METHOD FOR PRESERVING INK JET HEAD AND INK JET HEAD UNIT

Abstract: A method for preserving an ink jet head (1) and an ink jet head unit which can prevent the worsening of the ink discharging features even when the ink jet head (1) is preserved or stored before it is assembled to an ink jet recording apparatus. The preserving method and the ink jet head unit are characterized in that terminals (9) connected respectively to a plurality of energy generating means for generating energy for discharging ink are connected to each other in common by means of a conductive means.

Description: The present invention relates to a method for preserving an ink jet head and an ink jet head unit provided with such ink jet head, said ink jet head having a plurality of energy generating means for generating energy utilized to discharge ink. More particularly, the invention relates to a method for preserving an ink jet head which is to be preserved before assembled to an ink jet printer or which is to be circulated as a service part, and an ink jet head unit provided with such ink jet head. A recording apparatus such as a printer, a facsimile and the like is constructed to form a predetermined dot pattern on a sheet (recording medium such as a paper, a plastic web and the like) supported by, for example, a platen, by energizing an energy generating means provided on a recording head according to recording information. Such recording apparatuses are grouped, according to their recording patterns, into an ink jet system, wire dot system, thermal printing system or the like. As recording heads, i.e., ink jet recording heads of the ink jet system, there are a head using piezo-electric elements (electrical-mechanical converters) provided for the respective ink discharging openings as energy generating means for generating energy utilized to expel ink droplets from the ink discharging openings, a head using exothermic elements (electrical-thermal converters) provided for the respective ink discharging openings, for example as a bubble jet system, and the like. The piezo-electric elements of such a recording head are normally attached around a chamber in an ink path by means of an adhesive. Consequently, when surrounding temperature is changed, the piezo-electric elements are subjected to stress, due to the difference in coefficient of thermal expansion between the piezo-electric elements and the adhesive or between the piezoelectric elements and the material forming the chamber. On the other hand, conventionally, such a recording head, before assembled to the recording apparatus, has been preserved or stored in a condition that electrical connection terminals of the piezo-electric elements are electrically insulated. Therefore, when the recording head was in the preserved condition before it was assembled to the recording apparatus, for example, when the recording head has been stored as a service part for a long time, the piezo-electric elements were subjected to stress due to the change in the surrounding temperature, with the result that electric charges were generated on the piezo-electric elements, thus frequently destroying polarization of the piezo-electric element. Consequently, in the conventional ink jet recording head, there was a problem that, when the recording head itself was stored for a long time before it was assembled to the recording apparatus, due to the reduction of polarization rate of the piezo-electric elements, diameter of each ink droplet was reduced or discharge speed of the ink droplet was decreased, thus losing the recording dignity. Further, in the ink jet head particularly having the exothermic elements (electrical-thermal converters), there was a problem that, when the ink jet head was preserved, if the foreign matter contacted the electrical connection terminals of the exothermic elements, static electricity was generated in the head, which caused the concentration of electric potential into a heater to affect a bad influence upon the latter, thus worsening the discharging feature of the ink jet head or destroying the ink jet head itself. Ink jet heads according to the preamble of the independent claims 1 and 15, that is, ink jet heads having a plurality of energy generating means for generating energy utilized to discharge ink are also known from U.S. patent documents 4 567 493 and 4 380 018. If, however, as has been described in more detail before, an ink jet recording head of this type is preserved or stored for a long time it may happen that oxidation of the electrical terminals (electrodes) and/or static electricity may influence the ink jet recording head, thus impairing the discharging properties of the ink jet recording head or destroying the ink jet recording head. In "PATENT ABSTRACTS OF JAPAN, Vol. 8, Number 226 (E-272)[1663], October 17, 1984" a method for protecting a piezoelectric acoustic transducer is