JPH0551457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an inkjet printer capable of expressing gradation.

[Prior Art] The following methods have conventionally been proposed as methods for reproducing the gradation of printed images in inkjet printers.

First, there is a method in which gradation is expressed by varying the diameter of printed dots by varying the amount of liquid ejected from an ink jet. A second method is to configure one pixel as a matrix of, for example, 4×4 micropixels, and use a dither method on this matrix to express gradation. A third method is to express gradation by changing the amount of liquid ejected from the ink jet, but varying the amount that reaches the recording member.

However, in the first method, it is difficult to increase the range from the minimum dot diameter to the maximum dot diameter that can be printed, and only a few gradations can be reproduced. The second method ameliorates the shortcomings of the first method. With this method, for example, if one pixel is configured with a 4×4 matrix, it is possible to reproduce 17 gradations.
However, compared to the first method, the printing speed becomes 1/16 by increasing the number of pixels by 4 x 4 = 16 times, or the number of print heads must be increased by 16 times to increase the printing speed. Must be. However, doing so not only complicates the configuration of the print head, but also increases the scale of the electrical circuit for image processing using the dither method, resulting in a significant overall cost increase. The third method is
This is a method disclosed in USP 3416153 and USP 3673601, in which electrically charged droplets that are continuously ejected are reduced to small droplets by an electric field, and the droplets are sucked and collected unnecessarily for recording. However, this method has problems in that a large amount of liquid is collected and the structure per nozzle is complicated, making it difficult to obtain high-density arrays and high-resolution images.

〔the purpose〕

The purpose of the present invention is to provide an inkjet printer that eliminates the drawbacks of the above-mentioned conventional examples, and at the same time realizes the reproduction of gradation, which is essential for an image printer, with a simple configuration, and can obtain high-quality prints. There is.

The present invention provides an inkjet head having an ejection means that generates energy used to eject ink as droplets, and an inkjet head that selectively irradiates electromagnetic energy to the ejected droplets to impart thermal energy to the ejected droplets. a droplet forming means for selectively forming droplets into small droplets; and a droplet forming means for selectively forming droplets into small droplets; irradiated position control means for controlling the irradiated position to a predetermined position;
This is an inkjet printer characterized by comprising: Further, in an inkjet storage method in which ink is ejected as droplets to perform desired recording on a recording medium, the ejected droplets are selectively ejected in a flying region from a nozzle for ejecting the droplets to the recording medium. By irradiating electromagnetic energy and applying thermal energy, the droplets are made into small droplets and scattered at a predetermined solid angle, and a part of the scattered droplets is selectively transferred to the recording medium by a slit that is a droplet area regulating member. This is an inkjet recording method characterized by expressing gradation by adjusting the inkjet to the medium.

That is, by irradiating the ejected droplets with electromagnetic energy, such as laser light, the droplets are atomized and made into small droplets. Note that the term "small droplets" as used in the present invention includes fine droplets in the form of clogged mist droplets. The present invention is an inkjet printer that can easily realize recording with high resolution and gradation by using at least a portion of the droplets for recording. The driving force behind the droplet formation is thought to be due to the impact when the light energy absorbed by the ejected droplet is converted into heat and vaporizes a portion of the droplet.

Since the present invention uses electromagnetic wave energy such as laser light to form droplets into small droplets, it is easier to control the density recorded on the recording member compared to conventional methods that use electric charges to turn droplets into atomized droplets. The advantage is that it can be done. That is, the amount of small droplets arriving at the recording member can be controlled by irradiating a laser beam or the like at a position during the ejected droplet's flight from the nozzle to the recording member. Furthermore, the irradiation position of the laser beam can be easily set to any desired position.

Therefore, according to the present invention, there is provided an inkjet printer that not only allows for more precise control of shading, but also allows for excellent high-quality image recording without causing fogging on unnecessary portions of the recording member. provided.

〔Example〕

Preferred embodiments of the present invention will be described below with reference to the drawings.

