JPH07195697A - Ink jet recording head, method and apparatus for ink jet recording - Google Patents

Abstract

PURPOSE:To communicate air bubbles formed in an ink to the outside air by properly setting a ratio of a product of a height of a path of an ink jet recording head and a distance from a center of a thermal energy feed means to a final end of the path with a square of a distance from the thermal energy feed means to a confronting discharge port. CONSTITUTION:In order to communicate air bubbles in an ink which are generated by a heater 2 to the outside air through a discharge port 5 thereby to discharge the ink, a size of the heater 2, a distance between the discharge port 5 and heater 2, a width, a length and a height of a liquid path 12, dimensions of the discharge port 5, etc., should be suitably set. Particularly, a relationship of a distance H between the discharge port 5 and a center of the heater 2, a height (h) of the liquid path 12 and a length L of the liquid path 12 is important, and a discharging direction of the ink, the growth of air bubbles 6 and the continuous discharge of the ink are required to be stabilized. In other words, when the values H, (h) and L are set to satisfy an expression 0.1<Lh/H<2=10, the air bubbles 6 are efficiently communicated to the outside air through the discharge port 5 thereby to discharge liquid drops.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording head and an ink jet recording method for recording an ink droplet by flying it onto a recording material such as paper, resin sheet, cloth or the like by utilizing thermal energy. , And an inkjet recording device.

[0002]

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

A recording apparatus used for such an ink jet recording method is generally provided with an ejection port for ejecting ink as a flying ink droplet, an ink path communicating with this ejection port, and a part of this ink path. A recording head having an energy generating unit that gives ejection energy for ejecting ink in the ink path is provided. For example,
Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 61-59912
No. 61-59913, 61-59991
Each of the gazettes of No. 4 discloses a method in which an electrothermal converter is used as the energy generating means, and the thermal energy generated by the electric pulse is applied to the ink to eject the ink.

That is, in the recording method disclosed in each of the above publications, the ink subjected to the action of thermal energy causes a state change accompanied by a sharp increase in volume, and bubbles in the film boiling region based on this state change. Mainly due to growth and contraction,
Ink is ejected from an ejection port at the tip of an inkjet recording head, and the ejected ink droplets adhere to a recording medium to form an image. According to this recording method, since the ejection openings in the recording head can be arranged at high density, it is possible to record an image of high resolution and high quality at high speed, and a recording apparatus using this recording method. Can be used as an information output means in a copying machine, a printer, a facsimile, or the like.

On the other hand, as an ink jet recording method which uses thermal energy but whose realization conditions are unknown, there is a method described in JP-A-54-161935.
In the recording method disclosed in this publication, the ink in the liquid chamber is gasified (probably due to nucleate boiling) by the cylindrical heating element, and this gas is ejected from the ink ejection port together with the ink droplet. According to this recording method, the gas is ejected in the form of microdroplets, resulting in poor image quality. Further, due to the ejection of this gas, the gasified ink may cause a splash or a mist, which may result in background stains on the recording paper or stains in the recording apparatus.

Further, for example, Japanese Patent Laid-Open No. 61-197246.
The publication describes a thermal transfer recording apparatus using a method obtained by modifying a conventional inkjet recording method using thermal energy. This device discharges ink only once and, in addition, it is difficult to completely bring the recording medium and the heating element into close contact with each other. Therefore, thermal efficiency is higher than that of an inkjet recording method using a recording head having a conventional discharge port. However, there is a problem in that it is not suitable for high speed recording.

[0007]

BACKGROUND OF THE INVENTION In order to solve the problems of the ink jet recording method as described above, the present applicant makes air bubbles generated by film boiling generated by heating ink for ejection communicate with the outside air near the ejection port. Of an inkjet recording method (hereinafter, this method is also referred to as a continuous discharge method) in which discharge is performed by using the following method (Japanese Patent Application Nos. 2-112832, 2-112833, 2-112834,
Japanese Patent Application No. 2-114472 and Japanese Patent Application No. 3-169962
issue).

According to the continuous discharge method, the gas forming the bubbles is not ejected together with the ejected ink droplets, so that the generation of splash or mist is reduced, and the ground on the recording medium is reduced. It is possible to prevent dirt and dirt inside the device.

Further, as a basic operation of the above-described continuous discharge method, there is a principle that all the ink on the discharge port side of the portion where bubbles are generated is discharged as ink droplets. Therefore, the amount of ejected ink can be determined by the structure of the recording head, such as the distance from the ejection port to the bubble generating portion. As a result, according to the above-described continuous discharge method, it is possible to perform stable ink discharge with a stable discharge amount without being significantly affected by changes in ink temperature and the like.

[0010]

However, if it is premised that the heat generating portion as the heat energy generating means and the discharge port are opposed to each other, the bubbles formed in the ink may be efficiently exposed to the outside air depending on the structure of the recording head. In some cases, the ejection characteristics were changed without communication.

