JP3298442B2 - Inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head used for a printer, for example.

[0002]

2. Description of the Related Art An ink jet printer has been proposed in which halftone reproduction is performed by changing the diameter of ink dots flying from nozzles of an ink jet head in accordance with image information. For example, US Pat.
In the inkjet printer disclosed in Japanese Patent No. 208605, a large-diameter nozzle row and a small-diameter nozzle row are provided so that the diameters of ink dots ejected from each nozzle row are made different.

[0003]

However, in recent years,
There is an increasing demand for reproduction of images having high gradations such as photographic images, and as described in the related art, it is possible to obtain a sufficient gradation image simply by changing the size of the nozzle diameter. Could not. In particular, in the case of the above-mentioned conventional inkjet head, the larger the nozzle diameter, the worse the frequency response of ink droplet ejection becomes, and conversely, the smaller the nozzle diameter, the more easily clogging occurs, the more difficult the processing becomes, and the desired processing becomes. It tends to be difficult to obtain accuracy. For this reason, there is a problem that the variable width of the gradation cannot be made sufficiently large. The present invention has been made in view of the above problems, and has as its object to provide a novel ink jet head capable of performing high gradation expression.

[0004]

According to a first aspect of the present invention, a plurality of ink channels for containing ink, a plurality of ink ejection ports communicating with each ink channel, and a plurality of ink channels are provided. Pressurizing means for pressing ink in the ink to discharge ink droplets from the ink discharge ports, an ink supply chamber for supplying ink to each ink channel,
The said ink supply chamber and a plurality of ink inlets communicating with each ink channel, the plurality of ink inlets, Ri Do different magnitude of flow resistance to each other, the flow
And configured to include a plurality of ink inlets that cause ink droplets having different diameters by differences in the road resistance.

According to a second aspect of the present invention, the plurality of ink inlets include a plurality of ink inlets having different cross-sectional areas.

In a third aspect of the present invention, the plurality of ink inlets include a plurality of ink inlets having different lengths.

In a fourth aspect of the present invention, a plurality of ink channels respectively communicating with the plurality of ink inlets having different flow path resistances have different physical properties according to the flow path resistances. It was configured to accommodate.

In a fifth aspect of the present invention, the inks having different physical properties are colored in different colors.

[0009]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 to 3 show an ink jet head according to a first embodiment of the present invention. This ink jet head has a structure in which a channel plate 1, a partition 2, a piezoelectric plate 3, and a substrate 4 are integrally laminated. I have. The channel plate 1 includes a nozzle plate 5 and a channel wall 6. The nozzle plate 5 is made of a metal such as nickel or stainless steel, ceramic, or another hard material, and has a number of nozzles 12 for discharging the ink 11. The channel wall 6 is a nozzle plate 5
A plurality of ink channels 13 and a plurality of ink inlets 14 provided on one side of the
a, 14b and an ink supply chamber 15 for guiding the ink 11 to each ink channel 13 via the ink inlets 14a, 14b.

The partition 2 is a film formed of a metal such as nickel or stainless steel or another conductive material, and is fixed to the channel wall 6. The piezoelectric plate 3 is made of a well-known piezoelectric material, and is fixed on the substrate 4 with a conductive adhesive, for example, and is formed by a vertical groove 21 and a horizontal groove 22 formed by a method such as dicing. It is divided every thirteen. The portion of the piezoelectric plate 3 facing the ink channel 13 is a vibrating portion that is an actuator for pressing ink,
Other parts are non-vibrating parts. That is, the individual electrodes 23 are provided on the surface of the vibrating portion on the substrate 4 side of the piezoelectric plate 3, while the common electrode 24 is provided on the surface of the piezoelectric plate 3 on the partition 2 side.
Is provided. Further, a portion of the vibrating portion facing the ink channel 13 is activated in advance by applying a polarization treatment by applying an electric field in a vertical direction while heating, and the portion between the common electrode 24 and the individual electrode 23 is heated. By applying a voltage to the active portion, the active portion (see the symbol A in FIG. 1) is caused to vibrate. Due to this vibration, the ink 11 guided from the ink supply chamber 15 into the ink channel 13 via the ink inlet 14 is ejected from the nozzle 12.

In this embodiment, a plurality of nozzles 12
Are formed in two rows as shown in FIG. 1, and the corresponding vibrating portions of the ink channels 13 and the piezoelectric plates 3 are also formed in two rows. Further, two ink supply chambers 15 are provided corresponding to the respective nozzle rows. In FIG. 1, the portion including the upper nozzle row is a large-diameter ink drop ejection section 30 for ejecting large-diameter ink drops, and the portion including the lower nozzle row is used to eject small-diameter ink drops. And a small-diameter ink droplet ejection section 40 for performing the operation. The volume of the ink inlet 14a of the large-diameter ink droplet ejection unit 30 and the volume of the ink inlet 14b of the small-diameter ink droplet ejection unit 40 are different, and the volume of the ink inlet 14a is smaller than the volume of the ink inlet 14b. is there.
Specifically, each of the ink inlets 14a and 14b is formed in a rectangular shape, and has the same length and width, and the height h1 of the ink inlet 14a is smaller than the height h2 of the ink inlet 14b.

