JPH06340073A - Ink jet head - Google Patents

Abstract

PURPOSE:To provide an ink jet head enabling high density printing in an ink on-demand type ink jet printer. CONSTITUTION:A center axis interval is provided between the pressure center of each of pressure chambers 1a and the center axis of each of nozzles 3a. In a large number of nozzles 3a laterally arranged on a nozzle plate 3 in one row, on the basis of the relation between the center axial interval and the liquid droplet shift quantity of the liquid droplets 5 emitted by 1.2mm in a printing direction from the nozzles 3a and the center axes of the nozzles 3a, the interval between the nozzles 3a in the vicinity of the center of the nozzle plate 3 is narrowed and the interval between the nozzles 3a on the outside of the nozzle plate is gradually widened so that the emitting directions of the liquid droplets 5 go toward one point (Z-point). By this constitution, as the position of paper to be printed is allowed to approach a certain one point, many liquid droplets can be allowed to reach the narrow range of the paper to enable high density printing.

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 for an ink on demand type ink jet printer, and more particularly to an ink jet head for realizing high density printing.

[0002]

2. Description of the Related Art An ink jet printer is a printer that prints by ejecting ink from an ink jet head and adhering it onto paper. FIG. 4 is a cross-sectional view near the nozzle of the inkjet head. In the pressure chamber 1a whose both walls are formed of a piezoelectric material, both walls are deformed by the electrostrictive effect, so that the pressure chamber 1a is pressurized.
Ink is ejected from the nozzle 6a. Such an ink jet head is generally called a piezoelectric ink jet head. In order to increase the volume change in the pressure chamber 1a and increase the ink ejection amount, the pressure chamber 1a is formed on the piezoelectric lower substrate 1 in the ink ejection direction. It has a long groove shape.
Conventionally, the ejection direction of each droplet 5 ejected from the nozzle 6a is made parallel to the pressure center of the pressure chamber 1a in order to improve the landing accuracy when the droplet 5 lands on the paper. For the above reason, the center of the pressure chamber 1a and the nozzle 6a
It was configured to match the center of the. Therefore, as a method of performing high-density printing, a method of narrowing the interval (p) between the nozzles 6a and between the pressure chambers 1a directly connected to the nozzles is generally used.

[0003]

However, there is a limit in processing technology in reducing the distance between the nozzles and the distance (p) between the pressure chambers directly connected to the nozzles. Further, there is a limit to narrowing the interval (p) between the pressure chambers also because the wall forming the pressure chambers needs to have a certain thickness in order to have rigidity. Since the distance between the droplets discharged in parallel from each nozzle is determined by the distance between the nozzles and the distance (p) between the pressure chambers directly connected to the nozzles, in the conventional inkjet head in which the center of pressure and the center of the nozzle are aligned, The limit of the interval (p) between the pressure chambers is the limit of the print density.

[0004]

In order to solve the above-mentioned problems, the ink jet head of the present invention provides a space between the center of pressure in the pressure chamber or the center axis of the flow path and the center axis of the nozzle. Depending on the relationship between the center axis of the pressure chamber or the center axis of the flow path and the center axis of the nozzle, the distance between the center axis of the nozzle and the center of the pressure in the pressure chamber is set so that the droplets discharged from the nozzle are discharged toward a certain point. It is set for each.

Further, the distance between the nozzles is made narrower than the distance between the pressure chambers or the distance between the flow passages (p), and the distance between the center axis of the nozzle and the pressure center of the pressure chamber or the center axis of the flow passage is The nozzle is narrow near the center of the nozzle plate and gradually widens toward the outer nozzle.

[0006]