described. Said piezoelectric acoustic transducer has prolonged leads at its electrical terminals, and said terminals can be short-circuited by twisting said leads, thus protecting the transducer. The short circuit is elimited by cutting off the twisted leads. In "EDN, vol. 25, no. 16, September 5, 1980, page 64, pictures a and b" a clip for connecting a flexible cable to a pc board is disclosed. If the flexible cable is pulled out, the clip automatically shorts all the board connections, thus providing antistatic protection for the board. None of the a.m. documents discloses a method suitable for the protection of an ink jet head. It is, therefore, an object of the present invention to provide an ink jet head unit and an ink jet head preserving method which can prevent the worsening of the ink discharging feature even if the head is stored for a long time before it is assembled to a recording apparatus. According to the invention, these objects are achieved by providing an ink jet head unit as claimed in claim 1 and by utilizing a method for preserving an ink jet head as claimed in claim 15. The ink jet head unit according to claim 1 comprises an ink jet head having a plurality of energy generating means for generating energy utilized to discharge ink. Furthermore, a conductive means is provided for electrically connecting to each other each of a plurality of electrodes disposed on the end of a conductive cable connected to said plurality of energy generating means, and said conductive means is made as a conductive clip including a plate-like member clipping said plural electrodes and an area adjacent thereto. The method according to the independent claim 15 for preserving an ink jet head having a plurality of energy generating means for generating energy utilized to discharge ink comprises the steps: providing conductive means for electrically connecting to each other each of a plurality of electrodes disposed on the end of a conductive cable connected to said plurality of energy generating means, and using as conductive means a conductive clip including a plate-like member clipping said plural electrodes and an area adjacent thereto. The invention will now be described in more detail, wherein reference is made to the attached drawings. Fig. 1 is a schematic perspective view of an ink jet head unit according to an embodiment of the present invention; Fig. 2 is a schematic longitudinal sectional view of a part of the ink jet head of Fig. 1; Fig. 3 is a partial schematic perspective view of another electrical connecting means according to the present invention; Fig. 4 is a schematic perspective view showing another embodiment of the ink jet head according to the present invention; Fig. 5 is a exploded perspective view showing further embodiment of the ink jet head according to the present invention; Fig. 6 is a schematic perspective view of an ink jet apparatus incorporating the ink jet head disengaged from the electrical connecting means. In the embodiment shown in Fig. 1, ink supply tubes 2 and a signal supplying flexible cable 3 are connected to an ink jet recording head 1 including ink passages communicating with a plurality (for example, thirty-two) of ink discharging openings, piezo-electric elements attached around chambers in the ink passages by an adhesive, and a sub-tank into which recording ink to be supplied to the ink passages is reserved. In Fig. 2 showing a schematic longitudinal sectional view of a part of the recording head of Fig. 1, the recording head 1 includes the sub-tank 5 within which the ink 4 is reserved, and a plurality of nozzles 6 sealingly communicated with the interior of the sub-tank and forming the respective ink passages. Each nozzle 6 has an ink discharging opening 7 at its tapered free end, and piezo-electric elements 8 are fixed around a chamber (a portion where energy utilized to discharge an ink droplet is supplied to the ink) of each nozzle 6. The piezo-electric elements 8 act as energy generating means for generating energy utilized to create the ink droplets discharged from the ink discharging opening 7, and are attached, for example, by an epoxy adhesive, to the corresponding nozzle 6 to enclose the circumference of the nozzle. The ink supply tubes 2 are extended from the head as shown in Fig. 1, the other ends of the tubes being connected to an main ink tank (normally, for example, a cartridge-type tank which is not shown). The ink is supplied from the main tank to the sub-tank. Each of the piezo-electric elements 8 is provided with electrode terminals 9, connected to electrical connecting terminals, and printed wirings on the flexible cable 3 are electrically connected to the electrode terminals 9 of each piezo-electric element 8. On the other end of the flexible cable 3, an electrical connecting terminal having a plurality of discrete electrodes 10 connected to the ends of the