JP2005205892A - Base body for inkjet head, inkjet head, driving method of inkjet head, and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maximumly make an efficiency of heat transfer to ink optimum by decreasing neither the insulation reliability of a protecting film nor the cavitation resistivity. <P>SOLUTION: The base body 20 for the inkjet head has a thermal storage layer 22, a heating resistor 23 and the protecting film (an insulating film 26 and a cavitation resisting film 27) formed on a substrate 21. A total thickness of the protecting film at a part above the heating resistor 23 is 0.2-0.6 μm, and a total thermal resistance value of the protecting film is 5×10<SP>-9</SP>to 50×10<SP>-9</SP>[m<SP>2</SP>×(K/W)]. A total thermal resistance value of the thermal storage layer 22 at a part below the heating resistor 23 is not smaller than twice of the total thermal resistance value of the protecting film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink-jet head driving method and an ink-jet recording apparatus that perform recording on a recording medium by discharging ink according to an ink-jet method, and more particularly to an apparatus that uses thermal energy to discharge ink.

  Note that “recording” in the present invention refers to not only giving a meaningful image such as a character or figure to a recording medium, but also giving a meaningless image such as a pattern. Is also meant.

  In recent years, devices such as printers, copiers, facsimiles with communication systems, word processors with printers, etc., which record on recording media such as paper, thread, fiber, cloth, metal, plastic, glass, wood, ceramics, Furthermore, many recording apparatuses are used in recording apparatuses combined with various processing apparatuses. For these recording apparatuses, high-speed recording, high resolution, high image quality, low noise, and the like are required. An ink jet recording apparatus is an example of a recording apparatus that meets such a demand. An ink jet recording apparatus uses an ink jet head having an ejection port, ejects and ejects ink (recording liquid) droplets from the ejection port, and attaches the droplets to a recording medium for recording. In the ink jet recording apparatus, since the ink jet head and the recording medium are not in contact with each other, a very stable recorded image or the like can be obtained.

  Among such ink-jet heads, an ink-jet head that ejects ink using thermal energy can arrange a large number of ejection openings at a high density, so that high-resolution recording can be performed and compactization is also easy. It has the advantages such as.

  Conventional inkjet heads that use thermal energy achieve a high density by arranging a plurality of heating resistors in a row on a substrate such as silicon, and a common heat storage for the plurality of heating resistors. A structure having a layer or an electric insulating film is generally used (see, for example, Patent Document 1 and Patent Document 2).

  FIG. 15 is a schematic cross-sectional view of a conventional heating head using thermal energy at one heating resistor.

  As shown in FIG. 15, the ink jet head 100 includes a base 120 on which a heating resistor (heater) 123 is formed, and a nozzle material 110 bonded on the base 120. The base 120 has a heat storage layer 122 composed of a plurality of layers such as a thermal oxide film on a surface of a substrate 121 made of silicon, a heating resistor 123 partially formed on the heat storage layer 122, and a heating resistor. Electrode wirings 124 and 125 for supplying electric power to 123, an electric insulating film 126 formed so as to cover the heating resistor 123 and the heat storage layer 122, and cavitation resistance made of Ta formed on the electric insulating film 126. A film 127. The protective film 128 is configured by combining the electrical insulating film 126 and the anti-cavitation film 127. The nozzle material 110 is bonded to the base 120 to form a liquid path having the ink chamber 112 above the heating resistor 123. Further, the nozzle member 110 has a discharge port 111 formed at a position facing the heating resistor 123.

  The ink chamber 112 is filled with ink, and the heating resistor 123 generates heat by applying a voltage to the heating resistor 123 through the electrode wirings 124 and 125 in this state. The ink in the ink chamber 112 is rapidly heated by the heat generated by the heat generating resistor 123 and the film boils. As a result, bubbles are generated in the ink, and the ink is discharged from the discharge port 111 by the pressure based on the growth of the bubbles.

  In order to efficiently transmit the heat energy generated in the heating resistor 123 to the ink, various ideas have been proposed so far regarding the film configuration of the substrate 120.

  With reference to FIG. 16, the principle of heat transfer by heat generation of the heating resistor 123 will be described. In FIG. 16, the amount of heat Q is applied by energizing the heating resistor 123. The amount of heat Q diffuses above and below the heating resistor 123 and becomes Q1 and Q2. The amount of heat Q1 diffused upward is transmitted to the ink 130 on the protective film 128 formed of an electrical insulating film or anti-cavitation film. As a result, bubbles 131 are generated in the ink 130, and ejection is performed as described above. At this time, in order to efficiently transmit the applied heat quantity Q to the ink as Q1, the following measures are taken.

  First, for the layer on the heating resistor 123, the protective film 128 is formed as a thin film having a relatively low thermal conductivity so that heat can be uniformly transmitted to the ink. Since the protective film 128 also serves as insulation from the ink, it is currently considered appropriate to form the protective film 128 with, for example, SiN and to have a thickness of about 0.2 to 0.5 μm.

  The reason why the thickness of the protective film 128 is about 0.2 μm or more is that when the thickness is less than 0.2 μm, the protective film 128 is protected by a step corresponding to the thickness of the electrode wiring generated at the boundary between the electrode wiring and the heating resistor 123. This is because the film 128 is likely to be cut. On the contrary, if the protective film 128 is too thick, the heat generated in the heating resistor 123 is not easily transmitted to the ink 130, resulting in poor energy efficiency. Further, it is thick from the viewpoint of manufacturing variation and manufacturing cost. Is about 0.5 μm.

On the other hand, with respect to the lower layer of the heating resistor 123, a contrivance is made such as sufficiently increasing the thickness of the heat storage layer 122. This thickness is determined empirically by the manufacturing method, the durability of the heating resistor 123, and the like, and is formed with a thickness of about 3 μm by, for example, SiO _x or the like.

