JPS6241112B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink droplet jetting method for recording an image by jetting thermofusible ink as ink droplets from a jetting nozzle.

The so-called inkjet recording method records images by jetting small ink droplets from a jetting nozzle.
It has the excellent advantage of being able to record images on plain paper or a recording medium of any shape.

However, the inks conventionally used for inkjet recording are those in which dyes are dissolved or pigments are dispersed in water or organic solvents, and volatile components in the ink evaporate from the nozzle ejection opening during recording stop. The problem was the clogging of the injection port, that is, the so-called nozzle hole clogging caused by the drying and solidification of the ink.

Furthermore, an inkjet recording system using a so-called multi-nozzle in which a plurality of jetting ports are arranged is considered to be promising as a method that enables high-speed recording. However, until now, nothing has been available that satisfies the demands for a simpler device configuration and higher recording pixel density.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for ejecting small ink droplets using multiple nozzles, which is the simplest method, enables high density recording pixels, and does not cause the problem of clogging of the ejection ports. That is, the simple method of the present invention is a method of controlling the ejection of ink droplets from individual ejection ports of a multi-nozzle, and ejecting ink droplets from the necessary ejection ports only when necessary for recording. In the case of a single nozzle, methods for controlling jetting have been put into practice, such as controlling the pressure excitation of the nozzle according to the pixel signal or controlling the electrostatic attraction force applied to the jet port, which is necessary for pixel recording. A method is adopted in which only small ink droplets are ejected. However, the method of ejecting by pressure excitation in a multi-nozzle requires a configuration in which a plurality of nozzles each having a piezoelectric element are arranged, and it is difficult to improve the nozzle arrangement density, that is, the recording pixel density. The result is an array that is expanded by the thickness of the wall. Furthermore, in the method of applying electrostatic voltage to each nozzle independently and injecting by electrostatic attraction, even if the multi-nozzle has a shape in which multiple nozzles are bored in a single injection container, the range of the electrostatic attraction There is a limit to how small it can be, and therefore the spacing between the injection ports cannot be narrowed below a certain level. Another method disclosed in Japanese Patent Application Laid-Open No. 54-59936, in which ink is ejected by applying thermal energy to the ink in the nozzle, has the same drawbacks as the piezoelectric element.

In addition, as a method that has been put into practical use in both single nozzle and multi-nozzle systems, only the ink droplets necessary for pixel formation are produced by continuously controlling the charging and electrostatic deflection of ink droplets from the ejection port. There is a method of selecting and recording on the recording medium. This method based on charging and electrostatic deflection is clearly more complex than the method aimed at by the present invention, which controls the ejection of ink droplets and ejects only the necessary ink droplets, and it is difficult to improve the recording pixel density. There are also limits.

The problem of nozzle clogging is an important drawback of the inkjet recording system, and many countermeasures have been attempted. The method of covering the nozzles with caps when recording is stopped is a method that can also be used in the case of multiple nozzles, but the structure of the mechanical parts becomes complicated and it is difficult to maintain sufficient airtightness.
Although there have been many more attempts, none have been made to date that can be applied to the ejection method of the present invention for controlling the ejection of ink droplets from multiple nozzles.

The present invention will be explained in detail below based on the drawings.
FIG. 1 shows the main parts of the configuration of an apparatus embodying the injection method of the present invention.

This main part is constructed as follows. That is, an injection container 1, a plurality of injection ports 2 arranged on one side wall of the injection container 1, and a thermal melt that can be melted at a temperature in the range of 40 to 170°C filled in the injection container 1. an ink heating means 4 capable of heating and melting the ink 3 to the above-mentioned temperature range; and an ink heating means 4 capable of cooling, solidifying, and heating melting the heat-melting ink 3 located at each of the injection ports 2. In addition, thermoelectric elements 5 and 6 for cooling and heating using the Bertier effect provided at the injection ports 2 and the entire injection container 1 are pressure-excited to simultaneously transfer the melted ink 3 from all the injection ports 2 into small inks. and an excitation element 8 which can be ejected periodically as drops 7. When the thermoelectric elements 5 and 6 are connected to the cathode and anode of a DC power source with an n-type thermoelectric element 5 and a p-type thermoelectric element 6, respectively, and are energized, heat is generated at the joint surface of both the thermoelectric elements 5 and 6, and this DC power source This is a known method that allows cooling by switching the polarity.

