INK JET RECORDING HEAD AND SUBSTRATE THEREFOR

Abstract: A substrate for an ink jet recording head comprising: a support member, an electro-thermal converter being provided on said support member and having a heat generating resistive layer and a pair of electrodes connected to said heat generating resistive layer, a glaze layer provided between said support member and said electro-thermal converter except at a heat generat­ ing portion defined between said pair of electrodes.

Description: This invention relates to a substrate for an ink jet recording head, to an ink jet recording head in which the aforesaid substrate is comprised, and to ink jet recording apparatus having the ink jet recording head. The support member of an ink jet recording head has previously been made of silicon, glass or ceramics such as alumina (see for example JP-A-5456453). A support member of silicon does not suffer from performance problems, but is difficult to manufacturing using existing techniques. For example, a silicon wafer long enough to extend the length of a side of A3 or A4 recording paper (Japanese standard) is expensive to produce. A support member of glass has poor heat conductivity so that heat can accumulate in it if the drive frequency is increased, which can cause bubbles to form in the recording liquid which can sometimes cause the problem that discharge of the recording liquid becomes impossible. In the case of a ceramic support member, surface defects can develop during the manufacturing process thereof. These surface defects may be pin-holes or projections of several µm to several tens of µm which are very difficult to find by visual or microscopic inspection and which cannot be detected until after film formation has been completed and film present on the defects comes off, and this has led to the problem that many defects occur during film formation. A ceramic support member also has the disadvantage that it is difficult to obtain a mirror surface having a surface roughness of several tens of Å or less, and usually they are used with a glaze layer provided on the whole of one surface thereof. Howevever, the glaze layer cannot for manufacturing reasons be made thinner than 40 to 50 um, and therefore suffers from the same problem as a glass support member, namely heat accumulation. The present invention provides a substrate for an ink jet recording head comprising a support member, an electro-thermal converter on the support member and having a heat generating resistive layer and a pair of electrodes connected to the heat generating resistive layer, and a glaze layer provided between the support member and the electro-thermal converter except at a heat generating portion defined between the pair of electrodes. The above mentioned substrate loses heat sufficiently rapidly that liquid in contact with it is not undesirably heated by the energy used during recording. It may also be relatively free of surface defects so that defects appearing during the subsequent film forming step are reduced. Furthermore, it can be made sufficiently long and bulky to form an ink jet printer head. The invention will now be further described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 3 are schematic plan views each showing an embodiment of the substrate for the ink jet recording head of the present invention. Figure 2 is a schematic cross-sectional view of the substrate for the ink jet recording head of Figure 1 taken along line A-A' of Figure 1. Figure 4 is a schematic perspective view showing an example of the essential portion of the ink jet recording head of the present invention. Figure 5 is a schematic perspective view of an ink jet recording apparatus provided with the ink jet recording head according to the present invention. Figure 6 is a graph showing the result of an experiment carried out with regard to the heat radiating property by the use of the substrate for the ink jet recording head according to an embodiment of the present invention and the substrate for the ink jet recording head according to a comparative example. DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will hereinafter be described in detail with reference to the drawings. Figure 1 is a schematic plan view showing the characteristic portion of a preferred embodiment of the substrate for the ink jet recording head of the present invention, and Figure 2 is a schematic cross-sectional view taken along line A-A′ of Figure 1. In this substrate for the ink jet recording head, a glaze layer 2 having an aperture in the form of a window is laid on a support member 1, and a heat accumulating layer 3 and a heat generating resistance layer 4 are layered so as to be disposed at least on that portion of the support member 1 on which the glaze layer 2 is absent ( the unglazed portion). A pair of electrodes 5 are connected to the head generating resistance layer 4 so that a current can be supplied to the latter. That is, in this substrate for the ink jet recording head, the heat generating resistance layer 4 on the unglazed portion forms a heat generating portion which is a portion generating heat energy available to discharge ink. In such a substrate for the ink jet recording head, the heat conduction in the direction of thickness of a portion X on which said heat generating portion is formed can be suitably determined by the heat accumulating layer 3 whose desired thermal characteristic can be chosen by