JPS6250309B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an inkjet printer using a novel printing method.

PRIOR TECHNOLOGY In general, inkjet printers print dots by hitting recording paper with ink particles ejected from a print head. Conventionally, predetermined dots are printed according to an external command (digital image signal). For this reason, two methods are available: a charged deflection method in which ink particles that are constantly ejected from a head are charged and deflection controlled according to an external command, and an ink-on-demand method in which the head that ejects ink particles is directly controlled by an external command. It has been adopted.

Recently, there has been a demand for higher quality output images from this type of inkjet printer, and for this reason, the nozzle diameter of the head has been made minute and dot printing is possible with high pixel density. This has created a need to improve resolution. By the way, in conventional dot printing, the ink particle diameter is around 100μm, but in order to achieve high pixel density, the ink particle diameter should be at least 50μm.
It needs to be around m.

As the pixel density of output images in such inkjet printers increases, it is necessary to make the nozzle diameter of the head minute, which causes ink to clog in that area, resulting in missing dots or the inability to print. At the same time, the accuracy during processing has become extremely high, resulting in a problem of poor mass productivity. In addition, in conventional inkjet printers, whether using the charge deflection method or the ink-on-demand method described above, ink is fed into the ink chamber in the head at a constant pressure, and the head is activated by an electrostrictive vibrator. A method is adopted in which the ink is made into particles and ejected from the nozzle by shaking or by exciting a thin wire bundle provided in the nozzle portion in the ink chamber with an ultrasonic signal. For this reason, especially when attempting to create a so-called multi-inkjet printer in which a plurality of heads and their control systems are installed in parallel to print dots at the same time, manufacturing variations in the nozzle diameter or nozzle length for each head, The kinetic energy of the ink droplets ejected from each nozzle changes due to the pulsation of the pump that supplies ink to the ink droplets, variations in the operation of the electrostrictive vibrator or the thin wire bundle, etc., and the electric field or The drawback is that the air flow disturbs the flight trajectory, causing a shift in the printing position and distorting the output image.

Purpose The present invention was made in consideration of the above points, and
As the pixel density of output images increases, even if the diameter of the ink particles ejected from the head is made smaller, no ink clogging will occur, and the processing precision of the head can be easily increased. An object of the present invention is to provide an inkjet printer using a new printing method that can obtain high-quality output images without causing misalignment.

The inkjet printer according to the present invention provides a needle electrode between the orifices, uses surface tension to swell the ink in the ink chamber to the tip of the needle electrode, and applies a voltage of opposite polarity to the needle electrode to the electrode provided on the back side of the recording paper. By applying this, an electrical suction force is applied to the ink piled up at the tip of the needle electrode, thereby causing minute ink particles to fly and dot printing.

Configuration An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, in the inkjet printer according to the present invention, an orifice 2 is provided in the front face of an ink chamber 1, and a needle electrode 3 with a pointed tip is placed in the center of the orifice 2. It is composed of a head portion formed so as to protrude somewhat forward (see Fig. 2), and an electrode 5 provided on the back side of the recording paper 4 provided corresponding to the head portion. has been done. The orifice plate 6 on the front side of the ink chamber 1 is made of an oil-repellent material with low surface energy, such as tetrafluoroethylene or a copolymer of tetrafluoroethylene and hexafluoroethylene. The electrode 3 is made of a lipophilic substance with high surface energy, such as tungsten. Therefore, when liquid oil-based ink 7 is fed into the ink chamber 1 at an appropriate pressure (low pressure), the ink 7 bulges at the tip of the needle electrode 3 due to surface tension (portion a in the figure). At this time, the orifice plate 6 is not wetted with ink (section b in the figure), and the ink 7 in the orifice 2 is in the state shown in the figure. At this time, the ink 7 is maintained at a static pressure that does not leak out from the orifice 2 due to its surface tension. It goes without saying that only the orifice surface of the orifice plate 6 may be surface-treated to reduce surface energy.

In an inkjet printer configured in this way, for example, a positive voltage +V ₁ is applied to the needle electrode 3,
Furthermore, when a negative voltage -V ₂ is applied to each of the electrodes 5, a force due to dielectric polarization and a force due to induced charge are applied to the ink 7 at the tip of the needle electrode 3 (the combined force becomes an attractive force). The ink at the tip of the needle electrode 3 is turned into particles, which are pulled toward the electrode 5 and fly, thereby printing dots on the surface of the recording paper 4. Note that the suction force F acting on the ink 7 at the tip of the needle electrode 3 is determined by the dielectric constant of the ink 7, the electric field strength near that part, and the conductivity of the ink 7, as shown in the following equation. Ru.