Figures 1a and 1b are diagrams for explaining the first embodiment. In both figures, 1 is a nozzle, 2 is a droplet discharged from the nozzle, 3 is a laser beam, and 4 is a small Droplet 5 is a recording member.

1W He・Ne on droplet 2 discharged from nozzle 1
When the laser beam 3 was irradiated for 2 μs, the droplet 2 was separated into small droplets 4 as shown in FIG. 1b. In the first embodiment, an inkjet head using a cylindrical piezoelectric element was used. or,
The diameter of the ejected droplet 2 was 60 μm, and the flight speed before laser irradiation was 10 m/sec.

2a and 2b are diagrams for explaining the second embodiment, the left diagram shows the laser irradiation position, and the right diagram shows how to record on the recording member 5. ing. As shown in the left figure, a slit 6 is provided between the laser irradiation position and the recording member 5 in order to control the recording area of the reduced droplet.
The closer the laser irradiation position is to the slit 6, the more
It was possible to record higher density in Figure 2b than in Figure 2a. The highest concentration was obtained in the case shown in FIG.
This is the case when it reaches .

FIGS. 3a and 3b show which part of the ejected droplet 2 is effectively irradiated with the laser beam 3. FIG. In both figures, the left figure shows where on the droplet 2 the laser beam 3 is irradiated, in other words, at what position the light energy is absorbed, and the right figure shows the irradiation of the laser beam 3. This is a schematic representation of the velocity vector distribution of the subsequent scattered droplet 4.

Figure 3a shows a case where the light absorption coefficient of the ejected droplet 2 is relatively large (10 ³ to ¹⁰⁵ /cm), and Figure 3b shows a case where the light absorption coefficient of the ejected droplet 2 is compared to that in Fig. 3a. This is the case when the diameter is small (10 ² to 10 ³ /cm). In the case of FIG. 3a, it was somewhat difficult to control the gradation because the distribution of velocity vectors varied greatly depending on the irradiation position of the laser beam. In comparison, the velocity vector distribution was more isotropic in the case of FIG. 3b, and the gradation at the laser beam irradiation timing shown in FIG. 3b could be well reproduced.

Note that if the light absorption coefficient of the ejected droplet 2 is too large, the light will be absorbed on the surface of the droplet 2 where the laser beam is irradiated, and if it is too small, the laser light will pass through the droplet 2. light is not absorbed. Therefore, it is necessary to select appropriate values for the light absorption coefficient of the droplet 2 and the light absorption coefficient of the clogged recording medium.

FIG. 4 is a diagram for explaining the third embodiment, and shows an example of laser beam irradiation when droplets are ejected from the multi-nozzle 9. 10 is a slit for multi-nozzle. In the apparatus shown in FIG.
3 input aperture. The reflector 12 is inserted to bend the optical path in order to reduce the space of the apparatus, and can be removed if not required. The modulation deflector 13 includes an acousto-optic modulator such as glass or crystal that utilizes the known acousto-optic effect, or KDP or ADP that utilizes the electro-optic effect.
In particular, electro-optical elements such as the following are used. However, liquid and gas modulated deflectors are also available.

In the modulation deflector 13, the laser beam is modulated in intensity according to the input signal to the modulation deflector 13.

Also, if the laser oscillator is a semiconductor laser,
Alternatively, when using a gas laser etc. that can perform current modulation or an internal modulation type laser that is built into the oscillation optical path of a modulation element, the modulation deflector 13 only performs minute deflection and the laser beam is The beam is guided to a beam expander 14. The beam diameter of the laser beam from the modulation deflector 13 is expanded by a beam expander while remaining a parallel beam. Furthermore, the laser beam whose beam diameter has been expanded is incident on a galvanometer mirror 15, which is a deflector having a mirror surface. The galvano mirror 15 is driven by a galvano mirror drive section 16. The laser beam swept in the main scanning direction by the galvano mirror 15 is converged by the imaging lens 17, then changed direction by the mirror 18, and focused on a predetermined portion of the droplets 1' to 9' discharged from the multi-nozzle. Image. A in the figure,
B and C show the trajectory of the laser. A
Those irradiated with laser light on the line correspond to lower density recording than those irradiated with B and C. It is more preferable that the laser beam imaging lens 19 be installed near the ejected droplets as shown in FIG. In addition, the irradiation light beam is emitted from a semiconductor laser array or LED array 20 as shown in Figure 6.
A similar effect could be obtained by replacing .
The irradiation light does not need to be limited to near the visible range like a laser, and it is also possible to use heat generated by other electromagnetic energy.

