JP2907338B2 - Liquid jet recording method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid jet recording method, and more particularly, to a method of driving a recording head in a liquid jet recording apparatus that performs recording by ejecting ink droplets using bubbles. Prior art When a droplet is ejected from a discharge orifice, it is applied to a thermal energy liquid using a heating resistor or the like, causing a state change accompanied by a steep volume increase in the energy-applied liquid, and the volume increase. A so-called bubble liquid ejection recording apparatus which performs recording by ejecting and ejecting a liquid by an action force based on the above is known, for example, from JP-A-55-16166. Thus, in the invention described in Japanese Patent Application Laid-Open No. 55-161665, an effective ejection performance is obtained by regulating the speed of the increase in the volume of bubbles, but this has a significant effect on the ink ejection performance. It seems that there is not much specific description about the bubble shrinkage that exerts an effect, and it is thought that effective discharge performance can be obtained only by the condition of volume increase. However, the ink ejection performance also has a performance that is affected by bubble contraction. For example, as the performance that is affected by bubble contraction, the ejection of ink droplets with good sharpness, the ejection without satellite droplets, and the next There is an ink supply speed (related to the response frequency speed) and the like. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has been made to improve ink ejection performance in a bubble jet type liquid jet recording apparatus. Configuration In order to achieve the above object, the present invention provides an orifice provided for discharging liquid droplets, and a heat communicating with the orifice and serving as a portion where thermal energy for discharging liquid droplets acts on the liquid. A liquid ejecting recording method using a recording head including a liquid discharging section having an action section and an electrothermal transducer as a means for generating thermal energy, comprising: By forming a heat storage layer, which is a thin layer with low conductivity, and an electric resistor layer as an electric heat converter, and applying a current to the electric resistor layer, a high heat flux of several μsec is given to the ink to remove bubbles. The droplets are ejected and ejected from the orifice substantially parallel to the plane on which the electric resistance layer is formed by the action force accompanying the increase in the volume of the bubbles, and the recording is performed by attaching the droplets to the recording surface. In the liquid jet recording method, Assuming that the time from the occurrence of the bubble to the maximum volume is ti and the time from the maximum volume to the disappearance is td, the movement of the ink accompanying the bubble generation, growth, shrinkage, and disappearance follows. To the extent that It is characterized in that recording is performed while satisfying the following relational expression. Hereinafter, a description will be given based on an example of the present invention. FIG. 4 is a perspective view showing an example of a liquid jet recording head to which the present invention is applied, and FIG. 5 is a lid substrate (FIG. 5A) and a substrate (FIG. 5 ( 6) is an exploded perspective view of b)), and FIG. 6 is a perspective view of the lid substrate as viewed from the back side, in which 1 is a lid substrate (flow path plate), 2 is a substrate, 3 is a liquid inlet, and 4 is a liquid inlet. Discharge port, 5 a groove, 6 a region for forming an ink chamber, 7 an individual (independent) electrode, 8 a common electrode,
Reference numeral 9 denotes a heating element. On the surface of the substrate 2, a heating element 9 is formed together with a common electrode 8. By joining the lid substrate 1 and the substrate 2, the groove 5 forms a liquid (ink) flow path and The discharge port 4 is formed, and the area 6 forms an ink chamber for containing a recording liquid (ink) introduced from the inlet 3.
As is well known, when the flow path plate 1 is joined to the substrate 2, an ink flow path is formed by the groove 5 of the flow path plate 1 and the upper surface of the substrate 2, and one of the lower surfaces of the ink flow path on the ink ejection side is formed. The heating element 9 is disposed in the portion, and the ink is heated by the heating element 9 to generate a bubble in the ink.
The ink droplet is ejected from the end of the ink flow path by the change in the volume of the bubble. FIGS. 18 (a) to 18 (g) are diagrams showing an ink droplet generation process in the ink jet drop generator using a bubble as described above, where 10 is ink, 20 is air bubbles, and 30 is air bubbles.
Is a generated ink droplet, and the other flow path plate 1, substrate 2, independent electrode 7, common electrode 8, heating element 9 and the like are as shown in FIG. The ink droplets 30 are ejected by the heating. As described above, the bubble ink jet is used for the liquid (ink) in the flow path.