As an example, h1 = 25 μm, h2 =
35 μm, and each ink inlet 14a, 14
By making the width of b equal, the cross-sectional area of the ink inlet 14a is made smaller than the cross-sectional area of the ink inlet 14b. Further, the lengths of the ink inlets 14a and 14b are made equal. Here, the height of the ink inlet refers to a distance from the nozzle plate 5 to a member (here, a channel wall) facing the nozzle plate 5 in the ink inlets 14a and 14b. Further, the length of the ink inlet means the ink supply chamber 1 in each of the ink inlets 14a and 14b.
5 to the ink channel 13. further,
The width of the ink inlet 14 is defined as each ink inlet 1
4a and 14b, the distance between the opposing channel walls 6 is indicated.

Thus, the flow resistance of the ink inlet 14a of the large-diameter ink droplet discharge section 30 is made larger than the flow resistance of the ink inlet 14b of the small-diameter ink droplet discharge section 40. As a result, even if the size of the nozzle 12 is not different between the large-diameter ink droplet ejection unit 30 and the small-diameter ink droplet ejection unit 40, or the viscosity of the ink to be used is not varied.
The large-diameter ink droplet ejection unit 30 ejects a large-diameter ink droplet, and the small-diameter ink droplet ejection unit 40 ejects a small-diameter ink droplet. This phenomenon is caused by a return pressure generated when the ink is pressed by the vibrating portion of the piezoelectric plate 3 which is a pressurizing means in the ink inlet 14a having a large flow path resistance. 15, the amount of ink pushed back to the ink supply chamber 15 increases, and in the case of the ink inlet 14b having a small flow path resistance, the amount of ink pushed back to the ink supply chamber 15 increases.
This is considered to result in a difference in the amount of ink to be ejected. Thus, halftone reproduction can be performed by changing the ink dot diameter according to the image information. Also,
Since the internal pressure due to the weight of the ink in the ink supply chamber acts relatively large on the ink near the ink inlet, even if the cross-sectional area of the ink inlet is large, it is difficult for the frequency follow-up property to decrease, and the cross-sectional area of the ink inlet is small. Even in the case, it is hard to cause clogging.

FIGS. 4 and 5 show an ink jet head according to a second embodiment of the present invention. The ink jet head shown in FIGS.
Are substantially the same except that the flow path resistance of each ink inlet 14a, 14b is changed by changing the length instead of the height of the ink inlets 14a, 14b. And the description is omitted. As shown in the figure, when the length of the ink inlet 14a is L1 and the length of the ink inlet 14b is L2, for example, L1> L2 so that L1> L2.
= 0.5 mm, L2 = 0.1 mm, and the heights and widths of the ink inlets 14a, 14b are made equal. Thus, similarly to the above-described embodiment, the ink inlet 14
The flow path resistance a is larger than that of the ink inlet 14b.

FIG. 6 shows an ink jet head according to a third embodiment of the present invention. The ink jet head shown in FIGS. 1 to 3 has a width different from that of the ink inlets 14a and 14b in place of the height. Thus, except that the ink inlets 14a and 14b are formed with different flow path resistances, the other portions are substantially the same, and the corresponding portions are denoted by the same reference numerals and description thereof is omitted. As shown in the drawing, this ink jet head is formed such that W1 <W2, where W1 is the width of the flow portion in the upper row, and W2 is the width of the flow portion in the lower row. The heights and lengths of the ink inlets 14a, 14b are formed to be equal. Thus, similarly to the above-described embodiment, the flow resistance of the ink inlet 14a is larger than that of the ink inlet 14b.

It should be noted that the height, length or width of the ink inlets 14a and 14b is not limited to one of which is different, but the volume of the ink inlets 14a and 14b is different. As a matter of course, it goes without saying that an ink jet head having a plurality of different dimensions among them is also included. Further, the present invention is not limited to the embodiment in which the dimensions of the ink inlets are different for each row as in the above embodiments, but may be any inkjet head having a plurality of types of ink inlets having different volumes.