wiring communicated with each of the plural piezo-electric elements 8 and a single common electrode 11 is formed. Incidentally, as shown in Fig. 2, a filter 12 is arranged at an ink inlet end of each nozzle 6. Fig. 1 shows, for example, an ink jet recording head (formed as a unit by connecting the flexible cable and the like) which is in a preserved condition before it is assembled to the recording apparatus. In such a condition, a conductive clip 13 which is one of electrical connecting means and which has a small value of resist sufficient to discharge the electric charges generated on the piezo-electric elements 8 or electrically short-circuits the electrode terminals 9 of the piezo-electric elements 8 is attached to the recording head (In Fig. 1, the clip not attached to the head is shown). The conductive clip 13 is a conductive part for discharging the electric charges generated on the piezo-electric elements 8 by the stress acting on the piezo-electric elements due to the change in the surrounding temperature. In the illustrated embodiment, the conductive clip is closedly attached to each of the electrical connecting terminals i.e., electrodes 10 and 11 formed on the end of the flexible cable 3. The conductive clip 13 shown in Fig. 1 can be attached to the end of the flexible cable 3 to pinch it by the action of a spring (not shown) provided in the clip. The clip can be easily removed from the flexible cable by pressing grips against the action of the spring to open the clip. According to the ink jet recording head as explained in connection with Figs. 1 and 2, since the electrode terminals 9 of each piezo-electric element 8 can be electrically short-circuited or can be dischargeably connected by connecting the conductive clip 13 to the head, even when the ink jet recording head itself is stored for a long time, it was found that the worsening of the recording ability of the recording head could be prevented. More particularly, in case of the ink jet recording head having the construction shown in Fig. 2, if the head is stored in lower temperature environment, the piezo-electric elements are subjected to external compressive force due to the difference in coefficient of thermal expansion between the piezo-electric elements 8 and the epoxy adhesive. By such external force, there arise electric charges having polarization opposite to the polarization of the piezo-electric element. Consequently, if the electric charges generated on the piezo-electric elements 8 cannot be discharged as in the case of the conventional ink jet recording head, when the head is stored in the lower temperature environment, an electric field having the polarization opposite to the polarization of the piezo-electric elements acts on the piezo-electric elements 8, thus frequently decreasing the polarization rate of the piezo-electric elements to worsen the piezo-electric feature. However, according to the present invention, since the electrode terminals 9 of each piezo-electric element 8 (or electrodes 10 and 11 of the flexible cable) are electrically short-circuited or the terminals of the piezo-electric element are connected to the small value of resister sufficient to discharge the electric charges generated on the piezo-electric element by the presence of the conductive clip 13, even when the head is stored for a long time in the environment where the temperature is changed, it was found that the feature of the piezo-electric elements was not worsened for a long time. The following Table 1 shows experimental data indicating the technical effects of the ink jet head according to the present invention, compared with the conventional ink jet recording head. Each Feature Non-Use of Conductive Clip Use of Conductive Clip Initial Feature Feature after stored -30°C, 360 hours Initial Feature Feature after stored -30°C, 360 hours Electrostatic Capacity of Piezo-Electric Element (nF) 4.8 4.1 4.9 4.6 Discharge Speed of Ink Droplet (m/s) 8.4 6.2 8.6 8.1 Diameter of Ink Droplet (µm) 72 65 69 68 (Values in the table show an average of ten samples) The Table 1 shows the comparison in electrostatic capacity of the piezo-electric element, discharging speed of the recording liquid droplet (ink droplet) and diameter of the recording liquid droplet after the ink jet recording heads are stored for 360 hours in a temperature of -30°C between the head not using the conductive clip (conventional head) and the head using the conductive clip (present invention). Each of the values indicated in the Table 1 is an average value of values obtained from ten samples. As apparent from the Table 1, when the head is stored in the lower temperature environment, the change in each of features regarding tne ink discharging if the conductive clip 13 is used (present invention) is apparently smaller than that in the case of non-use of the conductive clip (conventional head), which proves