With the above configuration, during recording, the ink heating means 4 melts the heat-melting ink 3 in the jetting container 1 and each jetting port 2 into a liquid state, and the jetting container 1 is pressure-excited so that each jetting port 2 is heated. The ink droplets 7 can be periodically ejected in unison, and the thermoelectric elements 5, 6 are then actuated, for example, to cool some of the jet orifices 2 so that the liquid ink in the area of the jet orifices 2 is cooled. 3 can be solidified to close the injection port 2 and stop the injection, and if the injection port 2 is in another position, for example, the injection port 2 is already solidified and the injection port 2 is solidified.
can be activated to heat the ink occluding it, melting it and initiating the ejection of ink droplets 7. Therefore, the stop and start of injection is controlled by the thermoelectric element 5,
6, pixels 10 are printed on the recording medium 9.
can be recorded. Further, when recording is stopped, all of the above operations are stopped, so that the heat-melting ink 3 is naturally cooled to room temperature and becomes solid.

According to the above-described method of the present invention, the configuration of the recording apparatus is simplified because there is no need to provide a control means for charging and electrostatic deflection of ink droplets, and the configuration is not a configuration in which a large number of individual nozzles are arranged. Since it is possible to form a multi-nozzle with a plurality of injection ports 2 drilled in the side wall of the integral injection container 1, the arrangement density of the injection ports 2 can be increased to the manufacturing limit by microfabrication technology. can.

Furthermore, the present invention makes effective use of the fact that recording is performed using the heat-melting ink 3 in a liquid state, and that the ink 3 becomes a solid state when recording is stopped. Even if the ink 3 is left in a solid state for a long period of time, or even after repeated heating and liquefaction and cooling and solidification, the ink 3 remains
Therefore, the thermofusible ink 3 at the jet nozzle easily becomes a liquid state during recording, and the jet nozzle becomes an obstacle to ink droplet jetting, which is caused by drying and solidification of conventional liquid ink. The problem of occlusion does not occur during recording.

Next, the thermofusible ink 3 used in the present invention will be described.

The melting point of the thermofusible ink 3 is approximately 40 to 170
Preferably in the range of ℃. This temperature range ranges from a low temperature at which the ink does not liquefy at room temperature and does not stain your hands with body heat when handling recorded images, to a low temperature at which the ink is heated and melted in the inkjet recording device by heating parts inside the device. This corresponds to a high temperature range that does not cause damage. It is desirable to keep the power consumption for heating as low as possible, and considering the stability of recorded images, it is approximately 50 to 100 degrees Celsius.
More desirable are thermofusible inks having a melting point of .
The basic components of thermofusible ink are a colorant and a thermofusible medium, and in some cases, additives may be added to adjust the melting point, increase heat transfer efficiency, or add small particles of ink that adhere to the recording medium. Powders such as metal may be added to facilitate cooling of the droplets, additives to sharpen images, and the like. These are mixed under heating to obtain a melted or dispersed heat-melting ink.

As the colorant, known pigments and dyes are used. Examples include pigments such as carbon black, aniline black, lamp black, and channel black, and dyes such as methylene blue, methyl violet, and Victoria blue. Other pigments may also be used, or only one type of pigment may be used. Instead, it may be a mixture of several types of dyes. Examples of the heat-melting medium include waxes such as known carnauba wax, montan wax, mitsu wax, and paraffin wax, thermoplastic resins such as petroleum resins, acrylic resins, vinyl resins, and cellulose resins. Alternatively, fatty acids such as palmitic acid, oleic acid, and stearic acid, as well as fatty acid metal salts, etc. may be used, or a mixture of several types of these heat-melting media may be used.

