, JP-A No. 54-161935, JP-A No. 61-185455, JP-A No. 61-24
Publication No. 9768 discloses that by applying heat to the recording liquid (ink), the recording liquid is gasified or a bubble is generated in the recording liquid, and the gas or the gas forming the bubble is ejected together with the recording liquid. It describes how to make a deposit.

That is, Japanese Patent 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 ink ejection port along with ink droplets.

Furthermore, in JP-A No. 61-185455, liquid ink filled in a minute M gap between a plate-like member having a small opening and a heating element head is heated by the heating element head, and the generated bubbles cause the liquid ink to flow from the small opening. Along with making ink droplets fly,
It is shown that the gas forming the bubble is also ejected from the small opening to form an image on the recording paper.

Furthermore, Japanese Patent Application Laid-Open No. 61-249768 discloses a method in which bubbles are formed by applying thermal energy to liquid ink, and ink droplets are formed and flown based on the expansion force of the bubbles, and at the same time, the gas forming the bubbles is released. It is also described that an image is formed by ejecting it into the atmosphere from a large opening.

Further, according to the above-mentioned publications, clogging of orifices and openings can be eliminated by ejecting gas together with the recording liquid.

Furthermore, Japanese Patent Application Laid-Open No. 197246/1983 describes a recording device that uses thermal energy, in which ink supplied to a plurality of holes provided in a recording medium is heated by a recording head having a heat generating element to cover ink droplets. A recording device for causing recording material to fly is shown. However, in the recording apparatus, it is difficult to bring the heating element and the recording medium into complete contact with each other, and the thermal efficiency may not be as good as expected. Therefore, there were cases where it was not possible to adequately support high-speed recording. Furthermore, although it is described that the pressure of the generated air bubbles is used to make ink fly, the specific principles are not shown, so there is no guideline for solving such problems. Problems to be Solved by the Invention> However, in the above-mentioned JP-A-54-161935, JP-A-61-185455, and JP-A-61-249768, gas forming bubbles is removed from ink droplets. Because the ink is ejected into the atmosphere as it flies, the gasified ink causes splashes and mist of the recording liquid, which can cause background stains on the recording paper and dirt inside the device. There were cases where problems occurred.

Furthermore, in the recording apparatus described in JP-A-61-197246, it is difficult to bring the heating element and the recording medium into complete contact with each other, and the thermal efficiency may not be as good as expected. Therefore, there were cases where it was not possible to adequately support high-speed recording. In addition, although it is described that the pressure of the generated bubbles is used to eject ink, the specific principle is not disclosed, so it is difficult to obtain a concrete policy for ejecting ink well. I could not do it.

Purpose of the present invention The present invention has been made in view of the above-mentioned problems, and its purpose is to stabilize the volume and speed of ejected droplets, suppress the generation of splash and mist, etc. It prevents background smudges on images and dirt inside the device when used as a device, improves ejection efficiency, prevents clogging, and extends the life of the recording head, making it possible to print high-quality images. An object of the present invention is to provide a droplet jetting method and a recording device using the method.

<Summary of the Invention> A droplet ejection method of the present invention that achieves the above object includes an ejection port for ejecting ink, a liquid path communicating with the ejection port, and a method for forming air bubbles in the liquid path. Using a recording head equipped with an ejection energy generating means that generates thermal energy used for ejecting ink supplied by The bubble generated by the discharge energy generating means is made to communicate with the outside air through the discharge port under negative conditions.

Further, the recording apparatus of the present invention that achieves the above object includes an ejection port for ejecting ink, a liquid path communicating with the ejection port, and a bubble formed in the liquid path to eject the supplied ink. A recording head is provided with an ejection energy generating means for generating thermal energy used to generate thermal energy, and the first differential value of the moving speed of the tip of the bubble in the ejection port direction, which is generated by the ejection energy generating means, is negative. a drive circuit for supplying a signal to the ejection energy generating means in order to communicate the bubbles generated by the ejection energy generating means with the outside air through the ejection port; It is characterized by having a platen on which a recording medium can be placed.

The inventor of the present invention discovered through numerous experiments that the above-mentioned problem is deeply related to the communication between the bubble and the outside air.

In other words, dirt on the recording paper or dirt inside the device due to ink splash or mist may cause the ink near the communication part to be excessively accelerated due to the ejection of ink when the bubble communicates with the outside air. Separation was recognized as a major technical issue. Due to this separation, it becomes noticeable that the ink in the vicinity scatters like a splash or becomes a mist, and if the ejection port is arranged in a high density, it may result in ejection failure due to ink adhering to the ejection port surface. However, the origin of the present invention lies in the clarification that this cause is due to acceleration.