An object of the present invention is to provide an ink jet which can further stabilize the formation of ink droplets and achieve higher quality image formation in a recording system in which air bubbles formed in ink are communicated with the outside air to eject ink. An object is to provide a recording head, an inkjet recording method, and an inkjet recording device.

[0012]

The ink jet recording head of the present invention applies heat energy to a liquid passage communicating with the ink supply source for receiving the ink supply from the ink supply source and the ink in the liquid passage. The bubble is provided with thermal energy supply means for generating a bubble by a temperature rise that rapidly exceeds nucleate boiling, and an ejection port provided opposite to the thermal energy supply means for ejecting the ink. In an inkjet recording head that discharges ink by communicating with outside air at the discharge port, the distance between the thermal energy supply unit and the discharge port is H, the height of the liquid path is h, and the thermal energy supply unit When the distance between the center and the end of the liquid path is L, 0.1 ≦ Lh / H
It is characterized by satisfying ² ≦ 10.

According to the ink jet recording method of the present invention, a liquid channel communicating with the ink source for receiving the ink from the ink source and a thermal energy is applied to the ink in the liquid channel to rapidly generate nucleate boiling. The thermal energy supply means for generating bubbles due to the temperature rise exceeding the temperature, and the ejection port provided opposite to the thermal energy supply means for ejecting the ink, and the thermal energy supply means and the ejection port. Is H, the height of the liquid passage is h, and the distance between the center of the thermal energy supply means and the end portion of the liquid passage is L, 0.1 ≦ Lh / H using an inkjet recording head that satisfies ² ≦ 10, to produce a bubble by rapidly than the temperature rise nucleate boiling to the ink by applying thermal energy to the ink by the heat energy supply means, the bubble Characterized in that in conjunction with communicating the gas-ejecting at least a part of the ink of the discharge opening neighborhood.

As conditions for further stabilizing the state in which the bubbles communicate with the outside air, firstly, the liquid passage is not blocked by the bubbles during the communication, and secondly, the communication is performed. When the internal pressure of the bubbles is equal to or lower than the external pressure, the bubbles are communicated with the outside air. Thirdly, during the communication, the acceleration of the moving speed of the tip portion of the bubbles in the discharge direction is not positive. At least one of communicating air bubbles with the outside air can be mentioned.

The ink jet recording apparatus of the present invention comprises the above ink jet recording head, means for relatively moving the ink jet recording head and the recording medium, and means for driving the thermal energy supply means. It is characterized by that.

[0016]

According to the present invention, in the structure of the continuous discharge system in which the thermal energy supply means and the discharge opening face each other, the distance H between the thermal energy supply means and the discharge opening, the height H of the liquid passage, and the heat By setting the distance L between the center of the energy supply means and the end portion of the liquid path so as to satisfy 0.1 ≦ Lh / H ² ≦ 10, the bubbles are made to communicate with the outside air and ink droplets are formed. When ejecting, it does not require a complicated configuration, achieves proper ejection of ink droplets even when the formation of bubbles changes due to the environment, etc., and stabilizes the image quality.
Realizes high-quality recorded images without image distortion.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 (a) and 1 (b) are explanatory views of the recording principle by the continuous discharge method which is the premise of the present invention, that is, the continuous discharge method which presupposes that the thermal energy generating means and the discharge port are opposed to each other. Is.

FIG. 1A is a sectional view of a main part of an ink jet recording head. In FIG. 1A, a heating resistance layer (heat energy supplying means) 2 is provided on a substrate 1 and mounted on the substrate 1. With the orifice plate OP
A liquid path B that communicates with the common liquid chamber C for ink and is bent, and a discharge port 5 are formed. The heat generation resistance layer 2 and the ejection port 5 face each other. Then, the heating resistance layer 2 is supplied with an electrode signal (pulse signal) corresponding to the recording signal, so that the ink in the liquid path B (shown by hatching) causes a rapid temperature rise that causes film boiling. Occurs within a short time (300 ° C
Above), the bubbles 6 are generated. That bubble 6
Grows and pushes out the ink in the thickness portion of the orifice plate OP, and dilutes the ink in that portion. After that, the bubbles 6 communicate with the atmosphere (outside air) in the area A2 near the outlet on the outside-side peripheral edge A1 of the outlet 5. According to such a communication state, a stable ink droplet 7 as shown by a broken line in FIG. 1A is ejected without splashing and without generating mist-like ink droplets. 5 can be discharged from the central part. At this time, since the growth of the bubbles 6 does not block the liquid path B, it is possible to leave the ink that does not have to go in the ejection direction as an aggregate that is continuous with the ink in the liquid path B. As a result, It is possible to realize the stabilization of the ejection amount of the ink droplet 7 and the stabilization of the ejection speed. In addition, since the bubble 6 can be rapidly and reliably generated in the vicinity of the discharge port 5 by utilizing the stabilization region of film boiling of 300 ° C. or more, the liquid passage B in the non-blocking state can be formed. Highly stable and high-speed recording can be achieved in combination with refillability.

