JPS6345308B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid jet recording method for recording by forming flying droplets, and particularly to a liquid jet recording method for forming flying droplets using thermal energy. 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 is an extremely powerful recording method that enables high-speed recording and does not require special processing such as fixing on so-called plain paper. Until now, various methods have been proposed and devices to realize them have been devised, and some have been improved and commercialized, while others are still being worked on to put them into practical use. be. Among them, for example, the liquid jet recording method described in Japanese Patent Application Laid-Open No. 54-51837 and German Publication of Publication (DOLS) No. 2843064 uses thermal energy to act on the liquid to generate the driving force for ejecting droplets. It has a different feature from other liquid jet recording methods in that it obtains the following information. In other words, the recording method disclosed in the above gazette is:
The liquid subjected to the action of thermal energy undergoes a state change accompanied by a sharp increase in volume, and due to the acting force based on this state change, droplets are ejected from the orifice at the tip of the recording head and fly to be recorded. It is characterized by being attached to a member and recording is performed. In particular, the liquid jet recording method disclosed in POLS2843064 is not only very effectively applicable to the so-called drop-on demand recording method, but also allows the recording head to be easily converted into a full line type high-density multi-orifice recording method. 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 characteristics, but in order to enable even more reliable recording, it is necessary to lower the peak temperature of the electrothermal converter and prevent its deterioration. There is a need. The above-mentioned liquid jet recording method records by ejecting liquid droplets flying from the orifice of the recording head due to the sudden change in state due to the generation of bubbles due to thermal action and their rapid volume increase and attenuation. However, at this time, if one pulse signal is applied to the pixel signal in an ON-OFF operation to the electrothermal converter, and bubbles are generated, grown, and reduced in the heat acting part, the electrothermal converter changes. The peak temperature of the heat-active surface becomes higher than necessary. This point will be explained with reference to FIG. When an electric signal P is input to the electric/thermal converter at time t ₀ during ON-OFF operation, the electric/thermal converter generates thermal energy according to the signal P. This thermal energy warms the liquid on the heat acting surface, which is the surface where the liquid and the electricity/thermal converter come into contact, until time t ₁ when the liquid reaches a temperature T _B at which the liquid vaporizes. time
From t ₁ , the liquid gains latent heat and begins to vaporize, forming bubbles in the liquid. The volume V of the bubble continues to expand as the liquid continues to receive heat. At this time, the signal P
At time _t2 when the power is turned off, the temperature of the heat-active surface reaches the maximum value _Tp , and then decreases in an attenuating manner. At this time, at temperatures above T _B , bubbles exist on the heat-active surface, creating a state close to adiabatic. Therefore, if more bubbles formed on the heat acting surface exist on the heat acting surface than necessary, the temperature of the heat acting surface increases more rapidly than necessary, giving rise to an excessive peak temperature. This excessive peak temperature
This not only accelerates the deterioration of the durable life of the heat converter, but also
This makes thermal decomposition of ink components, generation of insoluble products, etc. more likely to occur. This causes a decrease in the quality of the recorded image, and even causes recording to stop. Furthermore, thermal energy in an adiabatic state is difficult to convert efficiently into energy for forming droplets, leading to an increase in power consumption. The present invention has been developed in view of this point, and is a highly reliable method that can maintain stable and high-quality image recording at all times during continuous long-term recording compared to conventional methods. The purpose is to propose a liquid jet recording method. The liquid jet recording method of the present invention includes an orifice provided for ejecting liquid to form flying droplets, and a portion communicating with the orifice where thermal energy for ejecting the liquid acts on the liquid. In a liquid jet recording method using a recording head comprising a liquid discharge section having a certain heat acting section and an electric/thermal converter as a means for generating thermal energy, an input signal to the electric/thermal converter is used. One pixel signal is composed of a plurality of pulse signals, and one droplet is formed in response to input of one pixel signal. Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 1a is a partial front view of a liquid jet recording head to which the present invention is applied, seen from the side of one orifice, and FIG. FIG. The recording head 1 shown in the figure has a predetermined number of grooves of a predetermined width and depth at a predetermined linear density on the surface of a substrate 3 on which an electric/thermal converter 2 is provided. It has a structure in which an orifice 5 and a liquid discharge part 6 are formed by joining so as to be covered with an attached plate 4. 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 into the category of The liquid discharge part 6 has an orifice 5 at its terminal end for discharging droplets, and thermal energy generated by the electric/thermal converter 2 acts on the liquid to generate bubbles, causing the volume to expand and contract. It has a heat acting part 7 that causes a rapid state change. The heat acting part 7 is a heat generating part 8 of the electricity/thermal converter 2
The bottom surface thereof is a heat acting surface 9 which is located at the upper part of the heat generating section 8 and comes into contact with the liquid of the heat generating section 8. 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, However, it is not necessary to provide the heat generating resistor layer 11, and the heat generating resistor layer 11 may be designed as an electric/thermal converter having a structure in which the liquid comes into immediate contact with the surface of the heat generating resistor layer 11. The lower layer 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 present in the heat acting portion 7 and the generated air bubbles are rapidly cooled. In the liquid jet recording method of the present invention, in such a recording head, as shown in FIG.
