JP2889342B2 - Thermal inkjet head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a head structure in a thermal ink jet recording apparatus, and more particularly to a thermal ink jet head having a concave structure called a pit for defining a direction in which bubbles are generated. .

(Prior art) In the ink jet recording method, the thermal ink jet recording method in which ink drops are ejected by the pressure of a vapor bubble generated by the heat generated by a heater is capable of high-density recording at a high density due to its structural characteristics.
In addition, they are excellent in multi-nozzle formation and ease of production, and are being developed in various fields.

Steam bubbles generated by the heat generated by the heater are generated while spreading on the upper surface of the heater.
As described in Japanese Patent Application Laid-Open Publication No. H10-209, there is known a head structure having a concave structure for defining a direction in which bubbles are generated.

FIG. 4 shows an example of a thermal inkjet head having a concave portion, and is a perspective view with a part cut away.
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 pit layer, and 8 is a recess (pit). The electrodes, protective films, and the like are not shown.

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

5A and 5B are views for explaining the outline of the vicinity of the concave portion. FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view taken along line bb of FIG. The heater 3 is provided at the bottom of the recess 8. By the heating of the heater 3, a bubble 9 is generated, and the ink 10 is ejected from the nozzle port 5.
Thereby, the growth of bubbles in the lateral direction is restricted, and escape from the nozzle and suction of air are prevented.

However, since the recess surrounding the heater has a symmetrical structure with respect to the heater center line 3a, the bubble grows almost vertically above the heater. Since the bubble growth direction is 90 degrees with respect to the ink droplet ejection direction, the expansion energy of the bubble does not become sufficient ejection energy, causing energy loss and causing a low ink droplet ejection speed. I have.

In the thermal ink jet head described in JP-A-63-312843, a thermal delay means for covering a heating resistor element so that bubble formation is directed to a nozzle is provided for improving energy efficiency and ink refill.
There is a problem that the number of steps for forming the thermal delay layer is increased and the cost is increased.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned problems, and has a head structure having a concave portion called a pit on a heater so that there is no bubble departure or air suction. It is an object of the present invention to improve the ejection speed of ink droplets to further increase the ejection energy efficiency.

(Means for Solving the Problems) According to an aspect of the present invention, there is provided a thermal inkjet head having a pit layer, wherein a heating element is provided at the bottom of the recess formed in the pit layer. The shape is characterized in that the front width is wider than the rear width. According to a second aspect of the present invention, in a thermal ink jet head having a pit layer and a heating element provided at a bottom of a recess formed in the pit layer, a wall behind the recess is provided with a heating element. The recess is formed perpendicular to the same plane as the surface, and the front wall of the recess is formed so as to advance continuously or stepwise so that the opening area of the recess is larger than the bottom area of the recess. It is characterized by the following. According to a third aspect of the present invention, in a thermal ink jet head having a pit layer and a heating element provided at a bottom of a concave portion formed in the pit layer, the front and rear walls of the concave portion are It is characterized by being inclined forward as approaching the opening from the bottom. According to a fourth aspect of the present invention, in a thermal ink jet head having a pit layer and a heating element provided at a bottom of a recess formed in the pit layer, a length of the heating element is set to a length of the recess. The heating element is shorter than the length of the bottom, and the heating element is provided at a recessed position at the bottom of the recess.

(Operation) Bubbles generated from the heat generating element tend to expand in all directions, but the concave portions called pits provided in the ink flow path limit the expanding bubbles to spread in the horizontal direction.

In the case where the inner wall of the concave portion is in the shape of a prism formed vertically, the bubble grows upward and is restricted by the concave wall. Therefore, the component that spreads back and forth in the upper part of the concave portion is small.