[Function] With the center of pressure in the pressure chamber or the center axis of the flow path,
By providing a space between the central axis of the nozzle and the central axis of the flow passage and the central axis of the flow channel and the central axis of the nozzle by using the above means, the pressure in the pressure chamber can be adjusted. The ink ejected from the outer nozzle has a large distance between the center or the center axis of the flow path and the center axis of the nozzle. The ink is ejected at a large angle with respect to the center of the flow path, and the center of pressure in the pressure chamber or the center axis of the flow path The ink ejected from the inner nozzle having a narrow gap between the center axis of the nozzle and the central axis of the nozzle ejects at a small angle to the center of the flow path. Therefore, it becomes possible to eject the ejected droplet toward a certain point. By arranging the paper near a certain point and on the nozzle plate side, many droplets can be landed in a narrow area of the paper, and as a result, high-density printing is possible.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 7 is a diagram showing a printing mechanism of a general inkjet printer. The inkjet head 7 supported by the two head swing shafts 7a swings in the arrow direction along the head swing shafts 7a. A belt, a ball bearing or the like is generally used as the swinging method. In FIG. 7, those mechanisms for swinging the head are not shown. The ink stored in the ink tank 9 is supplied to the inkjet head 7 through the ink supply pipe 9a. The ink supplied to the inkjet head 7 is ejected according to the drive signal from the drive circuit 10. By matching this drive signal with the swing speed of the inkjet head 7, it is possible to print on the paper 8 as shown in FIG. In the case of such printing, by adjusting the drive cycle of the drive signal and the rocking speed of the inkjet head 7, it is possible to make the printing in the rocking direction as dense as possible, but in the rocking direction. It is very difficult to increase the density in the perpendicular direction.

In general, an ink jet head of an ink jet printer pressurizes a liquid chamber filled with ink and ejects the ink in the liquid chamber by utilizing the pressure change. A method utilizing deformation of a piezoelectric body to cause this pressure change is generally known. An example thereof will be described with reference to the drawings. FIG. 2 is an exploded perspective view of an inkjet head that ejects ink by utilizing the deformation of a piezoelectric body. Ink is supplied from the ink supply path 1b to the pressure chamber 1a formed of a piezoelectric material. The pressure chamber 1a is pressurized by the deformation of the piezoelectric body, and ink is ejected from the nozzle 6a.

FIG. 3 is a sectional view of the vicinity of the pressure chamber of the ink jet head. Pressure chambers 11 and 1 for ejecting ink
Reference numerals 2 and 13 are formed by the grooves formed in the piezoelectric lower substrate 1 and the flat upper substrate 2. Each pressure chamber 11, 12, 1
Independent drive electrodes 4a, 4b, and 4c are attached to the inner wall of the film 3 in a film shape. When ink is ejected from the pressure chamber 12, a voltage is applied to the drive electrode 4b attached to the inner wall of the pressure chamber 12, and the pressure chamber 11 and the pressure chamber 1 on both sides of the pressure chamber 12 are applied.
By grounding the drive electrode 4a and the drive electrode 4c attached to the inner wall of 3, the electric field is applied in the direction of the arrow shown in FIG. 3, and the pressure chamber wall 14 and the pressure chamber wall 15 are sheared as shown by the dotted line in the figure. Then, the volume in the pressure chamber 12 is reduced, and the reduced volume of ink is ejected as a suitable liquid through a nozzle provided corresponding to the pressure chamber 12 to perform printing. here,
The state of the wall after deformation indicated by the dotted line is exaggerated in order to clearly show the displacement of the wall.

FIG. 5 is an enlarged sectional view of the vicinity of the nozzle portion of the ink jet head showing the embodiment of the present invention. Nozzle 3
The shape of a is not particularly limited, but is preferably a perfect circle, and the more the shapes of the plurality of nozzles 3a are the same, the better the landing accuracy. Therefore, the nozzle of this example was formed by Ni electroforming, which can be formed with an accuracy of ± 1 μm or less, and in principle, the tapered shape inside the nozzle is always an R shape having the same dimension as the plate thickness. The hole shape is a round hole with a diameter of 40 μm. The present invention is also effective in that it is possible to use a nozzle formed by electroforming which is easy to process and can be processed with high precision. In FIG. 5 and FIG. 1 described later, the R shape inside the nozzle is neglected for the sake of simplicity.

The thicker the nozzle plate 3, the higher the flow resistance of the ink. Therefore, the ink ejection speed becomes slow. When the ejection speed is low, the landing accuracy is deteriorated because it is easily affected by a disturbance such as gravity. For this reason, it is desirable to make the thickness of the nozzle plate 3 as thin as possible for processing. Therefore, in this experiment, a nozzle having a thickness of 50 μm was used.