that the use of the conductive clip 13 improves the features regarding the ink charging ability of the ink jet recording head. Next, Fig. 3 shows another conductive clip 23 which can be used in place of the conductive clip 13 of Fig. 1 and which has a different construction from the clip 13. The conductive clip 23 is also made of conductive material and can be sealingly attached to each of the electrical connecting terminals 10 and 11 formed on the end of the flexible cable 3. In this case, the conductive clip 23 is attached to the flexible cable in such a manner that it pinches the end of the flexible cable 3 from both upper and lower sides and then a hook 24 formed on one free end of the clip 23 is latched to the other free end of the clip, thereby pressing inner surfaces of the clip against the electrical connecting terminals 10, 11 of the end of the flexible cable 3 by the action of elastic force of the clip itself. Alternatively, in a further embodiment of the present invention, in place of the clip 13 (Fig. 1) or clip 23 (Fig. 3), an conductive adhesive tape (not shown) may be adhered on the electrical connecting terminals 10, 11 formed on the end of the flexible cable 3, in which case substantially the same effect as in the case of the clips can be obtained. As mentioned above, in the present invention, various conductive members having various configurations other than the clip can also be used as the electrical connecting means, i.e., conductive means. Incidentally, as material for forming the electrical connecting means, metal or conductive organic material (conductive rubber, conductive resin and the like) can be used. Fig. 4 is a schematic perspective view of an ink jet head according to another embodiment of the present invention. This ink jet head can be used in place of the ink jet head of Fig. 1. In Fig. 4, the reference numeral 302 designates a discharging opening, 304 designates a liquid passage communicated with the corresponding discharging opening, 305 designates a liquid chamber communicated with the liquid passages, and 306 designates a supply port communicating with the liquid chamber 305. In each liquid passage 304, a heater portion 303 of an exothermic element (electrical-thermal converter) used as energy generating means for generating energy utilized to discharge the liquid or ink is provided. The electrical-thermal converter comprises an exothermic resist layer (not shown) and an electrode layer (not shown) electrically connected to the exothermic resist layer. The electrode layer is connected to the electrical connecting terminals 10 and 11 through the flexible cable 3 of Fig. 1. The ink is supplied to the head by means of the ink supply tubes 2 of Fig. 1 through the supply ports 305. Fig. 5 is a schematic perspective view of an ink jet head according to a further embodiment of the present invention. This ink jet head can also be used in place of the ink jet head of Fig. 1. In Fig. 1, the reference numeral 208 designates a discharging opening, 202 designates a liquid passage communicating with the corresponding discharging opening 208, 205 designates a first liquid chamber communicating with the liquid passages 202, 204 designates a supply port communicating with the first liquid chamber 205, and 206 designates a second liquid chamber communicated with the supply ports 204. Below each of the discharging openings 208, in each of the liquid passages 202, a corresponding heater portion (not shown) of an exothermic element (electrical-thermal converter) used as energy generating means for generating energy utilized to discharge the liquid or ink. The electrical-thermal converter comprises an exothermic resist layer (not shown) and an electrode layer (not shown) electrically connected to the exothermic resist layer. The electrode layer is connected to the electrical connecting terminals 10 and 11 through the flexible cable 3 of Fig. 1. The ink is supplied to the second liquid chamber 206 by means of the ink supply tubes 2 of Fig. 1 and then is supplied to the first liquid chamber 205 through the supply ports 204. The ink jet head of Fig. 5 mainly differs from that of Fig. 4 in the relation between a direction to which the ink is supplied to the heater portion and a direction to which the ink is discharged from the discharging openings. That is to say, in the ink jet head of Fig. 4, the above-mentioned directions are the substantially the same; whereas, in the ink jet head of Fig. 5, the above-mentioned directions are different from each other and are substantially orthogonal to each other. With respect to the ink jet heads having the energy generating means as shown in Figs. 4 and 5, when the head is preserved by utilizing the conductive means 13 shown in Fig. 1, it is possible to easily solve the problems arisen due to the static electricity and the like. Fig. 6 is a schematic perspective view of