JPS647871B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid jet recording method that performs recording by jetting liquid and forming flying droplets. Non-impact recording methods have recently attracted attention because the noise generated during recording is so small that it can be ignored. Among these, the so-called inkjet recording method (liquid jet recording method), which is capable of high-speed recording and does not require special processing such as fixing on so-called plain paper, is an extremely powerful recording method. Until now, various methods have been proposed and devices that embody them have been devised.
Some have been improved and commercialized, while others are still being put into practical use. Among them, for example, the liquid jet recording method described in Japanese Patent Application Laid-Open No. 54-51837 and German Opening Publication (DOLS) No. 2843064 applies thermal energy to the liquid to create a driving force for ejecting droplets. This method has a different feature from other liquid jet recording methods in that it obtains the following information. That is, in the recording method disclosed in the above-mentioned publication, the liquid subjected to the action of thermal energy undergoes a state change accompanied by a sharp increase in volume, and the acting force based on the state change causes the recording head portion to The feature is that droplets are ejected from an orifice at the tip, fly, and adhere to the recording member to perform recording. In particular, the liquid jet recording method disclosed in DOLS2843064 is not only very effectively applicable to the so-called drop-on demand recording method, but also can be easily implemented as a full line type recording head with high density multi-orifices. high resolution,
It has the characteristic of being able to obtain high-quality images at high speed. In this way, the liquid jet recording method described above has excellent features, but in order to record high-resolution, high-quality images at even higher speeds, it is necessary to It is necessary to increase the number of hits. In other words, the liquid jet recording method described above records by ejecting liquid droplets from the orifice of the recording head in a flying manner due to the generation of bubbles due to thermal action, rapid increase in volume, and sudden change in state due to attenuation. but,
By shortening the repetition time of this volume increase and decay,
It is necessary to increase No. (improve the ability to repeatedly eject droplets). In order to improve the repeatability of droplet ejection, it has been proposed to improve the attenuation rate of the increased bubble volume, which is the rate-determining step. In other words, the heat from the electrothermal converter, which is the source of heat acting on the liquid, acts on the liquid in the heat acting part, and the attenuation curve of the temperature change over time of the heat acting surface, which is the surface that comes into contact with the liquid. For example, by forcibly cooling the heat generating part of the electrothermal converter and the liquid using a cooling means such as a Peltier element (forced cooling), the result is a No. This is a device designed to increase the However, providing a special cooling means to the recording head as described above
This increases the complexity and cost of the device itself, and this problem becomes especially noticeable when a multi-orifice recording head is used. However, when creating a high-density multi-orifice recording head,
Advanced micro-precision technology is required in structure, processing, assembly, etc., resulting in higher costs, lower yields,
Maintenance problems arise and the result is not desirable. Furthermore, even if the volume of the generated gas is accelerated by forced cooling using the cooling means described above, it is not possible to cool the bubbles by cooling the liquid around the generated bubbles. The cooling efficiency is low, and it is necessary to drive the cooling means and the electrothermal converter in synchronization. Due to the slow response of the cooling means, there is a limit to the ability to repeatedly eject droplets.If you try to increase the cooling rate, the liquid around the cooling means will be cooled more than necessary, resulting in extreme physical properties of the liquid. This causes inconveniences such as a drop in droplet ejection characteristics due to the change. These inconveniences include unstable replenishment of liquid to the heat-acting section provided in the recording head, non-uniformity in the amount of ejected droplets, disturbance in the direction of droplet ejection, non-uniformity in droplet ejection speed, and problems with recording signals. This results in a decrease in the fidelity and reliability of responses to
This may even cause recording to stop. The present invention has been made in view of this point, and is a liquid jet recording method that can consistently record images at high speed, higher resolution, and higher quality even during continuous long-term recording. The purpose is to provide a method. In order to achieve the above object, the present invention was developed by examining various angles, actually designing and manufacturing a wide variety of recording heads, and repeatedly conducting experiments from various angles. If we find out that the attenuation curve of temperature change over time is largely dependent on the increase curve during heating, and if the temperature waveform of the heat-active surface takes the waveform state described later, we can solve the problem without forced cooling without causing the above problems. This invention was made based on the discovery that the object of the invention could be achieved. According to the results of experimental studies conducted by the inventor, an electric signal is input to an electrothermal converter provided in a recording head to generate thermal energy, and the thermal effect is applied to a heat acting section by the action of the thermal energy. When bubbles are generated in a liquid, a high-temperature liquid layer is formed on the surface of the generated bubbles, which has a relatively higher temperature than the surrounding area.
As the layer thickness of this high-temperature liquid layer increases, the rate of decrease in the bubble volume V decreases markedly. It has been found that the layer thickness of the high-temperature liquid layer is highly dependent on the heating rate of the liquid in the heat-acting zone. The present invention is based on comprehensive experimental studies in this regard. The liquid jet recording method of the present invention includes an orifice for causing a state change in the liquid by the action of thermal energy and ejecting the liquid to form a droplet based on the state change; A liquid jet recording method using a recording head comprising a liquid discharge part having a heat acting part, which is a part where energy acts on the liquid, and an electric heat exchanger for generating the thermal energy. Heat from the heat converter acts on the liquid in the heat acting part, and the time rate of change in temperature of the heat acting surface, which is the surface in contact with the liquid, from the rising start temperature Ti to the maximum temperature Tp. The recording is performed by inputting a pulse wave having a voltage and a pulse width component whose average value is 1×10 ⁶ °C/sec or more. In this way, the temperature at which the temperature of the heat acting surface starts to rise
If recording is performed with the average value of the time rate of change dT/dt (dT/dt) from Ti to reaching the maximum temperature Tp at 1×10 ⁶ °C/sec or more, the amount of ejected droplets can be made uniform. Stabilization of droplet discharge direction, uniformity of droplet discharge speed,
It is also possible to improve the fidelity and reliability of responses to recording signals, and it is extremely easy to record high-resolution, high-quality images at high speed. Furthermore, by making the temperature change of the heat effecting surface wave-like, the thermal energy generated by inputting an electric signal to the electrothermal converter in the heat effect part can be caused by the heat effect. It acts with high efficiency on the liquid in the area, and the resulting motive force for ejecting droplets is effectively consumed for ejecting droplets, making it easy to save energy for ejecting droplets. . Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 1a is a front partial view of a liquid jet recording head to which the present invention is applied, as seen from the orifice side;
