JP2003291349A - Ink jet recording head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a bubble jet (R) recording head in which excessive heat generation is controlled after bubbling of ink. <P>SOLUTION: A channel 9 is formed by bonding a nozzle forming member 7 to a substrate 6. A heating resistor 13 and a stack 14 are provided in the channel 9. A first electrode 15 and a part of the upper metal electrode 2 of the stack 14 are arranged on the upper surface of the heating resistor 13, and a PCT thermistor 1 having a positive temperature coefficient of resistance is connected in series with the heating resistor 13. When a voltage is applied from a power supply 10 between lower metal electrodes 3, the heating resistor 13 is driven through the PCT thermistor 1 and the upper metal electrode 2 to generate heat. Consequently, ink in the channel 9 is heated and bubbled and an ink drop 12 is ejected from an ejection opening 5. When the temperature of the PCT thermistor 1 exceeds a threshold level subsequently, the resistance increases abruptly to bring about an insulated state and power supply to the heating resistor 13 is interrupted thus stopping heat generation. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer, and more particularly, to an ink jet recording head used for a bubble jet recording type printer utilizing a bubbling phenomenon.

[0002]

2. Description of the Related Art A bubble jet recording method is generally a recording head having fine discharge holes, a flow path communicating with the discharge holes, and a heating element provided in a part of the flow path. A heating element is operated to locally raise the temperature of the ink in the flow channel to generate bubbles, and the high pressure at the time of bubbling is used to eject ink droplets from the ejection holes to It is a recording method to be attached to.

In order to make an image formed in this way highly vivid, a technique for ejecting minute ink droplets at a high density is required. For that purpose, it is necessary to form not only minute discharge holes but also minute flow paths and minute heating elements. Therefore, a method of making a high-density head by making full use of photolithography technology has been proposed, taking advantage of the advantage of the bubble jet recording method that the structure of the recording head can be relatively simple (for example, JP-A-8-15629). Disclosed in the official gazette).

Usually, the heating element has a thickness of 0.05 μm.
A thin-film resistor of tantalum nitride having a thickness of about m is used, and the ink is foamed by Joule heat when energized. In order to prevent damage to the surface of the heating element due to cavitation, such a heating element usually has a thickness of 0.2 μm through an insulating protective layer such as SiN having a thickness of about 0.8 μm.
An anti-cavitation film made of a metal such as Ta having a thickness of about m is provided.

Further, Japanese Patent Application Laid-Open No. 62-201254 proposes to use a heating element having a larger amount of heat generation in the central portion than in the end portions in order to adjust the discharge amount of droplets. Japanese Unexamined Patent Publication No. 5-47457 discloses a positive temperature coefficient (P
Organic sheet heating elements with TC) have been proposed. Japanese Unexamined Patent Publication No. 5-258840 proposes a PTC heating device in which a plurality of PTC elements are connected in parallel. Japanese Patent Laid-Open No. 4-
Japanese Patent Publication No. 97927 discloses an ink ejecting apparatus which uses a PTC thermistor to keep the temperature of ink within a desired temperature range.

[0006]

In the heating element for foaming ink in the recording head of the bubble jet recording system, it is necessary to avoid the influence of the voltage drop due to the dispersion of the resistance value and the wiring resistance on the image quality. For the purpose of, for example, as a drive voltage for driving the heater array composed of a plurality of heating elements, a voltage of about 1.2 times the voltage value that allows stable bubbling over the entire heating element is applied to each heating element. is doing. Therefore, for a normal heating element that is less affected by voltage drop due to resistance variation and wiring resistance, an excess voltage is applied to the entire surface, which is more than the voltage required for ink bubbling. There is a problem that continuous heating continues. Specifically, for example, when a heating element is driven by applying a voltage pulse of 1 μs, the heating element generally foams in about 0.6 μs, and unnecessary heating (excessive heating) by the heating element occurs even after bubbling of ink. Continue, foaming temperature is 3
The temperature of the heating element is 600 to 700 ° C even though it is about 00 ° C.
It may reach a high temperature, and it may become even higher depending on the conditions.

Continuation of such excessive heating is not preferable in terms of energy efficiency because wasteful energy is supplied even after the ink is foamed, and since the temperature of the heating element is excessively increased, the heating element is not heated. The heat resistance of the material is required to be higher than necessary, which may cause thermal destruction in some cases.In addition, repeated large temperature rises may cause deterioration of durability performance of the heating element and the entire recording head. May be.

Therefore, an object of the present invention is to provide an ink jet recording head of a bubble jet recording system which can suppress excessive heat generation after ink bubbling and is preferable from the viewpoint of energy saving, improvement of durability and prevention of thermal destruction. .