The heat-melting ink described above may further have a dispersant added thereto, or may be heated and circulated in an inkjet recording device to be uniformly dispersed.

Examples of the present invention will be described below. 1st
In the figure, heat-melting ink 3 has a melting point of about 80° C. and is a mixture of 25% by weight carbon black and 75% carnauba wax, which are thoroughly mixed together in a heat-melted state. The ink heating means 4 was adjusted so that the ink 3 could be heated to about 100°C.

One side wall of the injection container 1 is made of an insulating substrate with a thickness of about 2 mm, and a plurality of injection ports 2 with a diameter of about 50 μm are bored on the side wall at an arrangement density of 4 holes/mm, and further injection ports 2 are formed.
An n-type thermoelectric element 5 and a p-type thermoelectric element 6 are provided in the section, and by switching the current direction, cooling or heat generation can be selectively performed at the junction of the thermoelectric elements 5 and 6 as necessary. . The temperature at the tip of the injection port 2 is approximately 100°C by the thermoelectric elements 5 and 6.
The molten ink is cooled to 60℃ and solidified.
Furthermore, it is constructed so that the ink that has solidified at 60°C can be heated again to 100°C to melt it. The excitation element 8 may be a piezoelectric element or an ultrasonic vibrator, and is configured to excite the injection container 1 under pressure. Sho 1
Reference numeral 1 denotes a tube for supplying heat-melting ink 3 to the injection container 1 . 12 is a lead for supplying current to the thermoelectric elements 5 and 6. With the above-described structure and the method of the present invention already described, the ink droplets 7 can be ejected from the necessary injection ports 2 only when necessary, and an image can be recorded on the recording medium 9 such as plain paper. can.

In a practical recording device, it is possible to control the switching of the current direction of the thermoelectric elements 5 and 6 according to the image signal, and therefore the ejection of the ink droplets 7 can be controlled independently for each injection port 2. be able to. The thermofusible ink 3 did not undergo compositional change or deterioration even after repeated heating and cooling, and even when recording was performed again after a long period of suspension, no clogging of the injection port 2 occurred in the molten state.

In the above embodiment, the arrangement interval of the injection ports 2 is 4 pieces/mm.
However, it is possible to improve the array density to the limit of microfabrication technology. Further, as shown in FIG. 2, an injection container 1' having a shape in which both side walls are concentrically curved is used, and the hole axis of each injection port 2' provided on the inner side wall of the injection container 1' is aligned with the side wall. Center line of concentric circles 13
If the configuration is such that the intersection points are arranged at equal intervals on the center line 13, when the injection container 1' is pressure-excited and ink droplets are ejected from each injection port 2', the intersection points are arranged on the center line 13. Recorded object 9' positioned at
Since pixels 10' of higher density are recorded on the surface of the recording medium, the method of the present invention becomes even more effective.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of an apparatus that embodies the injection method of the present invention, and FIG. 2 shows a part of another example of the configuration of the same apparatus. In the figure, 1 and 1' are containers for injection, 2 and 2' are a plurality of injection ports, 3 is a thermofusible ink, 4 is an ink heating means, 5 and 6 are thermoelectric elements, 7 is an ink droplet, and 8 is an excitation element, and 9 and 9' are recorded objects.

Claims (1)

[Claims] 1 A heat-melting ink that is solid at room temperature and melts at 40°C or higher is filled into an injection container equipped with a plurality of injection ports, and the ink is heated and melted to become a liquid. The ink is ejected as ink droplets all at once from a plurality of ejection ports of the ejection container by pressure excitation, and the liquid ink is cooled, solidified, and heated to melt at each of the ejection ports, thereby forming the ink droplets. 1. A method for ejecting ink droplets, characterized in that stopping and starting ejection is controlled independently for each orifice.