According to the first aspect of the present invention, the planar shape of the concave portion has a shape in which the width of the front (in the direction of the nozzle opening) is wider than the width of the rear portion, thereby giving a generated force to the generated bubble in the direction of the nozzle opening. As a result, the ejection energy of the ink droplet can be increased, the ejection efficiency is higher, and the ink droplet ejection speed is higher. In the invention according to claim 2, the rear wall of the concave portion is formed perpendicular to the same plane as the surface of the heating element, and the front wall of the concave portion is configured to advance continuously or stepwise. By forming the opening area of the concave portion larger than the bottom area of the concave portion, it is possible to apply a component force to the generated bubble in the direction of the nozzle opening, to increase the ejection energy of the ink droplet, and to increase the ejection efficiency. Higher,
The ink droplet ejection speed also increases. According to the third aspect of the present invention, the front and rear walls of the recess are inclined forward from the bottom toward the opening, so that a generated force is applied to the generated bubble toward the nozzle opening. As a result, the ejection energy of the ink droplet can be increased, the ejection efficiency is higher, and the ink droplet ejection speed is higher. Further, in the invention according to claim 4, the length of the heating element is shorter than the length of the bottom of the recess, and the heating element is provided at a recessed position at the bottom of the recess, so that the generated bubble has a nozzle. A component force directed toward the mouth can be given, the ejection energy of the ink droplets can be increased, the ejection efficiency is higher, and the ink droplet ejection speed is faster.

(Embodiment) FIG. 1 is a view for explaining one embodiment of the thermal ink jet head of the present invention, wherein FIG. 1A is a plan view, and FIG. It is -b sectional drawing.
In the figure, the same parts as those in FIG. 5 are denoted by the same reference numerals.

The heater substrate 2 uses a Si wafer, and the channel substrate 1 also uses a Si wafer. An ink flow path 4 forming a nozzle port 5;
Anisotropic etching method (ODE method) utilizing the fact that the ink supply port changes the etching rate depending on the crystal orientation of Si
To produce a channel substrate. The pit layer 7 for forming the recess 8 was made of a photosensitive resin in this embodiment.
First, a photosensitive resin is spin-coated on the heater substrate 2 and heated for removing the solvent. Next, patterning is performed by exposing using a mask, and etching is performed to form a concave portion 8 having a trapezoidal planar shape. Next, heating is performed for curing, and thereafter, the channel substrate 1 on which the ink flow path 4 and the ink supply port 6 are formed is aligned and joined to form a head.

The recess 8 has a trapezoidal planar shape as shown in FIG. 1 (A). The long side of the long dimension is set to, for example, 65 μm, the upper side of the short dimension is set to, for example, 25 μm, and the bottom side of the long dimension is positioned on the nozzle port 5 side.

When the shape of the recess 8 is set in this manner, 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 concave portion 8 can spread to some extent in the horizontal direction, the upward growth is small. However, the bubble on the ink supply port side on the opposite side does not spread in the horizontal direction, but grows higher because all grow upward. Due to the difference in the upward growth height of the bubble, the bubble 9 grows toward the nozzle opening as a whole, 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 described above. Also, the planar shape is not limited to the trapezoidal shape, and may be any shape such as a triangle or the like that increases the recess area on the nozzle side.

2A and 2B are views for explaining another embodiment of the thermal ink jet head of the present invention. FIG. 2A is a plan view, and FIG. 2B is a bb cross section of FIG. FIG.
In the figure, the same parts as those in FIG. 5 are denoted by the same reference numerals.

In this embodiment, the structure is such that the side of the concave portion in the direction of the nozzle opening is spread with a step. In order to form a step, the pit layer was made into two layers, and the concave portion formed by the second pit layer 7b was formed to have a shape wider than the concave portion formed by the first pit layer 7a toward the nozzle opening. Bubble 9 generated
Only grows up to the first pit layer 7a, but when the bubble 9 reaches the second pit layer 7b, the bubble grows toward the nozzle opening. As a result, as described with reference to FIG. 1, the ejection energy efficiency is increased, and the ink droplet ejection speed is also improved.

