JPH0664171A - Thermal ink jet printing head - Google Patents

Abstract

PURPOSE: To prevent the fluctuations of the vol. of emitted ink droplets caused by that fluctuations are brought about in the emitting condition of ink droplets by air bubbles generated by the accumulation of residual air or uncondensed gas in ink carried over from the generation time of previous air bubbles in a thermal ink jet printing head. CONSTITUTION: A printing head is formed by placing a barrier layer 14 on the base plate 12 placed on a polygonal resistor 26 and placing an orifice plate thereon. In order to constituted an emitting chamber of ink droplets, the barrier layer 14 is partially notched for an ink inflow channel. A notched wall surface 16 takes a smooth shape such as a cylindrical shape and is formed so as to enter the inside from the range M of 10 μm of the periphery of the resistor.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to thermal ink jet technology, and more particularly to a new and improved thin film resistor (TFR) printhead architecture used in the manufacture of disposable thermal ink jet (TIJ) pens. And its geometry.

[0002]

BACKGROUND OF THE INVENTION In the design of thin film resistor printheads used in the manufacture of thermal ink jet pens, the usual practice is to provide multiple heater resistors on a thin film substrate, such as those made of tantalum aluminum. Photolithographically formed and interconnected, and corresponding multiple aligned firing chambers on and adjacent to these heater resistors.
And the orifice openings associated therewith are formed by photolithography. These firing chambers and orifice openings are used to eject ink onto the print medium from an area above the heater resistor and within the firing chamber. As is well known, these firing chambers generally consist of a selected polymeric material placed on a TFR substrate with an orifice plate such as a gold-plated nickel material on top of the firing chamber. It is positioned and aligned with the firing chamber. The polymer barrier layer is also photolithographically formed to have a predetermined firing chamber geometry and pattern, adjacent to which each supply chamber is provided with an ink supply channel or port. To be fluidly connected to.

In operation, electrical drive pulses are selectively applied to the conductive traces. This trace leads to various heater resistors located at the bottom of each firing chamber so that the ink is heated and boiled above the heater in each firing chamber. The energization of this resistance creates a vapor bubble and corresponding pressure field used to thermally eject the ink onto the adjacent print media.

In the past, the cross-sectional geometry of the firing chamber formed by the walls of the polymer barrier between the thin film resistor substrate and the orifice plate was partially rectangular in shape and generally three-sided sidewalls. It was the composition which has. This configuration formed a firing chamber region that surrounded the heater resistance on three sides. Not only are these firing chambers and the ink flow ports connected to these firing chambers useful in forming ink flow paths and ink firing chambers for each heater resistor, but the architecture also fluidly isolates adjacent heater resistors. It also helps to minimize unwanted crosstalk between heater resistors.

As an example of a rectangular shaped barrier layer geometry with three side walls as described above, a three-color disposable pen adapted for use in Applicants' thermal ink jet printer PaintJet. Are used in. This disposable pen and the printer PaintJet that makes good use of this pen is Hewlett Packar
Further details are described in the d Journal August 1988, Vol. 39, No. 4. A general architecture for PaintJet pen orifice plates and ink supply geometry is also described in US Pat. No. 4,771,295 assigned to Jeffrey F. Baker et al. And assigned to the present applicant. Has been done. In addition, both two-sided and three-sided barrier layer and firing chamber geometries have been used in other types of thermal ink jet pens to date. These thermal ink jet pens are disclosed, for example, in the following US patents: US Pat. Nos. 4,542,389 and 4,550,326 to Ross R. Allen; US Pat. No. 4,794,410 to Howard H. Taub. All of these US patents are assigned to the applicant.

Although the Applicants' thermal ink jet pen design for the three sided barrier layer and firing chamber configuration described above has been accomplished quite satisfactorily under almost all operating conditions, Nevertheless, there are some unfavorable situations. In such situations, the three-sided barrier layer design described above is quite adequate to achieve uniform drop volume within the tolerance range, dot and line uniformity, and correspondingly acceptable print quality. It wasn't. This has been a particular problem when thermal ink jet pens are operated at high frequencies in graphic mode.

[0007]

[Objective] The present invention solves the above-mentioned problems of the prior art,
An object of the present invention is to improve the print quality by making the volume of the ink drop constant even in the high speed operation.

[0008]

SUMMARY OF THE INVENTION According to the present invention, ink droplets ejected from a firing chamber and its corresponding orifice plate are provided when a wall of the firing chamber is provided which is accurately aligned with the heater resistance geometry and is continuously curved. Significant improvements in volume uniformity and consistency are observed. This leads to a significant improvement in overall print quality. The cause of the variations in printed dot size and corresponding ink drop volume created by conventional thermal ink jet pens described above is that the residual air generated from the vaporized liquid becomes a conventional design firing. It is believed that this was due to unnecessary accumulation in the rectangular even portion of the chamber or in the gap between the barrier layer wall and the resistive edge.