  Further, from the viewpoint of increasing the recording speed, a device for shortening the drive energization time (pulse width) of the heating resistor 123 is also devised. For example, if the driving frequency is 30 kHz and the driving is divided into 16 parts, the driving must be performed in about 2 μs or less. Considering the driving margin, shorter pulses are preferable.

It has also been found that more stable foaming can be obtained by shortening the drive energization time and increasing the heat flux. Stable foaming is extremely effective in a discharge method in which bubbles are communicated with the atmosphere, and a drive energization time of about 0.5 to 1.2 μs is an essential configuration for a high-quality recording inkjet head. . Furthermore, the ejection efficiency is further improved by dividing the drive pulse into a plurality of parts and using a double pass and a triple pass.
JP 2001-171127 A JP 2002-11886 A

  However, with the progress of high-quality recording of recording apparatuses, the size of ejected liquid droplets is becoming smaller every day, and now it is a very small liquid droplet of several pl. Therefore, it is necessary to increase the discharge amount with respect to the input energy, that is, the discharge efficiency by several to 10 times compared to the conventional case, which is a difficult problem.

  In order to avoid this problem, a method of thinning the protective film on the heating resistor has been taken, but as described above, in order to maintain the insulation state with high reliability at the stepped portion of the wiring, In consideration of variations and the like, the limit is about 0.2 μm even if it is thin. Even if a material having good thermal conductivity is used for the protective film, the insulation may not be sufficient, or heat may spread in the in-plane direction on the surface of the protective film. This caused a vicious cycle of further reducing the efficiency, and the proper thickness and thermal conductivity of the protective film were not well understood.

  Further, the protective film is formed of a cavitation-resistant film such as Ta in order to prevent discharge deterioration caused by adhering as “koge” due to the thermochemical reaction of the ink or carbonization of the ink composition. As for the material of this film, in order to improve the cavitation resistance, a noble metal material such as Ir exhibiting high durability has been studied. However, since Ir and the like have high thermal conductivity, if the film thickness is increased in order to provide sufficient coverage, the heat energy generated by the heating resistor escapes in the in-plane direction of the film, thus reducing efficiency. The harmful effect is also a problem, and the proper thickness and thermal conductivity of the anti-cavitation film have not been well understood.

  Furthermore, there is a method of increasing the number of heating resistors in order to improve the efficiency and durability of the heating resistors in a pseudo manner. However, increasing the number of heating resistors necessitates a considerable number of drive circuits and memories for this purpose, which not only increases the size of the substrate, but also increases the complexity of driving ICs for the recording apparatus main body. As a result, the cost increases due to the complexity of software and software.

  The present invention has been made in view of the above-mentioned problems, and optimizes the heat transfer efficiency to the ink to the maximum without reducing the insulation reliability of the protective film and without reducing the cavitation resistance. The purpose is to do.

In order to achieve the above object, a substrate for an ink jet head according to the present invention includes a heat storage layer, a heating element for generating thermal energy used for ejecting ink, and a protective film for protecting the heating element in this order. A formed substrate for an ink jet head, wherein a total thickness of a portion of the protective film on the heating element is 0.2 μm or more and 0.6 μm or less, and a thermal resistance of a portion of the protective film on the heating element The value of 5 × 10 ⁻⁹ m ² · K / W to 50 × 10 ⁻⁹ m ² · K / W and lower, and the thermal resistance value of the heat storage layer under the heating element is the value of the protective film It is characterized by being at least twice the thermal resistance value of the upper part of the heating element.

  In the present invention, the heating element or the heating resistor is not a whole layer formed on the heat storage layer, but a part of a region where the heat generated by energization is applied to the ink, that is, a protective film. If not, it refers to the part that heats the ink in direct contact with the ink.

According to the present invention, the heat transfer efficiency to the ink can be optimized to the maximum without reducing the insulation reliability of the protective film and without reducing the anti-cavitation performance. As a result, ink can be efficiently ejected utilizing the characteristics of the inkjet head. Further, the protective film has a thermal resistance value of 5 to 50 × 10 ⁻⁹ m ² · K / W, and the total thermal resistance value of the heat storage layer is more than twice the total thermal resistance value of the protective film. Since the configuration can be arbitrarily changed, there is an effect that the degree of freedom in design is improved and the cost can be reduced.

  In this specification, “(numerical value A) to (numerical value B)” indicates a range of “numerical value A or more and numerical value B or less”.

  Next, embodiments of the present invention will be described with reference to the drawings.

<Outline of the inkjet head of the present invention (examination by the inventors)>
First, the outline of the present invention will be described. It is an object of the present invention to make the protective film on the heating resistor have a proper thermal resistance. First, in the ink jet head having the film configuration as shown in FIG. 15, the inventors set an empirically optimum thickness of the protective film on the heating resistor from the viewpoint of insulation reliability and cavitation resistance. Assuming 0.3 μm to 0.5 μm, the total thermal resistance of the protective film was changed by changing its thermal conductivity, and the change in foaming efficiency was calculated using a three-dimensional heat conduction simulation. The result is shown in FIG.

FIG. 1 is a graph showing the relationship between the thermal resistance value of the protective film and the critical foaming pulse width, which is the minimum energization driving time necessary for ejecting ink, which is an index of heat conduction efficiency. As conditions at this time, the thickness of the heating resistor was 0.05 μm, the thickness of the electrode wiring was 0.2 μm, and the material was Al. As the heat flux, the input energy per unit volume of the heating resistor was 4.55 × 10 ¹⁶ W / m ³ . This is equivalent to a square heating resistor having a side of 26 μm, a resistance value of 100Ω, and a current of 120 mA flowing. At this time, what calculated the time for normal temperature water just above the center of the heating resistor to reach 300 ° C. is called a critical foaming pulse. In FIG. 1, the smaller the critical foaming pulse width is, the less foaming is performed, and thus the foaming efficiency of the heating resistor is improved.