As a means for ejecting droplets, any on-demand ejection form can be used. For example, in addition to using a piezoelectric element, a method using vapor bubbles generated by thermal energy is also possible. In the latter case, if thermal energy for ejection is supplied by a laser beam, it is possible to use the same laser for both ejection and miniaturization of ejected droplets.

Furthermore, it is of course possible to apply the present invention to a so-called continuous type inkjet system in which droplets are continuously ejected.

〔effect〕

As described in detail above, according to the present invention, by irradiating electromagnetic energy such as a laser beam, the ejected liquid droplets are made into small droplets and recorded on the recording member, thereby creating a natural transition from a dark area to a light area. It has become possible to express changes in concentration. Moreover, according to the present invention, a printer with excellent gradation reproduction can be obtained with a simple configuration.

[Brief explanation of the drawing]

FIG. 1a is a diagram schematically showing how a discharged droplet is irradiated with laser light, and FIG. 1b is a diagram schematically showing how the droplet is reduced to small droplets by laser light.
FIGS. 2a to 2c are conceptual diagrams showing how the print density differs depending on the laser irradiation timing. FIGS. 3a and 3b are diagrams schematically showing how the speed of a droplet that has been reduced to a small droplet differs depending on the part of the droplet that is irradiated with the laser. FIG. 4 is a diagram showing an example of arrangement when laser is irradiated to multiple nozzles. FIG. 5 is a diagram schematically showing a state in which a plate having a lens effect is installed near the ejected droplet. FIG. 6 is a diagram showing an example of arrangement when an LED array is used as a light source. DESCRIPTION OF SYMBOLS 1...Nozzle, 2...Droplet, 3...Laser beam, 4...Small droplet, 5...Recording member, 6...Slit, 7...Light absorption area of laser beam.

Claims (1)

[Scope of Claims] 1. An ink jet head having an ejection means that generates energy used to eject ink as droplets, and irradiating the ejected droplets with electromagnetic wave energy to selectively make them small droplets. a means for selectively reducing the droplets to small droplets by applying thermal energy; An inkjet printer comprising: an irradiation target position control means for controlling the irradiation target position to a predetermined position within the area. 2. The inkjet printer according to claim 1, wherein the ejecting means is an energy generating element that generates thermal energy as energy used for ejecting. 3. The inkjet printer according to claim 1, wherein the electromagnetic wave energy is used for both the droplet ejection means and the droplet formation means. 4. The inkjet printer according to claim 1, wherein the ejection means and the droplet forming means share the electromagnetic wave energy. 5. The inkjet printer according to claim 1, wherein the ejection means is a piezoelectric element. 6. The inkjet printer according to claim 1, wherein the inkjet printer is equipped with a slit, and the density is expressed depending on the distance between the slit and the irradiated position. 7. In an inkjet recording method in which ink is ejected as droplets to perform desired recording on a recording medium, the ejected droplets are selectively ejected in a flying region from a nozzle for ejecting the droplets to the recording medium. By irradiating electromagnetic wave energy and applying thermal energy, the droplets are made into small droplets and scattered at a predetermined solid angle, and a part of the scattered droplets is selectively placed on the recording medium by a slit that is a droplet area regulating member. An inkjet recording method characterized by expressing gradation by depositing droplets on an ink jet.