JPH0443515B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a non-impact type inkjet.
The present invention relates to printers, and particularly to the configuration of print heads.

As data processing technology advances, numerous devices have been developed to permanently record output data. Currently, printing devices can be classified into non-impact (non-mechanical impact) types such as thermal type, electrostatic type, magnetic type, electrophotographic type, ionic type, and inkjet type. Among these, the most important one is the inkjet type. This is because the print output can be easily and directly controlled electronically, and is also contactless, high speed, and particularly suitable for printing on flat paper.

The inkjet method can be classified into the following three basic types. Continuous method (applies constant pressure to ink and generates ink droplets continuously at a constant speed), electric field control method, and on-demand method (impulse jet method). The present invention relates to an on-demand method.

Traditionally, on-demand systems have used piezoelectric crystals to eject ink from an orifice in a narrow cross-section tube. This approach is described, for example, in US Pat. No. 3,832,579, in which a small cylindrical piezoelectric transducer is affixed to the outer surface of a cylindrical nozzle. Ink is conveyed to the nozzle end by an ink hose that connects the wide end of the nozzle to an ink reservoir.
When the transducer receives an electrical impulse, it generates a pressure wave that accelerates the ink toward the ends of the nozzle. An ink droplet is formed when an ink pressure wave overcomes the surface tension of the meniscus at the small end orifice of the nozzle.

A problem with this piezoelectric inkjet device is related to the relative dimensional mismatch between the piezoelectric transducer and the inkjet orifice. That is, the transistor is generally substantially larger than its orifice, limiting either the minimum separation distance between each jet section or the number of jets that can be mounted on a given printhead. Additionally, piezoelectric transducers are relatively expensive to manufacture and are not compatible with many of the current semiconductor fabrication techniques.

Another type of conventional on-demand method is described in U.S. Patent No.
No. 3,174,042, this system utilizes multiple ink-containing tubes. Electrodes within the tubes are in contact with the ink, and current flows through the ink itself in response to the occurrence of a trigger signal. This current heats the ink with high I ² R losses (where is the current value and R is the resistance value of the ink), vaporizes a portion of the ink in their tubes, and causes the ink and ink to evaporate. Gas is injected from those tubes.

The main drawbacks of this vapor-type method are that the ink mist is difficult to control since highly conductive inks require large currents to achieve the desired vaporization, and there are also limitations on the conductivity of the ink. This is what happens. Therefore, the types of ink that can be used are extremely limited.

Despite many years of research into each of the above-mentioned systems, on-demand inkjet technology still suffers from a number of fundamental problems that must be resolved.

The present invention relates to an on-demand inkjet printer, and the present invention relates to an ink-containing capillary tube having an orifice for ejecting ink, and an ink heating mechanism (for example,
(a resistor placed in or adjacent to the capillary tube).

An outline of the operation will be explained. The ink heating section heats rapidly and transfers the energy generated therein to the ink, thereby vaporizing a portion of the ink and generating bubbles within the capillary. This bubble then creates a pressure wave that propels the ink droplet from its orifice onto a nearby paper surface. By properly selecting the relative position of the ink heater and the orifice and by closely controlling the energy transfer, the bubbles can be placed on or near the ink heater before the ink gas escapes from the orifice. It disappears quickly. Much of the current hardware and software used to implement other dot matrix printing devices can be readily adapted to printers according to the present invention.

In the present invention, ink is ejected from an orifice located at the end of a capillary tube. The ink capillary then essentially defines a plane, and ink is ejected from the orifice in a direction perpendicular to the plane. Each of these configurations has advantages over the prior art in that they can be manufactured in large quantities using standard electronic manufacturing techniques. Furthermore, the size of printheads created using the principles of the present invention is virtually unlimited, and because space-consuming piezoelectric crystals are not required, very large arrays and very high resolutions are possible. Furthermore, this technique is independent of the conductivity of the wink used.

The present invention will be explained below using the drawings.