The method of forming the recesses is as follows: a first application of a photosensitive resin, exposure patterning, etching, and heat curing to form a first pit layer to a thickness of 15 μm, and then a second application of a photosensitive resin and exposure patterning Then, etching and heat curing were performed to form a second pit layer having a thickness of 25 μm. The thickness of the concave layer is
It is not limited to this.

3 (A) to 3 (C) are cross-sectional views for explaining another embodiment of the recess formed in the pit layer.
The same reference numerals are given to the same parts as those in FIG.

FIG. 3 (A) shows a configuration in which the nozzle opening side of the concave portion 8 is present even in a region without a heating element. Since the bubble 9 grows toward the region without the heating element, the growth direction of the bubble 9 can be directed to the nozzle opening side.

FIG. 3 (B) shows a shape in which the inner walls before and after the concave portion 8 are inclined toward the nozzle opening side. Since the bubble 9 grows along the inclined wall, the growth direction can be directed to the nozzle port side.

Also, as shown in FIG. 3 (C), the inclination angle of the inner wall of the concave portion 8 is different in front and rear, for example, the front wall is inclined more toward the nozzle opening side, and the rear wall is a substantially vertical wall. The shape may be set as follows.

(Effects of the Invention) As is clear from the above description, according to the present invention, there is an effect that a thermal inkjet head having good ejection energy efficiency and a high ink droplet ejection speed can be provided.

In addition, since the structure has the concave portion, there is an effect that a high-performance head with stable ejection characteristics can be obtained without escape of the bubble from the nozzle and air intake.

[Brief description of the drawings]

1A and 1B are views for explaining a concave portion of an embodiment of the thermal ink jet head of the present invention. FIG. 1A is a plan view, and FIG. 1B is bb in FIG. Sectional view, second
The drawings are for explaining the concave portions of another embodiment of the thermal ink jet head of the present invention, wherein FIG. 5A is a plan view, and FIG. 5B is a bb cross section of FIG. FIG. 3 is a sectional view of a concave portion of still another embodiment of the thermal ink jet head of the present invention. FIG. 4 is a perspective view of a part of an example of the thermal ink jet head having the concave portion. 4A and 4B are for explaining an outline of the vicinity of the concave portion in FIG. 4, wherein FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along line bb of FIG. DESCRIPTION OF SYMBOLS 1 ... Channel board | substrate, 2 ... Heater board, 3 ... Heat generating element, 4 ... Ink channel, 5 ... Nozzle port, 6 ... Ink supply port, 7 ... Pit layer, 8 ... Concave part, 9 ……bubble.

Continuation of the front page (56) References JP-A-60-157869 (JP, A) JP-A-60-133763 (JP, A) JP-A-63-312843 (JP, A) JP-A-60-116453 (JP) JP-A-1-255551 (JP, A) JP-A-2-95860 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/05 B41J 2/16

Claims (4)

(57) [Claims] 1. A thermal ink jet head having a pit layer, wherein a heating element is provided at the bottom of a concave portion formed in the pit layer, wherein the concave portion has a plan shape in which a front width is wider than a rear width. A thermal inkjet head, characterized in that: 2. A thermal ink jet head having a pit layer and a heating element provided at the bottom of a recess formed in the pit layer, wherein a wall behind the recess is flush with the surface of the heating element. Wherein the front wall of the concave portion is formed so as to advance continuously or stepwise, and the opening area of the concave portion is larger than the bottom area of the concave portion. Ink jet head. 3. A thermal ink jet head having a pit layer, wherein a heating element is provided at the bottom of a recess formed in the pit layer, wherein the front and rear walls of the recess face the opening from the bottom. A thermal inkjet head characterized by being inclined forward. 4. A thermal ink jet head having a pit layer, wherein a heating element is provided at the bottom of a recess formed in the pit layer, wherein the length of the heating element is shorter than the length of the bottom of the recess. Further, the heating element is provided at a position retreated at the bottom of the concave portion.