As is apparent from FIG. 1, the same tendency is shown in all film thicknesses of 0.3 μm, 0.4 μm, and 0.5 μm, and the thermal resistance value of the protective film is about 5 to 10 × 10 ⁻⁹ m ² · K. It has been found that the critical foaming pulse width becomes the minimum when about / W, that is, the extreme point at which the foaming efficiency of the heating resistor is maximized. In a conventional protective film composed of a 0.3 μm thick electric insulating film made of SiN and a 0.23 μm thick cavitation resistant film made of Ta, the thermal resistance value is about 2.5 × 10 ⁻⁷ m ^2.・ It is about K / W. This means that in the case of a protective film having a thin film thickness of 0.3 μm to 0.5 μm, even if the thermal resistance value is lowered to the above range, the thermal energy generated in the heating resistor is in the plane of the protective film. It shows that the foaming efficiency is improved as a result without divergence in the direction.

  If the thermal resistance value is further lowered from the above range, the critical foaming pulse width starts to rise, and the foaming efficiency deteriorates. This indicates that even in a protective film having a thin film thickness of 0.3 μm to 0.5 μm, the thermal energy generated by the heating resistor is diffused in the in-plane direction of the protective film.

Further, from FIG. 1, a region critical foam pulse width is minimized is relatively wide, even higher than ^{10 × 10 -9 m 2 · K} / W, foaming up to about ^{50 × 10 -9 m 2 · K} / W It is clear that the efficiency does not change much. Of course, the most preferable thermal resistance value is in the range of 5 to 10 × 10 ⁻⁹ m ² · K / W.

  In addition, FIG. 1 shows the result of simulating the thickness of the protective film in the range of 0.3 to 0.5 μm, but the same characteristics are obtained until the thickness of the protective film is in the range of 0.2 to 0.6 μm. This is confirmed by this simulation.

  Next, in order to realize the above-mentioned thermal resistance value, the degree of thermal conductivity of the protective film was calculated. As the conditions at this time, the cavitation-resistant film in the configuration shown in FIG. 15 is left as it is (material: Ta, film thickness: 0.23 μm) so as not to change the conventional inkjet head as much as possible. The calculation was performed again by changing the thickness (0.1 μm, 0.2 μm, 0.3 μm) and the thermal conductivity. This is because the thermal conductivity of Ta constituting the anti-cavitation film is larger than that of SiN constituting the insulating film and does not significantly affect the foaming efficiency. That is, it is considered that the foaming efficiency mainly depends on the insulating film. It is. As specific thermal conductivity values used in this simulation, the thermal conductivity of the thin film Ta is a value generally obtained from the literature, although the thermal conductivity of the thin film depends on the thickness and the film forming process. = 54 W / m · K, thermal conductivity of thin film SiN = 1.2 W / m · K was used. For example, the thermal conductivity of the thin film SiN varies from about 1.2 to 32 W / m · K, but is still smaller than the thermal conductivity of Ta.

  FIG. 2 shows the relationship between the thermal conductivity obtained as described above and the critical foaming pulse width. As is apparent from FIG. 2, the critical foaming pulse width is minimized when the thermal conductivity of the insulating film is in the range of 10 to 200 W / m · K. In this range, it can be seen that the critical foaming pulse width hardly changes, and good foaming efficiency can be obtained. In addition, FIG. 2 shows the result of simulation of the film thickness of the insulating film in the range of 0.1 to 0.3 μm, but the same characteristics are obtained even in the range of the film thickness of the insulating film from 0.3 to 0.4 μm. Show.

  Further, when the insulating film thickness was 0.3 μm, the thermal conductivity of the insulating film was changed in the range of 2 to 500 W / m · K, and the water just above the heating resistor became around 300 ° C. FIG. 3 shows the temperature distribution on the protective film in contact with water just before foaming. As is apparent from FIG. 3, the surface area of the heating resistor reaching 300 ° C. becomes smaller as the thermal conductivity becomes higher. This is because, as described above, when the thermal conductivity is high, the thermal energy generated in the heating resistor is diffused in the in-plane direction. According to FIG. 3, until the thermal conductivity is up to about 100 W / m · K, there is not much divergence in the in-plane direction, and there is no significant change compared to the thermal conductivity of the insulating film in the conventional inkjet head. . However, it can be seen that when the thermal conductivity is about 500 W / m · K, the equilibrium region at 300 ° C. is almost eliminated, and the thermal energy is diverged in the in-plane direction.

  From the above, when the protective film has an insulating film and a cavitation-resistant film made of Ta, the thermal conductivity of the insulating film is 10 to 200 W / m · K in order to improve the foaming efficiency. Is preferable, more preferably 10 to 100 W / m · K, and most preferably 10 to 50 W / m · K.

  Referring to FIGS. 1 and 2 again, the critical foam pulse width is about 0.2 to 0.6 μs. However, when the ink is actually foamed and ejected, in order to give a drive pulse that is increased by a certain percentage to this critical foaming pulse width in consideration of variations in manufacturing of the inkjet head, as described above, the bubble This is almost the same as the conventional driving condition of 0.5 to 1.2 μs, which is an appropriate condition of a high heat flow rate for performing stable discharge in a discharge method for communicating with the atmosphere. Furthermore, in consideration of not only the manufacturing variation of the inkjet head but also the temperature environment in which the inkjet head is actually used, if the drive pulse width for ejecting ink is 0.2 to 2.0 μs, Almost no problem.