the selection, for example, of a material (for example, an inorganic oxide such as SiO₂) and thickness. Therefore, according to the present embodiment, a good heat radiation property can be secured in the portion X, and the problem of heat accumulation as previously described does not arise. Moreover, since the glaze layer 2 covers most of the support member 1 and burries the surface defect of it therein, there can be obtained a mirror surface. Therefore, little or no defect occurs to the film formed and defects in film formation are reduced very much. That is, the heat generating portion of an electro-thermal converting member formed on the support member 1 and having a heat generating resistance layer and a pair of electrodes connected to the heat generating resistance layer does not occupy a large area if viewed from the area of the entire support member (or the area of the portion of the support member on which at least the electro-thermal converting member is provided) and therefore, the reduction in yield caused by the defective region of the support member can eventually be decreased sharply. Another embodiment of the present invention is shown in Figure 3. In this substrate for the ink jet recording head, an unglazed portion Y, including electrodes 5 between adjacent heat generating portions, is provided in the form of a band. That is, below some of the electrodes 5, there are also locations in which the glaze layer 2 is not layered. In this case, the ease with which the recording head is manufactured is improved. These embodiments should be chosen by the equilibrium or the like between the degree of requirement for the operational effect regarding said heat radiation property and smoothness and the case and cost with which the recording head is manufactured. In the present invention, it will suffice if the glaze layer 2 does not substantially exist at least in the portion X on which the heat generating portion is formed, and there are no special limitations in the size of the heat generating resistance layer 4, the connected state of the electrodes 5 and the heat generating resistance layer 4, the material of each portion, etc., and the heretofore known factors may safely be used. For example, the heat generating resistance layer 4 may be of a size substantially equal to the size of the portion X in which the heat generating portion is formed. However, in view of the problems enumerated with regard to the prior art, a ceramic material such as Al₂O₃, SiC or AlN may be mentioned as a suitable material of the support member. Also, in the present invention, it is preferable that the heat accumulating layer 3 is present as described above, but depending on the characteristic or the like of the material of the support member, the heat accumulating layer 3 may be omitted. Further, in the present invention, a protective layer may of course be provided on the upper surface or the like of the portion X in which the heat generating portion is formed. To form the glaze layer 2 partly on the support member 1 during the manufacture of the substrate for the ink jet recording head of the present invention, utilization can be made of a selective coating method using the screen printing, a method of carrying out the selective etching after the coating of the glaze layer 2, or the like. The heat accumulating layer 3 and the heat generating resistance layer 4 may be formed by a known method. As regards the heat accumulating layer 3, it may be formed on the support member 1 before the glaze layer 2 is formed on the support member 1. That is, the heat accumulating layer 3 may be provided between the support member 1 and the glaze layer 2. In order to form the glaze layer according to the invention, the conventional material for fused glass layer or glaze layer may be used. Such a glaze layer has an average composition as follows. SiO₂ 50 - 68 wt % BaO 5 - 18 wt % Al₂O₃ 5 - 13 wt % others rest The following may be used to form the glaze layer. GS-2, GS-3, GS-5 (Kyocera Corporation) GS-8, GS-21, XG-903 (Nippon Tokushu Togyô Corporation) HKG-1052 (Hitachi Chemical Corporation) An essential portion of the ink jet recording head of the present invention is of such structure as shown, for example, in Figure 4. The recording head shown in Figure 4 is provided with discharge ports 6 for discharging liquid and causing the liquid to fly as liquid droplets, liquid paths 7 communicating with the discharge ports 6, heat generating portions 4a which are portions provided in the liquid paths 7 and generating energy available to discharge the liquid and cause the liquid as liquid droplets, a liquid chamber 8 communicating with the liquid paths 7, and supply ports 9 for supplying the liquid to the liquid chamber 8. In the ink jet recording head shown in Figure 4, the direction in which the ink is discharged from the discharge ports and the direction in which the ink is supplied from the liquid chamber to the liquid paths are substantially parallel to each other, but this is not restrictive in the present invention. The present invention may be, for example, an ink jet recording head of the type in which said two directions are substantially perpendicular to each other. Figure 5 is a schematic perspective view of an ink jet recording apparatus carrying thereon the aforedescribed ink jet recording head according to the present invention. In Figure 5, the reference numeral 1000 designates the body