The thin film resistor energizes and heats the ink to rapidly boil the ink, and the ink droplets are ejected from the ejection ports by the pressure action of the generated bubbles, and the ejected droplets land on a recording material such as paper to record. Form pixels. The present invention relates to the bubble jet type ink jet as described above, in which bubble generation time, contraction time, and ink ejection performance, particularly, ink droplets with good sharpness, no satellite droplets, and the next ink supply after one droplet is ejected The relationship with speed and the like is optimized based on experimental data. First, the general principle of bubble jet will be described. The process of generating and extinguishing bubbles changes depending on the configuration of the heater and flow path, the conditions of heating, and the like. In order to be practical as an ink jet recording apparatus, the following conditions must be satisfied. (1) Sufficient pressure for ejection is obtained. (2) Good reproducibility of the phenomenon (bubble stability). (3) High response frequency. Such conditions seem to be difficult to achieve in view of the boiling phenomena seen on a daily basis. This is because (1) In order to discharge a droplet, it is necessary to form a droplet overcoming the surface tension of the liquid surface of the discharge port. However, in a normal boiling phenomenon, the boiling start temperature is equal to the boiling point of the liquid +
It is below a few degrees Celsius and the corresponding vapor pressure is not so high compared to atmospheric pressure. (2) Boiling is a complex heat transfer phenomenon involving phase change and flow, and is much more random than electrical and mechanical phenomena. Further, in order to drive repeatedly at a high frequency, the response time from foaming to defoaming must be short. However, there is a limit to reducing the time constant of temperature rise / fall under normal boiling conditions. In a bubble jet recording apparatus, a thin layer having low thermal conductivity (heat storage layer) and a thin electric resistance layer (heater) are formed on a substrate having high thermal conductivity, and the layer is formed by an extremely short heating pulse (up to several μsec). The above conditions are satisfied by applying a high heat flux to the ink. (1) By applying a high heat flux to the smooth heat transfer surface formed by the thin film technology, the ink can be heated to a very high temperature (up to 300 ° C. for water-based ink). The vapor pressure at this time reaches several tens of times the atmospheric pressure, and is sufficient to discharge droplets. (2) Bubbling in a bubble jet is different from a normal boiling phenomenon in which gas trapped in a dent on a heater surface or the like becomes a nucleus of foaming, and ink near a heat transfer surface vaporizes at once by reaching an overheating limit. Therefore, the reproducibility of the phenomenon is high. (3) At the time of heating, the ink is sufficiently heated by the effect of the heat storage layer. Since the heating time is short, only a small part of the ink (up to several μm above the heater) is heated, and after the bubbles are formed, the heat transfer from the heater almost stops due to the heat insulating effect of steam. Accordingly, the temperature of the ink and the pressure inside the bubble rapidly decrease with the growth of the bubble, and the state becomes a cavitation bubble. The rate of bubble disappearance is extremely high, and the destruction of the heater due to impact at the time of bubble disappearance becomes a problem. Excess heat escapes to the substrate through the heat storage layer. FIG. 1 is an enlarged cross-sectional view of an essential part for explaining an embodiment of the present invention, and FIG. 2 shows an example showing a temporal change of a volume V of bubbles generated in a heat acting portion (heater portion). In the figure, as shown in FIG. 2, the maximum bubble volume after the bubble is generated
The time until Vmax is reached is ti, and the time from when the maximum bubble volume Vmax is reached to when it disappears is td. FIG. 1 shows the state of the liquid chamber (in the vicinity of the orifice) after the ejection of ink droplets. The bubble 20 contracts in the direction of arrow A after reaching the maximum bubble. Accordingly, the meniscus retracts as indicated by arrow B on the orifice side. On the other hand, from the right ink supply side, the ink moves (supplies) as indicated by arrow C by the action force accompanying the bubble contraction. The movement of the meniscus or the movement (supply) of the ink greatly depends on the contraction speed of the bubbles. When the speed is not within a certain range, the following problems occur. For example, the movement of the meniscus may be caused by poor disconnection of the ejected ink droplets, generation of satellite droplets, suction of unnecessary air from the orifice, dripping of ink at the orifice surface, and movement (supply) of ink. If the bubble contraction speed is too high, the ink supply does not follow the response (the response speed cannot keep up), and if it is too slow, the recording speed is undesirably low. In the present invention, during the experiments and observations of the generation and shrinkage of bubbles, the above-mentioned phenomenon (point of inconvenience) causes the generation of bubbles,