FIG. 1 (b) is a sectional view showing the position of the cross section in FIG. 1 (a) shifted in the width direction of the liquid passage B (the display direction on the paper surface). As can be seen from FIG. 1 (b), the liquid path B
The ink inside (shown with diagonal lines) communicates with the ink droplet 7, and when the central portion of the bubble 6 communicates with the atmosphere in the vicinity of the ejection port 5, the ink deviates from the center of the bubble 6. It will be understood that the droplet 7 and the ink in the liquid path B maintain communication with each other at different positions. 6W has shown the shape of the edge part of a bubble.

The conditions for achieving more preferable droplet formation in the ink jet recording head shown in FIG. 1 are listed below.

The first condition is that the bubble 6 communicates with the outside air under the condition that the inner pressure of the bubble b is lower than the outer pressure.

That is, to make the bubble 6 communicate with the outside air under the condition that the internal pressure of the bubble 6 is lower than the outside pressure,
There is no problem that occurs when the internal pressure of the ink is communicated under the condition that the pressure is higher than the external pressure, that is, the problem that the unstable ink in the vicinity of the ejection port 5 is scattered. Since a force for drawing the unstable ink in the vicinity of the above into the liquid path B is small, it is possible to realize more stable ink ejection and prevent scattering of unnecessary ink.

The second condition is that the first differential value of the moving speed of the bubble 6 at the tip of the discharge port 5 is negative.
To communicate with the outside air. This second condition is also another expression of the above-mentioned first condition, and the expansion speed of the bubble 6 is 1
By making the bubble 6 communicate with the outside air when the second derivative becomes negative, the bubbles 6 communicate with each other under the condition that the internal pressure of the bubble 6 is lower than the outside atmospheric pressure. According to the second condition, when the bubble 6 and the outside air are communicated with each other, the ink in the vicinity of the communication portion is excessively accelerated due to the ejection of the ink, that is, the ink in the vicinity of the communication portion is the main ink droplet. It is also possible to solve the problem of being separated from. When the above-mentioned separation occurs, the ink in the vicinity thereof is significantly scattered in the form of a splash or becomes a mist, and when the ejection ports 5 are arranged at a high density, the ink adheres to the ejection port surface. In some cases, the ejection failure may be caused by the above, but this can be solved by the second condition.

2 (a) and 2 (b) disclose a partial structure of an ink jet recording head to which the present invention is applied, 5 is an ejection port having a circular cross section, 12 is an ink supply path (hereinafter, referred to as " Also referred to as a "liquid passage") 2 is a heat generating portion (heat energy supplying means) of a substantially square heat generating resistance portion. Reference numeral 1 is an insulating substrate having a heating resistor portion on its surface. The ink supply path 12 is bent at the position of the heat generating portion 2 (hereinafter, also referred to as “heater”), and the heat generating portion 2 and the ejection port 5 face each other. Reference numeral 8 is an orifice plate that forms the ink supply path 12 and the ejection port 5. The orifice plate 8 also forms a common liquid chamber 10 that communicates with the ink supply passage 12.

In order to make air bubbles in the ink generated in the heater 2 communicate with the outside air from the discharge port 5 to discharge the ink as described later, the size of the heater 2 and
It may be appropriately set in consideration of the distance between the discharge port 5 and the heater 2, the width, length and height of the liquid passage 12, the size of the discharge port 5, and the like. In particular, in order to efficiently communicate the bubble generated in the heater 2 with the outside air from the ejection port 5 and to keep the size (volume) of the ejected ink droplet, which is one of the features of this recording method, constant. As will be described later, among the above-mentioned conditions, the distance H between the discharge port 5 and the heater 2 is
And the relationship between the height h of the liquid passage 12 and the length L of the liquid passage 12 is important.

That is, in the case of the continuous discharge method in which the bubbles 6 are communicated with the outside air to discharge the ink, it is particularly required to stabilize the following functions.

Stabilization of ink discharge direction Stabilization of growth of bubble 6 Stabilization of continuous ink discharge The distance H between the discharge port 5 and the heater 2 and the height h of the liquid passage 12 are, in particular, as described above. Has a great influence on the stabilization of. That is, the bubble 6 communicates with the outside air and the ink droplet 7
As shown in FIG. 3, a meniscus is generated at the base end portion of the droplet 7 in the discharge port 5, and the height of the meniscus is higher on the liquid passage 12 side than on the opposite side. Will also be higher. Thus, the force F ₁ which portion M ₁ of the meniscus of the former side pulls the droplet 7, the portion of the meniscus of the latter side M ₂
Becomes larger than the force F ₂ that pulls the droplet 7, and these forces F
_When the difference between ₁ and F ₂ is large, the ejection direction of the droplet 7 is inclined in the direction of arrow D, and the stabilization of the ejection direction of the ink and the stabilization of the growth of the bubble 6 are impaired. Become. The height difference between the meniscus portions M ₁ and M ₂ , that is, the force F
The difference between ₁ and F ₂ is the distance H between the discharge port 5 and the heater 2.
, And the height h of the liquid passage 12 and the ratio h / H.