of the apparatus, the reference numeral 1100 denotes a main switch, and the reference numeral 1200 designates an operating panel. (EXAMPLE) The ink jet recording head according to an embodiment of the present invention whose characteristic portion is shown in Figures 1 and 2 and whose essential portion is shown in Figure 4 was made in the following manner. A glass paste layer (GS-5, Kyocera Corporation) formed with a plurality of apertures in the form of windows was formed on a support member 1 of Al₂O₃ (an alumina smooth support A-491, Kyocera corporation 35x37x thickness 0.635) by the screen printing method and then after drying, a glaze layer 2 (thickness: 45µm is formed by calcining at 1200°C. A heat accumulation layer 3 (thickness: 2.75 µm) of SiO₂ and a heat generating resistance layer 4 (thickness : 1500 Å) of HfB₂ were layered on the glaze layer 2 by the utilization of the RF sputtering method. Subsequently, a layer (thickness : 6000 Å) of Al electrode material was formed by the electron beam vapor deposition method (a first step). Electrodes 5 of a predetermined pattern were formed by the photolithography technique, whereafter an ink protecting film (not shown) of SiO₂ was formed by the RF sputtering method, and a substrate 10 for an ink jet recording head according to the present embodiment was formed. A wall member 11 was then provided on said substrate by the use of photoresist, and a cover member 12 was provided thereon by the use of photoresist, whereby liquid paths 7 and an ink path having a liquid chamber 8 were made. Finally, the end portions of the substrate 10, the wall member 11 and the cover member 12 were sectioned along a plane containing them to form ink discharge ports 6 which are the opening portions of the liquid paths 7 in the cross-section, whereby an ink jet recording head as shown in Figure 4 was completed (a second steps). (COMPARATIVE EXAMPLE) An ink jet recording head was made in the same manner as the example except that the support member was a glass support member, an alumina support member having a glaze layer formed on the whole of one surface thereof or an alumina support member. (EVALUATION) The substrates for the ink jet recording heads in the course of making of the ink jet recording heads of the example and each comparative example (after being made up to the first step) were formed separately from the head and they were driven at each driving frequency and the surface temperatures of the heat generating portions thereafter were measured when the driving pulse is not applied in a state of equilibrium between the heat accumulation and the heat discharge, and the substantial heat radiating properties of the ink jet recording heads which were the finished products were examined. The result is shown in Figure 6. The drive conditions were as follows: the size of the heat generating portion : 20 x 100 µm, the driving voltage : 1.2 V, the pulse width : 10 µs. As shown in Figure 6, in the substrate (1) for the ink jet recording head according to the present embodiment, as compared with the substrate (2) for the ink jet recording head according to the comparative example using a glass support member or an alumina support member having the glaze layer formed on the whole of one surface thereof, the heat radiating property was improved greatly and a necessary sufficient heat radiating property could be secured for the generally most frequently used frequency range of the order of 0-7 or 8 KHz. As to the number of surface defects, estimation was made by examining the rate of production of defective products after the formation of the heat generating resistance layer. A hundred substrates each having eighty-seven heat generating portions are prepared for each example and comparative example, and the substrates having a wire break or a poor connection were estimated as unsuitable products. With regard to the substrate for the ink jet recording head of the comparative example using an alumina support member, the rate of production of deflective products was about 80%, whereas with regard to the substrate for the ink jet recording head according to the present embodiment, it decreased greatly, namely, to about 0.4%. As described above in detail, according to the present invention, there can be provided a substrate for an ink jet recording head, and an ink jet recording head which can cope with the elongation and bulkiness of the recording head while securing a sufficient heat radiating property necessary to keep the quality of printing, and an ink jet recording apparatus provided with such ink jet recording head. Moreover, according to the present invention, there can be provided a substrate for an ink jet recording head and an ink jet recording head in which the occurrence of defects during the formation of the electrodes and heat generating resistance layer can be minimized and ceramics or the like can be used for the support member and in addition, the yield can be made very high, and an ink jet recording apparatus provided with such ink jet recording head. Further, according to the present invention, there can be provided a substrate for an ink jet recording head and an ink jet recording head in which a mirror surface is formed by a glaze layer and therefore it is easy to recognize an alignment mark during patterning and the accuracy of alignment is good, and an ink jet recording apparatus provided with such ink jet recording head.

