JPS59207262A - Printing head - Google Patents

Abstract

PURPOSE:To permit the thermal shock jet of ink with good efficiency from nozzle as well as lengthen the life of resistor elements by a method in which plural resistor elements are set separately from each other and also from the position facing the center of a nozzle for one nozzle and they are connected in series with one another. CONSTITUTION:Heating resistors 8 and conductor layers 10 are provided through a heat insulator layer 4 on a base plate 2, and an orifice 20 is formed through a passivation layer 12 and barrier elements 14 and 16 on an orifice plate 18. In a thermal shock ink jet head having such the orifice plate 18, plural resistor layers 8' and 8'' are set separately from each other and also from the position facing the central part of the orifice 20 and connected in series with conductor layers 10, 10' and 10''. Damage to the heating resistor elements by cavitation phenomenon to be caused in the position facing the central part of the orifice 20 can thus be completely prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to ink jet printers, and more particularly to print heads for ink jet printers.

[Prior art]

Since data processing has traditionally been done quickly, there has been a demand for devices that can print at ultra-high speeds. Impact printing, in which a print head consisting of a molded printing element is brought into physical contact with a recording medium, has the drawbacks of slow speed and inability to be miniaturized. Therefore,
Non-printing that uses various techniques to print on recording media
Printers using the impact printing method are attracting attention. Some of these techniques use electrostatic or magnetic fields to deposit visible image-forming materials, either solid (i.e., dry powder) or liquid (i.e., ink), onto a recording medium (usually paper). I am using it.

Others use an electrophotographic system or an ion system that irradiates a medium with an electron beam or ion beam to change the color of the irradiated area.

There are also systems that use thermal imaging to create color changes in desired shapes. One recent development is ink-jet printing, which electronically bombards a recording medium with tiny droplets of ink to form selected characters anywhere at extremely high speeds. Ink jet printing is a non-contact system that does not require a specially treated recording medium (regular plain paper is suitable) and does not require any vacuum equipment or bulky mechanisms. The present invention relates to a printing system of this type.

Ink jet systems are classified as follows.

(1) a continuous system in which ink droplets are continuously ejected from the nozzle at a constant ink pressure and constant velocity; (2)
Electrostatic systems in which charged ink droplets are propelled by a controllable electrostatic field; (3) Impulse or ink-on-demand systems in which ink droplets are propelled from a nozzle by a controllable functional force on demand; system.

The present invention is a printing system used in the system of method (3).
・About Sodo.

A representative example of an ink-on-demand system is described in US Pat. No. 3,832,579. In this system, a cylindrical piezoelectric transducer is affixed to the outer surface of a cylindrical nozzle. Ink is delivered through a hose connected between one end of the nozzle and the ink container. The piezoelectric 1-transducer throttles the nozzle when it receives an electrical pulse, causing the nozzle to generate a pressure wave that accelerates ink toward the ends of the nozzle. An ink drop is formed when an ink pressure wave overcomes the surface tension of the meniscus present at the orifice at the small end of the nozzle.

Another type of ink-on-demand printing system is described in US Pat. No. 3,174.042.

This system uses some ink-containing tubing and current is passed through the ink itself. Due to the high resistance of the ink, the ink becomes superheated and some of it vaporizes within the tube, causing ink and ink vapor to be expelled from the tube. Also, U.S. Patent Application No. 415°29! describes an ink-on-demand printing system that uses an ink-containing capillary tube with an orifice through which the ink is ejected. In the vicinity of this orifice, up to the capillary tube, there is an insulator consisting of a resistive element placed adjacent to it.
・An overheating mechanism is provided. Properly passing current through a resistive element causes the resistive element to heat up rapidly. A significant amount of thermal energy is transferred to the ink, vaporizing a small portion of the ink near the orifice and creating bubbles within the capillary.

This bubble generation generates a pressure wave that causes a single drop of ink to be ejected from the orifice onto the nearby writing surface or recording medium. Proper selection of the relative position of the ink heating mechanism with respect to the orifice and careful control of heat transfer from the heating mechanism to the ink will allow ink bubbles to rapidly build up on or near the ink heating mechanism before any vapor dissipates from the orifice. It will collapse.