FIG. 1B is a partial cross-sectional view taken along the dashed line XY in FIG. 1A. The recording head 1 shown in the figure has a grooved surface in which a predetermined number of grooves of a predetermined width and depth are provided at a predetermined linear density on the surface of a substrate 3 on which an electrothermal transducer 2 is provided. It has a structure in which an orifice 5 and a droplet discharge part 6 are formed by joining the plate 4 so as to cover it. Although the recording head shown in the figure is shown as having a plurality of orifices 5, the present invention is of course not limited to this, and the present invention can also be applied to a recording head with a single orifice. It falls within the range of The liquid discharge part 6 has an orifice 5 at its end for discharging liquid droplets, and thermal energy generated by the electrothermal converter 2 acts on the liquid to generate bubbles.
It has a heat acting part 7 which causes a rapid state change due to expansion and contraction of its volume. The heat acting part 7 is located above the heat generating part 8 of the electrothermal converter 2, and has a heat acting surface 9 that contacts the liquid of the heat generating part 8 as its bottom surface. The heat generating section 8 is a lower layer 1 provided on the substrate 3.
0, heating resistance layer 1 provided on the lower layer 10
1. Upper layer 12 provided on the heating resistance layer 11
It consists of The heating resistance layer 11 includes electrodes 13, 1 for supplying electricity to the layer 11 to generate heat.
4 is provided on its surface. The electrode 13 is an electrode common to the heat generating part of each liquid discharge part, and
Reference numeral 4 denotes a selection electrode for selectively generating heat in the heat generating section of each liquid discharge section, and is provided along the flow path of the liquid discharge section. The upper layer 12 isolates the heating resistance layer 11 from the liquid in the liquid discharge part 6 in order to chemically and physically protect the heating resistance layer 11 from the liquid used, and also connects the electrodes 13 and 14 through the liquid. The heating resistor layer 11 has a protective function of preventing short circuits. The upper layer 12 has the above-mentioned functions, but if the heating resistance layer 11 is liquid resistant and there is no fear of electrical short circuit between the electrodes 13 and 14 through liquid, , it is not necessarily necessary to provide it, and it may be designed as an electrothermal transducer having a structure in which the liquid comes into immediate contact with the surface of the heat generating resistance layer 11. The lower part 10 mainly has a heat flow control function.
That is, when ejecting a droplet, the proportion of heat generated in the heat generating resistor layer 11 being conducted toward the heat acting section 7 side is as large as possible than being conducted toward the substrate 3 side, and the droplet is ejected. After that, electricity is not applied to the clogged heat generating resistor layer 11.
After being turned off, the heat acting part 7 and the heat generating part 8
This is provided so that the heat present in the heat acting portion 7 is quickly released to the substrate 3 side, and the liquid in the heat acting portion 7 and the generated bubbles are rapidly cooled. In this way, when discharging a droplet, the proportion of the heat flow toward the heat acting part 7 side is as large as possible, and when the power to the heating resistor layer 11 is turned off, the heat flow rate toward the substrate 3 side is as large as possible. In order to increase the ratio of In order to stabilize the droplet ejection direction, equalize the droplet ejection speed, and improve the fidelity and reliability of the response to the recording signal, the above relationship must be established in the temperature change curve of the heat acting surface. All you have to do is record as shown below. This point will be explained more specifically. FIG. 2 shows the temporal change in the surface temperature of the heat acting surface 9 when an electric signal having a pulse waveform indicated by the symbol P is input to the electrothermal converter 2 provided in the recording head. Now, at time to and time tp, the electrothermal converter 2
When a pulsed electric signal P that is turned ON and OFF is input, the surface temperature T of the heat acting surface 9 starts to rise from the rising start temperature Ti at time to, and at time tp
The maximum temperature Tp is reached at . Note that the starting temperature Ti is determined automatically by the physical properties of the ink used and the environmental temperature in which the recording head is placed, and the maximum temperature Tp
is determined by the voltage and pulse width of the electrical signal applied to the recording head, and means the temperature necessary for heating the ink to cause a change in state accompanied by a sharp increase in volume. Then, at the time tp, the electric signal p is turned off, and the surface temperature T begins to decrease. The speed at which the surface temperature T decreases when the electric signal p is turned off is largely influenced by the temporal rate of change in the surface temperature T over time to. That is, as mentioned in the present invention, the electric signal p can be changed by creating a temperature curve such that the average value of the rate of change over time during heating is 1×10 ⁶ °C/sec or more.
It is possible to effectively steepen the attenuation curve of the surface temperature of the heat-acting surface when it is turned off without using any special cooling means, and the object of the present invention as described above can be more than achieved. . In the present invention, the average value of the time rate of change (dT/dt) described above is 1×10 ⁶ °C/sec or more, more preferably 3×10 ⁶ °C/sec or more, most preferably 1×10 ⁷ °C/sec or higher. The present invention will be specifically described below with reference to Examples. Example _Two layers of SiO (lower layer) were formed on an alumina substrate by sputtering to a thickness of 3 μm, then HfB ₂ was layered to a thickness of 1000 Å as a heating resistance layer, and aluminum was laminated to a thickness of 3000 Å as an electrode, followed by selective etching. A heating resistor pattern of 80 μm x 200 μm was formed. Next, _two layers of SiO are added by sputtering.
Laminated as a protective layer (upper layer) to a thickness of 0.5 μm to form an electrothermal converter on the substrate, then width 80 μm x depth
A glass plate with a groove of 80 μm cut thereon was bonded so that the groove and the heating resistor matched. Subsequently, the end face of the orifice was polished so that the distance between the tip of the heating resistor and the orifice was 300 μm, thereby creating a recording head.
0.1 ink mainly composed of black dye and ethanol
10 μs while supplying the heat acting part with atmospheric back pressure.
When a 40V rectangular voltage pulse printing signal was continuously applied to the electrothermal converter at a cycle of 200μs for 10 hours,
Droplets were faithfully and reliably ejected according to the print signal. The results of measuring the discharge status of droplets from the orifice of the recording head and the time change in the volume of bubbles formed on the heat-active surface by blinking the strobe while synchronizing with the voltage application, and the surface of the heat-active surface. Table 1 shows the results of measuring temperature changes using an infrared thermometer. At the same time, we also showed the discharge status, maximum response frequency, energy consumption, and discharge speed when (dT/dT) was varied in various ways by varying the applied pulse width. These results revealed that the range of the present invention exhibited particularly excellent ejection performance.

