JPH10264393A - Thermal ink-jet print head suitable for viscous ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge ink in an optimum manner by forming a cavity defined by a channel plate so that a lateral sectional area from a manifold part through a heating part to a nozzle part is smaller stepwise. SOLUTION: A channel is formed at a face of a heating chip 10 where a primary plane where a heating element 60 is arranged and a channel plate 12 butt. A part of the channel plate 12 immediately adjacent to a heating part 20 where the heating element 60 is arranged is formed as a nozzle part 22. An end part of the heating part 20 at the opposite side is formed as a manifold part 24. A lateral sectional area of a cavity formed by the channel plate 12 is made smaller stepwise from the manifold part 24 to the nozzle part 22 through the heating part 20. A liquid ink particularly of a larger viscosity than 2P is discharged in an optimum manner accordingly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a printhead for a thermal ink jet printer specially formed so that the fluid flow channel of each ejector works optimally, and more particularly to ejecting liquid ink with a viscosity greater than 2 centipoise. About doing.

[0002]

2. Description of the Related Art In thermal ink jet printing,
Ink drops are selectively ejected from a plurality of drop ejectors of the printhead. These jets are operated according to digital commands to produce the desired image on the print sheet moving with respect to the printhead. These jets are typically connected to one or more common ink supply manifolds, capillary channels, or
Another ink passage is provided. Ink is retained in each channel until the ink in the channels is rapidly heated in response to an appropriate digital signal by a heating element disposed on a surface within the channel. This rapid vaporization of the ink close to the channel creates bubbles,
This bubble creates an amount of liquid ink that is ejected onto the print sheet through the opening associated with the channel. The rapid vaporization that produces bubbles is commonly known as "nucleation".

[0003] In many designs of thermal ink jet ejectors, the volume of the cavity around the heating element is relatively large, having a narrower portion forward and backward of the heating element. This narrow portion of the nozzle area limits the amount of droplets pushed out of the ejector, prevents air from being trapped in the cavity, and provides capillary force for rapid refilling after the ink droplet has been ejected. give.
The narrow portion on the manifold (ink supply) side contains bubbles formed on the heating element, restricting the backflow of ink during and after nucleation and weakening the ink refill once the cavity is refilled. To prevent the ink from protruding outside the nozzle. The present invention describes an ejector design in which the manifold side of the ejector cavity is much larger than the periphery of the heating element, which imposes small physical restrictions on the ink on the manifold side. The usual limiting function on the manifold side is provided by a combination of the narrowed nozzle section and the viscosity of the ink itself. This "open" shape provides rapid replenishment after nucleation, which is facilitated by the collapse of the bubble.

US Pat. No. 4,994,826 discloses one design of a “side shooter” thermal ink jet printhead. A simplified diagram of the basic printhead design shown in this patent is shown here as FIG. Regardless of the typical design of a side shooter inkjet printhead, the individual ejectors of the printhead are essentially
A “heating chip” (here shown as 10 in FIG. 1) and a “channel plate” (here 12 in FIG. 1)
(Shown as). According to the design of the '826 patent, between the abutting surfaces of the heating chip 10 and the channel plate 12, a "thick insulating layer", here designated 50 (FIG. 1).
(Shown in two parts in the cross-sectional elevation view). For each ejector of the conventional printhead of FIG. 1, the channel plate 12 is provided with two cavities, one manifold 52, and one channel. Inside the channel plate 12 itself, the manifold 52 and the channel 54 are not directly connected to each other, but rather, as shown in FIG.
Manifold 52 communicates with channel 54 via a depression, here shown as 56, located in thick film insulation layer 50. Disposed within the channel 54 of each ejector of the printhead is a heating element 60 operable to a voltage source through circuit elements whose general structure is shown as 58. Attached to. With any thermal ink jet printhead, the application of a voltage to the heating element 60 causes the desired nucleation of the adjacent liquid ink, where the liquid ink is always in a particular ejector channel 54. Is held.