Furthermore, the present inventors examined the influence of the heat storage layer on the heat transfer efficiency to the ink. First, in the ink jet head having the film configuration as shown in FIG. 15, the protective film is a 0.3 μm thick SiN film (insulating film) and a 0.23 μm Ta film (anti-cavitation film). When the heat storage layer is a SiO ₂ film with a film thickness of 2.5 μm and when it is a SiO ₂ film with a film thickness of 1.5 μm, the heating resistor is driven with a driving pulse width of 0.8 μs. The change with time of the surface temperature from the time of applying the body drive pulse was calculated using a three-dimensional heat conduction simulation. The result is shown in FIG.

  As is clear from FIG. 4, when the two types of heat storage layers are compared, the maximum peak temperature is approximately the same at about 500 ° C., but the subsequent temperature decreases more rapidly as the film thickness is thinner. From this result, it is considered that the heat transfer efficiency to the ink does not decrease even if the thickness of the heat storage layer is reduced.

  Next, to what extent the heat storage layer can be thinned without reducing the effect of heat transfer to the ink was calculated using a three-dimensional heat conduction simulation. The result is shown in FIG.

  FIG. 5 is a graph showing the relationship between the thickness of the heat storage layer and the critical ink foaming energy per unit area of the heating resistor, obtained by the simulation. The critical ink foaming energy per unit area of the heating resistor is an index of heat transfer efficiency to the ink. The ink critical foaming energy is a critical thermal energy value necessary for the temperature of the heating resistor surface to exceed the ink foaming temperature of 300 ° C., and the larger this value, the worse the heat transfer efficiency. I mean. The calculation was performed by changing the heat energy application time (Pw), which is the drive energization time, from 0.5 μs to 3.0 μs. This heat energy application time is an appropriate time obtained as a condition that it is necessary to drive at high speed from the viewpoint of the recording speed of the inkjet head and is not too short from the drive pulse accuracy. Further, this time includes an appropriate condition of high heat flux for performing stable discharge in the discharge method in which bubbles communicate with the atmosphere, that is, the drive energization time of 0.5 to 1.2 μs described above.

  As is apparent from FIG. 5, when the thickness of the heat storage layer is thinner than about 0.7 μm, the efficiency of heat conduction to the ink is abruptly deteriorated. This shows that the thickness of the heat storage layer may be 0.7 μm or more. Moreover, it is difficult to stably form a heat storage layer thinner than 0.7 μm.

  Furthermore, it can be seen from FIG. 5 that the heat transfer efficiency is worse as the heat energy application time (Pw) is longer, and the influence of the thickness of the heat storage layer is larger as Pw is longer. Specifically, when Pw is 1.2 to 2 μs, the thickness of the heat storage layer is 1.0 μm or more, and when Pw is 1.2 μs or less, which is a high heat flux condition, the thickness of the heat storage layer is 0.7 μm or more. However, it turns out that efficiency does not fall and is appropriate.

From the above, when the protective film is a SiN film with a film thickness of 0.3 μm and a Ta film with a film thickness of 0.23 μm, in order to improve the heat transfer efficiency, the thickness of the heat storage layer made of SiO ₂ Is suitably 1.0 μm or more, and further, it can be said that the drive energization time is proper when the Pw is 1.2 μs or less and the thickness of the heat storage layer is 0.7 μm or more. The drive energization time is not limited to one pulse, but may be a pulse drive divided into a plurality of pulses. In this case, the total energization time of each pulse width corresponds to Pw. The relationship shown in FIG. 5 is consistent with the simulation in the prototype head described above.

  Here, the materials and thicknesses of the protective film and the heat storage layer are specifically exemplified, but the present invention is not limited to these. In the present invention, the applied thermal energy is efficiently transmitted to the ink. Therefore, the above-described conditions can be replaced with the thermal resistance ratio between the protective film and the heat storage layer.

The result of the replacement is shown in FIG. FIG. 6 shows the relationship between the thickness of the heat storage layer and the heat resistance ratio of the heat storage layer / protective film, in which the condition of the heat storage layer in the condition of the protective film described above is replaced with the thermal resistance ratio between the heat storage layer and the protective film. It is a graph to show. The thermal conductivity of each film at this time was as described above for the thin film SiN and the thin film Ta, and the thin film SiO ₂ was set to 1.38 W / m · K. This value was also a value generally obtained from literature. The thermal resistance value Rs of the thin film is given by Rs = d / K, where K is the thermal conductivity of the material constituting the thin film and d is the film thickness. Further, the thermal resistance value of the laminated film is the sum of the thermal resistance values of the respective films.

  As is apparent from FIG. 6, the heat storage layer thickness condition in the protective film made of the 0.3 μm thick SiN film and the 0.23 μm thick Ta film is 0.7 μm or more. The resistance ratio can be replaced by about twice or more. From this, it is understood that it is appropriate that the ratio of the thermal resistance of the heat storage layer to the thermal resistance of the protective film is about twice or more.

  The relationship described above was obtained by simulation, but the thermal conductivity and foaming efficiency of the actually manufactured inkjet head are not exactly the same as the simulation, but the same result as the result verified by the simulation. Is obtained.

<Inkjet recording device>
Next, an ink jet recording apparatus on which the ink jet head of the present invention is mounted will be described with reference to FIG.

  FIG. 13 is a schematic perspective view showing an example of the ink jet recording apparatus of the present invention. In FIG. 13, a lead screw 5004 in which a spiral groove 5005 is engraved is rotatably supported on the main body frame. The lead screw 5004 is driven to rotate through driving force transmission gears 5009 to 5011 in conjunction with forward and reverse rotation of the drive motor 5013.