On the other hand, the length L and the distance H of the liquid passage 12 have a great influence particularly on the above-mentioned stabilization. That is,
The length L is measured from the end of the boundary with the common liquid chamber 10 to the heater 2
Is the length of the liquid path 12 between the center of the bubble, that is, the bubble point P at which the bubble 6 is generated, and the distance H is the length between the bubble point P and the discharge port 5. The ink is supplied to the bubbling point P through the portion 12A of the liquid path 12 corresponding to the length L of the above, and the ink is ejected from the bubbling point through the portion 12B of the liquid path 12 corresponding to the latter distance H. The relationship between the flow path resistance of the ink in the portions 12A and 12B greatly affects the refillability of the ink, that is, the stability of continuous ink ejection. Since the flow path resistances of both parts 12A and 12B change according to the length L and the distance H, their ratio L / H
Has a particularly great influence on the stabilization of the continuous ejection of the ink.

Therefore, in the present invention, the values of H, h, and L are set so as to satisfy the relationship of the following expression (1).

[0031]

[Equation 1]

In other words, the constitution is such that the relation of 0.1 ≦ Lh / H ² ≦ 10 is satisfied.

When the above relational expression is not satisfied, for example,
When Lh / H ² <0.1, that is, when H is relatively large and h and L are relatively small, the valve 6 generated in the heater 2 is efficiently communicated with the outside air from the ejection port 5 to eject ink. It becomes difficult to cause the bubble 6 to grow, and the bubble 6 generated in the heater 2 easily grows in the direction of the liquid path 12, and it becomes difficult to efficiently communicate the bubble 6 with the outside air. Further, after the bubble 6 communicates with the outside air, ink may remain between the ejection port 5 and the heater 2, and the ink droplet 7
Becomes unstable.

Further, when Lh / H ² > 10, that is, when H is relatively small and h and L are relatively large, the length L of the liquid passage 12 is substantially long, and the ink after ink ejection is long. Therefore, it takes a long time to refill, and it becomes difficult to drive the recording head at a high frequency.

In the above relational expression, the more preferable range is 0.3 ≦ Lh / H ² ≦ 7.
The ink droplet 7 can be ejected by efficiently communicating the bubble 6 with the outside air from the ejection port 5, and ink residue is not generated substantially in the vicinity of the ejection port 5, and a particularly small ink droplet is formed. The volume of 7 can always be stabilized. Moreover, it becomes possible to drive the recording head at a practically high frequency.

A more preferable range is 0.5≤Lh / H
^{In the case of 2} ≦ 5 and within this range, it is possible to improve the refillability of the ink and surely direct the growth of the bubble 6 not to the liquid passage 12 side but to the ejection port 5 side, which causes other instability. Even with the elements, extremely stable recording can be performed. Therefore, particularly in the case of a so-called multi-nozzle in which a large number of ejection ports 5 are formed adjacent to each other, it is possible to suppress the influence of variations in the inner diameter accuracy of the ejection ports 5 and variations in the width accuracy of the liquid passages 12 to be small.

Table 1 below shows experimental examples for explaining the effects of the present invention.

[0038]

[Table 1]

In Table 1, the unit of length is μm,
In Experimental Examples 1 to 5, the ejection frequency was 4 KHz and the driving pulse was 3 μsec. In Experimental Examples 1, 3, 6, and 7, the inner diameter B of the ejection port 5 (see FIG. 2B) and the width of the liquid passage 12 were set. b
(See FIG. 2B), both are set to 30 μm, and in other experimental examples 2, 4 and 5, the inner diameter B and the width b are both set to 50 μm.
And Although the experimental results are good in Experimental Examples 1 to 3 that satisfy the condition of the relational expression (1) of the present invention, Experimental Examples 4 and 5
However, since this condition is not satisfied, stable ink ejection was not possible.

By the way, the inner diameter B of the discharge port 5 and the width b of the liquid passage 12 do not significantly affect the above-described stabilization of. In the portion 12B of the liquid passage 12, the reaction forces generated on the inner peripheral surface of the ejection port 5 due to the ejection pressure of the ink cancel each other out.
In 2A, the portion 12 is affected by the ink ejection pressure.
This is because the reaction forces generated on the inner surface of A are considered to cancel each other out.