It is preferable that impurities (including ink) do not easily adhere to the surface of the nozzle plate 3. This is because the impurities may change the ink ejection direction to a direction different from the intended direction. Therefore, it is desirable that the surface of the nozzle plate 3 be water repellent. In this embodiment, the surface of the nozzle plate 3 is coated with Teflon so that the contact angle with respect to the ink is 70 degrees or more. Generally, it can be said that the larger the contact angle, the higher the water repellency.

The shape of the nozzle 3a, the thickness of the nozzle plate 3, and the coating on the surface of the nozzle plate 3 as described above further improve the landing accuracy. Therefore, according to the conditions of the above-described embodiment, the high density achieved by the present invention becomes more effective.

The distance between the center axis of the pressure chamber 1a (center of pressure) and the center axis of the nozzle 3a is defined as the center axis distance (s1) at a place where a sheet for landing ink from the ejection side surface of the nozzle 3a is placed. The distance between the droplet 5 and the central axis of the nozzle 3a is defined as the droplet deviation amount (s2). The distance from the ejection side surface of the nozzle 3a to the paper is preferably short in order to reduce the influence of factors such as gravity and wind force that deteriorate the landing accuracy. However, if this distance is too short, the risk of contact between the ejection side surface of the nozzle 3a and the sheet increases. For these reasons, the distance from the ejection side surface of the nozzle 3a to the paper is preferably about 1 to 2 mm. In this embodiment, this distance is 1.2
Although it was set to mm, it is not necessary to limit to this value as long as it is within the above range.

By pressurizing the ink in the pressure chamber 1a, pressure is propagated from the pressure chamber 1a to the nozzle 3a through the ink, and as a result, the ink droplet 5 is ejected from the nozzle 3a. Here, by adjusting the central axis interval (s1) which is the interval between the central axis of the pressure chamber 1a (center of pressure) and the central axis of the nozzle 3a, the pressure distribution in the nozzle 3a during ink ejection and Along with this, the velocity distribution changes, and the amount of droplet deviation (s2) in the ink ejection direction, here, changes. A certain relationship is established between the center axis interval (s1) and the liquid droplet displacement amount (s2). Therefore, the discharge direction of the droplet 5 can be controlled by accurately knowing the relationship between the center axis interval (s1) and the droplet displacement amount (s2).

In FIG. 6, the hole diameter of the nozzle 3a is 40 μm.
(Refer to FIG. 5), the groove width of the pressure chamber 1a is 140 μm (see FIG. 5), and the central axis interval (s1) and the droplet deviation when the droplet 5 is ejected 1.2 mm in the right angle direction from the ejection side surface of the nozzle 3a It is a graph showing the relationship between the central axis interval (s1) and the droplet displacement amount (s2) based on the experimental result of examining the relationship with the amount (s2). The circles are the experimental results. As the experimental conditions at this time, the ink used is a water-based ink containing a pigment,
The driving voltage was 40 V, and the ejection speed was 5 m / s. As a result, it was confirmed that s1≈s2 in the range where s1 was 30 μm or less. From this result, the central axis interval (s
It can be seen that the droplet deviation amount (s2) changes in proportion to the size of 1), and the ejection direction can be easily controlled. Although this result is the result when using the water-based ink, almost the same result was obtained when using pure water or ethanol.

When s1 = 30 μm, s2 = 30 μm
Therefore, as can be seen from FIG. 5, the deviation amount between the droplet 5 ejected 1.2 mm from the ejection side surface of the nozzle 3a and the central axis (pressure center) of the pressure chamber 1a is s1 + s2 = 60 μm. In the conventional general inkjet head, as shown in FIG. 4, since the trajectory of the droplet 5 is drawn on an extension line of the central axis (pressure center) of the pressure chamber 1a, the maximum ink amount of the ink is 60 μm, compared with the conventional inkjet head. It can be seen that it is possible to control the droplets. Further, according to the above experimental results, when the central axis interval at a certain nozzle is s1 = α, by setting the central axis interval s1 _n of the nozzles adjacent to the nozzle by s1 _n , The ink ejected from the nozzle can be concentrated at one point. However, β
Is an arbitrary numerical value. s1 _n = α + nβ (1) (n = ...- 2, -1, 0, 1, 2 ...)