Further, when we analyzed this point, we found that when the first differential value of the moving speed of the tip of the bubble in the direction of the discharge port is constant, the above-mentioned problem occurs when the bubble communicates with the outside air.

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

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

In FIG. 1(a) to FIG. 1(e), 1 is a base, 2
is a heater, 3 is ink, 4 is a top plate, 5 is an ejection port, 6 is a bubble, and 7 is a droplet. Note that the liquid path is formed by the base 1, the top plate 4, and a wall (not shown).

FIG. 1(a) shows the initial state, in which the inside of the liquid path is filled with ink 3. Ink 3 First, when a current is instantaneously applied to the heater (for example, an electrothermal converter) 2 and the ink 3 near the heater is rapidly heated in a pulsed manner, bubbles 6 are generated on the heater 2 due to so-called film boiling of the ink. , it begins to expand rapidly (Fig. 1(b)). Further, the bubble 6 continues to expand, mainly growing toward the side of the outlet 5 where the inertial resistance is smaller, and finally exceeds the outlet 5 and communicates with the outside air (Fig. 1 (C)). At this time, in the present invention, -
The first differential value of the moving speed of the tip of the bubble in the direction of the discharge port is negative so that the bubble communicates with the outside air. Note that the tip of the bubble in the direction of the ejection port here refers to the gas-liquid interface between the bubble and the ink 3 that is closest to the ejection port 5 (see Fig. 1(b)
). Until this moment, the ink 3 pushed out from the ejection port 5 continues to fly forward due to the momentum given by the expansion of the bubble 6, and finally becomes an independent droplet and heads toward a recording medium such as paper. (Fig. 1(d)). Furthermore, the gap created at the tip of the ejection port 5 side is supplied with ink 3 toward the right in the drawing due to the surface tension of the ink 3 at the rear and the wetting of the member forming the liquid path (Fig. 1(e)), and the initial state is reached. return.

As described above, when the first derivative of the moving speed of the tip of the bubble in the direction of the ejection port is negative, the ink near the communication portion does not receive excessive acceleration, so the ink near the communication portion The ink droplets do not form smudges or mist, but are ejected as part of the main ink droplets, combining with the main ink droplets, thereby preventing background smudges and stains within the apparatus.

In addition, if the moving speed of the tip of the bubble in the direction of the ejection port is negative and communicates with the outside air, sufficient kinetic energy can be transmitted to the ink, improving ejection efficiency and further increasing the bubble volume. Then, since the bubble communicates with the outside air, almost all of the ink near the ejection port can be ejected, and the ejection volume is stabilized. In addition, there is no ink remaining near the ejection ports, and there is no problem such as air being taken in by the ink in the liquid path, resulting in non-ejection.

Next, a method for determining the moving speed of the tip of the bubble in the discharge port direction and the first derivative value of the moving speed will be described below when carrying out the present invention.

The position of the tip of the bubble in the direction of the ejection port at each time after the start of bubbling is determined by illuminating the bubble generated inside the nozzle from the top plate surface or side of the recording head with pulsed light from a strobe, LED, laser, etc., and using a microscope. can be observed. Specifically, as shown in chronological order as schematic cross-sectional views in FIGS. 2(a) and 2(b), the direction of the bubble outlet from the start of foaming until the bubble communicates with the outside air is Amount of displacement of the tip heater section from the discharge port end Xb-
It is possible to measure changes in h over time. Based on the measurement results, the moving speed vx of the tip of the bubble in the discharge port direction is determined by determining the first derivative dxb-h/dt of the displacement amount. Next, the first derivative dv, /dt(
The second derivative d2Xb-h/d"t) of the amount of displacement can be obtained.

Note that in this case, it is necessary that the bubble be visible from the outside of the recording head. In order to observe bubbles from the outside of the print head, it is desirable that a portion of the print head be formed of a transparent member so that bubble formation, growth, etc. can be observed from the outside of the print head. If the constituent members of the recording head are non-transparent, for example, the top plate of the recording head or the like may be replaced with a transparent member. At this time,
It is desirable to select the same hardness, elasticity, etc. of the replaced member and the replaced member as much as possible.

As for replacing components, if the top plate of the recording head is made of metal, opaque ceramic, or colored plastic, for example, it may be replaced with transparent plastic (for example, transparent acrylic), glass, etc. The replacement location and the materials used therein are not limited to the locations and materials described above. .