The particular structure of the conventional printhead of FIG. 1 shows the heating element 60 located in a "pit" in the channel 54, and the actual nozzle 62,
The liquid ink is ejected from the nozzle, and this nozzle exists in the same plane as the thick film insulating layer 58.
You will understand. The general purpose of this construction is to allow the ink to be supplied to the manifold 5 as described in the referenced patent.
When nucleating the second ink, the fluid effect of the back pressure is minimized, and air is prevented from protruding outside through the nozzle 62 immediately after the nucleus ejection. The printhead structure relies on a thick-film insulating layer 50, which is typically formed of a material such as polyimide, and is sandwiched between the heating chip 10 and the major surface of the channel plate 12.

[0006]

SUMMARY OF THE INVENTION According to a feature of the present invention, there is provided an ink jet printing apparatus having at least one ejector, the ejector comprising a structure for forming a channel for passing a flow of liquid ink, and a channel in the channel. And a heating element arranged at the same time. The channel includes a heating portion immediately adjacent the heating element, a nozzle portion adjacent the first end of the heating portion along the channel, and a manifold portion adjacent the second end of the heating portion along the channel. And The nozzle portion has a smaller cross-sectional area than the heated portion and the manifold portion has a larger cross-sectional area than the heated portion. According to another aspect of the present invention, there is provided a method of operating an ejector of an inkjet printhead. The ejector has a structure defining a channel and a heating element disposed within the channel. The channel includes a heating portion immediately adjacent the heating element, a nozzle portion adjacent the first end of the heating portion along the channel, and a second portion of the heating portion along the channel.
And a manifold portion proximate an end of the heating portion, the manifold portion having a cross-sectional area greater than a cross-sectional area of the heating portion. Liquid ink having a viscosity greater than 2 centipoise at operating temperature is supplied into the channel. The heating element is actuated to nucleate the liquid ink in the channel to produce an amount of liquid ink to be ejected from the nozzle portion, this actuation step occurring more than 20,000 times per second. I do.

[0007]

FIG. 2 is a sectional elevation view of a cavity forming one ejector of an ink jet print head according to an embodiment of the present invention, and FIG. 3 is a sectional plan view thereof. As shown in these figures, the ejector has a channel formed at the abutting surface between the main plane of the heating tip 10 and the channel plate 12. According to an embodiment of the present invention, the heating tip 10
Is substantially flat, and the heating element 60 is arranged in the flat main surface of the heating chip 10. The general design of the heating element 60 is well known in the art,
The 0 is then connected to a voltage source (not shown) that can operate selectively. When the channel plate 12 is abutted against the heating tip 10, the heating element 60 of each ejector will cause the channels formed in the channel plate 12 to be referred to herein as “heating portions” (shown here as 20). ) Is placed in close proximity to.

[0008] Immediately adjacent the heated portion of the channel of the channel plate 12, here the nozzle portion 22
There is a smaller channel, called the channel plate 1, at the opposite end of the heating section 60.
2, there is a larger cavity, here called the manifold portion 24. As is apparent from the drawing, the manifold portion 24, the heating portion 20, and the nozzle portion 22 combine to form a channel, and the cross-sectional area of the large cavity formed in the channel plate 12 is reduced from the manifold portion 24 to the heating portion 20. Until it finally reaches the nozzle portion 22. FIG. 4 is a perspective view of one ejector as shown in FIG. 2 or FIG. FIG.
Outlined in dashed lines is the shape of a cavity according to a preferred embodiment of the present invention, the cavity being formed in the channel plate 12 for each ejector. According to one embodiment of the present invention, the nozzle portion 22, the heating portion 20, and the manifold portion 24 are formed as cavities in the channel plate 12, which channel plate 12 includes a plurality of ejectors of a printhead. For a single monolithic piece of silicon. As shown in FIG. 4, the nozzle portion 22 and the heating portion 20 are generally triangular when viewed in a cross section perpendicular to the axis of the fluid flow, and one side of the triangular shape is It is formed by the main flat surface of the heating tip 10 and has the remaining two triangular shapes.
One side is formed by the <111> plane of the crystal structure of silicon forming the channel plate 12. Such a structure, shown in FIG. 4, can be obtained through orientation-dependent etching of silicon. For example, at the junction 21 between the nozzle portion 22 and the heating portion 20, the exposed surface of silicon forming the channel plate 12 is generally substantially a <210> surface of silicon. Similarly, the main surface of the manifold portion 24 is <1
11> faces can be formed in the same way, and the joints 23 between them are formed at least in part by <210> faces. It is also possible to provide the channel plate 12 in a desired form made of a plastic material, however, whatever material is used for the channel plate, the effective part of that material is tailored to a single piece. It is generally desirable to form various parts of an ejector consisting of the following materials.