The life of a thermal ink jet blink depends on the life of the resistive element. It is known that most of the damage to resistive elements is caused by cavitation damage when bubbles collapse. Therefore, it is desirable to minimize wear and tear on the resistive element due to cavitation damage. No. 44,711, the idea is that most bubble damage occurs at or near the center of the resistive element, so a "cold" area of conductive material is provided in the center of the resistive element. There is. Due to the cold area of the body, bubbles are generated.
The bubbles are oak-shaped, and when they collapse, they are not concentrated in a narrow area at the center of the resistance element, but are randomly dispersed on the surface of the resistance element.

This 7'4 area is actually formed by depositing gold on the center of the resistor element. This gold effectively shorts out the underlying resistive element or portion, preventing heat generation in that area.

When a cold region is formed as described above, the ink immediately above the region is heated unevenly, resulting in 1. This is not preferable for the purpose of forming suitable bubbles. Further, even though the resistive element is separated from the resistive element by the gold in the central part, there is no guarantee that the bubble will not collapse in the central part of the resistive element. If such a phenomenon occurs, the gold area will be eroded and the resistive element will eventually be damaged.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a verint belly button 1- which is free from bubble damage.

[Summary of the invention]

The invention comprises a resistance region consisting of two legs with an open center section therebetween. Even if the center of the resistor element is bubbled or touched, it will not affect any of the materials of the legs of the resistor element. Additionally, each resistive element leg can be made to form two squares, so that each leg has the same resistance as that of a single square resistive element conventionally practiced in the thermal ink jet blinking art. It will have twice the resistance. Thus, for example, if a single square resistive element in a conventional thermal ink jet printer imposes a resistance of 50 ohms, each leg of the resistive element of the present invention forms a resistance of 100 ohms per square. The total resistance is 200 ohms.

Therefore, the present invention not only prolongs the life of the resistive element by eliminating bubble collapse and cavity damage in the center of the thin film resistive region, but also reduces the operating current connected to the resistive element. This phenomenon is caused by power loss in conductive elements. Additionally, the reduced current required increases the reliability of the thermal ink jet printhead.

〔Example〕

FIG. 1 shows a partial cross-sectional view of a conventional single orifice print head. The main support structure is a substrate 2 of single crystal silicon. On two sides of the silicon substrate 2, the thickness is 3.5I.
A thermally insulating layer 4 of silicon dioxide of jm is provided.

A resistive element 8 made of tantalum and aluminum is formed on the upper surface of the thermally insulating layer 4 of silicon dioxide. Conductors 10, 10'' are likewise provided on the silicon dioxide layer 4 and are made of aluminum or an alloy of aluminum and copper. It is on the resistive element 8. A passivation layer 12 made of silicon carbide and having a thickness of 0.5 to 2.5 μm is provided on the resistive element 8 and the conductor 10, 10'.

On the top surface of the passivation layer 12, a barrier (lit) element 14,16 is provided. These barrier elements 14,
16 is made of an organic plastic material such as RISION or VACREL, which are organic polymer materials manufactured and sold by DuPont. These barrier elements 14,16 can take various forms. As shown in FIG. 1, the barrier element 14,16 is formed on the side of the resistive element 8 below it. FIG. 2 is a plan view of FIG. 1 with the orifice plate removed. As shown in FIG. 2, these barrier structures utilize three sides of each resistive element. Barrier element 1.
4.16 controls the level of bubble replenishment, prevents sputtering from adjacent orifices, and reduces crosstalk and acoustic reflections between adjacent resistive elements.

Barriers 14, 16 hold orifice plate 18 on top of the print assembly.
The materials used can withstand high temperatures of 300'c.

Orifice plate 18 is made of nickel. As shown in the figure, the inner body of the orifice 2o is provided directly above the resistance element 8 so as to form a negative line therewith.

Although only one orifice is shown, the printhead has an array of orifices with resistive and conductive elements below each orifice to selectively direct ink drops from any orifice. It is designed so that it can be released. Hariya 1i.

14'', 16.16' space the orifice spray 1-18 above the passivation layer 12B to form an ink reservoir and allow ink to enter the ink reservoir, resistive elements 8.8', Infter X is fed to the orifice above 8”. The barriers 14.14', 16.16' may simply extend between the resistive elements 8.8', 8'', or they may be joined at one end and connected around each resistive element as shown. A barrier structure may be formed on three sides.

When a current is passed through the resistive element 8, the thermal energy generated thereby is transmitted through the passivation layer 12, heating the ink 22 in the orifice 2o directly above the resistive element 8, and partially vaporizing it. Due to the evaporation of the ink 22,
An ink droplet 22' is ejected and impinges on a nearby recording medium (not shown). heating.

