JPH04353459A - Ink jet printing head - Google Patents

Abstract

PURPOSE:To provide inexpensive head constitution highly integrating the printing dot density of an ink jet printing head having ink orifices formed in a multinozzle system at the pitch of the ink jet orifices or more. CONSTITUTION:A nozzle plate 11 has a recessed curved surface on the side opposed to printing paper 15. Since ink jet orifices 12 are formed on the curved surface, the opening timings of ink droplets from the side surfaces of the nozzle plate 11 at the time of the injection of ink are shifted with respect to an ink jet direction 18. Therefore, the ink droplets injected from the ink jet orifices 12 have different flight directions and the pitch of the impact points 16 on the surface of the paper 15 becomes P1 and P0>P1 is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ink jet printers, and more specifically to the structure of ink jet holes in an ink jet printer head.

0002

2. Description of the Related Art Conventionally, inkjet printers have been developed and commercialized as non-impact printers, along with laser printers and the like, in response to demands for lower noise and higher quality printing for printers. In drop-on-demand type inkjet printer heads, heads that use electromechanical transducers or electrothermal transducers as energy generators for ejecting ink droplets have been proposed. There is a strong demand for these heads to be smaller and more highly integrated, and multi-nozzle design is progressing. Conventionally, as a method for achieving miniaturization and high integration, microfabrication techniques and photoforming methods have been used to miniaturize and increase integration of ink ejection holes, ink channels, and ink chambers.

0003

[Problems to be Solved by the Invention] However, conventional miniaturization and high integration have the following problems. The first is the limit of miniaturization and high integration due to the materials used in the head construction including the energy generator. For example, when a piezoelectric material or a heat-generating material is used as an energy generator, in order to efficiently obtain the energy necessary for ejecting ink droplets by converting electrical energy, the minimum area and volume of the energy generator are required. There is easy miniaturization,
High integration is not possible.

The second problem is the increase in manufacturing costs due to miniaturization and high integration. Recent technological developments in microfabrication technology and photoforming technology have been remarkable.
By applying the technology to inkjet printer heads,
It has become possible to manufacture heads with a printing dot density of about 150 to 300 dpi. However, the miniaturization of the head
High integration inevitably leads to lower yields and higher costs. On the other hand, there is a strong demand for lower prices for inkjet printer heads, and there is a desire for the development of new head manufacturing methods and the design of head structures with new configurations.

The present invention has been made to solve the above-mentioned problems, and consists of ink ejection holes having two or more different shapes, and at least one of the different shapes being an asymmetric shape. The purpose of the present invention is to provide an inkjet printer head that is low in price and has excellent integration of printing dot density.

[0006]

Means for Solving the Problems To achieve this object, the inkjet printer head of the present invention is an inkjet printer head equipped with an array having a plurality of ink jetting holes, in which the ink jetting holes are of two or more types. and at least one of the ink ejection holes of the different shapes has an asymmetric shape such that the velocity distribution in the ink droplet ejection direction at the outlet of the ink ejection hole is an asymmetric distribution. The printing dot pitch is made to be more integrated than the pitch of the ink ejection holes by forming the ink jet holes.

[0007]

[Operation] In the inkjet printer head of the present invention having the above means, an electric signal is sent to the head recording section in response to an input signal for printing, thereby causing a change in the inkjet groove volume. Ink droplets are ejected as the groove volume changes. Ink droplets ejected through the ink ejection holes have an asymmetric velocity distribution in the ink droplet ejection direction at the exit of the ink ejection hole during ink ejection, and the flying direction changes. Therefore, by controlling the shape of the ink ejection holes, it is possible to control the flying direction of the ink and achieve a printing dot pitch that is higher than the integration pitch of the ink ejection holes.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to the drawings. First, the structure and principle of the ink ejection holes will be explained. FIG. 1 shows an example of the configuration of an ink ejection hole and a schematic cross-sectional view in the flying direction of ink droplets. A nozzle plate 11 in which ink ejection holes 12 are formed at a pitch P0 in a positional relationship corresponding to the ink flow paths 13 in a member in which grooves acting as ink flow paths (pressure chambers) 13 are formed at a pitch P0. are bonded together via an adhesive layer 14. The nozzle plate 11 has a concave curved surface on the side facing the printing paper 15. Each ink injection hole 1
2 is formed on a curved surface, so that the timing of release of ink droplets from the side surface during ink ejection is shifted with respect to the ink ejection direction 18. Therefore, as shown in the figure, the ink droplets ejected from each ink ejection hole 12 have different flight directions, and the pitch of the landing points 16 on the surface of the paper 15 is P1, and P0>P1.