F=α·grad(E) ² +qE where α is the polarizability of the ink 7, q is its electric charge, and E is the electric field strength.

Therefore, in the inkjet printer according to the present invention, ink particles are not ejected from the nozzle by mechanical vibration using an electrostrictive vibrator as in the past, but by ejecting the ink particles in the orifice 2 by electric suction force. The conductive ink at the tip of the needle electrode 3 is caused to fly in a predetermined direction with constant kinetic energy according to the electric field, which simplifies the structure of the head part and improves its processing accuracy. This means that the dots are not required to be very expensive, and dots can always be printed reliably at predetermined positions on the four sides of the recording paper. Furthermore, even when obtaining ink particles of the same diameter as when using a conventional micro-diameter nozzle, the orifice diameter can be made much larger than the nozzle diameter, which prevents ink from clogging in that area. Furthermore, the fear disappears.
In addition, in the ink jet link according to the present invention, by changing the sharpness of the tip of the needle electrode 3 or by changing the amount of protrusion of the tip of the needle electrode 3, the size of the ink droplet for dot printing can be controlled within a certain range. This means that it can be adjusted. Furthermore, since the distance between the head portion and the recording paper 4, that is, the flying distance of the ink particles, can be shortened, the influence of disturbances such as air currents can be almost ignored.

The liquid oil-based ink 7 used in the inkjet printer of the present invention is Isopar H mixed with a dye and a conductivity control material.

FIG. 3 shows another embodiment of the present invention, in which a slit-shaped orifice 2' is formed laterally in the front surface of the ink chamber, and a plurality of needle electrodes 31 to 31 are formed in the orifice 2'. 34 are arranged at a predetermined distance d from each other to create multiple heads.In this case, although not particularly shown, a plurality of the electrodes 5 are arranged on the back surface of the recording paper in correspondence with the multiple heads. or the electrode 5 needs to be formed into a bar shape.

The operation of the inkjet printer according to the present invention, which is multi-purpose as described above, is exactly the same as that described above, but considering the operating principle of printing dots using electric force, the processing of each part is different. Even if there is some error in the number of ink droplets, unlike conventional multiple nozzles, the flight trajectory of each ink droplet will not vary, and dot printing without deviation can be performed.

In addition, in the inkjet printer according to the present invention, if the resistivity of the ink used is too low, the electrical insulation between the needles will deteriorate, and recording will also occur in the surrounding non-printing area, resulting in a decrease in the resolution of the output image. However, the resistivity of the ink should be set to 10 ⁸ Ω・cm.
It has been experimentally confirmed that by doing the above, sufficient kinetic energy can be obtained during flight, and a high-quality output image that is unaffected by external disturbances can be obtained.

Effects As described above, in the inkjet printer according to the present invention, an orifice plate in which an oil-repellent orifice is formed is provided on the front surface of the ink chamber, and a needle formed of a lipophilic substance is installed in the orifice. The electrode is arranged so that its tip protrudes outward, and conductive liquid oil-based ink is raised on the tip of the needle electrode by surface tension, and the electrode is placed on the back side of the recording paper. By applying a voltage of opposite polarity to that of the needle electrode, the ink raised at the tip of the needle electrode is ejected by electrical suction force, and a dot is printed on the surface of the recording paper. It is simple and has excellent controllability, and when aiming to increase the pixel density of the output image, it is possible to print dots reliably without clogging the ink in the orifice even if the ink particle size is made minute. It has the advantage that it is possible to obtain a high-quality output image without any printing deviation, and it is extremely advantageous in terms of processing, especially when multi-printing.

[Brief explanation of the drawing]

FIG. 1 is a simplified configuration diagram showing one embodiment of an inkjet printer according to the present invention, FIG. 2 is a front view of the head portion of the same embodiment, and FIG. 3 is a head showing another embodiment of the present invention. FIG. 1... Ink chamber, 2, 2'... Orifice,
3, 31-34... Needle electrode, 4... Recording paper, 5...
...electrode, 6...orifice plate, 7...ink.

Claims (1)

[Scope of Claims] 1. An orifice plate with an oil-repellent orifice formed therein is provided on the front surface of the ink chamber, and a needle electrode formed of a lipophilic substance is placed inside the orifice with its tip facing outward. The tip of the needle electrode is arranged so as to protrude, and conductive liquid oil-based ink is raised on the tip of the needle electrode by surface tension. An inkjet printer configured to apply a voltage to cause ink raised at the tip of a needle electrode to be ejected by electrical suction force to print dots on a recording paper surface. 2. The description of item 1 above, characterized in that a slit-shaped orifice is formed in the front surface of the ink chamber, and a plurality of needle electrodes are arranged within the orifice at a predetermined interval to achieve multi-head design. Inkjet printer.