The ink vapor bubbles generated during evaporation collapse in the area directly above the resistive element 8. Resistance element 8, passivation layer 12
protected from the harmful effects of ink bubbles. The silicon carbide passivation 12 is the layer that is in direct contact with the ink and protects the underlying material due to its high hardness and high resistance to cavity formation.

In fabricating the printhead structure of the present invention, film deposition and f.
Ormati.

It will be appreciated that any element or brow geometry may be achieved using techniques well known in the art of n). Some of these techniques include forming a layered device using photoresist - an etching process that exposes the hollow areas, followed by a deposition of the material to form the device.
osit). These processes for forming the various layers and elements of printhead assemblies are well known in the art.

The present invention will be explained below using examples.

Figure 3.4 is a perspective view and a top view of a resistive element structure used in the print head of the present invention. The passivation layer and orifice plate have been omitted from these figures to better illustrate and explain the resistor structure used in the present invention.

In FIGS. 3 and 4, the resistive elements 8.8', 8'' can be formed by depositing tantalum and aluminum on a passivation layer 4 of silicon dioxide formed on a silicon substrate. Instead of one resistor element, one
A pair of resistive elements 8', 8 is provided. This divided resistance element structure is, for example, about 5.08 μm×101.6 μm each.
The structures have dimensions of 2 mils x 4 mils and are spaced approximately 15.24 μm (0.6 mils) apart from each other. The electrical energy for heating is supplied to both of these resistance elements 8.
10.10 in contact with the ends of ', 8'', respectively.
°, 10" are supplied to the resistive elements 8", 8".

In reality, an inert layer (
(not shown) is provided.

FIG. 5 shows the relationship between the print 7F of FIGS. 3 and 4 and ink droplets. In FIG. 5, in this split-axis resistance structure, the ink bubbles 22 that are formed and collapsed on the resistive elements 8'' and 8 act on the non-resistive area between these resistive elements, causing damage to these resistive elements. is greatly reduced or completely prevented.

FIG. 6A shows a typical geometry of a conventional resistance element 8. As shown in the figure, the resistive element 8 is provided with conductors 10, 10' in contact with both ends thereof. In addition, this resistance element is square (typically 101.6 μm on a side)
(4mi1). Resistance element 8 shown in Figure 68
The sheet resistance of is 50Ω per square. FIG. 6B shows the structure of a resistive element according to the present invention.
The dimensions are (3 mil x 1.5 + nil).

Therefore, the constant resistance element 8°, 8” is 38.1 μm x 38.1
It can be seen that it is made up of two squares of μm (1.5 ml x 1.5 mil). Since the sheet resistance of one square is 50Ω, each leg has a resistance of 100Ω, and the entire resistive element structure has two legs, so it has a resistance of 20Ω. Since the net resistance is four times that of a single square, considerably less current is required to produce the same amount of heating. For example, a conventional device consisting of a single resistive element of approximately 50 ohms required approximately 40 mA to provide the heating necessary to generate sufficient bubbles and droplets.

With the resistive element structure of the present invention consisting of four squares of 50 ohms each, the desired current was reduced to about 200 mA. This means that the power loss in the conductive element was approximately 5%.

〔Effect of the invention〕

The resistive element structure of the present invention does not suffer from damage, and
This allows the operating current to be significantly reduced.

Therefore, such a geometry, coupled with reduced operating current, increases the reliability and lifetime of the resistive element structure.

[Brief explanation of the drawing]

FIGS. 1 and 2 are views showing a conventional print head t". FIGS. 3 and 4 are a perspective view and a plan view, respectively, of a resistive element structure used in the print head of the present invention. Figure 5 is a diagram showing the relationship between the resistive element structure in Figure 3 and ink droplets. Figure 6A is a layout diagram of resistive elements used in a conventional print head. Layout diagram of the resistive elements used. 2: Substrate, 4: Thermal insulation layer, 8.8', 8": Resistive element 10.10', 10": Conductor, 12: Pasihysion layer, 14, 16, 14°, 16':
Barya element. 18 niorifice spray t'+ 20 niorifice. 22: Ink. Applicant Yokogawa Huyuret Paso Card Co., Ltd. Agent Patent Attorney Tsuguo Hasegawa FIG I FIG 2 FIG 4

Claims (1)

[Claims] A print head comprising a plurality of resistive elements provided apart from each other at positions corresponding to one nozzle, and a conductive element electrically connecting the plurality of resistive elements in series.