FIG. 1 is an exploded perspective view of a printhead of a certain type of inkjet printer, and FIG. 2 is an overall perspective view after assembly. 11 is a substrate made of sapphire, glass, or an inert composite material (eg, composite metal or coated silicon). A portion of one side of the substrate 11 is covered with a thin metallization layer 13 . This thin film metallization layer 13 has a width D1 (~0.1
mm) and a narrow non-conductive strip 14 with a width D2
(approximately 0.1 mm) conductive strip. A suitable resistance value is approximately 3Ω.
In a typical configuration, resistor 16 is placed at a distance D3 from the edge of substrate 11 (nominally approximately 0.1 mm, but
Generally, they are made at positions separated by a range of approximately 0.05 mm < D3 < approximately 0.25 mm. A capillary block 15 is bonded to the top surface of the thin film metallization layer 13. Capillary block 15 is generally made of glass and has a capillary channel 17 with an orifice at each end.
The width of channel 17 is approximately 0.08mm, and the depth is approximately 0.08mm.
, the width of which corresponds to the width of the non-conductive strip 14 of the metallization layer 13.

Behind the capillary block 15 and above the substrate 11, parallel to the capillary block 15, a reservoir 19 for holding ink is arranged. Channel 17 draws ink from the reservoir 19 by capillary action into the vicinity of an orifice on the opposite side of the reservoir. In the completed configuration, as seen in FIG. 2, the printer has two electrodes 23 and 25 attached to the thin film metallization layer 13, which provide a potential difference across the resistor 16. FIG. 3 is a cross-sectional view of the inkjet printer shown in FIGS. 1 and 2, showing the relative positions of ink 21, capillary block 15, resistor 16, and printing surface 27. FIG.
In operation, the distance D5 between the printer orifice and the printing surface 27 is approximately 0.8 mm.

FIG. 4 is a partial cross-sectional view showing the process of ink droplet generation during one cycle of printing operation. When a voltage is applied to electrodes 23 and 25,
The current passing through resistor 16 generates Joule heat, heating the ink. A bubble 12 is then created on the resistor 16 as shown in Figure 4a. The bubble continues to rapidly expand in the direction of the orifice, as shown in Figure 4b. However, its expansion is limited by the energy transferred to the ink. By carefully controlling this total energy and controlling the time distribution of energy delivered to resistor 16, valves of various sizes can be created. However, it is necessary to control the total energy absorbed by the ink so that it is not so great as to displace gas from the orifice. The bubble begins to deflate towards and above the resistor 16 as shown in Figure 4c, while the forward momentum imparted to the ink by the expansion of the bubble causes an ink droplet to be ejected from the orifice (however, It should be noted that depending on the ink used, the orifice geometry and the applied voltage, one or more subsequent ink droplets will result.) After the droplet leaves the orifice,
The bulb retracts to or near its point of origin and disappears, as shown in Figure 4d. The ink begins to refill by capillary action (Figure 4e), while the ink droplets rest on the printing surface. Figure 4f shows the channel filled with ink to its original position in preparation for the next cycle. Printing is accomplished by continuously applying voltage to resistor 16 in the appropriate sequence. The orifice and print surface are moved relative to each other to create the desired print pattern.

It should be noted that dimensions such as substrate dimensions, capillary block dimensions, and capillary channel dimensions may vary widely depending on desired mass, materials of construction and technology, droplet size, capillary filling rate, ink viscosity and surface tension, etc. it is obvious. Also, in contrast to conventional devices, there is no need to balance the conductivity of the ink with high I ² R heat losses or to make the ink electrically conductive.

A feature of the configuration described above is that the impulse required to eject an ink droplet from an orifice is created by the expansion of a bubble rather than by a pressure wave applied by a piezoelectric crystal or other element. That's true. By carefully controlling the energy transfer from resistor 16 to the ink, ink gas can be prevented from escaping from the orifice along with the ink droplets. The bubble disappears on its own to prevent ink gas from scattering. Furthermore, it is extremely important to have close control over the temporal sequence of energy transfer.

through resistor 16 with a period of approximately 5 μsec.
Although a single square wave current pulse of 1 A achieves the above results, such direct methods are generally not applicable to various jet configurations. Furthermore, problems arise when it is desired to create larger bubbles (eg, use a larger orifice) or to obtain faster droplet ejection rates. If the pulses are lengthened to impart more energy to the ink, the statistical nature of bubble formation results in substantial time jitter. That is, the time from the time of pulse application to the time of bubble completion varies for each applied pulse (or the ratio of the time from the time of pulse application to the time of bubble generation to the width of the applied pulse becomes relatively large). On the other hand, increasing the pulse height to improve the time jitter problem will result in premature burnout of the resistor due to the substantially higher current density required.