  Further, a guide rail 5003 for slidably guiding the carriage HC is fixed to the main body frame. The carriage HC is provided with a pin (not shown) that engages with the spiral groove 5005. When the lead screw 5004 is rotated by the rotation of the drive motor 5013, the carriage HC reciprocates in the directions indicated by arrows a and b. It can be done. The paper pressing plate 5002 presses the recording medium P against the platen 5000 over the moving direction of the carriage HC.

  An ink jet recording unit IJC is mounted on the carriage HC. The ink jet recording unit IJC may be in the form of a cartridge in which the above-described ink jet head is integrated with the ink tank IT, or may be in a form in which they are detachably combined with each other. The inkjet recording unit IJC is fixedly supported on the carriage HC by positioning means and electrical contacts provided on the carriage HC, and is detachably attached to the carriage HC.

  The photocouplers 5007 and 5008 constitute home position detection means for confirming the presence of the lever 5006 of the carriage HC in this region and performing reverse rotation of the rotation direction of the drive motor 5013 or the like. A cap member 5022 that caps the front surface of the ink jet head (the surface on which the discharge ports are opened) is supported by a support member 5016 and further includes suction means 5015 to perform suction recovery of the ink jet head through the cap opening 5023. A support plate 5019 is attached to the main body support plate 5018, and the cleaning blade 5017 slidably supported on the support plate 5019 is moved in the front-rear direction by driving means (not shown). It goes without saying that the form of the cleaning blade 5017 is not limited to that shown in the figure, and a known one can be applied. The lever 5021 is for starting the suction recovery operation of the inkjet head, and moves with the movement of the cam 5020 that contacts the carriage HC, and the driving force is transmitted from the driving motor 5013 to a known transmission such as a gear 5010 or latch switching. The movement is controlled by the means.

  These capping, cleaning, and suction recovery processes are performed at the corresponding positions by the action of the lead screw 5004 when the carriage HC moves to the home position side region, but at known timings. Any of these examples can be applied as long as a desired operation is performed.

  FIG. 14 is a block diagram of a control circuit that controls the operation of the above-described ink jet recording apparatus. 14 includes an interface 1700 to which a recording signal is input from an external device such as a computer, a control unit that controls the operation of the ink jet recording apparatus based on the recording signal input through the interface 1700, and a recording head ( A head driver 1705 for driving an inkjet head) 1708, a motor driver 1706 for driving a conveyance motor 1709 for conveying a recording medium (rotating the platen 5000 shown in FIG. 13), and a carrier motor 1710 (of FIG. 13). And a motor driver 1707 for driving a drive motor 5013).

  The control unit receives a recording signal from the interface 1700 and controls the supply of recording data to the recording head 1708. The gate array (GA) 1704, the MPU 1801, and the ROM 1702 that stores a control program executed by the MPU 1701. And a DRAM U 1703 for storing various data such as the recording signal and recording data supplied to the recording head 1708. The gate array 1704 also performs data transfer control between the MPU 1701 and the DRAMU 1703.

  When a recording signal is input to the interface 1700, the recording signal is converted into recording data for recording between the gate array 1704 and the MPU 1701. The motor drivers 1706 and 1707 drive the conveyance motor 1709 and the carrier motor 1710, and the recording head 1708 is driven in accordance with the recording data sent to the head driver 1705 to perform recording. The driving energization time of the heating resistor is also controlled by the MPU 1701.

<Inkjet head>
Next, an example of an inkjet head suitably used in the present invention will be described.

(Inkjet head configuration example 1)
FIG. 7 is a plan view of an essential part of an example of an ink jet head suitably used in the present invention, viewed from the discharge port side. FIG. 8 is a plan view of the base body showing an enlarged view of one of the heating resistors shown in FIG. In FIG. 7, the nozzle material 10 is shown in a transparent state so that the internal structure can be understood.

  The inkjet head 1 includes a base body 20 on which a plurality of heating resistors 23 are formed, and a nozzle material 10 bonded to the base body 20. The heating resistors 23 are arranged in a line. However, in the case of an inkjet head for color, it can be arranged in a plurality of rows for each color. In the nozzle material 10, the discharge port 11 is formed at a position facing each heat generating resistor 23 with its center positioned on the center of the heat generating resistor 23. Further, the nozzle material 10 is formed with a nozzle wall 13 that partitions between adjacent heating resistors 23, and the discharge port 11 is provided for each heating resistor 23 by joining the base 20 and the nozzle material 10. An open liquid path is formed.

  A supply port (not shown) is formed in the base 20 so as to penetrate the base 20 in order to supply ink from the outside of the inkjet head 1 onto each heat generating resistor 23. The supply port opens to an ink chamber common to each flow path. A filter 29, which is a columnar structure, is provided between the ink chamber and each flow path in order to prevent foreign matter from entering the flow path. The insulating film (not shown in FIG. 8) and the anti-cavitation film 27 are provided so as to cover all the heating resistors 23 arranged in a row. Further, as shown in FIG. 5, an electrode wiring 25 is connected to the heating resistor 23.

  The ink is supplied from the supply port into the flow path and flows on the heating resistor 23. In this state, the heat generating resistor 23 is energized through the electrode wiring 25 to generate heat energy, whereby the ink on the heat generating resistor 23 is foamed, whereby the ink is discharged from the discharge port 11. The ink jet head 1 of this example is a so-called side shooter type in which the heating resistor 23 and the discharge port 11 are opposed to each other. The discharge method of the side shooter type inkjet head 1 can be broadly divided into a method in which bubbles generated by driving the heating resistor 23 are communicated with the atmosphere and a method in which bubbles are not communicated with the atmosphere. The present invention is applicable to any of these. In the latter discharge method, the generated bubbles disappear without communicating with the atmosphere.

  FIG. 9 shows a cross-sectional view of the inkjet head shown in FIG. With reference to FIG. 9, the ink jet head 1 of this example will be described focusing on the layer structure of the substrate 20.