If the design of the thermal ink jet drop generator is such that residual air or gas generated in the previous print cycle accumulates on or near the heater resistance, these residual air and gas will be generated. Low temperature nucleation site on the heater resistance
Is generated, and this changes the time when the evaporation of ink is started to the drive pulse width. As a result of this time variation, the pressure applied to the ink ejected from the print head varies. The variation in ink drop volume within the ink firing chamber decreases as the firing frequency of the thermal ink jet decreases. Therefore, we conclude from this that this variation is due to some time-dependent process that decreases after the ejection of an ink drop, and the re-melting process of residual air resulting from the bubble evaporation process is such a time-dependent process. Is.

Therefore, the general purpose and main purpose of the present invention is to improve the overall print quality of hardcopy output, when thermal ink jet printing in both text mode and graphic mode, It is to significantly improve the uniformity of ink drop volume and the corresponding size of dots and lines. This aim and purpose are achieved, inter alia, by placing the barrier layer and ink firing chamber of the novel architecture on a thin film resistor substrate having thereon a plurality of polygonal heater resistors. This barrier layer forms a plurality of ink firing chambers. Each ink firing chamber is formed by a continuously curved, or arcuate, concave wall laterally within its extent to the boundary defined by the resistance and its 10 μm wide edge. In this way, the walls of the firing chamber are placed close to the sides of the resistor while preventing the resistor apex from being too deep below the barrier layer.

The orifice plate is disposed on top of the barrier layer and has a corresponding plurality of orifice openings, each orifice opening being for ejecting a uniform volume of ink drops therefrom during ink jet printing. Are aligned with each other.

Another object of the present invention is to provide a new and improved thermal ink jet printhead of the type described above. With this printhead,
Significant in high frequency performance and print quality due to minimal process and design modifications to existing thermal ink jet printhead manufacturing process and TIJ pen design Improvements are achieved.

[0013] Another purpose is to improve the conventional TI in two respects: ink drop ejection stability and ink drop consistency.
It is to provide a new and improved heat of the type described above, which is a significant improvement over the J-Pen design.

[0014]

DETAILED DESCRIPTION In the following detailed description and some of the drawings, like elements are designated by like reference numerals.

Referring to FIG. 1, the thermal ink jet printhead shown therein is generally designated at 10. The printhead 10 includes a substrate member 12. Board member 12
A polymer barrier layer 14 is deposited and formed in the geometry shown above. Substrate 12 is generally composed of any material such as glass, silicon, or any other suitable insulating semiconductor material. The surface of this material is oxidised, upon which a plurality of polygonal heater resistors 2 are placed in a layer of resistive material such as tantalum aluminum.
6 is formed by photolithography. These heater resistors 26 are electrically connected by a pattern of conductive traces (not shown). The pattern of conductive traces is
Used to supply drive current pulses to these heater resistors. In addition, an insulating layer (not shown) for surface passivation and protection is also provided between the upper polymer barrier layer 14 and the lower heater resistor 26 and pattern of conductive traces. For details of the configuration of this TIJ printhead, refer to the above-mentioned Hewlett Packard Journal.
l, Vol. 36, No. 4, and Vol. 36, No. 5, 1985
It is described in the May issue of the year.

The polymer barrier layer 14 is formed from a well known polymeric material such as Vacrel available from DuPont Company of Wilmington, Delaware, known from photolithographic masking and etching. Optically shaped by using the process. These processes are used to form the geometric shape of the firing chamber 18. The firing chamber 18 is formed by a continuously curved or arcuate concave wall 16 extending upwardly from the resistor and having an edge around or near the border of the resistor. The ends of the continuously curved concave wall 16 form a single ink feed opening to the firing chamber 18 and are also joined to the sides of a rectangular ink supply channel 28. The ink supply channel 28 extends as shown to allow the polymer barrier layer 14 to
The ink is received at the angled or angled withdrawal end 30 which forms the ink inlet port of the. In this manner, the firing chamber 18 is integrally coupled to the rectangular ink supply channel 28 and its associated ink inlet port 30. Channel 28 and inlet port 30 operate to supply ink to firing chamber 18 as ink drops are ejected from the thermal ink jet printhead.

A continuously curved concave firing chamber wall 16
Overlies the resistor and fits within the boundaries of the region formed by the polygonal resistor and the 10 μm wide edges that surround the resistor, thereby creating a continuously curved wall 16
Are clamped close to the edges of the polygonal resistance.
In other words, this continuously curved concave wall 16
It is contained within an upward extension or protrusion around the region formed by the polygonal resistance and the 10 μm wide edge surrounding the resistance. In some implementations, a continuously curved concave wall 16 may pass inside some of the corners of the polygonal resistor. It is also possible for the continuously curved wall to fit entirely within the boundaries of the resistance, for example a part of this wall touching some of the sides of the polygonal resistance.