Each of the above-mentioned problems is substantially solved by the method shown in FIG. 5 and 6 are waveform diagrams of pulses used for bubble formation. Here, no DC bias level is required, but
The pre-pulse IP is used to preheat the ink near resistor 16 at a rate low enough to avoid bubble nucleation. That is, the temperature of resistor 16 is kept below the boiling point of the ink. The leading pulse IP is followed by a nucleation pulse IN. This nucleation pulse IN rapidly heats the resistor 16 close to the heating limit of the ink, ie, to the point where bubbles spontaneously nucleate within the ink. The bubble core thus formed grows very rapidly and its maturing size is determined by the volume of ink heated by the preceding pulse IP.
During this bubble growth process, the voltage applied to resistor 16 is generally attenuated to zero. This is because heat transfer to the ink during this period is not very efficient and maintaining the current would cause resistor 16 to overheat.

Typically, resistor 16 is approximately 3Ω;
The preceding pulse IP is about 0.3A and about 40μsec
, and the nucleation pulse IN is 1A
It has a width of about 5μsec and a width of TN.
However, these parameters vary over a fairly wide range, so that the typical ranges encountered in practical operation, i.e. 0<R<100Ω;10<
TP<100μsec,0<IP<3A,0<TN<10μsec,
It is appropriate to consider 0.01<IN<5A.

Many other methods for controlling bubble formation are available as well, such as, for example, pulse spatial modulation or pulse height modulation. A further method is shown in FIG. In this method, the magnitude of the preceding pulse is reduced from an initial value of about 0.5A to a value of about 0.2A (the value just before the nucleation pulse begins).
The leading pulse shape decays by 1/√t as a function of time. This allows the temperature of the resistor to be maintained at a nearly constant temperature before nucleation,
The ink near the resistor is heated to a temperature below the boiling point of the ink. In this state, a narrow nucleation pulse for nucleation is applied. Since the nucleation pulse is applied after the temperature of the resistor is maintained at a substantially constant desired temperature, the energy amount of the nucleation pulse can be easily controlled, and the width of the required nucleation pulse can be reduced. . Furthermore, since the pulse width of the nucleation pulse is narrowed, the above-mentioned problem of time jitter can be reduced, and the reproducibility of nucleation is improved. Note that there is a conventional device that preheats a resistor by applying a square wave pulse, but since the pulse is a square wave, after the pulse is applied,
The temperature of the resistor continues to rise gradually, and the resistor temperature before nucleation cannot be approximately constant at the desired temperature. Therefore, the amount of energy of the nucleation pulse, etc. cannot be controlled in accordance with the previously held constant temperature. The method described above preheats the ink without the need for a constant DC bias current and maintains the temperature of the resistor at a substantially constant desired temperature prior to its formation, thus facilitating control of the nucleation pulse; Moreover, the problem of temporal jitter can be solved.

FIG. 7A is an exploded perspective view of another type of inkjet print printer head, and FIG. 7B is an assembled perspective view of the print head shown in FIG. 7A. The print head shown in both figures has multiple orifices. This so-called "edge-shooter" device consists of a substrate 71 and a capillary block 75 which has several ink capillary channels 77 located at the interface between itself and the substrate 71. ing. Typical materials used for substrate 71 include electrically insulating materials such as glass, ceramic, coated metal or coated silicon, while materials used for capillary block 75 include ink capillaries. Regarding the channel 77, one that is easy to manufacture is selected. For example, as standard, capillary block 75 is made of molded or etched glass. In that configuration, substrate 71 and capillary block 75 are sealed together in a number of ways, for example with epoxy, anodic bonding or sealing glass. Channel spacing D ₆ and channel width D ₇ are determined by the desired separation and dimensions of the inkjet. Channel 79 is a storage channel for supplying ink from a remote ink reservoir (not shown) to ink capillary channel 77 .