[0009]

A feature of the present invention is that, in an ink jet recording head for ejecting droplets by utilizing thermal energy, a resistance heating element and a resistance heating element are connected in series, It has a PTC thermistor whose resistance value rapidly increases when the temperature exceeds a threshold value due to heat generation. The threshold value at which the resistance value of the PTC thermistor sharply rises is preferably in the range of 50 ° C. or higher and 250 ° C. or lower.

According to this structure, after the resistance heating element generates heat and the temperature rises to the extent that the ink is foamed, the PTC
The resistance value of the thermistor can be rapidly increased to cut off the power supply to the resistance heating element. As a result, excessive heat generation and temperature rise of the resistance heating element that does not contribute to ink foaming can be prevented, and energy saving and durability improvement can be achieved.

The PTC thermistor is sandwiched between a pair of electrodes to form a laminated body, the laminated body is arranged in the vicinity of the resistance heating element, and the upper electrode of the lamination body extends to the upper surface of the resistance heating element. It may extend and also function as an electrode of the resistance heating element. According to this, the configuration in which the resistance heating element is switched by the PTC thermistor can be simplified.

A pair of PTC thermistors may be arranged close to each other on both sides of the resistance heating element. With this configuration, the current can be reliably controlled by the pair of PTC thermistors. Further, the structure is substantially symmetrical with respect to the resistance heating element, and the temperature distribution during foaming is also substantially symmetrical, which facilitates thermal design.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
2 is a schematic cross-sectional view of the ink jet recording head according to the embodiment of the present invention, and FIG. 2 is a plan view of relevant parts. The structure of this ink jet recording head will be described. The substrate 6
The nozzle forming member 7 is joined to the above, and the flow path 9 is formed between both. Then, an ejection hole 5 penetrating the nozzle forming member 7 and an ink supply port 8 penetrating the substrate 6 are formed so as to communicate with the flow path 9. Board 6,
The heat storage layer 4 is laminated on the joint surface with the nozzle forming member 7. A resistance heating element 13 and a laminated body 14 are provided on the heat storage layer 4 at appropriate positions for each flow path 9.
The laminated body 14 has a configuration in which the PTC thermistor 1 is sandwiched between a pair of metal electrodes 2 and 3. A first electrode 15 is arranged on the upper surface of the resistance heating element 13, and a part of the metal electrode 2 is arranged so as to face the first electrode 15 with a gap. That is, the metal electrode 2
Is an upper electrode of the laminated body 14 and also functions as a second electrode of the resistance heating element 13, and the PTC thermistor 1
And the resistance heating element 13 are connected in series. An insulating protection layer 16 is provided on the upper surface of the resistance heating element 13 between the first electrode 15 and the upper metal electrode 2. A power supply 10 for applying a drive voltage is connected to the metal electrode 3 below the laminated body 14 and the first electrode 15 of the resistance heating element.

As shown in the temperature-resistance characteristics of FIG.
The C thermistor 1 has a positive resistance temperature coefficient in which the resistance value R rapidly rises when the temperature rises above a predetermined threshold value Tc. Since the bubbling temperature of a normal ink used in an inkjet printer is about 300 ° C. and the thermal energy of the resistance heating element 13 at this time causes the temperature of the adjacent PTC thermistor 1 to be about 50 to 250 ° C., In this embodiment, the threshold value Tc at which the resistance value R rapidly increases is set to 50 to 250 ° C. Therefore,
The resistance value R of the PTC thermistor 1 rapidly increases in response to the temperature rise at the time of ink bubbling due to the heat generation of the resistance heating element 13.

In the ink jet recording head of this embodiment, the power source 10 is connected to the first electrode 1 of the resistance heating element 13.
5 and a voltage applied between the lower metal electrode 3 of the laminated body 14, the resistance heating element 13 is driven through the PTC thermistor 1 and the upper metal electrode 2 to generate Joule heat, and the heat energy causes the Joule heat. The ink in the flow path 9 foams, and the ink droplet 12 is ejected from the ejection hole 5 to the outside.
Since the PTC thermistor 1 in which the resistance value R sharply increases in response to the temperature rise due to the thermal energy of the resistance heating element 13 is arranged in the vicinity of the resistance heating element 13, the PTC thermistor 1 of the PTC thermistor 1 is formed when the ink is foamed. The resistance value R rapidly increases and the supply of electric power to the resistance heating element 13 is cut off.
Therefore, the resistance heating element 13 for foaming the ink of the inkjet recording head is not continuously driven even after the foaming of the ink, and excessive heat generation and temperature rise in the flow path 9 can be prevented.