However, in order to avoid differences in foaming properties due to differences in the physical properties of the members, it is desirable to select a material whose physical properties, such as wettability to ink, are as close to those of the original member as possible. Whether or not the foamed state is equivalent to that of the original member can be confirmed by discharging it and checking whether the discharge speed and discharge volume are the same as the original state.

If it is made of a transparent member in advance, the above operation is not necessary.

In the recording head used in the present invention, the heater 2 is located at the ejection port 5.
It is located close to the direction of. This is the simplest method for communicating the bubble with the outside air. However, simply moving the heater closer to the discharge port does not satisfy the above 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,
Driving conditions, area, heat capacity of the substrate on which the heater is installed, etc.), ink physical properties, size of each part of the recording head (distance between the ejection port and heater, width and height of the ejection port and liquid path), etc. can be adjusted as desired. By selecting the desired conditions, the bubble can be communicated with the outside air in a desired state.

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

FIGS. 3(a) and 3(b) show a schematic assembled perspective view and a schematic top view of one suitable recording head. In addition,
FIG. 3(b) shows a state in which the top plate shown in FIG. 3(a) is not provided.

The structure of the recording head shown in FIGS. 3(a) and 3(b) will be briefly described.

In the recording head shown in FIGS. 3(a) and 3(b), a wall 8 is provided on a base 1, a top plate 4 is joined to cover the wall 8, and a common liquid chamber 10 and A liquid path 12 is formed. The top plate 4 has a supply port 1 for supplying ink.
1 is provided, and ink can be supplied into the liquid path 12 through a common liquid chamber 10 with which the liquid path 12 communicates.

Further, the base body 1 is provided with heaters 2, and each liquid path is provided corresponding to each of these heaters 2. Heater 2
has a heating resistor layer and an electrode (both not shown) electrically connected to the heating resistor layer, and is energized by this electrode in accordance with a recording signal. This energization causes the heater 2 to generate thermal energy, which can be applied to the ink supplied into the liquid path. This thermal energy can generate bubbles in the ink according to the recording signal.

Further, another configuration of the recording head suitable for use in the present invention will be explained.

FIGS. 4(a) and 4(b) show a schematic cross-sectional view and a schematic plan view of the recording head, respectively. The difference between this print head and the print head shown in FIG. 3 is that in the print head shown in FIG. In contrast, what is shown in Fig. 4 is that the supplied ink is bent along the liquid path (in the figure, the ejection port is formed directly above the heater, and 1. .)
.

In addition, in FIG. 4(a) and FIG. 4(b), the third
The same numbers as those shown in FIG. 3(a) and FIG. 3(b) refer to the same components.

In FIG. 4(a) and FIG. 4(b), 16 is an orifice plate in which discharge ports 5 are formed, and here, walls 9 provided between each discharge port 5 are also integrally formed. There is.

The present invention will be explained below using specific examples.

<Example 1> In this embodiment, the recording end shown in FIG. 3 was used.

In this example, the top plate was made of glass. In addition, the dimensions and positional relationship of the liquid path 12, heater 2, ejection port 5, etc. of the recording head used are as follows: The height of the liquid path is 25 μm, the width is 35 μm, and the size of the heater is 30 μm wide x 25 μm long.
The length of the first heater position from the end closest to the ejection port to the ejection port was 25 μm. 48 liquid channels and discharge ports were arranged at a density of 360 lines per inch.

To this recording head, C.1. Food black 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 of each component was stirred in a container, mixed and dissolved uniformly, and then filtered through a Teflon filter with a pore size of 0.45 μm.The resulting ink had a viscosity of 2.0 cps (at 20°C). An attempt was made to supply the liquid to the liquid chamber IO from the port 11 and discharge it.

The heating conditions for the heater 2 of the recording head are 9. OV, 5jL
sec, and was driven at a frequency of 2 kHz.

First, when ink was ejected from 16 consecutive nozzles and observed using a pulsed light source and a microscope, it was confirmed that the bubbles were communicating with the outside air about 2 μsee after the start of bubbling. In addition, the amount of displacement of a portion of the heater at the tip of the bubble in the direction of the discharge port from the end of the bubble in the direction of the discharge port from the start of bubbling until the bubble communicates with the outside air is measured, and the first and second derivatives ( The results of determining the first-order differential value of the moving speed are shown in FIG. From the figure, it was confirmed that the first differential value of the moving speed of the tip of the bubble in the direction of the discharge port was negative.