【table】

【table】 [Brief explanation of drawings]

FIG. 1a is a partial front view of a preferred embodiment of a liquid jet recording head to which the present invention is applied, as viewed from the orifice side, and FIG. 1b is a portion indicated by a dashed line XY in FIG. FIG. 2, which is a partial cross-sectional view of the recording head, is a timing chart showing temporal changes in the electric signal input to the recording head and the surface temperature of the heat-active surface 9. DESCRIPTION OF SYMBOLS 1... Liquid jet recording head, 2... Electrothermal converter, 3... Substrate, 4... Grooved plate, 5... Orifice, 6... Liquid discharge section, 7... Heat acting section, 8... Heat generating part, 9...Heat action surface, 10...Lower part, 11
...Heating resistance layer, 12... Upper layer, 13... Common electrode, 14... Selective electrode.

Claims (1)

[Claims] 1. An orifice for causing a state change in a liquid by the action of thermal energy and ejecting the liquid to form droplets based on the state change, and a part communicating with the orifice where the thermal energy acts on the liquid. A liquid jet recording method using a recording head comprising a liquid discharge section having a heat acting section and an electrothermal converter for generating the thermal energy, wherein the heat from the electrothermal converter generates the heat energy. The average value of the rate of change over time of the temperature of the heat action surface, which is the surface that acts on the liquid in the heat action part and comes into contact with the liquid, from the start temperature Ti to the maximum temperature Tp is 1 × 10 ⁶ °C. A liquid jet recording method characterized in that recording is performed by inputting a pulse wave having a voltage and a pulse width component of /sec or more.