The substrate 20 includes a substrate 21 made of silicon, a heat storage layer 22 that also serves as an electrical insulating film, a heating resistor 23 that is partially formed on the heat storage layer 22, and a heating resistor 23. It has electrode wirings 24 and 25 for supplying electric power, an insulating film 26 formed so as to cover the heating resistor 23 and the heat storage layer 22, and an anti-cavitation film 27 formed on a part of the insulating film 26. . The heat storage layer 22 has a three-layer structure in which a thermal oxide film 22a and interlayer films 22b and 22c are stacked in this order from the substrate 21 side. In this example, the thermal oxide film 22a and the interlayer films 22b and 22c are all made of SiO ₂ , and the total heat resistance of the heat storage layer 22 is the total heat resistance of the heat storage layer 22. The film is formed so as to be at least twice the total thermal resistance of the covering film (insulating film 26 and anti-cavitation film 27), that is, the protective film. However, the material of these films constituting the heat storage layer 22, the number of layers and the structure of the heat storage layer 22, can be arbitrarily changed within a range in which the total thermal resistance satisfies the above conditions. For example, at least one layer of the heat storage layer 22 can be an SiO _x film or a BPSG (Boro-phospho silicate glass) film, and any film forming method such as a thermal oxidation method or a CVD method can be used. Can be used.

  The heating resistor 23 is made of TaSiN in this example. The electrode wirings 24 and 25 are made of AlCu. However, the electrode wirings 24 and 25 are not limited to this, and may be Al or other Al alloys. The thickness can be 0.1 to 1.0 μm.

  The insulating film 26 has a two-layer structure in which a SiC film 26b is formed on a SiN film 26a. The film thickness of the SiN film 26a was 0.05 μm, and the film thickness of the SiC film 26b was 0.2 μm. By configuring the insulating film 26 with a plurality of layers in this way, the thermal resistance can be reduced and the insulation reliability can be optimized with respect to the coating of the stepped portion of the electrode wiring 25. However, the structure of the insulating film 26 is not limited to this, and it is three or more layers, the film thickness of the SiC film 26b is 0.2 μm or more, or the film thickness of the SiN film 26b is 0.05 μm or more. You can also. Regarding the anti-cavitation film 27, the material was Ta and the film thickness was 0.23 μm. That is, in this example, the thickness of the entire protective film on the heating resistor 23 is 0.48 μm.

  The nozzle material 10 is bonded onto the base 20 to form the ink chamber 12 between the heating resistor 23 and the ejection port 11.

What is important here is that the thermal resistance values of the insulating film 26 and the anti-cavitation film 27 which are protective films on the heating resistor 23 are made appropriate. In the configuration of the conventional inkjet head shown in FIG. 15, the protective film is composed of an insulating film made of SiN having a film thickness of 0.3 μm and an anti-cavitation film made of Ta having a film thickness of 0.23 μm. Regarding the thermal conductivity of the thin film, the thermal resistance value of the protective film in the conventional ink jet head is assumed to be 54 W / m · K for the thin film Ta, 1.2 W / m · K for the thin film SiN, and 70 W / m · K for the thin film SiC. When calculated, it becomes about 2.5 × 10 ⁻⁷ m ² · K / W. On the other hand, in the inkjet head 1 of this example, the thermal resistance value is about 48 × 10 ⁻⁹ m ² · K / W. On the other hand, in the heat storage layer 22, the thicknesses of the thermal oxide film 22a and the interlayer films 22b and 22c are 1.0 μm, 0.8 μm, and 0.7 μm, respectively. When the thermal conductivity of the thin film SiO ₂ is 1.38 W / m · K, the thermal resistance value of the heat storage layer 22 is about 1.81 × 10 ⁻⁶ m ² · K / W. Therefore, in this example, the total thermal resistance value of the heat storage layer 22 is about 39 times the total thermal resistance value of the protective layer.

  The planar size of the heating resistor 23 is a 26 μm × 26 μm square in this example. However, the size of the heating resistor 23 is not limited to this, and it has been confirmed that there is no problem at least from about 16 μm × 16 μm to about 39 μm × 39 μm. Further, the shape of the heating resistor 23 is not limited to a square, but may be a rectangle. Furthermore, it is also possible to adopt a configuration in which a plurality of heating resistors 23 per discharge port 11 are connected in series, for example, two rectangular ones of 10 μm × 24 μm.

  As described above, by making the thickness and thermal resistance value of the protective film appropriate, the discharge method can be either a method for communicating bubbles with the atmosphere or a method for preventing bubbles from communicating with the insulation reliability and cavitation resistance of the protective film. In terms of optimizing the efficiency of heat transfer to the ink without degrading the properties, there is no significant difference and the same excellent effect can be obtained.

(Inkjet head configuration example 2)
FIG. 10 is a cross-sectional view similar to FIG. 9, showing another example of an ink jet head suitably used in the present invention. In FIG. 10, the same components as those in FIG. 9 are denoted by the same reference numerals as those in FIG.

  The inkjet head of this example is different from the configuration example 1 of the inkjet head in that the insulating film 26 is a single layer and the anti-cavitation film 27 is two layers. Other configurations are the same as those of the configuration example 1 of the inkjet head.

  In this example, the insulating film 26 is made of SiC, and the film thickness is 0.35 μm. The anti-cavitation film 27 has a structure in which a Ta film 27a and an Ir film 27b are stacked from the insulating film 26 side. The film thickness of the Ta film 27a was 0.2 μm, and the film thickness of the Ir film 27b was 0.05 μm. Therefore, the total thickness of the protective film on the heating resistor 23 is 0.6 μm.