FIG. 4A shows the resistance heating element 13 as described above.
4B shows the change over time of the surface temperature of the resistance heating element 13 when a voltage is applied between the first electrode 15 and the metal electrode 3 below the laminated body 14, and FIG. Fig. 4 (c) shows the PTC at that time.
The time-dependent change of the resistance value R of the thermistor 1 is shown. These drawings will be described in detail. First from the power supply 10,
When a voltage is applied between the first electrode 15 and the metal electrode 3,
The resistance value of PCT thermistor 1 is very low (R = R1)
Therefore, a voltage is applied to the resistance heating element 13 and the resistance heating element 1
The surface temperature of 3 rises and the ink in the flow path 9 is heated. Then, the ink is thermally foamed, and the ink drop 12 is ejected from the ejection hole 5 to the outside by the foaming pressure. On the other hand, the channel 9
The temperature of the PCT thermistor 1 also rises as the temperature of the ink inside rises, and the resistance value rapidly increases when the threshold value Tc is exceeded (R = R2). The resistance value R has greatly increased,
Since the T thermistor 1 is almost electrically insulated, the metal electrode 3 and the metal electrode 2 are almost not electrically connected to each other, and the voltage is not applied to the resistance heating element 13. Therefore, the driving of the resistance heating element 13 is stopped. In this way, heat generation and temperature rise are suppressed after the bubbling of ink droplets. As a result, excessive heat generation above the foaming temperature is suppressed, the temperature rise of the resistance heating element 13 after foaming can be prevented, and useless power input is suppressed, which is effective for energy saving.

In this embodiment, the resistance R2 of the PTC thermistor 1 at a low temperature is set so that the resistance R2 at a high temperature equal to or higher than the threshold value Tc is at least 10 times or more (different by one digit or more). There is.

In FIGS. 4 (a) and 4 (b), the changes over time in the power consumption and the surface temperature of the resistance heating element in the conventional configuration not using the PTC thermistor 1 are indicated by broken lines.
In the conventional ink jet printer, as described above, normally, a voltage of about 1.2 times the voltage value required for stably foaming ink over the entire surface of each resistance heating element is a plurality of resistance heating elements. Is applied to the heater array. Therefore, an excessive voltage is applied to the resistance heating element over the voltage required for ink bubbling over the entire surface, so that excessive heating continues even after ink bubbling. About 40% of the total power consumption is wasted irrespective of ink bubbling, and the temperature rise of the resistance heating element continues after the ink bubbling. Specifically, for example, when the resistance heating element is driven by a pulse of 1 μs, the temperature is raised to about 300 ° C. in about 0.6 μs to foam the ink, and the resistance heating element is not necessary after the ink bubbling. Heating (excessive heating) continues, and the surface of the resistance heating element reaches a high temperature of about 600 to 700 ° C.

On the other hand, in the present invention, it is possible to save energy by about 40% as compared with the conventional structure, and to suppress the rise of the surface temperature of the resistance heating element 13 to the ink foaming temperature (usually about 300 ° C.). To be

To illustrate a more specific structure of this embodiment, the substrate 6 is made of, for example, Si having a crystal axis <111>.
And has a thickness of 0.625 mm. The nozzle forming member 7 is made of synthetic resin. The ink supply port 8 is formed in the substrate 6 by anisotropic etching of Si. The heat storage layer 4 is made of a Si thermal oxide film having a thickness of 2.75 μm. Metal electrodes 2, 3 and first electrode 15
Is a platinum thin film having a thickness of 0.2 μm.

The resistance heating element 13 has, for example, a film thickness of 0.05.
The TaN thin film of μm has a size of 40 μm × 20 μm that effectively functions as a heating element, and its resistance value is about 100Ω. The insulating protection layer 16 has a thickness of 0.3 μm.
m SiN thin film.

The PTC thermistor heating element 1 is, for example, a barium titanate (BaTiO ₃ ) thin film having a thickness of 0.2 μm, a specific resistance at room temperature of about 10 Ω · cm, and a Curie point Tc of about 100 ° C. The specific resistance at 120 ℃ is about 10
It is 000 Ω · cm. P sandwiched between metal electrodes 2 and 3
The size of the effectively functioning part of the TC thermistor 1 is 20
The device resistance R of the PTC thermistor 1 at room temperature is about 12.5Ω, and the device resistance at 120 ° C. is about 12.5 kΩ.