In order to find that it depends heavily on the shrinkage behavior, and to find favorable bubble generation and shrinkage behavior conditions, we studied from various angles and actually designed and manufactured a wide variety of recording heads, and from various angles The following conditions were repeated and the following conditions were found. That is, In such a relationship, the generation and shrinkage speed of the bubbles are specified, but more preferably, And optimally, It is said. The generation and contraction speeds of bubbles are as follows: applied signal voltage, pulse width, pulse waveform, pulse current, ink physical properties, ink temperature, liquid chamber dimension, heat generating part configuration, heat generating part material,
It can be changed according to the heating part dimensions and the like. FIG. 3 shows an example of data showing a stable ejection area (good print quality area) by changing each parameter and changing the value of td / ti and examining the relationship between the parameter and the ejection performance. The unusable area and the BE area are the practical print quality area, and the C-
The E area is a good print quality area, the DE area is a best print quality area, and the EF area is an unusable area. In the above formula, td /
Although the upper limit of ti is shown by the numbers 3, 5, and 10, this is an average value, and actually has a variation range of 3 ± 0.3, 5 ± 0.3, 10 ± 0.3. It is considered that the reason for this is that the factors that determine the speed of generation and contraction of the bubbles have variations in actual experiments. Effects As is apparent from the above description, according to the present invention, by setting the conditions of the generation and contraction speed of the bubbles within the range of the above-mentioned formula (1), Discharge of ink droplets with good sharpness, b. Discharge without satellite drops, c. Discharge of uniform droplets that do not form mist, d. E. No discharge of unnecessary air from the orifice, e. Discharge without dripping at the orifice surface, f. It is possible to perform ejection with a high response frequency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged sectional view of an essential part for explaining an embodiment of the present invention, FIG. 2 is a diagram showing a time change of a bubble volume, FIG.
FIG. 4 is a diagram showing an example of a stable ejection area. FIG. 4 is a perspective view showing an example of a liquid jet recording head to which the present invention is applied.
FIG. 5 is an exploded perspective view of a lid substrate (FIG. 5 (a)) and a substrate (FIG. 5 (b)) constituting the recording head, and FIG. 6 is a perspective view of the lid substrate as viewed from the back side. FIG. 7 is a diagram for explaining a process of generating ink droplets in bubble jet recording. DESCRIPTION OF SYMBOLS 1 ... Lid board (flow path plate), 2 ... Substrate, 3 ... Liquid inflow port, 4 ... Liquid discharge port, 5 ... Groove, 6 ... Ink liquid chamber,
7 individual (independent) electrodes, 8 common electrodes, 9 heating elements, 10 inks, 20 air bubbles, 30 ink drops,

Claims (1)

(57) [Claims] A liquid discharge unit having an orifice provided for discharging liquid droplets, and a heat acting unit which is in communication with the orifice and which is a part where heat energy for discharging liquid droplets acts on the liquid; and What is claimed is: 1. A liquid jet recording method using a recording head comprising an electrothermal transducer as a means for generating, comprising: a heat storage layer which is a thin layer having low heat conductivity on a substrate having high heat conductivity; By forming an electric resistor layer as a heat converter and applying a current to the electric resistor layer, a high heat flux of several μsec is applied to the ink to generate bubbles, and the action force accompanying the volume increase of the bubbles is generated. In a liquid jet recording method in which droplets are ejected from the orifice, fly, and are attached to a recording surface to perform recording substantially in parallel with the plane on which the electric resistor layer is formed, the method includes the steps of: Until it reaches the maximum volume Time ti, when the td time to disappear after becoming maximum volume, to the extent that occurs - growth of the bubble, the movement of the ink due to shrinkage-annihilation follows, A liquid jet recording method characterized by performing recording by satisfying the following relational expression.