  Thus, by forming the anti-cavitation film 27 in a two-layer structure, the thermal resistance is reduced while maintaining the covering property as described above, and also caused by the thermochemical reaction of the ink and the carbonization of the ink composition. It is possible to prevent the discharge characteristics from being deteriorated due to kogation. Here, the anti-cavitation film 27 has a two-layer structure, but may have three or more layers. In addition, although a part of the anti-cavitation film 27 is made of Ir, a noble metal such as Pt having a film thickness of 0.05 μm or more or an alloy thereof can be used instead.

The thermal resistance value of the protective film in this example is about 9.1 × 10 ⁻⁹ m ² · K / W when the thermal conductivity of the thin film Ir is calculated to be 127 W / m · K. Further, since the total thermal resistance value of the heat storage layer 22 is the same as that of the configuration example 1 of the inkjet head, in this example, the total thermal resistance value of the heat storage layer 22 is about 199 times the total thermal resistance value of the protective layer. .

(Inkjet head configuration example 3)
FIG. 11 is a cross-sectional view similar to FIG. 9, showing still another example of an ink jet head suitably used in the present invention. In FIG. 11, the same components as those in FIG. 9 are denoted by the same reference numerals as those in FIG.

  This example is different from the above-described configuration examples 1 and 2 of the inkjet head in that the insulating film 26 and the anti-cavitation film 27 are each formed as a single layer. Specifically, the insulating film 26 is a film made of SiC with a film thickness of 0.35 μm, and the cavitation-resistant film 27 is a film made of Ta with a film thickness of 0.2 μm. Therefore, the total thickness of the protective film on the heating resistor 23 is 0.55 μm.

When the thermal resistance value of the protective film in this example is calculated, it is about 8.7 × 10 ⁻⁹ m ² · K / W, which is the smallest among the configuration examples 1 to 3 of the inkjet head. In other words, it can be said that this example has the optimum foaming efficiency among the configuration examples 1 to 3 of the inkjet head. However, if sufficient performance can be obtained in consideration of the covering reliability of the stepped portions of the electrode wirings 24 and 25 by the insulating film 26, the heat resistant chemical reactivity of the cavitation resistant film 27, and the resistance to kogation adhesion, the protection is possible. When the thermal resistance value of the film is in the range of 5 to 50 × 10 ⁻⁹ m ² · K / W, the foaming efficiency can be further improved by setting a smaller value. The total thermal resistance value of the heat storage layer 22 is about 208 times the total thermal resistance value of the protective film.

  As described above, the ink jet head applied to the present invention has been described by taking a preferable embodiment as an example. In each of the above-described examples, a so-called side shooter type inkjet head in which the discharge port 11 is formed at a position facing the heating resistor 23 has been described as an example. However, the present invention is not limited to this. The present invention can also be applied to a so-called edge shooter type inkjet head 30 as shown in FIG.

  The edge shooter type inkjet head 30 also has a base 50 and a nozzle material 40 bonded thereto, as in the side shooter type inkjet head. The structure of the nozzle material 40 is a side shooter type inkjet head. Is different. Specifically, the position of the discharge port 41 is formed not on the position facing the heat generating resistor 53 but on the end face of the nozzle material 40, and the ink is discharged in a direction substantially parallel to the upper surface of the substrate 50.

  Also in such an edge shooter type inkjet head 30, by applying the above-described configuration of the present invention to the configuration of the protective film including the insulating film 56 and the anti-cavitation film 57 and the heat storage layer 52 in the base body 50, the side shooter The same effect as that of the ink jet head of the type can be obtained.

As described above, when the inkjet head is driven with a drive pulse width of 0.2 μs to 2.0 μs, the total thickness of the protective film formed on the heating resistor is about 0.2 to 0.6 μm. In addition, the total thermal resistance value is set to 5 to 50 × 10 ⁻⁹ m ² · K / W, and further, the thermal resistance value of the heat storage layer under the heating resistor is set to be twice or more, thereby insulating the protective film. The heat transfer efficiency to the ink can be optimized to the maximum without lowering the reliability and without reducing the anti-cavitation performance, thereby enabling efficient ink ejection. In addition, any film configuration may be used as long as the thermal resistance value is within the above range. Therefore, various materials can be used as long as the coating reliability of the heating resistor is maintained. It also has the effect that it can be raised. Furthermore, a film structure that further improves the coating reliability can be obtained, and the cost can be reduced. Also, with regard to cavitation resistance, since the film configuration can be freely designed so that the thermal resistance value falls within the above range, it can also be a film structure with further improved thermal chemical reactivity and resistance to kogation, Not only does the design freedom increase, it also has the effect of improving durability.

It is a graph which shows the relationship between the thermal resistance by simulation, and a critical foaming pulse width explaining the outline | summary of this invention. It is a graph which shows the relationship between the thermal conductivity and the critical foaming pulse width by simulation explaining the outline | summary of this invention. It is a graph which shows the surface temperature distribution of the heating resistor by simulation explaining the outline | summary of this invention. The outline of the present invention will be described. When the heating resistor is driven at 0.8 μs. It is a graph by the simulation which shows the relationship of the change by the time passage of the surface temperature of the heating resistor from the time of the drive pulse application. It is a graph which shows the outline | summary of this invention, and shows the relationship between the thickness of the thermal storage layer by simulation, and the critical ink foaming energy per unit area of a heating resistor. It is a graph which shows the relationship between the thickness of a thermal storage layer, and the thermal resistance ratio of a thermal storage layer / protective film explaining the outline | summary of this invention. It is a principal part top view seen from the discharge outlet side of an example of the inkjet head used suitably for this invention. It is a top view of a base | substrate which expands and shows one of the heating resistors shown in FIG. FIG. 8 is a cross-sectional view of the inkjet head shown in FIG. It is sectional drawing similar to FIG. 9 of the other example of the inkjet head used suitably for this invention. It is sectional drawing similar to FIG. 9 of the further another example of the inkjet head used suitably for this invention. It is sectional drawing of an example of the edge shooter type inkjet head to which this invention is applied. 1 is a schematic perspective view showing an example of an ink jet recording apparatus of the present invention. It is a block diagram of an example of the control circuit which controls operation | movement of the inkjet recording device shown in FIG. It is typical sectional drawing in the part of one heating resistor of the conventional inkjet head. It is a schematic diagram explaining the principle of the heat transfer in an inkjet head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,30 Inkjet head 10,40 Nozzle material 11,41 Ejection port 12 Ink chamber 13 Nozzle wall 20,50 Base 21 Substrate 22,52 Thermal storage layer 23,53 Heating resistor 24,25 Electrode wiring 26,56 Insulating film 27, 57 Anti-cavitation film

