JPH04118248A - Thermal ink jet head - Google Patents

Abstract

PURPOSE:To improve ink droplet ejection speed and thereby increase ejected energy efficiency by providing a constitution in which generated bubbles are directed to a nozzle by the form of an inner wall where a recessed part is created in an ink flow path. CONSTITUTION:The bottom of a long size of the trapezoidal shape of a recessed part 8 instead of being flat is positioned at a nozzle orifice 5 side. Bubbles developed to grow on a thermal element 3 tend to spread in every direction, but the bubble on the nozzle side of the recessed part 8 can spread laterally to some extent and therefore, the upward growth of the bubble is insignificant. Yet the bubble at the ink supply orifice side opposite to the nozzle side cannot spread laterally but grows entirely upward to a larger height. The bubble 9 grows entirely to the nozzle orifice side due to the difference in growth height upward of the bubble, and thus moves ink in a direction close to an ejection direction. Consequently, the ejection efficiency of energy is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a head structure in a thermal inkjet recording device, and particularly to a thermal inkjet head having a concave structure called a bit that defines the direction in which bubbles are generated. (Prior Art) In the inkjet recording method, the thermal inkjet recording method, in which ink drops are ejected by the pressure of vapor bubbles generated by heat generated by a heater, is capable of high-density and high-speed recording due to its structural characteristics. It is excellent in multi-nozzle design and ease of production.
Development is underway in many areas.

Steam bubbles generated by the heat generated by the heater spread over the top surface of the heater.
As described in Japanese Patent No. 48, a head structure having a concave structure that defines the direction in which bubbles are generated is known.

FIG. 4 is a partially cutaway perspective view showing an example of a thermal inkjet head having a recessed portion. In the figure, 1 is a channel substrate, 2 is a heater substrate, 3 is a heater, 4 is an ink flow path, 5 is a nozzle port, 6 is an ink supply port, 7 is a bit layer, and 8 is a recess (bit). In addition,
Electrodes, protective films, etc. are not shown.

A thermal inkjet head is constructed by aligning and bonding a channel substrate 1 and a heater substrate 2, and the bit layer 7 is formed on the heater substrate.

FIG. 5 is for explaining the outline of the vicinity of the recess; FIG. 5 (A) is a plan view, and FIG.
-b sectional view. The heater 3 is provided at the bottom of the recess 8. Due to the heating of the heater 3, a bubble 9 is generated and the ink 10 is ejected from the nozzle port 5, but the concave portion 8
This limits the lateral growth of bubbles, prevents them from escaping from the nozzle, and prevents air from being sucked in.

However, since the concave portion surrounding the heater has a symmetrical structure with respect to the heat generation center line 3a of the heater, the bubble grows almost perpendicularly above the heater. Since the growth direction of this bubble is 90 degrees with respect to the ink droplet jetting direction, the expansion energy of the bubble does not become sufficient jetting energy, resulting in energy loss and causing the ink droplet jetting speed to be low. There is.

In the thermal inkjet head described in Japanese Patent Application Laid-Open No. 63-312843, in order to improve energy efficiency and ink refill, a thermal inkjet head is provided with a heat delaying means that covers the heating resistor element so that bubble formation is directed toward the nozzle. There is a problem in that the number of steps for forming the heat retardation layer increases, making the cost high.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems, and has a head structure that has a recess called a bit on the heater to prevent bubble deviation and air intake. The purpose of this invention is to improve the ink droplet ejection speed and further increase the ejection energy efficiency.

(Means for Solving the Problems) The present invention provides a thermal inkjet head that has a recess in the ink flow path and a heating element is provided at the bottom of the recess. It is characterized by being configured to direct the bubble toward the nozzle.

By increasing the internal volume of the recess toward the nozzle with respect to the center of the heater, generated bubbles can be directed toward the nozzle.

The inner wall of the recess can be inclined toward the nozzle so that generated bubbles can be directed toward the nozzle.

(Function) Bubbles generated from the heating element try to expand in all directions, but a concave portion called a bit provided in the ink flow path restricts the expanding bubble from spreading laterally.

When the inner wall of the recess is vertically formed into a prismatic shape, the bubble is restricted by the wall of the recess and grows high upward. Therefore, the component that spreads back and forth in the upper part of the recess is small.

If the inner wall of the recess is configured so that generated bubbles are directed toward the nozzle, the component that causes bubbles to grow upward is reduced, the ejection energy of ink droplets can be increased, the ejection efficiency is higher, and the ink droplet ejection speed is increased.

(Example) FIG. 1 is for explaining one example of the thermal inkjet head of the present invention, and FIG. 1 (A) is a plan view,
Figure (B) is a sectional view taken along line b in Figure (A). The same reference numerals in the figure are given to the same parts as in FIG. 5.