The volume of ejected flying droplets is 18±lpl for each nozzle.
fell within the range. Also? &A discharge speed is approximately 9 m/
It was see.

Next, an electrical signal was applied to the 16 heaters 2 to form a checkered pattern for each pixel, and the ink was ejected and adhered to the recording paper, resulting in the desired checkered pattern with no uneven printing on the recording paper. A pattern was drawn. When this image was enlarged and observed, it was clear that there was no excess ink scattering or background smearing.

<Example 2> In this example, a recording head shown in FIG. 4 was used.

The ejection port C±diameter of the recording head used in this example is 3
The size of the heater is 22 μm x 22 μm.
m, and the length from the heater surface to the discharge port surface was 25 μm. Further, 48 liquid channels and discharge ports were arranged at a density of 360 lines per inch.

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

Heating condition C of heater 2 of the recording head: 9.0■, 5μ
sec, and was driven at a frequency of 2 kHz.

First, when we observed the situation in which ink was ejected from 16 consecutive nozzles using a pulsed light source and a microscope, it was confirmed that nokuburka≦communicated with the outside air about 3 μsec after the start of bubbling. In addition, from the start of foaming until the bubble communicates with the outside air, the amount of displacement of the part of the heater at the tip of the bubble in the direction of the discharge port (force at the end in the direction of the discharge port) is measured, and the first derivative value and the second derivative of the displacement amount are measured. The results of determining the differential value (first-order differential value of the moving speed) are shown in FIG. From the figure, it was confirmed that the first differential value of the moving speed of the tip of the bubble in the direction of the discharge port was negative. Furthermore, the volume of independent flying droplets is 1 for each nozzle.
The droplet ejection speed was within the range of 7±lpl, and the droplet ejection speed was about 7 m/see.

Then, when an electric signal was applied to the 16 heaters 2 to eject ink and adhere to the recording paper so that a checkered pattern was formed for each pixel, similar to Example 1, uneven printing was observed on the recording paper. The desired checkerboard pattern was drawn without any blemishes. When this image was enlarged and observed, it was clear that there was no excess ink scattering or background smearing.

<Example 3> Using the recording head used in Example 1 (Fig. 3), C, 1, Direct Black 1543.5% by weight glycerin 5.0% by weight diethylene glycol 25.0% by weight polyethylene glycol
28.0% by weight (average molecular weight 300) Ion-exchanged water 38.5% by weight of each component was stirred in a container to uniformly mix and dissolve.
Ejection was attempted by supplying ink with a viscosity of 10.5 cps (20° C.) obtained by filtering through a Teflon filter with a pore size of 0.45 μm. As a result, although the discharge speed was 61111/sec, which was lower than in Example 1, it was confirmed that stable discharge was performed.

<Comparative Example 1> A recording head was manufactured with the configuration of the recording head shown in FIG. 3, and the heater 2 was arranged at a position of 4 μm from the ejection port 5.
When an ejection test was performed using the ink used in Example 1.2, the ejection itself could be performed, but continuous and stable ejection was not performed. Furthermore, when the image recorded on the recording paper was observed, it was observed that the image had many fine background stains, so this phenomenon was observed in more detail.

In order to analyze this phenomenon in detail, as in Example 1, bubbles are formed by the heating of the heater 2, and droplets are emitted from the ejection port 5.
The process up to discharge was observed using a pulsed light source and a microscope. Droplets were ejected by the bubbles formed until the first few pulses after the start of heating, but these droplets were not droplets like in Example 1, but a large number of microscopic liquids as shown in FIG. 7(a). It was a collection of 21 drops. After the few pulses, the air 22 became bubbles and was taken into the nozzle and remained as shown in FIG. 7(b). No droplets were ejected in this state.

Furthermore, it was confirmed that the bubbles communicated with the outside air about 0.4 μsec after the start of foaming. Therefore, we measured the amount of displacement of part of the heater at the tip of the bubble in the direction of the discharge port from the end of the bubble in the direction of the discharge port from the start of foaming until the bubble communicated with the outside air.
The results of determining the first-order differential value and second-order differential value (first-order differential value of the moving speed) of the amount of displacement are shown in FIG. From the figure, it was confirmed that the first differential value of the moving speed of the tip of the bubble in the direction of the discharge port was positive.

<Effects of the Invention> As explained above, according to the droplet jetting method of the present invention, the generated bubbles are communicated with the outside air and the droplets are ejected, so the volume of the droplets is always stabilized and high quality can be achieved. A recorded image can be obtained.