In the present embodiment, in the above configuration,
A pulse voltage having a pulse width of about 1.0 μsec and a pulse height of about 10 V is applied between the electrodes 3 and 15. by this,
A current of 0.09 A flows, the ink in the flow path 9 is heated and foamed, and the ink droplet 12 can be ejected at a speed of about 15 m / s. When the temperature of the PTC thermistor 1 exceeds the Curie point Tc, the element resistance of the PTC thermistor 1 rapidly increases, current supply to the resistance heating element 13 is suppressed, power consumption is drastically reduced, and excessive heat generation is prevented. It

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, unlike the first embodiment, the PTC thermistors 1a and 1b are arranged on both sides of the resistance heating element 13. The rest of the configuration is substantially the same as that of the first embodiment, and the same parts are assigned the same reference numerals and explanations thereof are omitted.

In the present embodiment, the resistance heating element 13 is arranged in the heat storage layer 4 on the substrate 6, and a pair of laminated bodies 14a and 14b are provided on both sides of the resistance heating element 13, respectively. The laminated body 14a has P between the pair of metal electrodes 2a and 3a.
The laminated body 14b has a structure in which the TC thermistor 1a is sandwiched between the PTC thermistor 1b and the pair of metal electrodes 2b and 3b.
On the upper surface of the resistance heating element 13, the metal electrodes 2a, 2 which are the upper electrodes of the laminated bodies 14a, 14b are sandwiched between
The parts b are arranged so as to face each other. That is, the metal electrodes 2 a and 2 b also function as the first and second electrodes of the resistance heating element 13, and the PTC thermistor 1 is provided.
The a and 1b and the resistance heating element 13 are connected in series. The insulating protection layer 16 on the resistance heating element 13 has a cavitation resistant film 1 made of a Ta thin film having a thickness of about 0.2 μm.
7 are formed.

In the present embodiment, since the PTC thermistors 1a and 1b are arranged close to both sides of the resistance heating element 13, the current can be reliably controlled by the two PTC thermistors 1a and 1b. In addition, the structure is substantially symmetrical about the resistance heating element 13, and the temperature distribution during foaming is also substantially symmetrical, which facilitates thermal design.

[0028]

As described above, according to the present invention, the resistance value of the PTC thermistor rapidly increases as the temperature rises when the resistance heating element generates heat to foam ink. The power supply to is cut off. As a result, the drive of the resistance heating element is stopped after the ink is foamed, and it is possible to prevent excessive heat generation and temperature rise of the resistance heating element that does not contribute to the bubbling of the ink, and it is possible to save energy and improve durability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an inkjet recording head according to a first embodiment of the present invention.

FIG. 2 is a plan view of a principal part of the ink jet recording head shown in FIG. 1 with a nozzle forming member removed.

3 is a PTC of the ink jet recording head shown in FIG.
It is a graph which shows the logarithm of the resistance value of a thermistor, and the relationship of temperature.

4A is a graph showing the relationship between operating time and power consumption of the inkjet recording head shown in FIG. 1, FIG.
Is a graph showing the relationship between the operating time of the inkjet recording head shown in FIG. 1 and the surface temperature of the resistance heating element, and (c) is
Operating time and PT of the inkjet recording head shown in FIG.
It is a graph which shows the logarithmic relationship of the resistance value of a C thermistor.

FIG. 5 is a cross-sectional view of essential parts of an inkjet recording head according to a second embodiment of the present invention.

[Explanation of symbols]

1,1a, 1b PTC thermistor 2,2a, 2b Metal electrode on top of stack 3,3a, 3b Metal electrode under the laminated body 4 Heat storage layer 5 discharge holes 6 substrate 7 Nozzle forming member 8 ink supply port 9 channels 10 power supplies 12 ink drops 13 Resistance heating element 14,14a, 14b laminate 15 Electrode of resistance heating element 16 Insulation protection layer 17 Anti-cavitation film

Claims (4)

[Claims] 1. An ink jet recording head for ejecting liquid droplets by utilizing thermal energy, wherein a resistance heating element and a resistance heating element are connected in series,
An ink jet recording head, comprising: a PTC thermistor whose resistance value rapidly increases when the temperature exceeds a threshold value due to heat generated by the resistance heating element. 2. The ink jet recording head according to claim 1, wherein the threshold value at which the resistance value of the PTC thermistor sharply rises is within a range of 50 ° C. or higher and 250 ° C. or lower. 3. The PTC thermistor is sandwiched between a pair of electrodes to form a laminated body, the laminated body is arranged in proximity to the resistance heating element, and the electrode on the upper portion of the laminated body is The ink jet recording head according to claim 1, which extends to the upper surface of the resistance heating element and also functions as an electrode of the resistance heating element. 4. The ink jet recording head according to claim 1, wherein the pair of PTC thermistors are arranged close to each other on both sides of the resistance heating element.