The shape of the ink inlet is not limited to the rectangular shape shown in each of the above embodiments, but can be arbitrarily changed. In short, what is necessary is just to include a plurality of ink inlets having different flow path resistances. Further, in the ink jet head having a plurality of types of ink inlets having different volumes, for example, in the ink jet head according to the above-described first embodiment, the diameter of the nozzle 12 is set to a state where clogging is difficult without sacrificing the frequency tracking ability. By maintaining the design within the range of the degree of freedom of the design, the gradation can be further improved. FIG. 7 shows the results of an experiment performed using the inkjet head according to the first embodiment described above. The nozzle diameter d was 35 μm.
Applied voltage (V) to the piezoelectric plate 3 in each case of h1 = 25 μm (○ mark) and h2 = 35 μm (● mark)
And the dot diameter (μm) of ink droplets printed on recording paper. Due to the difference in the flow path resistance, the same voltage is applied to each piezoelectric plate 3 to discharge ink droplets and the dot diameter when printing on recording paper is also different, and the flow path resistance is smaller than that in the case of h2 = 35 μm. Big h1
= 25 μm, the print dot diameter is larger.

FIG. 8 shows that, as described above, the volume of the flow section is changed and the nozzle diameter is also changed, so that the nozzle diameter d1 of the large-diameter ink drop discharge section 30 is changed to the small-diameter ink drop discharge section 4.
The experimental results when the nozzle diameter was larger than the nozzle diameter d2 of 0,
The voltage (V) applied to the piezoelectric plate 3 and the ink droplets printed on the recording paper when the nozzle diameter d1 = 35 μm, h1 = 25 μm (marked by 印), the nozzle diameter d2 = 25 μm, h2 = 35 μm (marked by ●) Is shown in relation to the dot diameter (μm). By making the nozzle diameter d1 in the case of h1 = 25 μm larger than the nozzle diameter d2 in the case of h2 = 35 μm, the difference between the two curves is more remarkable than in the case of FIG.

In each of the above-described embodiments, ink of the same color is used, while the same ink is used in each nozzle row, or inks having substantially the same physical properties such as surface tension and viscosity are used. However, the present invention is not limited to this, and a plurality of inks having different ink physical properties may be used. In this case, not only the size of the ink droplet is made different for each type of ink, but also the flow path resistance of the ink inlet is appropriately examined and adjusted so that the dot diameter of the ink droplet becomes equal for each ink. It is also possible to use it. Therefore, when a color image is formed using a plurality of color inks, the size of each color ink droplet varies due to the variation in physical properties between the inks caused by different colors of the inks. Can be suppressed. For each row where the flow path resistance is different, according to the viscosity of the ink,
Different colors of ink may be used.

[0020]

As is apparent from the above description, according to the present invention, a plurality of ink inlets communicating with an ink channel and an ink supply chamber have different flow path resistances.
Ink droplets of different diameters due to this difference in flow path resistance.
By to include a plurality of ink inlets allowed Ru time difference, is to provide a novel ink jet head capable good halftone reproducibility.

[Brief description of the drawings]

FIG. 1 is a front view showing a part of an inkjet head according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a front view showing a part of an inkjet head according to a second embodiment of the present invention.

FIG. 5 is a sectional view taken along line VV of FIG. 2;

FIG. 6 is a front view showing a part of an inkjet head according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between an applied voltage (V) to a piezoelectric plate and a dot diameter (μm) as a result of an ink droplet ejection experiment performed using the inkjet head shown in FIGS.

FIG. 8 shows a result of an ink droplet ejection experiment performed using an ink jet head having a different nozzle diameter for each nozzle row in addition to the configuration shown in FIG. (Μm).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Channel plate 2 Partition wall 3 Piezoelectric plate 4 Substrate 11 Ink 12 Nozzle 13 Ink channel 14a, 14b Ink inlet 15 Ink supply chamber

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/205 B41J 2/045 B41J 2/055

Claims (5)

(57) [Claims] A plurality of ink channels for accommodating ink, a plurality of ink ejection ports communicating with each ink channel, and an ink droplet ejecting ink droplets from the ink ejection ports by pressing ink in each ink channel. and pressure means, an ink supply chamber for supplying ink to each ink channel, and a plurality of ink inlets communicating with the respective ink channels and the ink supply chamber, the plurality of ink inlets, the flow path from each other the size of the resistor Ri is Do different, the flow path
Ink jet head, characterized in that it comprises a plurality of ink inlets that cause ink droplets having different diameters by differences in resistance. 2. The ink jet head according to claim 1, wherein the plurality of ink inlets include a plurality of ink inlets having different cross-sectional areas. 3. The ink inlet according to claim 1, wherein the plurality of ink inlets include a plurality of ink inlets having different lengths.
2. The inkjet head according to item 1. 4. The ink channel according to claim 1, wherein the plurality of ink channels communicate with the plurality of ink inlets having different flow path resistances, respectively, containing ink having different physical properties according to the flow path resistance. Or three
An inkjet head according to any of the above. 5. The ink jet head according to claim 4, wherein the inks having different physical properties are colored in different colors.