Claims: A substrate for an ink jet recording head comprising a support member (1), an electro-thermal converter on the support member (1) and having a heat generating resistive layer (4) and a pair of electrodes (5) connected to the heat generating resistive layer (4), and a glaze layer (2) provided between the support member (1) and the electro-thermal converter except at a heat generating portion defined between the pair of electrodes (5). A substrate for an ink jet recording head comprising a support (1), a plurality of electro-thermal converters on the support member (1) each defined by a heat generating resistive layer (4) and a respective pair of electrodes (5) connected to the heat generating resistive layer (4); and a glaze layer (2) provided between the support member (1) and the electro-thermal converter except at the heat generating portions between the respective pairs of electrodes and at belt-like regions (Y) defined between each pair of heat generating portions. A substrate according to claim 1 or 2 wherein the support member is formed by ceramic material (1). A substrate according to claim 3 wherein the ceramic material comprises at least one selected from Al₂O₃, SIC and AlN. A substrate according to any preceding claim wherein a heat accumulation layer (3) is provided between the glaze layer (2) and the electro-thermal converter (4,5). A substrate according to claim 5, wherein said heat accumulation layer (3) is formed by an inorganic oxide. A substrate according to claim 6, wherein the inorganic oxide comprises SiO₂. A substrate according to any preceding claim wherein a heat accumulation layer is provided between the glaze layer (2) and said support member (1). A substrate according to claim 8, wherein the heat accumulation layer comprises an inorganic oxide. A substrate according to 9, wherein the inorganic oxide comprises SiO₂. A substrate according to any preceding claim wherein a protective layer is provided on the electro-thermal converter. A substrate according to claim 11, wherein the protective layer is formed by SiO₂. An ink jet recording head comprising: a substrate according to any preceding claim; a member (11,12) provided with a recess (6,8) and connected to an ink space defined within said recess (6,8), said ink space communicating with a discharge port (6) for discharging ink. An ink jet recording head according to claim 13, wherein the ink space comprises a region defining a liquid chamber (8) and a plurality of regions (7) defining liquid paths from the chamber (8) to discharge ports (6). An ink jet recording head according to claim 13 or 14, wherein said member having a recess is formed as a unitary member. An ink jet recording head according to claim 13, or 14 wherein said member having a recess has a wall member (11) forming a wall for said ink path (7,8) and a cover member (12) for covering said wall member (11). An ink jet recording head according to claim 16, wherein said member (11) having a recess is formed by photosensitive material. An ink jet recording head according to claim 17, wherein said photosensitive material comprises photosensitive resin. An ink jet recording apparatus having an ink jet recording head according to any of claims 13 to 16. An ink jet recording apparatus according to claim 19 further comprising a switch (1100) for controlling a source of electric power. An ink jet recording apparatus according to claim 19 further comprising an operating panel (1200).

Inventors: TERAI, HARUHIKO, WATANABE, YASUTOMO
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J2
IPC codes: B41J2