A plurality of resistors 73 are provided on the substrate 71, the position of each resistor corresponding to the bottom of each capillary channel 77. A corresponding number of electrical connections 72 are provided to supply power to each resistor 73. Resistor 73 and electrical connection 72
are formed using standard electronic fabrication techniques such as physical or chemical vapor deposition. Electrical connection 72
Typical materials for this include chromium/gold (ie, a thin chromium bottom layer for adhesion, and a thin chromium top layer for conductivity), or aluminum. Suitable materials for resistor 73 include, as standard, platinum, titanium-tungsten, tantalum-aluminum, diffused silicon or amorphous alloys. Obviously, other materials can be used for these various functions, but electroplated materials that are corroded by the various inks used should be avoided. For example, in the case of water-based inks, aluminum and tantalum-aluminum present such problems at the current and resistivity used as standards (i.e., resistances in the range of 3-5 Ω and currents on the order of 1 A). . However, even these two materials can be used if a passivation layer is used to isolate the electrical conductor and resistor from the ink.

FIG. 8 is a sectional view of a print head of another type of inkjet printer.
Showing the edge shooter inkjet print head. In this configuration, the thermal energy for generating bubbles within the ink is provided by resistor 83. As in the previous version, resistor 83 is placed a very small distance (~0.1 mm) from the orifice of ink channel 82 (note: the cross-section in Figure 8 shows resistor 83).
3, so its ink channel orifice is not shown). In this type, a substrate 81 of glass is provided as standard and is bonded to an etched silicon capillary block 89. Block 89 defines ink channel 82. Overlying capillary block 89 and ink channel 82 is typically a heat resistant, non-conductive, thermally conductive material such as silicon carbide, silicon dioxide, silicon nitride or boron nitride. A thin film 87 made of a flexible material. Resistor 83 is mounted on membrane 87 by standard techniques, and power to resistor 83 is provided through metallization 85 on each side of the resistor.

The advantage of this configuration over non-flexible structures is that
It is possible to improve the lifespan of the device.
Also, a substrate 81, a capillary block 89 and a thin film 8
7 is essentially completed prior to forming the resistor and metallization layers, thereby simplifying its construction technique. Furthermore, as in the previous model,
This structure is easily adapted to multi-channel devices and mass production techniques. Various variations on techniques for forming resistors on flexible thin films will occur to those skilled in the art. For example, with proper selection of materials, flexible thin films as isolation structures can be completely eliminated by providing resistors that are themselves flexible and self-supporting.

FIG. 9A is an exploded perspective view of a print head of another type of inkjet printer, and FIG. 9B is an assembled perspective view. The structure shown in both figures is a so-called “Side Shooter”.
This is an alternative configuration of a thermal inkjet print head called a "shooter" device. Substrate 9
1 is typically constructed of glass or other inert, rigid, thermally insulating material. The electrical connection to resistor 93 is made using two conductors 92 as in the structure shown in FIGS. 7A and 7B.
It will be given at Two plastic spacers 94 are used to maintain separation between lid 95 and substrate 91, thereby creating a capillary channel 96 for ink flow to the resistor. However, it is clear that many other techniques may be used to provide adequate spacing.
For example, instead of plastic, the glass substrate 91 itself may be etched to provide such channels.

The lid 95 in this type is constructed of silicon which provides a convenient crystalline structure for etching the tapered hole which acts as an orifice 97 for the ink jet. Orifice chair 9
7 is arranged opposite to the resistor 93. This orifice 97 is made, for example, using the technique shown in US Pat. No. 4,007,464. Orifice 97 is
As a standard, it is about 0.1mm. Many other materials can be used for the side shooter ink jet lid 95. For example, a metal layer or even plastic with holes in the portion opposite each resistor could be used.

FIG. 10A is a partially sectional perspective view of a printhead of another type of inkjet printer, and FIG. 10B is a plan view of the substrate of the printhead shown in FIG. 10A. This type is a side shooter device with multiple jets. The substrate 101 is made of glass, and two glass spacers 104 for holding the ink 102 are placed thereon. Silicon lid 105 is provided with a series of etched tapered holes, such as those represented by holes 107 . Each hole has a trough 108
is formed inside. Thicker lids can thus be used, and thicker lids can provide better structural stability to support larger print heads in composite jets. Element 109 is a fill tube connected to a remote ink reservoir (not shown) to allow a continuous supply of ink to the resistor/orifice system.