The heater substrate 2 is a Si wafer, and the channel substrate 1 is also a Si wafer.
Uses wafer. The ink flow path 4 forming the nozzle port 5 and the ink supply port are etched using an anisotropic etching method (OD
A channel substrate is fabricated using the E method). The bit layer 7 forming the recess 8 was made of photosensitive resin in this example.

First, a photosensitive resin is spin-coded onto the heater substrate 2, and heated for the purpose of removing the solvent. Next, exposure is performed using a mask for patterning, and etching is performed to form a recess 8 having a trapezoidal planar shape. Next, heating is performed for curing, and then the ink flow path 4 and the ink supply port 6 are heated.
A head can be manufactured by aligning and bonding the channel substrate 1 on which is formed.

As shown in FIG. 1(A), the recessed portion 8 has a trapezoidal planar shape. The base of the long dimension is, for example, 65 μm, the upper side of the short dimension is, for example, 25 μm, and the base of the long dimension is positioned on the nozzle port 5 side.

When the recess 8 is shaped like this, the bubble 9 generated and grown from above the heating element 3 tends to spread in all directions.

Here, since the bubbles on the nozzle side in the recess 8 can extend laterally to some extent, their growth upward is small. However, the bubbles on the opposite side of the ink supply port do not spread laterally and all grow upwards, so they grow higher.

Due to the difference in the height of the upward growth of the bubbles, the bubble 9 grows generally toward the nozzle opening, as shown in FIG. move in the direction. Therefore, the injection energy efficiency is improved.

The dimensions of the trapezoidal shape are not limited to the values mentioned above. Further, the planar shape is not limited to a trapezoid, but may be any shape such as a triangle that increases the area of the recess on the nozzle side.

FIG. 2 is for explaining another embodiment of the thermal inkjet head of the present invention, in which (A) is a plan view and (B) is a cross section taken along the line B in (A) It is a diagram. The same reference numerals in the figure are given to the same parts as in FIG. 5.

In this embodiment, the concave portion has a structure in which the side toward the nozzle opening widens with a step. In order to form a step, two bit layers are used, and the recess formed by the second bit layer 7b is formed by the recess formed by the first bit layer 7a.
It has a shape that widens toward the nozzle mouth side. Bubble 9 generated
The bubbles 9 only grow upward up to the first bit layer 7a, but when the bubbles 9 reach the second bit layer 7b, they grow toward the nozzle mouth side. This increases the ejection energy efficiency and improves the ink droplet ejection speed, as described in FIG. 1.

The method for producing the recesses is to create a first bit layer with a thickness of 15 μm by applying the photosensitive resin for the first time, exposing it to patterning, etching it, and curing it with heat. A second bit layer having a thickness of 25 μm was prepared by etching, etching, and heat curing. The thickness of the recess layer is not limited to this.

FIGS. 3A to 3C are cross-sectional views for explaining other embodiments of recesses formed in the bit layer. Components similar to those in FIG. 5 are designated by the same reference numerals, and their explanation will be omitted.

In FIG. 3(A), the nozzle opening side of the recess 8 extends to an area where there is no heating element. Since the bubble 9 grows toward the area where there is no heating element, the bubble 9
The growth direction can be directed toward the nozzle opening.

In FIG. 3(B), the front and rear inner walls of the recess 8 are inclined toward the nozzle opening. Along the sloping wall
Since the bubble 9 grows, the growth direction can be directed toward the nozzle mouth side.

Further, as shown in FIG. 3(C), the inclination angle of the inner wall of the recess 8 may be different in the front and back, for example, the front wall is inclined more toward the nozzle opening, and the rear wall is a substantially vertical wall. It may also be shaped like this.

(Effects of the Invention) As is clear from the above description, the present invention has the effect of providing a thermal inkjet head with good ejection energy efficiency and high ink droplet ejection speed.

Further, since the structure has a concave portion, escape of bubbles from the nozzle and intake of air do not occur, and a high-performance head with stable jetting characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is for explaining the recessed portion of one embodiment of the thermal inkjet head of the present invention. Cross section, 2nd
The figures are for explaining the recessed portion of another embodiment of the thermal inkjet head of the present invention, where (A) is a plan view and (B) is a cross section taken along line bb in Figure (A). 3 is a sectional view of a recessed portion of still another embodiment of a thermal inkjet head of the present invention, FIG. 4 is a partially cutaway perspective view of an example of a thermal inkjet head having a recessed portion, and FIG. 5 4A is a plan view, and FIG. 4B is a sectional view taken along line bb in FIG. 4A. 1... Channel board, 2... Heater board, 3...
... Heat generating element, 4... Ink channel, 5... Nozzle port, 6... Ink supply port, 7... Bit layer, 8...
Concavity, 9...bubble. Patent applicant Fuji Xerox Co., Ltd.

Claims (1)

[Claims] In a thermal inkjet head that has a recess in the ink flow path and a heating element provided at the bottom of the recess, the shape of the inner wall forming the recess is configured to direct generated bubbles toward the nozzle. Features a thermal inkjet head.