an ink jet apparatus into which the ink jet head obtained by removing the electrical connecting means or conductive means from the above-mentioned ink jet unit is incorporated. In Fig. 6, the reference numeral 1000 designates a body of the ink jet recording apparatus, 1100 designates a switch for a power source, and 1200 designates a control panel. As apparent from the afore-mentioned explanation, according to the ink jet head of the present invention, when the ink jet head is in the stored or preserved condition, for example, before it is assembled to the recording apparatus, since the electrode terminals of the energy generating means of the ink jet recording head are electrically connected to be short-circuited or to be discharged, even if the head is stored for a long time in the environment where the surrounding temperature changes, it is possible to prevent the worsening of the recording features regarding the ink discharge, such as the descreasing of the discharging speed of the ink droplet or the reduction of the diameter of the ink droplet. A method for preserving an ink jet head and an ink jet head unit which can prevent the worsening of the ink discharging features even when the ink jet head is preserved or stored before it is assembled to an ink jet recording apparatus. The preserving method and the ink jet head unit are characterized in that terminals connected respectively to a plurality of energy generating means for generating energy for discharging ink are connected to each other in common by means of a conductive means.

Claims: An ink jet head unit, comprising an ink jet head having a plurality of energy generating means (8) for generating energy utilized to discharge ink, characterized in that a conductive means is provided for electrically connecting to each other each of a plurality of electrodes (10) disposed on the end of a conductive cable (3) connected to said plurality of energy generating means (8), and in that said conductive means is made as a conductive clip (13; 23) including a plate-like member clipping said plural electrodes (10) and an area adjacent thereto. An ink jet head unit according to claim 1, characterized in that said energy generating means (8) generates thermal energy. An ink jet head unit according to claim 1, characterized in that said energy generating means (8) are electrothermal converters. An ink jet head unit according to claim 3, characterized in that each of said energy generating means (8) comprises an exothermic resist layer and an electrode layer electrically connected to said exothermic resist layer. An ink jet head unit according to claim 1, characterized in that said energy generating means (8) are electromechanical converters. An ink jet head unit according to claim 5, characterized in that said electromechanical converters are piezoelectric elements. An ink jet head unit according to claim 1, characterized in that a direction to which the ink is supplied to said energy generating means (8) is substantially the same as a direction to which the ink is discharged. An ink jet head unit according to claim 1, characterized in that a first direction to which the ink is supplied to said energy generating means (8) differs from a second direction to which the ink is discharged. An ink jet head unit according to claim 8, characterized in that said first and second directions are substantially orthogonal to each other. An ink jet head unit according to any one of the preceding claims, characterized in that said conductive means is made of material selected among metal and conductive organic material. An ink jet head unit according to claim 10, characterized in that said conductive organic material is selected among conductive rubber and conductive resin. An ink jet head unit according to any one of the preceding claims, characterized in that said electrodes (10) are directly connected to said energy generating means (8). An ink jet head unit according to any one of the claims 1 to 11, characterized in that said electrodes (10) are connected to said energy generating means (8) through a connecting means. An ink jet head unit according to claim 13, characterized in that said connecting means is a flexible cable. A method for preserving an ink jet head having a plurality of energy generating means (8) for generating energy utilized to discharge ink, characterized by providing conductive means for electrically connecting to each other each of a plurality of electrodes (10) disposed on the end of a conductive cable (3) connected to said plurality of energy generating means (8), and by using as conductive means a conductive clip (13; 23) including a plate-like member clipping said plural electrodes (10) and an area adjacent thereto.

Inventors: HIROSAWA, TOSHIAKI, SHIMODA, JUNJI, TANABE, SAKIKO
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J2
IPC codes: H05K9, H01R13, B41J2