In FIG. 10B, a second resistor 106 is also shown lying along the trough 108 of FIG. 10A. Power to resistors 103 and 106 is provided through two independent electrical connections 110 and 1.
11 and a common ground 112. A barrier 113 is formed between resistors 106 and 103 to prevent ink from being ejected from orifice 107 when resistor 106 is energized. In the above configuration, barrier 13
1 is constructed of glass, silicon, photopolymer, glass bead-filled epoxy, or electroless plated metal and is formed on the inner surface of the substrate or lid. If a metal lid is used, other methods are available to provide the barrier. For example, the barrier may be constructed by metal plating directly onto the inner surface of the metal lid.

FIG. 11 is a partially sectional perspective view of an inkjet print printhead according to one embodiment of the present invention, incorporating the thin film and external resistor shown in FIG. 8. The details of this embodiment are as follows, except that the substrate is replaced by a thin film 120 and a substrate 121 of silicon carbide, silicon dioxide, silicon nitride or boron nitride.
It is the same as the one shown in the figure. The resistor 123 is a thin film 1
20 and outside the ink. As in the previous type, electrical connection to resistor 123 is provided by two conductors 122.
Substrate 121 is relatively thick for structural stability;
Usually made of etched glass or etched silicon.
On the other hand, the substrate 121 has a recessed portion to enable heat to be supplied to the ink and to allow the thin film 120 to bend while maintaining structural stability. A resistor 123 is placed on this thin film to maintain this characteristic. A trough is also formed in the lid, and a tapered hole is formed within the trough. A thicker lid can be used,
A thicker lid can provide better structural stability to support larger print heads in composite jets.

Many other embodiments are possible constructed of various materials and having many different geometries depending on the particular nature and needs of the application. For example, within certain limits and depending on the ink used, the orifice size can be increased to increase the droplet size, or the orifice can be decreased to decrease the droplet size. can do. Similarly, the maximum frequency for ink droplet ejection depends on the substrate relaxation time and the ink refill time. Different geometric structures may be required depending on the electrical properties of the ink. for example,
If, for highly conductive inks, current flowing through the ink is a problem, a passivation layer may be placed on top of the resistor itself and on the conductors to avoid current conduction.

[Brief explanation of the drawing]

Figure 1 is an exploded perspective view of the print head of a certain type of inkjet printer;
Figure 3 is a cross-sectional view of the print head shown in Figure 2, and Figure 4 shows the process of ink droplet generation during one cycle of printing operation. Figures 5 and 6
The figure shows the waveform diagram of the electric pulse used for bubble formation.
FIG. 7A is an exploded perspective view of a printhead of another type of inkjet printer, FIG. 7B is an assembled perspective view of the printhead shown in FIG. 7A, and FIG. 8 is an exploded perspective view of a printhead of another type of inkjet printer. Cross-sectional view of the print head of No. 9A
9B is an exploded perspective view of the print head of an ink jet printer according to another model, FIG. 9B is an assembled perspective view of the print head shown in FIG. 9A, and FIG. FIG. 10B is a plan view of the substrate of the printhead shown in FIG. 10A, and FIG. 11 is a partially cross-sectional perspective view of the printhead of an inkjet printer according to an embodiment of the present invention. It is. 11: substrate, 13: thin film metallization layer, 14: non-conductive strip, 15: capillary block, 16: resistor, 17: capillary channel, 19: ink reservoir, 23, 25: electrode, 21: ink, 71: Substrate, 72: Electrical connection part, 73: Resistor, 75:
Capillary block, 77: Capillary channel, 81:
Substrate, 82: Channel, 83: Resistor, 85: Metallized layer, 87: Thin film, 91: Substrate, 92: Conductor,
93: Resistor, 94: Spacer, 95: Lid, 9
7: Orifice, 112: Common ground, 101: Substrate, 102: Ink, 103: Resistor, 104:
Spacer, 108: Trough, 120: Thin film, 12
1: Conductor, 123: Resistor.

Claims (1)

[Claims] 1. A substrate having an opening formed by a recessed portion, a non-conductive, thermally conductive and flexible thin film disposed on the surface of the substrate including the opening, and a thin film formed by a portion of the opening. a resistance heating element disposed on the thin film, a lid having a groove and a tapered hole at the bottom of the groove that widens from the top to the bottom; a coupling means having an opening at a position opposite to the resistive heating element and defining an ink channel between the lid and the thin film; An inkjet printer comprising an electrode for the resistive heating element formed on the side surface.