However, when the change in the environmental temperature is large, it is possible that stable ink ejection is hindered by the large change in the viscosity of the ink. Therefore, considering the ratio b / B of B and b, It is desirable to set the values of H, h, and L so as to satisfy the relational expression of the following expression (2).

[0042]

[Equation 2]

Incidentally, the lower limit value 0.1 and the upper limit value 10 in the above equation (1) are more preferably 0.3 and 7, similarly to the case of the above-mentioned embodiment, and further, 0. 5
It is desirable to set to 5.

FIG. 4 shows an example of a suitable structure when a large number of ejection ports 5 are formed close to each other. When a large number of ejection ports 5 are brought close to each other, a so-called back wave generated by the ejection pressure of ink, that is, from the liquid passage 12 to the common liquid chamber 1 at the time of ink ejection
The pressure fluctuation transmitted to 0 may be transmitted to another adjacent liquid passage 12 and adversely affect stable ejection of ink droplets. Therefore, as shown in FIG. 4, the discharge ports 5 are arranged in a so-called zigzag pattern, and the liquid passages 12 are vertically displaced in the drawing. As a result, the discharge ports 5 can be arranged at a high density.

FIGS. 5 (a) to 5 (e) are explanatory views of changes in the internal pressure and volume of the bubble 6 with time. When the bubble 6 communicates with the outside air, it is preferable that the bubble communicates with the outside air under the condition that the internal pressure of the bubble is lower than the outside atmospheric pressure in order to prevent the mist of the ink and the splash from contaminating the inside of the recording paper and the apparatus.

In order to satisfy this condition, FIG.
The bubble 6 and the outside air may be communicated with each other at the time of t ≧ t1 in (a). In reality, since the ink is ejected as the bubble 6 grows, a graph of the relationship between the internal pressure or volume of the bubble 6 and time is as shown in FIG. 5B. That is, t = tb in FIG.
The bubble may be communicated with the outside air at the time of (t1 ≦ tb).

When the ink droplet 7 is discharged under this condition, compared with the case where the bubble 6 is communicated with the outside air and the droplet is discharged under the condition that the internal pressure of the bubble 6 is higher than the outside pressure (gas is ejected into the atmosphere). As described above, it is possible to prevent the recording paper and the inside of the apparatus from being contaminated by the mist of the ink and the splash. Further, since the bubble 6 is communicated with the outside air after the volume of the bubble 6 is increased, sufficient kinetic energy can be transmitted to the ink, and the effect of increasing the ejection speed can be obtained. Further, it is more desirable to make the bubble 6 communicate with the outside air under the condition that the internal pressure of the bubble 6 is lower than the outside pressure because the above effect can be made more remarkable.

That is, making the bubble 6 communicate with the outside air under the condition that the internal pressure of the bubble 6 is lower than the outside air pressure causes unstable in the vicinity of the discharge port which occurs when the inside pressure of the bubble 6 is communicated under the condition that the inside pressure of the bubble 6 is higher than the outside air pressure. The liquid is not scattered, and moreover, the force that draws the unstable liquid into the liquid passage works slightly more than in the case where the pressure is equal, so that more stable liquid discharge and unnecessary liquid It is possible to prevent scattering.

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 atmospheric pressure can be known by the method shown below or by appropriately combining these methods. First, a method of knowing the magnitude relationship between the internal pressure of the bubble and the external atmospheric pressure by measuring the time change of the volume of the bubble or the volume of the ink outside the ejection port will be described.

The volume relationship V between the internal pressure and the external pressure of the bubble is determined by measuring the volume V of the bubble from the time when the ink starts foaming to the time when the bubble communicates with the outside air and obtaining the second derivative of V d2V / dt2. 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 equal to or lower than the external pressure. Explaining with reference to FIG. 5C, the internal pressure of the bubble becomes higher than the external pressure and becomes d2V / dt2> 0 from t = t0 to t = t1 from the start of foaming, and the time t from the time t = t1 until the bubble communicates with the external air. The internal pressure of the bubble is equal to or lower than the external atmospheric pressure until tb, and d2V / dt2 ≦ 0. As described above, the magnitude relationship between the internal pressure of the bubble and the external atmospheric pressure can be known by obtaining the second derivative d2V / dt2 of V.

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

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

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

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 relation between the internal pressure and the external pressure of the bubble is known by the following method. be able to.