Next, FIG. 2 shows another example of the structure of the ink ejection hole and a schematic cross-sectional view in the direction of ink droplet flight. This is an ink flow path (pressure chamber) 13 formed with a pitch P0.
This is an example of a configuration in which the grooves that act as ink jet holes 12 function as they are. Therefore, the groove formed in the nozzle plate 11 shown in FIG. 1 serves as an ink flow path (pressure chamber).
It will operate as an ink ejection hole. The nozzle plate 11 has a concave curved surface on the side facing the printing paper 15, as in the example of FIG. Since each ink ejection hole 12 is formed on a curved surface, the timing of release of ink droplets from the side surface during ink ejection is shifted with respect to the ink ejection direction 18. In other words, as shown in the figure, the ink droplets ejected from each ink ejection hole 12 have different flight directions, and the pitch of the impact points 16 on the paper 15 is P1, P0
>P1.

FIG. 3 shows an example of the structure of a nozzle plate 11 having four different shapes of ink ejection holes. Ink injection holes 21a, 21b, 22a, 22b, 23a, 23b, 2
4a and 24b are each a set of four different shapes, and the ink jet holes 21a and 21b, 22a and 22b, and 23a and 23b
, 24a and 24b have the same shape of the recessed part of the injection hole, but the directions are opposite.

FIG. 4 shows another example of the structure of the nozzle plate 11 having four different shapes of ink ejection holes. Ink injection holes 31a, 31b, 32a, 32b, 33a, 33b
, 34a and 34b are each a set of four different shapes, and the ink ejection holes 31a and 31b, 32a and 32b, 33a and 3
3b, 34a, and 34b have the same shape of the convex part of the injection hole, but the directions are opposite.

FIG. 5 shows an example of the structure of the nozzle plate 11 provided with ink ejection holes of two different shapes. The ink jet holes 41 and 42 each have two different shapes, and the ink jet holes 41 have a circular cross-sectional shape, and the ink jet holes 42 have the same convex shape and are all directed downward.

Next, the principle and operation of the flight of ink droplets will be briefly explained.

FIGS. 6(a) to 6(c) are cross-sectional views of the ink injection holes 12 in FIG. 1, the ink injection holes 32 in FIG. An outline of the velocity distribution during injection is shown. In the case of the ink ejection holes 52, the ejection holes have a circular shape and are symmetrical with respect to the central axis AB. Therefore, the velocity distribution is also symmetrical with respect to the central axis AB, and the ink droplets fly straight in the jetting direction. In the case of the ink ejection hole 12, the ejection hole has a circular cross section, but the lengths are different on both sides of the central axis AB with respect to the ink droplet ejection direction. Therefore, when considering the velocity distribution along C-D in the longitudinal cross-sectional view, it becomes asymmetrical with respect to the central axis A-B. This is because the timing at which the ejected ink droplets are released from the sides of the ejection hole on the left and right sides with respect to the central axis A-B is shifted.

In the longitudinal cross-sectional view CD, the left side with respect to the central axis A-B is still restricted by the side surface of the injection hole, but the right side is free from restriction. In other words, the flying direction of the ink droplets is bent to the right. In the case of the ink ejection hole 32, the cross-sectional shape of the ejection hole is asymmetrical and has a convex portion on the left side of the central axis AB. Therefore, the velocity distribution of the ejected ink droplets at the exit of the ejection hole becomes asymmetrical with respect to the central axis AB. At this time, the speed of the ink droplet is smaller on the left side with respect to the central axis A-B, and larger on the right side. When such a velocity distribution occurs, the force acting on the ink droplet is large on the left side and small on the right side. Therefore, the ink droplet flies to the right. The direction of flight is almost determined at the moment the ink droplet is ejected from the ejection hole (until the ink droplet becomes spherical due to surface tension). Based on the asymmetry of the velocity distribution as described above, in the embodiment shown in FIG. 3, ink droplets ejected from each ink ejection hole formed at a pitch P0 fly so as to converge to the center, and the printing dot pitch P1 on the paper surface is P0>P1. Similarly, in the embodiment of FIG. 4, P0>P1, and high integration of the printing dot pitch is achieved. In the case of the embodiment of FIG.
The landing points on the paper surface of the ink droplets ejected from two sets of ink ejection holes that are vertically offset by 2 can be aligned in a straight line.