In addition, by communicating the bubble with the outside air from the ejection port under the condition that the moving speed of the tip of the bubble in the ejection port direction is negative, it is possible to prevent background stains on the recording paper due to ink mist and splash, and to prevent dirt inside the device. Can prevent dirt.

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

Furthermore, since there is no defoaming process for generated bubbles, the phenomenon of heater destruction due to defoaming is eliminated, and the life of the recording head is extended. However, in the case of an on-demand type, in particular, it is possible to apply an electrothermal transducer that corresponds to the recorded information to the sheet that holds the liquid (ink) or the electrothermal transducer that is placed corresponding to the liquid path. By applying a single drive signal that causes a rapid temperature rise exceeding nucleate boiling, the electrothermal transducer generates thermal energy, causing film boiling on the thermally active surface of the recording head, resulting in This is effective because bubbles in the liquid (ink) can be formed in one-to-one correspondence with this drive signal.

The recording head using the liquid ejection method of the present invention is not limited to those described in the above embodiments,
Many forms and modifications are conceivable, such as 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. Further, as a full-line type recording head, it may be configured to satisfy the length by combining multiple recording heads, or it may be configured as a single recording head formed integrally. The invention can more effectively exhibit the effects described above.

In addition, a replaceable chip-type recording head that is attached to the device body enables electrical connection to the device body and ink supply from the device body, or a chip-type recording head that is installed integrally with the recording head itself. The present invention is also effective when using a cartridge type recording head.

Further, in addition to the recovery means for the recording head as described above, which is provided as a component of the recording apparatus of the present invention, it is preferable to add a preliminary auxiliary means etc., since this further stabilizes the effects of the present invention. It is something. Specifically, these include a cleaning means for the recording head, a preheating means using an electrothermal converter, a separate heating element, or a combination thereof. Furthermore, it is also effective to perform a preliminary ejection mode in which ejection is performed separately from printing in order to perform stable printing.

Furthermore, the recording mode of the recording apparatus is not limited to only a mainstream color such as black (although it is also possible to configure the recording head integrally or by combining a plurality of them, it can also be used for multiple colors of different colors or The present invention is also extremely effective for devices equipped with at least one full color by color mixture.

[Brief explanation of the drawing]

1(a) to 1(e) are schematic sectional views for explaining the discharge state of the present invention, and FIG. 2(a) and 2(b) are respectively schematic sectional views of the bubble of the present invention. FIGS. 3(a) and 3(b) are schematic cross-sectional views for explaining the amount of displacement of the heater portion at the tip in the direction of the discharge port from the end of the discharge port, which is an embodiment of the present invention. A schematic perspective view and a schematic top view for explaining the recording head used, FIG.
) and FIG. 4(b) are a schematic cross-sectional view and a schematic plan view for explaining a recording head used in another embodiment of the present invention, and FIG. A diagram illustrating the moving speed of the tip and the time change of the first derivative of the moving speed. FIG. Diagrams explaining changes, Figures 7(a) and 7(b)
) is a schematic cross-sectional view for explaining the discharge state of a comparative example,
FIG. 8 is a diagram illustrating the moving speed of the tip of the bubble in the discharge port direction and the time change of one differential of the moving speed in a comparative example. l...Substrate 2...Heater 3...Ink 4...Top plate 5...Discharge port 6...Bubble 7...Droplet
8...Wall x Leh Me b-h b-h b-h (α) (b) (b> U (m/5ec) '?I (7n/Sec) τ '7J (Moe/sec)

Claims (2)

[Claims] (1) An ejection port for ejecting ink, a liquid path communicating with the ejection port, and generating thermal energy that is used to form air bubbles in the liquid path and eject the supplied ink. Using a recording head equipped with an ejection energy generating means, the bubble generated by the ejection energy generating means is ejected under the condition that the first differential value of the moving speed of the tip of the generated bubble in the ejection port direction is negative. A droplet jetting method characterized by communicating with outside air through a discharge port. (2) An ejection port for ejecting ink, a liquid path communicating with the ejection port, and generating thermal energy that is used to form air bubbles in the liquid path and eject the supplied ink. a recording head equipped with an ejection energy generating means, and a condition in which the first differential value of the moving speed of the tip of the bubble generated by the ejection energy generating means in the ejection port direction is negative;
a drive circuit for providing a signal to the ejection energy generating means in order to communicate the bubbles generated by the ejection energy generating means with the outside air through the ejection port; and a recording medium for attaching the ejected liquid to the ejection energy generating means. 1. A recording device comprising: a platen on which a platen can be aligned;