Another method is to measure the volume Vd of the ink ejected from the ejection port in the time from the start of foaming until the ink droplet is ejected, and the second derivative d2V of Vd is measured.
By determining d / dt2, it is possible to know the magnitude relationship between the internal pressure and the external pressure of the bubble. 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 below the external pressure. FIG. 5D shows a time change of the first derivative dVd / dt of the volume Vd of the ink ejected from the ejection port when the bubbles are communicated with each other in a state where the inner pressure of the bubble is higher than the outer pressure. From the start of foaming t = t0 until the time t = ta until the bubble communicates with the outside air, the internal pressure of the bubble is higher than the outside air pressure, and d2Vd / dt2> 0. On the other hand, FIG. 5B shows the first derivative dVd / of Vd when the bubble is communicated with the outside air in a state where the inside pressure of the bubble is equal to or less than the outside pressure.
It shows the change over time of dt. From the figure, from the start of foaming t = t0 to t = t1, the internal pressure of the bubble is higher than the external pressure and is d2Vd / dt2> 0, but from t = t1 to t = tb, the internal pressure of the bubble is below the external pressure. Yes d2V
d / dt2 ≦ 0.

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

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

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

As another condition when the bubble and the outside air are communicated with each other, the bubble and the outside air are communicated with each other under the condition that the primary differential value of the moving speed of the tip of the bubble toward the discharge port is negative as shown in FIG. Conditions are preferred.

That is, this condition has a technical problem that the ink in the vicinity of the communication portion is excessively accelerated due to the ejection of the ink during the communication between the bubble and the outside air, so that the ink is separated from the main ink droplet. It is the one I have recognized. According to this separation, it is noticeable that the ink in the vicinity thereof is splashed or becomes a mist, and in addition, in a high-density ejection port arrangement, ejection failure due to adhesion of ink to the ejection port surface is caused. Become. Such a problem occurs in the case of the curve A shown in FIGS. 6A and 6B, respectively, and the first-order differential value of the moving speed of the tip of the bubble in the discharge port direction is positive. It was confirmed.

The curves B shown in FIGS. 7A and 7B are obtained by communicating the generated bubbles with the outside air under the condition that the first differential value of the moving velocity of the tip of the bubble in the outlet direction is negative. Since the droplets are ejected, the volume of the droplets can always be stabilized and a high quality recorded image can be obtained. Therefore, it is possible to prevent the background stain of the recording paper and the stain inside the apparatus due to the ink mist and the splash.

Furthermore, since the kinetic energy of the bubble can be sufficiently transmitted to the ink, the ejection efficiency is improved and clogging can be eliminated. Further, since the droplet discharge speed is improved, the droplet discharge direction is stabilized, and the distance between the recording head and the recording paper can be increased, which facilitates device design. Further, since there is no defoaming process of the bubble that has occurred, the heater destruction phenomenon due to the defoaming is eliminated and the life of the recording head is improved.

Next, in carrying out the present invention, a method of obtaining the moving speed of the tip of the bubble in the discharge port direction and the first-order differential value of the moving speed will be described below.

The position of the tip of the bubble in the direction of the ejection port at each time after the start of foaming is controlled by illuminating the bubble generated in the nozzle from the top plate surface or side surface of the recording head with pulsed light from a strobe, an LED, a laser, etc. Can be used and observed. Specifically, as shown in time series as a schematic cross-sectional view in FIG. 7, the displacement of the tip of the bubble in the discharge port direction from the discharge port end part from the start of foaming until the bubble communicates with the outside air. The time variation of the quantity xb-n can be measured. The moving speed vx of the tip of the bubble in the discharge port direction is calculated by calculating the first derivative dxb-n / dt of the displacement amount based on the measurement result. Next, the first derivative dvx / dt of the moving speed (second derivative d2x of the displacement amount)
b−n / d2t) can be obtained.

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

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

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

FIG. 8 is a schematic perspective view showing a main part of an embodiment of an ink jet recording apparatus constructed by using the recording head according to the above embodiment.

In FIG. 8, the recording head 101 has a plurality of ink ejection ports (not shown) on the surface facing a recording medium 107 such as paper (hereinafter referred to as “recording paper”) in the conveying direction of the recording paper 107. Equipped with. The recording head 101 has the same configuration as the recording head of the above-described embodiment. That is, the recording head 101 is provided with liquid passages (not shown) communicating with each of the plurality of ejection ports, and is used for ejecting ink to the substrate constituting the recording head 101 corresponding to each liquid passage. A heater is formed which acts on the generated heat energy. The electrothermal conversion element corresponding to the heater generates heat by the electric pulse applied to the heater according to the recording data, thereby causing a boiling film in the ink,
Ink is ejected from the ejection port as bubbles are generated by the boiling film. Each liquid passage is provided with a common liquid chamber that communicates with them in common, and the ink stored therein is supplied to the liquid passage according to the ejection operation in each liquid passage.

The carriage 102 carries the recording head 101 and slidably engages with a pair of guide rails 103 extending parallel to the recording surface of the recording paper 107. As a result, the recording head 101 can move along the guide rail 103, and along with this movement, recording is performed by ejecting ink toward the recording surface at a predetermined timing. After the above movement, the recording paper 107 is conveyed by a predetermined amount in the direction of the arrow in the drawing, and the above movement is performed again to perform recording. By repeating such an operation, the recording paper 1
Recording will be sequentially performed at 07.