Next, FIG. 7 shows a schematic diagram of the configuration of a recording section to which an inkjet printer head using an electrothermal conversion element as an energy generator is applied. A heating element 62 divided into parts and an electrode (not shown) for supplying electricity to the heating element 62 are patterned and formed on the surface of the silicon substrate 61. A cover plate 63 in which fine grooves 64 are formed corresponding to the positional relationship between the substrate 61 and the split heating element 62 is adhered. The front surface of this joined body is curved. The space formed by the groove 64 and the substrate 61 functions as an ink flow path and also as a pressure chamber. Further, the front surface of the ink ejection hole is a curved surface, and acts as an ejection hole when ink is ejected when bubbles are generated by energizing the heating element.

Next, the operation will be described. When an electrode voltage is applied in response to an input signal, the heating element 62 generates heat, bubbles are generated, and ink droplets fly. At this time, since the front surface of the ink ejection hole is a curved surface, an asymmetrical distribution of the ink ejection speed occurs, and the flying direction of the ink droplets changes. Therefore, a print dot density that is higher than the groove (ink ejection hole) pitch can be achieved.

FIG. 8 shows a schematic diagram of a recording section of an inkjet printer head using an electromechanical transducer as an energy generator. Fine grooves 72 are formed in a piezoelectric ceramic plate polarized in the thickness direction using a diamond cutter blade. A nickel drive electrode 74 and a nickel drive electrode 72 are formed on both sides of the groove 72 by sputtering.
A lead-out electrode (not shown) is formed for applying a voltage to. This piezoelectric element 71 and a cover plate 75 having an ink supply port 76 are bonded together via an adhesive layer. The ink ejection holes 77 are configured with ejection holes having an asymmetric cross-sectional shape. Further, a nozzle plate 79 is adhered to the front surface of the joined body.

Next, the operation will be described. When a voltage is applied to the drive electrode 74 in response to an input signal, the piezoelectric ceramic wall 73 undergoes shear deformation in the lateral direction without any dimensional change in the height direction because the polarization direction and the electric field application direction are perpendicular to each other. . At this time, the space formed by the groove 72 and the cover plate 75 changes its volume and acts as an ink flow path and a pressure chamber, causing ink droplets to be ejected. Ink droplets are ejected through a nozzle plate 79 provided on the front.
The ink is ejected from the ink ejection hole 77 of. The ink ejection holes 77 are formed of ejection holes having an asymmetrical cross-sectional shape, and an asymmetrical distribution of ink ejection speed occurs at the ejection outlet of the ink ejection holes 77, causing a change in the flight direction of the ink droplets. Therefore, a print dot density that is higher than the groove (ink ejection hole) pitch can be achieved.

In the case of the embodiment shown in FIGS. 1 and 2, the front surface of the ink injection hole can be easily formed into a curved surface using a grindstone formed into the required shape. In addition, in the method of forming ink ejection holes having different cross-sectional shapes as shown in FIGS. 3 to 5, glass or resin sheets can be used as the nozzle plate material and can be easily processed using an excimer laser or the like. Therefore, an inkjet printer head with a highly integrated printing dot density can be realized at a low cost.

[0021]

[Effects of the Invention] As is clear from the above explanation, the inkjet printer head of the present invention has ink ejection holes having two or more different shapes, and at least one of the different shapes is asymmetrical. Due to this shape, it becomes an inexpensive inkjet printer head that can realize a printing dot density higher than the density of the ink ejection hole pitch.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the configuration of an ink ejection hole section and a flying direction of ink droplets according to the present embodiment.

FIG. 2 is a schematic diagram showing another example of the structure of the ink ejection hole section of the present embodiment and the flying direction of ink droplets.

FIG. 3 is a schematic diagram showing the asymmetrical shape of the ink ejection holes of this embodiment.

FIG. 4 is a schematic diagram showing the asymmetrical shape of the ink ejection holes of this embodiment.

FIG. 5 is a schematic diagram showing the asymmetrical shape of the ink ejection holes of this embodiment.

FIG. 6 is a schematic diagram showing the cross-sectional shape and velocity distribution of the ink ejection holes of this example.

FIG. 7 is a schematic diagram showing the configuration of the recording section of the inkjet printer of this embodiment.

FIG. 8 is a schematic diagram showing another configuration of the recording section of the inkjet printer of this embodiment.

[Explanation of symbols]

11 nozzle plate 12 Ink injection hole 13 Ink flow path 14 Adhesive layer 15 Paper

Claims (1)

[Claims] 1. An inkjet printer head equipped with an array having a plurality of ink ejection holes, wherein the ink ejection holes are configured with two or more different shapes, and at least one of the different shapes By forming the above ink ejection holes into an asymmetrical shape such that the velocity distribution in the ink droplet ejection direction is asymmetrical at the outlet of the ink ejection hole, the printing dot pitch is more concentrated than the pitch of the ink ejection holes. An inkjet printer head characterized by being designed to