FIG. 1 is a sectional view of the vicinity of a nozzle of an ink jet head according to the present invention. Six groove-shaped pressure chambers 1a are arranged parallel to each other in a direction perpendicular to the groove direction. One nozzle 3a is directly connected to each pressure chamber 1a. In the inkjet head of the present invention, the gap between the nozzles 3a is made narrower than the gap between the pressure chambers 1a, thereby providing a gap between the central axis of the pressure chambers 1a and the central axis of the nozzles 3a. In addition, a plurality of nozzles 3a arranged in a horizontal line on the nozzle plate 3 and a plurality of pressure chambers 1a arranged in a horizontal line.
Are attached symmetrically to each other, the positional relationship between the plurality of nozzles 3a arranged side by side on the nozzle plate 3 and the pressure chambers 1a corresponding to the plurality of nozzles 3a is as follows.
In a, the central axis interval (s1) is narrowed, and the outer nozzle 3a
The central axis interval (s1) can be gradually widened as At this time, the interval between the nozzles 3a is in accordance with the equation (1) based on the relational expression of the central axis interval (s1) and the droplet displacement amount (s2), and the ejection direction of the ink droplet 5 is one point ( It is aimed at the Z point).

For example, in FIG. 1, when the space between the pressure chambers 1a is 240 μm, the space between the nozzles 3a is 230.
.mu.m, and six nozzles 3a arranged in a horizontal line on the nozzle plate 3 and six pressure chambers 1a arranged in a horizontal line are laminated symmetrically to form two nozzles 3a near the center of the nozzle plate 3. The central axis interval (s1) from the corresponding pressure chamber 1a is s1 = 5 μm. The two nozzles 3a
It is possible to set s1 = 15 μm for the two nozzles 3a on both sides of s1 and set s1 = 25 μm for the two outermost nozzles 3a. This satisfies the relationship of Expression (1), and in this case, the droplet 5 is ejected toward the Z point and focused.

As described above, according to the present invention, a space is provided between the center of pressure in the pressure chamber or the center axis of the flow path and the center axis of the nozzle, and the center of pressure in the pressure chamber is set by using the above means. Alternatively, by adjusting the distance between the central axis of the flow path and the central axis of the nozzle, it is possible to eject the ejected droplet toward a certain point. By arranging the paper near that one point and on the nozzle plate side, many droplets can be landed in a narrow area of the paper, and as a result,
Enables high-density printing.

[Brief description of drawings]

FIG. 1 is a cross-sectional view near a nozzle of an inkjet head showing an embodiment of the present invention.

FIG. 2 is an exploded perspective view of an inkjet head.

FIG. 3 is a sectional view of the vicinity of a pressure chamber of the inkjet head.

FIG. 4 is a cross-sectional view near a nozzle of a conventional inkjet head.

FIG. 5 is an enlarged cross-sectional view of the vicinity of the nozzle of the inkjet head according to the present invention.

FIG. 6 is a graph showing the relationship between the central axis interval (s1) and the droplet displacement amount (s2) in FIG.

FIG. 7 is a diagram showing a printing mechanism of a general inkjet printer.

[Explanation of symbols]

 1 Piezoelectric Lower Substrate 1a Pressure Chamber 1b Ink Supply Path 2 Upper Substrate 3 Nozzle Plate 3a Nozzle 4a Drive Electrode 4b Drive Electrode 4c Drive Electrode 5 Droplet 6a Nozzle 7 Inkjet Head 7a Head Swing Axis 8 Paper 9 Ink Tank 9a Ink Supply Pipe 10 Drive circuit 11 Pressure chamber 12 Pressure chamber 13 Pressure chamber 14 Pressure chamber wall 15 Pressure chamber wall

Claims (4)

[Claims] 1. A plurality of pressure chambers arranged in parallel at equal intervals,
An inkjet head having a nozzle directly connected to a pressure chamber, wherein an interval is provided between a center of pressure in the pressure chamber and a central axis of the nozzle. 2. An ink jet head having a plurality of flow paths arranged in parallel at equal intervals and a nozzle directly connected to the flow path, wherein a space is provided between the center axis of the flow path and the center axis of the nozzle. Characteristic inkjet head. 3. The ink jet head according to claim 1, wherein the distance between the nozzles is narrower than the distance between the pressure chambers. 4. The ink jet head according to claim 2, wherein the distance between the nozzles is narrower than the distance between the flow paths.