The above-described conveyance of the recording paper 107 is performed by the pair of conveying rollers 1 disposed above and below the recording surface.
This is done by rotating 04 and 105. A platen 106 for maintaining the flatness of the recording surface is provided on the back side of the recording surface of the recording paper 107.

The carriage 102 can be moved by driving a belt (not shown) attached to the carriage 102 by a motor, and the transport rollers 104 and 105 are also rotated by the motor. It becomes possible by being transmitted to.

FIG. 9 is a block diagram showing the control arrangement of the ink jet recording apparatus shown in FIG.

In FIG. 9, the CPU 200 executes control processing, data processing, etc. of the operation of each part of the apparatus. ROM2
The processing procedure and the like are stored in 00A. Also, RA
The M200B is used as a work area for executing the above processing.

Ink ejection from the recording head 101 is
The CPU 200 supplies print data and drive control signals for driving the heater to the head driver 101A. The CPU 200 also includes a carriage motor 220 for moving the carriage 102.
The rotation of the paper feed (PF) motor 50 for rotating the feed rollers 104 and 105 is controlled via motor drivers 220A and 50A, respectively.

(Others) The present invention is particularly provided with a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for ejecting ink, even in the ink jet recording system. The present invention brings about excellent effects in a recording head and a recording apparatus of the type in which the state of ink is changed by the heat energy. This is because such a system can achieve high density recording and high definition recording.

Regarding its typical structure and principle, see, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740.
What is done using the basic principles disclosed in 796 is preferred. This method is a so-called on-demand type,
It can be applied to any of the continuous type, but especially in the case of the on-demand type, it can be applied to the sheet holding the liquid (ink) or the electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal corresponding to the recording information and giving a rapid temperature rise exceeding nucleate boiling, heat energy is generated in the electrothermal converter, and film boiling is caused on the heat acting surface of the recording head. Liquid (ink) corresponding to this drive signal in a one-to-one correspondence
It is effective because bubbles can be formed inside. Due to the growth and contraction of the bubbles, the liquid (ink) is ejected through the ejection opening to form at least one droplet. It is more preferable to make this drive signal into a pulse shape because bubbles can be immediately and appropriately grown and contracted, so that liquid (ink) ejection with excellent responsiveness can be achieved. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the rate of temperature rise on the heat acting surface are adopted, more excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the linear liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned specifications, US Pat. No. 4,558,333, US Pat. No. 4,558,333, which discloses a configuration in which a heat acting portion is arranged in a bending region.
The structure using the specification of No. 59600 is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-123670 discloses a configuration in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters, and an opening for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is effective even if the configuration corresponding to the ejection portion is disclosed in JP-A-59-138461. That is, according to the present invention, recording can be surely and efficiently performed regardless of the form of the recording head.

Further, the present invention can be effectively applied to a full line type recording head having a length corresponding to the maximum width of a recording medium which can be recorded by the recording apparatus. Such a recording head may have a configuration that satisfies the length by a combination of a plurality of recording heads or a configuration as one recording head integrally formed.

In addition, even in the case of the serial type as in the above example, the recording head fixed to the apparatus main body, or the electrical connection with the apparatus main body or the ink from the apparatus main body by being attached to the apparatus main body The present invention is also effective when a replaceable chip-type recording head that can be supplied or a cartridge-type recording head in which an ink tank is integrally provided in the recording head itself is used.

Further, as the constitution of the recording apparatus of the present invention, it is preferable to add the ejection recovery means of the recording head, the preliminary auxiliary means and the like because the effects of the present invention can be further stabilized. Specifically, heating is performed by using a capping unit, a cleaning unit, a pressure or suction unit for the recording head, an electrothermal converter or a heating element other than this, or a combination thereof. Examples thereof include a preliminary heating unit for performing the discharge and a preliminary discharge unit for performing discharge different from the recording.

Regarding the type and number of recording heads to be mounted, for example, only one is provided corresponding to a single color ink, or a plurality of inks having different recording colors and densities are supported. A plurality of pieces may be provided. That is, for example, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but it may be either the recording head is integrally formed or a plurality of combinations may be used. The present invention is also extremely effective for an apparatus provided with at least one of full-color recording modes by color mixing.