This one pixel signal is input as a pulse waveform signal obtained by dividing the one pixel signal into a plurality of parts. here,
The first pulse is turned off within the time from the temperature T _B at which the liquid vaporizes to T _p , which is 20% higher than the temperature at which the liquid vaporizes, on the heat effect surface, and is left until the temperature of the heat effect surface cools to T _B. do. Again, the temperature on the heat-active surface is
When T _B is reached, the second pulse is turned on, and like the first pulse, it is turned off at the same time as T _p is reached. The third and subsequent pulses are the same as the second pulse, and the final pulse
One pixel signal is decomposed into a plurality of pulse signals and the recording head is driven in a time width such that the OFF time does not exceed the time _t7 when the gas finishes condensing. As a result, the peak temperature of the heat acting surface 9 of the electric/thermal converter 2 is lowered, and when the thermal energy above T _B is the same, the thermal energy to be supplied can be kept low. Therefore, the durability of the recording head is improved, and the recording head can be designed to save power. 4 to 6 show preferred waveform examples of a plurality of pulse signals constituting one pixel signal in the present invention. The waveform example shown in FIG. 4 is a case where one pixel signal is composed of pulse signals P ₁ , P ₂ , and P ₃ of different signal levels with equal pulse width and pulse interval.
In the figure, the second pulse signal P ₂ and the third pulse signal P ₃ have the same signal level, and the signal level of the first pulse signal P ₁ is one step higher than the signal level of these two signals. It's getting expensive. The waveform example shown in FIG. 5 is the second pulse signal
P ₂ has a pulse width of 4 compared to the first pulse signal P ₁ .
This is an example of a single pixel signal in which the signal level is approximately 1/3. FIG. 6 is a waveform example in which one pixel signal is composed of three pulse signals P ₁ , P ₂ , and P ₃ having different signal levels and pulse widths. The present invention will be specifically described below with reference to Examples. Example: _Two SiO layers (lower layer) were formed on a silicon substrate to a thickness of 3 μm by sputtering, then HfB ₂ was layered to a thickness of 1000 Å as a heat generating resistor 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.
After laminating a protective layer (upper layer) to a thickness of 0.5 μm to form an electrical/thermal converter on the substrate, a glass plate with grooves of 80 μm wide x 80 μm deep was placed so that the grooves and the heating resistor matched. It was joined to. 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. While supplying ink containing black dye and ethanol as main components to the recording head with a back pressure of 0.01 atm to the heating section, the first pulse was 10 μs at 40 V, the second pulse was 2 μs at 40 V, and the third pulse was
2μs, 40V, and the interval between the first pulse and the second pulse, and between the second pulse and the third pulse, was 3μs. When a continuous rectangular voltage printing signal was applied continuously for 24 hours to the electric/thermal converter 2 with 200 μs synchronization, the output was 40 V for 20 μs.
Compared to the case where a rectangular voltage pulse signal with a period of 200 μs was continuously applied for 24 hours, both the image quality and head life improved. Table 1 shows the results of image evaluation over time for 50 head samples prepared in the same manner as above under the above conditions. Furthermore, Table 2 shows the results of examining the state of disconnection over time in the 50 samples mentioned above. In addition, in the table, the criteria for image evaluation are: 〇...extremely high quality, △...quality that is sufficient for practical use, ×...
The quality is inappropriate for practical use. Further, the criteria for head life evaluation are: ○...50 sample break line rate 0%, △...50 sample break line rate within 5%, ×...50 sample break line rate within 10%. Here, if the voltage of the first pulse signal in the above embodiment is increased to 50V, the temperature increase rate on the heat acting surface increases and the time to reach T _B can be shortened. Therefore,
It becomes possible to shorten the width of the first pulse,
The responsiveness of head jetting can be further improved. Furthermore, when each pulse width is set to be the same as shown in FIG. 4, the same effect as described above can be expected by changing the applied voltage for each pulse signal. As explained above, in the liquid jet recording method in which flying droplets are formed by vaporizing liquid with a single pixel signal input to an electric/thermal converter, the gas condenses and turns into a liquid. It is divided into multiple pulse signals within the time until the end of the signal, and these multiple pulse signals are used as one pixel signal to generate electrical signals.
Forming flying droplets by inputting them to a heat converter has the effect of significantly increasing the durability of the recording head and reducing energy consumption. Furthermore, the quality of the image is also significantly improved during continuous ejection over a long period of time.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 shows the temporal changes in the surface temperature T of the heat-active surface of the electrothermal converter and the volume V of the bubbles formed when a one-pixel signal composed of one pulse signal is input to the recording head. Timing diagram shown in Figure 2a
2 is a partial front view from the orifice side of a preferred embodiment of the liquid jet recording head to which the present invention is applied, and FIG. A partial cross-sectional view, FIG. 3, is for explaining the present invention, and shows the surface temperature of the heat acting surface 9 of the electric/thermal converter 2 when a multi-pulse signal is input as a one-pixel signal to the recording head. Timing diagrams showing temporal changes in T and bubble volume V, and FIGS. 4 to 6 are diagrams showing configuration examples of one pixel signal in the present invention, respectively. DESCRIPTION OF SYMBOLS 1...Liquid jet recording head, 2...Electrical/thermal converter, 3...Substrate, 4...Grooved plate, 5...Orifice, 6
...Liquid discharge part, 7...Heat action part, 8...Heat generation part, 9...
Heat action surface, 10... Lower layer, 11... Heat generating resistance layer, 1
2... Upper layer, 13... Common electrode, 14... Selection electrode.

Claims (1)

[Claims] 1 An orifice provided for discharging liquid to form flying droplets, communicating with the orifice,
A liquid that uses a recording head that includes a liquid ejecting part that has a heat acting part that is a part where thermal energy acts on the liquid to eject the liquid, and an electric/thermal converter as a means for generating thermal energy. In the jet recording method, one pixel signal input to the electric/thermal converter is composed of a plurality of pulse signals, and one droplet is formed for each input pixel signal. Law.