JPH0474187B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses thermal energy to eject a liquid containing a recording agent from an ejection port (orifice),
The present invention relates to an on-demand inkjet recording method for recording, and particularly to an inkjet recording method that can significantly extend the service life of a recording head. 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 can record without the need for 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, and if they have been improved and commercialized, efforts are still being made 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 Opening of Publication (DOLS) No. 2843064 applies thermal energy, which is droplet formation energy, to the liquid. It has a different feature from other liquid jet recording methods in that it obtains the motive force for ejecting droplets. 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 this state change causes the recording head portion to Droplets are ejected from the 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 realized by making the recording head part a full line type with high density multi-orifices. Therefore, it has the advantage of being able to obtain high-resolution, high-quality images at high speed. In this way, the liquid jet recording method described above has various advantages, but it is useful when recording high-resolution, high-quality images at higher speeds for longer periods of time, or when dramatically improving the usable life of the device. Therefore, it is necessary to improve the repeated use life (durable life) of the recording head. The factors that determine the service life of the recording head applied to the above recording method include the life of the electric/thermal converter included, as well as the deposition of solid matter on the surface of the converter. . That is, the recording head applied to the above recording method has a structure as shown in FIG. 1, for example. In the figure, the electric/thermal converter 102 is in contact with the liquid introduced from arrow A through a heat action surface 109 as an energy action surface in a heat action section 107 that is a droplet formation energy action section. Such a configuration is adopted for the purpose of causing the generated thermal energy as droplet formation energy to act effectively and efficiently on the liquid in the heat acting section 107. For this reason, although it depends on the recording liquid used, when using a recording liquid that uses ordinary water as a liquid medium, it is necessary to prevent electrical leakage between the electrodes 113 and 114 through the recording liquid. and heating resistance layer 11
1 from the recording liquid or from thermal oxidation, an upper layer 112 is formed on the heat generating resistor layer 111 in the heat generating section 108 during head fabrication. The principle of droplet formation in the recording method using such a recording head is that, as described above, when electricity is turned on to the electric/thermal converter, thermal energy, which is droplet formation energy, is applied. The recording liquid in the heat acting part 107 undergoes a state change accompanied by a rapid increase in volume, that is, the recording liquid in the heat acting part 107 reaches a vaporized state within a very instant of approximately μsec. At step 107, bubbles are generated and grow instantaneously, and the recording liquid present between the heat acting portion 107 and the orifice 105 is ejected as droplets. Since the recording liquid is exposed to high temperatures during the repeated generation and disappearance of bubbles, it is expected that the thermally unstable recording liquid will undergo chemical changes. In fact, if the generation and disappearance of bubbles continues for a long time,
As a result, insoluble matter is generated and deposited in the vicinity of the surface of the heat acting section 107, and the efficiency of heat transfer from the heat acting surface 109 to the recording liquid decreases significantly, resulting in the formation of bubbles of sufficient size. does not occur,
This has been experienced and observed in many experiments resulting in head failure. In particular, the present invention is directed to an on-demand inkjet in which the recording liquid is ejected by applying thermal energy to the recording liquid from the heat acting surface of an electrothermal converter that is provided in direct contact with the recording liquid. This was done in order to solve the above-mentioned problem specific to recording methods, such as the head ejection failure due to a decrease in the efficiency of heat transfer from the heat-active surface to the recording liquid, and is described in the above-mentioned publication. It is possible to significantly extend the service life of the recording head applied to the recording method, and also to significantly reduce the failure rate of the head.
The object of the present invention is to provide an on-demand inkjet recording method that can improve its reliability. The on-demand inkjet recording method of the present invention that achieves the above object comprises a recording agent and an aqueous liquid medium, and includes a recording liquid containing CI Food Black 2 as the recording agent, and a flow rate of the recording liquid. Applying thermal energy to a part of the path from a heat-active surface of an electrothermal converter provided in direct contact with the recording liquid to form a droplet, and perform recording using this droplet. It is characterized by: The above-mentioned recording agent used in the present invention is particularly suitable for heating at 250°C
Azo bond (-N=
Even upon cleavage of N-), the decomposition product has sufficient solubility in the liquid medium. Therefore, even when bubbles are repeatedly generated and extinguished over a long period of time, no insoluble matter is generated or deposited on the surface of the heat-acting part, and the head does not become incapable of discharging. Or, the dye as a recording agent used in the present invention is
The solubility in a fluid medium is sufficiently satisfactory, and the solubility in water is particularly excellent, so that it can be used very effectively when forming an aqueous recording liquid. In addition, the recording liquid used in the present invention is prepared by adding appropriate solvents such as water and organic solvents, as well as additives such as surface tension modifiers and viscosity modifiers as necessary, in addition to the dye that is the recording agent. By doing so, a liquid composition called so-called ink is obtained. If you use this recording liquid to record with a recording head like the one shown in Figure 1, the usable life of the recording head will be longer than in the case of using a conventional recording liquid, as shown in the following example. can be dramatically improved. The content of CI and food black 2 in the recording liquid used in the present invention is determined depending on the type of liquid medium components, the characteristics required of the recording liquid, etc., but in general, the content of CI and food black 2 is determined based on the total weight of the recording liquid. in weight percent
The range is 0.5 to 20%, preferably 0.5 to 15%, more preferably 1 to 10%. The recording liquid used in the present invention has water as a main liquid medium component, and not only water alone but also preferably a mixture of water and various water-soluble organic solvents is used. Examples of water-soluble organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol.
~4 Alkyl alcohols: Amides such as dimethylformamide and dimethylacetamide: Ketones or ketone alcohols such as acetone and diacetone alcohol: Ethers such as tetrahydrofuran and dioxane: Polyethylene glycol,
Polyalkylene glycols such as polypropylene glycol: Polyalkylene glycols with 2 to 6 alkylene groups such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, etc. Alkylene glycols containing carbon atoms: Glycerin: ethylene glycol methyl ether, diethylene glycol methyl (or ethyl) ether,
Examples include lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether. Among these many water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are preferred. The content of the water-soluble organic solvent in the recording liquid is generally 5 to 5% by weight based on the total amount of the recording liquid.
95%, preferably 10-80%, more preferably 20-80%
It is said to be in the range of 50%. The water content at this time depends on the type of solvent component mentioned above,
Although it is determined within a wide range depending on the composition and desired properties of the recording liquid, it is generally 10 to 90%, preferably 10 to 70%, more preferably 20 to 70% of the total weight of the recording liquid. considered to be within the range. The recording liquid used in the present invention prepared from such components has its own recording properties (signal response, stability of droplet formation, ejection stability, long-term continuous recording, long-term recording cessation, etc.). It is well-balanced and has excellent storage stability (ejection stability), fixing ability to recording materials such as paper, etc. In order to further improve such properties, various conventionally known additives may be further added. Examples include various surfactants, surface tension regulators such as diethanolamine and triethanolamine, and pH regulators using buffer solutions. The present invention will be specifically described below with reference to Examples. Example 1 _Two SiO layers (lower layer) were formed on an alumina substrate to a thickness of 5 μm by sputtering, then HfB ₂ was deposited to a thickness of 1000 Å as a heating resistance layer, and aluminum was deposited to a thickness of 3000 Å as an electrode, followed by selective etching. Thus, a heating resistor pattern of 50 μm×200 μm was formed. Next, _two layers of SiO are added by sputtering.
After laminating a protective layer (upper layer) to a thickness of 3500 Å to form an electrical/thermal converter on the substrate, a glass plate with grooves of 50 μm wide x 50 μm deep was cut so that the grooves matched the heating resistor. Joined. Subsequently, the end face of the orifice was polished so that the distance between the tip of the heating resistor and the orifice was 250 μm, thereby creating a recording head.
Using this recording head, ink having the liquid composition shown below was ejected. CI Food Black 2 3 parts by weight Diethylene glycol 25 〃 N-Methyl-2-pyrrolidone 20 〃 Water 52 〃 In this case, when the recording head was driven for 10 μsec and a 40 V rectangular voltage pulse print signal was applied at a cycle of 200 μsec, it took 140 hours. It had a long enough lifespan to withstand continuous printing. Example 2 Similar results to Example 1 were obtained when triethanolamine was used instead of N-methyl-2-pyrrolidone in the ink composition used in Example 1. Example 3 Similar results to Example 1 were obtained when ethylene glycol was used in place of diethylene glycol in the ink composition used in Example 1. (Comparative Example) Comparative Experiment Example 1 Of the ink compositions used in Example 1,
Recording was performed in the same manner as in Example 1 using Sulfur Black 1, Direct Black 163, Acid Black 186, Direct Black 19, Direct Black 38, and Direct Blue 1 instead of CI Food Black 2. The printing life was short.