In addition, in the above-described embodiments of the present invention, the ink is described as a liquid, but an ink that solidifies at room temperature or lower and that softens or liquefies at room temperature may be used. Or, in the inkjet system, it is common to control the temperature of the ink itself within the range of 30 ° C. or higher and 70 ° C. or lower to control the temperature so that the viscosity of the ink is within the stable ejection range. Sometimes, a liquid ink may be used. In addition, the temperature rise due to thermal energy is positively prevented by using it as the energy of the state change of the ink from the solid state to the liquid state, or in order to prevent the evaporation of the ink, it is solidified and heated in the standing state. You may use the ink liquefied by. In any case, by applying thermal energy such as ink that is liquefied by applying thermal energy according to the recording signal and liquid ink is ejected, or that begins to solidify when it reaches the recording medium. The present invention can be applied to the case where an ink having a property of being liquefied for the first time is used. In this case, the ink is
JP-A-54-56847 or JP-A-60-7
As described in Japanese Patent No. 1260, it may be configured to face the electrothermal converter in a state of being held as a liquid or a solid in the concave portion or the through hole of the porous sheet. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, as a form of the ink jet recording apparatus of the present invention, other than the one used as an image output terminal of an information processing apparatus such as a computer, a copying apparatus combined with a reader or the like, and a facsimile apparatus having a transmitting / receiving function are provided. It may be a form or the like.

[0086]

As described above, according to the present invention, in the structure of the continuous discharge system in which the thermal energy supply means and the discharge opening face each other, the distance H between the thermal energy supply means and the discharge opening, the liquid The height H of the passage and the distance L between the center of the heat energy supply means and the end of the liquid passage are 0.
By setting so that 1 ≦ Lh / H ² ≦ 10, when the bubble is communicated with the outside air and the ink droplet is ejected, the formation of the bubble changes depending on the environment without requiring a complicated configuration. Even in this case, it is possible to achieve proper ejection of ink droplets, and as a result, it is possible to stabilize the image quality and obtain a high-quality recorded image without image distortion.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a recording principle by a continuous discharge method.

FIG. 2 is a diagram illustrating a recording head according to an exemplary embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of a main part of the recording head shown in FIG.

FIG. 4 is a diagram illustrating a recording head according to another embodiment of the present invention.

FIG. 5 is an inkjet recording method to which the present invention is applied.
FIG. 6 is an explanatory diagram of a new specific example of the apparatus, and is a diagram sequentially illustrating temporal changes in the internal pressure and volume of the bubble.

FIG. 6 is an inkjet recording method to which the present invention is applied;
It is explanatory drawing of the other novel example of an apparatus and.

FIG. 7 is a diagram showing changes in the tip of a bubble per unit time.

FIG. 8 is a perspective view of a main part of the inkjet recording apparatus of the present invention.

9 is a block configuration diagram of a control system of the inkjet recording apparatus shown in FIG.

[Explanation of symbols]

 2 Heat generating resistance layer 5 Discharge port 6 Bubble 7 Droplet 6W End (bubble) A Communication part B Liquid path

Claims (6)

[Claims] 1. A liquid channel communicating with the ink source for receiving the ink from the ink source, and thermal energy to the ink in the liquid channel to rapidly increase the temperature to rapidly exceed the nucleate boiling to cause bubbles. And a discharge port provided to face the heat energy supply unit to discharge the ink, and the bubble is communicated with the outside air at the discharge port to discharge the ink. In the ink jet recording head to be performed, the distance between the thermal energy supply means and the ejection port is H, the height of the liquid passage is h, and the center of the thermal energy supply means and the end portion of the liquid passage are provided. An ink jet recording head characterized by satisfying 0.1 ≦ Lh / H ² ≦ 10, where L is a distance. 2. A liquid passage communicating with the ink supply source for receiving the ink supply from the ink supply source, and thermal energy is given to the ink in the liquid supply passage to rapidly increase the temperature beyond the nucleate boiling. A thermal energy supply unit for generating the ink, and an ejection port provided to face the thermal energy supply unit for ejecting the ink, and a distance between the thermal energy supply unit and the ejection port is Where H is H, the height of the liquid passage is h, and the distance between the center of the thermal energy supply means and the end portion of the liquid passage is L, 0.1 ≦ L
Using an ink jet recording head satisfying h / H ² ≦ 10, thermal energy is applied to the ink by the thermal energy supply means to generate bubbles in the ink due to a temperature rise that rapidly exceeds nucleate boiling, and the bubbles are used as outside air. An ink jet recording method, characterized in that the ink is made to communicate with each other and at least a part of the ink in the vicinity of the ejection port is ejected. 3. The ink jet recording method according to claim 2, wherein the liquid path is not blocked by the bubbles during the communication. 4. The ink jet recording method according to claim 2, wherein at the time of the communication, the bubbles are communicated with the outside air under the condition that the internal pressure of the bubbles is equal to or less than the outside atmospheric pressure. . 5. The bubble is communicated with the outside air under the condition that the acceleration of the moving speed of the tip portion in the discharge direction of the bubble is not positive at the time of the communication.
Or the inkjet recording method according to any one of 4 above. 6. An ink jet recording head according to claim 1, comprising means for relatively moving the ink jet recording head and a recording medium, and means for driving the thermal energy supply means. Inkjet recording device.