By way of example, FIG. 1 shows an embodiment of the invention having a square resistor 26 and a firing chamber wall 16 in the form of a part of a cylinder, and FIG. 2 is a schematic plan view of this embodiment. Is. The resistor 26 has a linear dimension L, for example in the range of about 35-60 μm, and has a partially cylindrical firing chamber wall 16
The cylinder tip CA of is perpendicular to the resistor 26 (and to the plane of FIG. 2) and passes through the center of the square of the resistor 26. This barrier wall is the surface end 16a of the wall of the cylinder.
It is a partial cylinder in the sense that the part between them is removed. As shown in FIG. 2, the cross section of this partial cylinder is close to the periphery of the resistor 26 and, for example, the resistance helicopter dimension L.
It has a large arc on a circle containing the cross section between the ends 16a of the wall, which are separated by less than. Here, the term "large" in the term "large arc" means the longer path between the endpoints on a circle containing the cross section of a partially cylindrical wall. The cross section of the smaller portion of the cylinder removed to form the wall opening will be a small arc between such endpoints.

From another point of view, the partial cylindrical wall is such that the cylinder is parallel to the axis CA of this cylinder and at both ends 16 of the wall.
It is a portion that remains after cutting with a plane including a.

The partial cylindrical wall 16 has a square resistance 26.
And having a diameter D selected such that the wall fits within the boundaries of the region defined by the 10 μm wide edge M surrounding the resistance. In other words, as long as any part of the firing chamber wall 16 is outside the boundary of the resistance, the radial distance S between the partially cylindrical wall 16 and each side of the resistance is
The radial distance S must be less than 10 μm, including the maximum distance between the sides of the resistance and the outer part of the partial cylindrical wall. Therefore, according to the invention, the diameter D of the cylinder
Is selected to be less than L + 20 μm. Also,
FIG. 2 shows an example where the diameter of the cylinder is less than L + 20 microns and greater than L, which causes the wall 16 to pass inside the corner of the resistor.

FIG. 3 shows another example in which the side dimension is L.
And a partially cylindrical firing chamber associated with it having a resistance D and a diameter D approximately equal to L.

FIG. 4 shows, as another example, a firing chamber associated with a resistance, which is formed from a rectangular resistance and a barrier wall which is an elliptical cylinder whose cross section is a partial ellipse. There is.

Referring again to FIG. 1, an orifice plate 32 of conventional construction, typically made of gold-plated nickel, includes a polymer barrier layer 1 as shown.
4 is disposed on the upper surface. The orifice plate 32 is tapered and typically has an orifice opening 34 aligned with the center of the heater resistor 26. However, in some cases, the orifice opening may be slightly offset from the center of the heater resistance to control the direction of the fired ink drop in the desired manner.

In accordance with the present invention, the above-described relationship between the continuously curved concave wall 16 and the underlying square resistor 26 to improve overall print quality,
It has been discovered that the stability of drop generation and volume consistency from drop to drop is significantly improved. Such an arrangement prevents a large amount of residual air and gas from the preceding cycle from accumulating on and near the surface of the heater resistor, which causes unwanted pressure fluctuations within firing chamber 16. Such unwanted pressure fluctuations
If such a measure is not taken, it affects the ejected fluid, impairing the overall volume consistency of each ink drop and the stability of ink drop ejection. The improved performance of this new architecture is clearly visible in terms of cleanliness, uniformity and print quality of the printed media.

While the above description has described and described specific embodiments of the present invention, those of ordinary skill in the art will appreciate against these embodiments the scope and spirit of the invention as defined in the claims. Various modifications and changes can be made without departing from the above.

[0026]

As described above in detail, according to the present invention,
Compared with the conventional thermal ink jet print head, the uniformity of the ink droplet size can be greatly improved, and the print quality can be improved.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a thermal ink jet printhead according to one embodiment of the present invention.

2 is a schematic plan view of a firing chamber of the thermal ink jet printhead of FIG.

FIG. 3 is a schematic plan view of a firing chamber of a thermal ink jet printhead according to another embodiment of the present invention.

FIG. 4 is a schematic plan view of a firing chamber of a thermal ink jet printhead according to yet another embodiment of the present invention.

[Explanation of Codes] 10: Thermal Ink Jet Print Head 12: Substrate Member 14: Polymer Barrier Layer 16: Concave Walls 16a: Both Ends 18: Firing Chamber 26: Heater Resistance 28: Ink Supply Channel 30: Ink Inlet Port 32 : Orifice plate M: Edge

Claims (2)

[Claims] 1. A thermal ink jet printhead provided with the following (a) to (c): (a) provided with a plurality of thin film resistors each having a polygonal shape when viewed from above. A thin film substrate; (b) a barrier layer covering the substrate; (c) a firing chamber formed in the barrier layer for each of the resistors: each of the firing chambers being the resistor and the periphery of the resistor. Formed by a continuously arcuate concave barrier within a boundary of a region defined by a 10 μm extension, said barrier having an end proximate the periphery of said resistance associated therewith, said firing chamber To form a single opening. 2. A thermal ink jet printhead provided with the following (a) to (c): (a) a thin film provided with a plurality of thin film resistors each having a square shape when viewed from above. A substrate; (b) a barrier layer over the substrate; (c) a firing chamber formed in the barrier layer for each of the resistors: each of the firing chambers is a partially cylindrical barrier layer. And the axis of the cylinder passes through the center of the square shape of the resistance associated with it, and the diameter of the cylinder is such that L is the side length of the square (L + 2
0) μm and the barrier has an end proximate the periphery of the resistance associated with it, forming a single opening to the firing chamber.