【table】

[Table] Comparative Experimental Example 2 The following evaluation was performed regarding the inability of the head to eject, which is caused by the formation and deposition of insoluble matter near the surface of the heat-acting part in the recording head. (Evaluation method) Using the same recording head as in Example 1 and under the same driving conditions, continuous ejection was performed using the seven types of inks described in Example 1 and Comparative Example 1. Ink ejection start point (initial), 1 hour later, 5 hours later, and
At each point after 10 hours, the above ink was replaced with a transparent ink (composition: 25 parts of diethylene glycol, 20 parts of N-methyl-2-pyrrolidone, 25 parts of water), and the heating resistor (heat acting part) in the recording head was replaced. The foaming length in the longitudinal direction during the above drive is determined by using a strobe.
It was determined by directly measuring the image on a monitor through a microscope, synchronized with a cycle of 200 μsec. (Results) The measurement results of foaming length are shown in the table below.

[Table] As is clear from the above table, in the ink using Food Black 2 as the dye, no decrease in foaming length was observed at all, and stable ejection was possible from beginning to end. In addition, in the comparative ink using other dyes, deposits were observed to be formed on the heating resistor (heat acting part) in the recording head.

[Brief explanation of the drawing]

FIG. 1a is a front partial view of a liquid jet recording head applied to the present invention from the orifice side;
FIG. 1B is a partial cross-sectional view of FIG. 1A taken along the dashed line XY.

Claims (1)

[Claims] 1. A recording liquid comprising a recording agent and an aqueous liquid medium, and containing CI Food Black 2 as the recording agent, is provided in a part of the flow path of the recording liquid so as to be in direct contact with the recording liquid. 1. An on-demand inkjet recording method characterized in that droplets are formed by applying thermal energy from the heat-active surface of an electrothermal converter, and recording is performed using these droplets.