The joints 21 and 23 between the heating section 20, the nozzle section 22 and the manifold section 24 preferably have a reduced channel cross section along an axis from the ink supply to the nozzle section 22. In this regard, separate "steps" are formed, i.e., transition regions, which should be distinguished from designs where the cross-section of the channel from the manifold portion to the nozzle is continuously reduced. is there. Nevertheless, heating part 2
In steps 21 and 23 between 0 and the nozzle portion 22 and the manifold portion 24, the channel is, as shown in FIG. 4, to prevent sources of undesired flow impedance that can be caused by sudden changes in cross-section. It has been tapered. According to one preferred embodiment of the present invention, the nozzle portion 22 comprises a heating portion 2 for all dimensions.
It is considerably smaller than zero. In one embodiment for a 600 dpi printhead, if nozzle portion 22 is 20 micrometers long along the axis of fluid flow,
The preferred length of the heating section 20 along its axis is 60 to 200 micrometers, including the length taken by step 21 between the nozzle section 22 and the heating section 20. Also, a preferred length range from the front opening of the nozzle portion 22 (i.e., the front of the printhead) to the leading edge of the heating element 60 is 40-70 micrometers. A corresponding preferred length along the axis of the heating element 60 is 25 to 1
00 micrometer range. Similarly, the preferred cross-sectional width for the nozzle portion 22 is between 10 and 20 micrometers, while the corresponding preferred range for the cross-sectional width of the heated portion 20 is between 20 and 30 micrometers. Assuming the particular cross-sectional shape of the nozzle section 22 and assuming that each section tapers somewhat along the length of the channel, the cross-sectional area of the body of the heating section 20 will generally be Should be at least twice that of the body.

In general, the range of these relative dimensions within the cavity forming the ejector is relatively high in viscosity, in particular,
Ink in close proximity to the heating element 60 has been found to be useful in ejecting liquid ink having a viscosity of greater than 2 centipoise at normal operating temperatures immediately prior to ejection. The relative dimensions described above are useful for ejecting approximately 3.5 centipoise of ink at operating temperatures, and quite satisfactory results can be obtained with viscosities greater than 12 centipoise. 600
The dimensions described above for the dpi printhead are:
It will be appreciated that it may be designed to scale to obtain printheads for other resolutions, such as 300 dpi. A practically significant advantage of the printhead design of the present invention is that the relative sizes of the manifold portion 24, the heating portion 20, and the nozzle portion 22 are such that when liquid ink is attempted to be ejected from the ejector at a high frequency. It is to reduce many performance bottlenecks. An important functional limitation for any thermal inkjet printhead design is the rate at which the ejector is refilled with liquid ink from the ink supply manifold immediately after the ejection of the ink drop through the nozzle. With the printhead design of the present invention, the combination of the relatively narrow nozzle portion 22 and the relatively "open" manifold portion 24 causes the nucleated vapor bubble to collapse immediately within the heated portion 20 immediately after collapse. The heating portion 20 is replenished with the liquid ink at a high speed. Thus, the ejector according to the invention dispenses small discrete ink drops,
It can be generated accurately and with a high frequency of operation. Using cavity dimensions in the range described above, and 2
If a liquid ink having a viscosity greater than centipoise, ie, preferably 3.5 centipoise, is used, the ejector may, for example, have air introduced into the nozzle portion 22 or the liquid ink supplied through the manifold portion 24. Ink droplets can be ejected uniformly at a rate exceeding 20,000 ejections per second without the failures caused by insufficient ink jetting.

FIG. 5 is a cross-sectional elevational view of a cavity forming one ejector of an ink jet printhead according to another embodiment of the present invention, based on a "top shooter" type ink jet geometry, and FIG. FIG. As can be seen in these figures, the ejector is located on the nozzle portion 22 directly above the heating element 60.
And a heating section 20 around the heater and a manifold section 24 connected to an ink supply (not shown). According to this embodiment of the invention, the heating part 2
The 0 is not limited and is a constant cross-section up to the transition region expanding to join the manifold portion 24, as shown in FIG. As with the design shown in FIGS. 2, 3, and 4, this design provides a large opening to the manifold area, which provides the maximum refill capability possible. It works like that. Replenishment is not due to restrictions in the back channel,
Rather, it is weakened by the viscosity of the ink.