Claims (17)

A substrate for an inkjet head in which a heat storage layer, a heating element that generates thermal energy used to eject ink, and a protective film that protects the heating element are sequentially formed on a substrate,
The total thickness of the protective film on the heating element is 0.2 μm or more and 0.6 μm or less, and the thermal resistance of the protective film on the heating element is 5 × 10 ⁻⁹ m ² · K / W to 50 × 10 ⁻⁹ m ² · K / W or less, and the thermal resistance value of the heat storage layer below the heating element is 2 of the thermal resistance value of the protective film above the heating element A substrate for an inkjet head that is twice or more. ^2. The inkjet head substrate according to claim 1, wherein the total thermal resistance value of the protective film is 5 × 10 ⁻⁹ -m ² · K / W to 10 × 10 ⁻⁹ m ² · K / W.   The substrate for an inkjet head according to claim 1, wherein the protective film is formed of a plurality of thin films.   The substrate for an ink jet head according to claim 1, wherein the protective film includes a SiC film having a thickness of 0.2 μm or more.   The substrate for an ink jet head according to claim 1, wherein the protective film includes a SiN film having a thickness of 0.05 μm or more.   The substrate for an ink jet head according to claim 1, wherein the protective film includes a Ta film having a thickness of 0.2 μm or more.   The protective film is an insulating film having a thickness of 0.1 μm or more and 0.4 μm or less and a thermal conductivity of 10 W / m · K or more and 200 W / m · K or less, and the Ta film formed on the insulating film. The substrate for an inkjet head according to claim 6, further comprising an anti-cavitation film including a film.   The base for an inkjet head according to claim 7, wherein the insulating film includes a SiC film having a thickness of 0.2 μm or more.   The substrate for an ink jet head according to claim 8, wherein the insulating film further includes a SiN film.   8. The ink jet head substrate according to claim 7, wherein the anti-cavitation film further includes a thin film made of a noble metal or an alloy thereof.   The substrate for an ink jet head according to claim 1, wherein the protective film includes a thin film made of a noble metal having a thickness of 0.05 μm or more or an alloy thereof. 3. The substrate for an ink jet head according to claim 1, wherein the heat storage layer is at least one thin film made of SiO ₂ and has a total thickness of 0.7 μm or more. 3. The substrate for an ink jet head according to claim 1, wherein the heat storage layer is formed of a plurality of thin films, at least one of which is a SiO _x film or a BPSG film.   The substrate for an ink jet head according to any one of claims 1 to 13, wherein an electrode wiring for energizing the heating element is made of Al or an alloy thereof and has a thickness of 0.1 µm to 1.0 µm. A discharge port for discharging ink having a heat storage layer, a heating element for generating thermal energy used for discharging ink, and a substrate on which a protective film for protecting the heating element is sequentially formed on a substrate. Is an inkjet head provided corresponding to the heating element,
The total thickness of the protective film on the heating element is 0.2 μm or more and 0.6 μm or less, and the thermal resistance of the protective film on the heating element is 5 × 10 ⁻⁹ m ² · K / W to 50 × 10 ⁻⁹ m ² · K / W or less, and the thermal resistance value of the heat storage layer below the heating element is 2 of the thermal resistance value of the protective film above the heating element An inkjet head that is more than doubled. A discharge port for discharging ink having a heat storage layer, a heating element for generating thermal energy used for discharging ink, and a substrate on which a protective film for protecting the heating element is sequentially formed on a substrate. Is provided corresponding to the heating element, and the total thickness of the part of the protective film on the heating element is 0.2 μm or more and 0.6 μm or less, and the heat of the part of the protective film on the heating element is The resistance value is 5 × 10 ⁻⁹ m ² · K / W or more and 50 × 10 ⁻⁹ m ² · K / W or less, and the thermal resistance value of the heat storage layer under the heating element is Using an inkjet head that is twice or more the thermal resistance value of the portion above the heating element,
A method for driving an inkjet head, wherein the heating element is driven for a drive energization time of 0.2 μs or more and 2 μs or less to discharge ink from the discharge port. A discharge port for discharging ink having a heat storage layer, a heating element for generating thermal energy used for discharging ink, and a substrate on which a protective film for protecting the heating element is sequentially formed on a substrate. Is provided corresponding to the heating element, and the total thickness of the part of the protective film on the heating element is 0.2 μm or more and 0.6 μm or less, and the heat of the part of the protective film on the heating element is The resistance value is 5 × 10 ⁻⁹ m ² · K / W or more and 50 × 10 ⁻⁹ m ² · K / W or less, and the thermal resistance value of the heat storage layer under the heating element is An inkjet head that is at least twice the thermal resistance of the portion above the heating element;
An ink jet recording apparatus comprising: driving means for driving the heating element with a driving energization time of 0.2 μs or more and 2 μs or less;

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