FIG. 7 shows another embodiment of the universal shape of the ejector according to the invention, in which a throttle, shown as 30, is provided between the heating section 20 and the manifold section 24. . The cross section of this constricted part is the heating part 2
0 is smaller than the entire cross section. This constriction has the desired effect of reducing vibration "cross talk" between multiple ejectors of the printhead. This oscillation "cross talk" is usually caused by the back pressure of the expanding steam bubble from one ejector increasing the pressure in one ink manifold shared by multiple ejectors. Restrictor 30
Creates a cross-sectional area in the channel that is not less than 20%, preferably not less than 10%, of this cross-sectional area than the cross-sectional area of the portion immediately adjacent to the heating portion 20.

While the invention has been described with reference to the disclosed structures, it is not limited to the details described, but also covers variations and modifications that may fall within the scope of the appended claims. .

[Brief description of the drawings]

FIG. 1 is a simplified sectional elevation view of a conventionally known ink jet ejector.

FIG. 2 is a sectional elevation view of a cavity forming one ejector of an inkjet printhead according to one embodiment of the present invention.

FIG. 3 is a sectional plan view taken along a line 2B in FIG. 2;

FIG. 4 is a perspective view showing a cavity configuration of one injector as shown in FIGS. 2 and 3;

FIG. 5 is a cross-sectional elevation view of a cavity forming one ejector of an inkjet printhead according to another embodiment of the present invention.

FIG. 6 is a cross-sectional plan view taken along line 4B of FIG. 5;

FIG. 7 is a plan view of an ink ejection channel according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heating chip 12 Channel plate 20 Heating part 22 Nozzle part 24 Manifold part 60 Heating element

Continuing the front page (72) Inventor James F. O'Neill United States of America New York 14526 Penfield Pine Brook Cycle 60 (72) Inventor Narayan Vee Despande United States of America New York 14526 Penfield Highage Drive 101 (72) Inventor Eric Peters United States of America California 94041 Mountain View High School Way 900-2204 (72) Inventor Reinhold E Drooze United States of America New York 14534 Pittsford Highview Trail 17 (72) Inventor Dale Earl Eames United States of America New York 14580 Webster Little Pond Way 926 (72) Inventor Constance Jay Thornton United States of America New York 14519 Ontario County Line Road 64 82

Claims (3)

[Claims] 1. An inkjet printing apparatus having at least one ejector, the ejector comprising: a structure for forming a channel through which a flow of liquid ink flows; and a heating element disposed in the channel. The channel is a heating portion immediately adjacent a heating element; and a nozzle portion along the channel proximate a first end of the heating portion, the nozzle having a cross-sectional area smaller than a cross-sectional area of the heating portion. A manifold portion along a channel proximate a second end of the heating portion, the manifold portion having a cross-sectional area greater than a cross-sectional area of the heating portion. Equipment to do. 2. The apparatus of claim 1, wherein the cross-sectional area of the heating section is at least twice the cross-sectional area of the nozzle section. 3. The method of operating an ejector of an inkjet printhead, the method comprising: providing a structure for forming a channel and a heating element disposed in the channel to the ejector, wherein the channel is directly connected to the heating element. An adjacent heating portion; a nozzle portion adjacent a first end of the heating portion along a channel, the nozzle portion having a cross-sectional area smaller than a cross-sectional area of the heating portion; and a heating portion along the channel. A manifold portion proximate to a second end of said manifold portion, said manifold portion having a cross-sectional area greater than a cross-sectional area of a heated portion, said step having a viscosity greater than 2 centipoise at operating temperatures. Supplying the liquid ink to the channel; and nucleating the liquid ink in the channel to be ejected from the nozzle portion. To produce liquid ink of a quantity, the method comprising: operating the heating element, the actuating step and the actuating step occurring more than every second 20,000 times,
A method comprising: