BASE PLATE FOR AN INK JET RECORDING HEAD

Abstract: A base plate for ink jet recording head provided with an electricity-heat convertor and an ink jet recording head using the same are provided. The electricity-heat convertor (9) comprises a substrate (1), a pair of electrodes (3) electrically connected to said heat-­ generating resistor, an oxidized film (13) provided by local anodic oxidation of the surface of said heat-­ generating resistor between said electrodes, and an organic insulating film (12) provided on said electrodes and on at least a part of said heat-generating resistor between said electrodes.

Description: This invention relates to a base plate for an ink jet recording head, the base plate having on it an electro-thermal transducer protected by an organic insulating film and by a protective oxide film formed by anodic oxidation and positioned so as to correspond to a heat generation region of the transducer. Ink jet recording is carried out by discharging a recording liquid (ink) through an orifice (ink discharge port) which is provided in a recording head and fixing the ink onto a recording medium such as paper. This method has a number of advantages in that the amount of noise generated is extremely small, high speed recording is possible, and ordinary paper can be used, that is no special paper is required. Recording heads of various types have been developed. One type is a recording head in which ink is discharged through an orifice by applying heat energy to the ink. This has the advantage that there is a good response to the recording signals, and it allows for the easy formation of many orifices of a high density etc. Typical recording heads of the type that use heat as the ink discharging energy are shown in figures 1A and 1B. Figure 1A is a sectional view of the recording head in the direction of the flow passage and figure 1B is a partially exposed view showing the positional relationship of the bonding between the base plate and the ceiling plate. The recording head of figures 1A and 1B, shown as an example, comprise electricity-heat converters arranged on a base plate 1, each converter having a pair of electrodes 3 and a heat generating resistor 9 positioned between the electrodes, the electrodes and the generator resistors 9 being provided on the base plate with a further protective layer provided on the heat generating resistors 9 and the electrodes 3. These are then positioned under the flow passages 6 and the liquid chamber 11 and a ceiling plate is bonded thereto, the plate having the flow passages 6 and the liquid chamber 11 formed thereon. The ink discharging energy is imparted by the electricity-heat converters. Specifically, when heat is generated from the heat-generating resistor 9 by a current flowing between the electrodes 3, the ink in the flow passage 6 in the vicinity of the heat generating resistor 9 is instantaneously heated to generate bubbles. Ink droplets are discharged from the orifice due to the volume change which is the result of the instantaneous volume expansion and shrinkage due to the generation of the bubbles. The protective layer as described above is provided to protect the electrodes and the heat generator resistors against the ink to prevent the leak of current between the pair of electrodes. For the purpose of protecting the electricity-heat convertors from shock during generation of the discharging energy, a so called cavitation resistance layer may be further provided. It is known to use inorganic materials for example metal oxides etc, which have insulating properties, and to use organic materials such as resins etc for the protective layer. Amongst these materials, anodically oxidised coatings obtained by anodic oxidation of metal materials having good insulating properties have been used. The equipment necessary to prepare these is not as large as that used in the vacuum vapour deposition method, thus having the advantage of high productivity. These are therefore attracting attention as suitable material for the protective layer. However, recording heads which use the anodically oxidised coatings still exhibit a number of problems to allow for then effective use as a protective layer. In DE-A-3403643 a protective layer having higher reliability is obtained by anodic oxidation of the electrode surface. It is also described that anodically oxidised coatings may be formed on the surface of the heat-generating resistor at the same time. When a protective layer which comprise the anodically oxidised coatings are formed on both the electrode surface and the heat-generating resistor surface, if the material of the electrode and the heat-generating resistor are different, then the anodically oxidised coatings formed on these surfaces will be different in, amongst other things, composition and volume expansion. Thus, the protective performance may not be sufficient, and defects such as cracks are liable to be formed at the boundary portion of the anodically oxidised coating between the electrodes and the heat generating resistor. Selecting the conditions and the materials for obtaining good protective performances from the anodically oxidised coatings for both the electrode surfaces and the heat generating resistor surfaces are greatly limited as compared with the case where a single anodically oxidised coating is formed. There is also the difficulty that the constituent materials of the recording head, for example for the electrodes, heat generating resistors, etc and the conditions for anodic oxidation cannot be freely selected. DE-A-3502900 discloses an ink jet recording head which has an inorganic insulating film for the protective layer which is formed according to a thin film forming technique such as CVD. Its defective portions are subjected to anodic oxidation so that anodically oxidised coatings are formed in the defective portions of the electrodes and heat-generating resistor surfaces. However, even if the protective performances of the inorganic insulating film, and the anodically oxidised film which has been additionally provided, are good, the protective performance at the boundary may not necessarily be sufficient. As the inorganic insulating film is formed using a thin film forming technique which requires a large scale apparatus and is complicated, productivity and workability are inferior compared to anodic oxidation or photolithography using a photo sensitive resin. In US 4532530 a bubble type ink jet printing device is described in which a protective layer of an oxidised coating obtained by thermal oxidation of the heat-generator resistor surface at a high temperature of 1000°C is formed on the heat generator resistor surface. An anodically oxidised coating is also formed on the electrode. While this device has the advantage of been capable of production using IC production techniques, these are large scale and complicated. Moreover, it is not suitable for producing an ink jet recording head of the so called full multi-type which has a large area using a simple apparatus and with good workability. US 4535343 discloses a thermal ink jet printing head having an anodically oxidised coating provided on the heat-generating resistor surface and the electrode surface. However, this has the same problem as those mentioned with regard to DE-A-3502900. In the first aspect of the invention, there is provided a base plate for an ink jet recording head wherein the organic insulating film is continuous with the protective oxide film so as to define therewith an unbroken protective layer for the transducer. In the second aspect of the invention, there is provided an ink jet recording apparatus having an ink jet recording head comprising a liquid chamber, a liquid path communicating liquid chamber with an orifice, and base plate according to the invention of which the organic insulating film and the protective oxidised film forming part of an inner wall of the liquid path the arrangement being such that the recording is brought about when the electro-thermal transducer is driven by a recording signal to bring about discharge of ink from an orifice by means of thermal energy so as to cause the ink to be emitted onto a recording medium. In a further aspect of the invention there is provided a method for making a base plate for an ink jet recording head, said method comprising: providing a substrate; depositing a layer of resistive material on the substrate; depositing electrically conductive material on the resistive layer and patterning the conductive material to form a pair of electrodes on the resistive layer spaced apart to define therebetween a heat generation region of an electro-thermal transducer; characterised in that the method further comprises the steps of: forming at the heat generation region of the transducer an anodically oxidised film; and forming an organic insulating film that is continuous with the protective oxide film to define therewith an unbroken protective layer for the transducer. In a fourth aspect of the invention there is provided a method for making a base plate for an ink jet recording head comprising: providing a substrate; depositing a layer of resistive material on the substrate; depositing electically conductive material on the resistive layer and patterning the conductive material to form a pair of electrodes on the resistive layer, said electrodes being spaced apart to define therebetween a heat generation region of an electro-thermal transducer; characterised in that the method further comprises the steps of: depositing a photosensitive resin over the electrodes and the electroconductive region and selectively exposing the photosensitive resin to a pattern of light so as to produce an organic insulating film covering the electrodes and extending onto at least part of the heat-generation region between the electrodes; and anodically oxidising the resistive material exposed at the heat generation region to form a protective oxide film that defines with the organic insulating film an unbroken protective layer for the transducer. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are illustrations showing a typical constitution of the ink jet recording head, Fig. 1A being the sectional portion along the flow passage, and Fig. 1B being a partially exploded view showing the positional relationship between the ceiling plate and the substrate. Figs. 2(a) - 2(h), Figs. 3(a) - 3(j) and Figs. 4(a) - 4(h) each illustrate schematically the main steps of an example of the method for forming the base plate for ink jet recording head of the present invention. Fig. 5 to Fig. 7 are graphs showing the evaluation results of the recording heads obtained in Examples 1 - 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to its production steps by use of the drawings, the constitutions of the base plate for ink jet recording head and the recording head by use thereof are to be described in detail. [Type A] Figs. 2(a) - 2(f) illustrate diagramatically as a section of substrate an example of the steps for preparation of an embodiment of the base plate for ink jet recording head of the present invention which provides an electricity-heat convertor. For preparation of the base plate for ink jet recording head of the present invention, first, a heat-generating resistor layer 2 and an electrode layer 3 are laminated in this order on a substrate 1 as shown in Fig. 2(b) by such method as sputtering, etc., and these are subjected to patterning to a predetermined shape by utilizing the photolithographic steps as shown in Fig. 2(c) to provide a heat-generating resistor 9 between a pair of electrodes 3 constituted of the return structure as shown in Fig. 1 B. As the material to be used for the substrate 1, the heat-generating resistor layer 2 and the electrode layer 3, any materials which can be used for these portions of the ink jet recording head can be utilized without limitation. Further, a heat accumulating layer may be provided on the substrate surface. Also, in the operations up to this stage, not only the method by combination of lamination and patterning as described above, but also various methods can be used by suitable selection. Next, on the substrate is laminated as shown in Fig. 2(d) an organic insulating film 12 comprising a resin capable of easy patterning and forming a coating excellent in performance as a protective film to be provided on the electrodes 3 and the heat-generating resistor 9 such as a photosensitive polyimide resin, specifically polyimidoisoindoloquinazolinedione (trade name: PIQ, produced by Hitachi Kasei), a polyimide resin (trade name: PYRALIN, produced by Du Pont), a cyclized butadiene (trade name: JSR-CBR, CBR-M901, produced by Japan Synthetic Rubber Co.), Photoneece (trade name, produced by Toray), etc. Further, the organic insulating film 12 is subjected to patterning as shown in Fig. 2(e), so that the surface of the heat-generating resistor 9 at which the anodically oxidized coating is to be provided may be exposed. Here, under the state with the exposed heat-generating resistor surface being contacted with a solution for the anodic oxidation treatment, the electrode end portion exposed at the electrode take-out portion is connected to the anode of power source, and the reaction is carried out for a predetermined time to have the anodically oxidized coating 13 formed at the exposed portion of the heat-generating resistor 9 as shown in Fig. 2(f). The method to be used for the anodic oxidation treatment is not particularly limited, provided that it is a method capable of forming an anodically oxidized coating excellent in the characteristics as protective film as described above by anodic oxidation of the material constituting the heat-generating resistor 9. For example, it may be possible to utilize the method generally used or known as the method for oxidation treatment of a metal material such as Al, Mg, Ti, Ta, etc. Thus, the base plate for ink jet recording head of the present invention comprising the substrate 1 formed as an electricity-heat convertor having the protective layers 12, 13 can be prepared. Fig. 2(g) shows a plan view of the base plate prepared showing as shadowed portion the anodically oxidized coating. Further, on the base plate is bonded a ceiling plate having a flow passage and a liquid chamber as shown in Fig. 1B while effecting registration so that the heat-generating resistor may be arranged at the predetermined position within the flow passage, and then the bonded product is cut at the predetermined position on the downstream side of the heat-generating resistor, if necessary, to form an orifice, thus completing the ink jet recording head of the present invention. As shown in Fig. 2(h), the organic insulating film 13 may be provided with a band-shaped interval therebetween, as a matter of course. [Type B] Figs. 3(a) - 3(h) illustrate as a section of substrate an example of the steps for providing an electricity-heat converter during preparation of another embodiment of the base plate for ink jet recording head of the present invention. For preparation of the base plate for ink jet recording head of the present invention, first, a heat-generating resistor layer 2 and an electrode layer 3 are laminated in this order on a substrate 1 as shown in Fig. 3(b) by such method as sputtering, etc., and these are subjected to patterning to a predetermined shape by utilizing the photolithographic steps as shown in Fig. 3(c) to provide a heat-generating resistor 9 between a pair of electrodes 3 constituted of the return structure as shown in Fig. 1B. As the material to be used for the substrate 1, the heat-generating resistor layer 2 and the electrode layer 3, any materials which can be used for these portions of the ink jet recording head can be utilized without limitation. Further, a heat accumulating layer may be provided on the substrate surface. Also, in the operations up to this stage, not only the method by combination of lamination and patterning as described above, but also various methods can be used by suitable selection. Next, on the substrate is laminated as shown in Fig. 3(d) a resist film 12 comprising a photosensitive resin, etc. capable of easy patterning and functioning as the mask in the anodic oxidation treatment performed later such as a photosensitive polyimide resin. As the resist film used here, there may be also used those photosensitive polyimide films capable of forming a coating excellent in performances as a protective film to be provided on the electrodes 3 and the heat generating resistor 9, in addition to the above characteristics, including specifically polyimidoisoindoloquinazolinedione (trade name: PIQ, produced by Hitachi Kasei), a polyimide resin (trade name: PYRALIN, produced by Du Pont), a cyclized butadiene (trade name: JSR-CBR, CBR-M901, produced by Japan Synthetic Rubber Co.), Photoneece (trade name, produced by Toray), etc. Next, the resist film 12 is subjected to patterning as shown in Fig. 3(e) by the photolithographic steps, etc. so that a part of the electrode 3 (electrode take-out portion 3a), and the surface of the heat-generating resistor 9 at which the anodically oxidized coating is to be provided may be exposed. Here, under the state with the exposed heat-generating resistor surface being contacted with a solution for the anodic oxidation treatment, the electrode end portion exposed at the electrode take-out portion is connected to the anode of power source, and the reaction is carried out for a predetermined time to have the anodically oxidized coating 13 formed at the exposed portion of the heat-generating resistor 9 as shown in Fig. 3(f). The method to be used for the anodic oxidation treatment is not particularly limited, provided that it is a method capable of forming an anodically oxidized coating excellent in the characteristics as a protective film as described above by anodic oxidation of the material constituting the heat-generating resistor 9. For example, it may be possible to utilize the method generally used or known as the method for oxidation treatment of a metal material such as Al, Mg, Ti, Ta, etc. Further, when the anodically oxidized film 13 is formed, if the resist film 12 cannot be utilized as such as a protective film, it is removed from the substrate 1. If it can be utilized as a protective film such as a photosensitive polyimide resin, it may be left to remain as such as shown by the dotted line. Next, as shown in Fig. 3(g), on the substrate 1 is further laminated an organic insulating film 14 comprising a resin utilizable as a protective layer such as a photosensitive polyimide resin previously mentioned, and the film is again subjected to patterning as shown in Fig. 3(h) by the photolithographic steps so that the principal portion of the anodically oxidized coating already formed and the electrode take-out portion 3a may be formed, to give the base plate for ink jet recording of the present invention. Fig. 3(i) shows a plan view of the base plate in which the anodically oxidized portion is shown as shadowed portion. Finally, on the base plate having the electricity-heat convertor having protective layers 13, 14 formed thereon is bonded a ceiling plate having a flow passage and a liquid chamber as shown in Fig. 1B while effecting registration so that the heat-generating resistor may be arranged at the predetermined position within the flow passage, and then the bonded product is cut at the predetermined position on the downstream side of the heat-generating resistor, if necessary, to form an orifice, thus completing the ink jet recording head of the present invention. As shown in Fig. 3(j), the organic insulating film 13 may be provided with a band-shaped interval therebetween, as a matter of course. [Type C] Figs. 4(a) - 4(h) illustrate as a section of substrate an example of the preparation steps of still another embodiment of the base plate for ink jet recording head of the present invention. For preparation of the base plate for ink jet recording head of the present invention, first, a heat-generating resistor layer 2 and an electrode layer 3 are laminated in this order on a substrate 1 as shown in Fig. 4(b) by such method as sputtering, etc., and these are subjected to patterning to a predetermined shape by utilizing the photolithographic steps as shown in Fig. 4(c) to provide a heat-generating resistor 9 between a pair of electrodes 3 constituted of the return structure as shown in Fig. 1B. As the material to be used for the substrate 1, the heat-generating resistor layer 2 and the electrode layer 3, any materials which can be used for these portions of the ink jet recording head can be utilized without limitation. Further, a heat accumulating layer may be provided on the substrate surface. Also, in the operations up to this stage, not only the method by combination of lamination and patterning as described above, but also various methods can be used by suitable selection. Here, under the state with the exposed heat-generating resistor surface being contacted with a solution for the anodic oxidation treatment, the electrode end portion exposed at the electrode take-out portion 3a is connected to the anode of power source, and the reaction is carried out for a predetermined time to have the anodically oxidized coating 13 formed at the exposed portion of the heat-generating resistor 9 as shown in Fig. 4(d). The method to be used for the anodic oxidation treatment is not particularly limited, provided that it is a method capable of forming an anodically oxidized coating excellent in the characteristics as a protective film as described above by anodic oxidation of the material constituting the heat-generating resistor 9. For example, it may be possible to utilize the method generally used or known as the method for oxidation treatment of a metal material such as Al, Mg, Ti, Ta, etc. Also, the portion of the electrodes 3 to be applied with the anodic oxidation treatment may be other than the terminal portion for connecting electrically with the external portion, and about half on the heat-generating resistor side of the substrate may be anodically oxidized for dipping into the oxidation treatment solution. Next, on the substrate 1 is laminated as shown in Fig. 4(e) an organic insulating film 13 comprising a photosensitive resin, etc. resin capable of easy patterning and having excellent performance as a protective film to be provided on the electrodes 3 and the heat-generating resistor 9, including specifically polyimidoisoindoloquinazolinedione (trade name: PIQ, produced by Hitachi Kasei), a polyimide resin (trade name: PYRALIN, produced by Du Pont), a cyclized butadiene (trade name: JSR-CBR, CBR-M901, produced by Japan Synthetic Rubber Co.), Photoneece (trade name, produced by Toray), etc. Subsequently, as shown in Fig. 4(f), the organic insulating film is removed by photolithographic steps, etc. from the principal part 12a of the anodic oxidation coating 13 and the electrode take-out portion 3a on the substrate 1, whereby the base plate for ink jet recording head of the present invention can be obtained. Fig. 4(g) shows a plan view of the base plate in which the anodically oxidized portion is shown as shadowed portion. Finally, on the base plate having the electricity-heat convertor having protective layers 13, 14 formed thereon is bonded a ceiling plate having a flow passage and a liquid chamber as shown in Fig. 1B while effecting registration so that the heat-generating resistor may be arranged at the predetermined position within the flow passage, and then the bonded product is cut at the predetermined position on the downstream side of the heat-generating resistor, if necessary, to form an orifice, thus completing the ink jet recording head of the present invention. As shown in Fig. 4(h), the organic insulating film 13 may be provided with a band-shaped interval therebetween, as a matter of course. The present invention, is described below in more detail by referring to Examples. Example 1 (Type A) Preparation of an ink jet recording head of the present invention (Type A) was practiced in the following manner by performing formation of an electricity-heat convertor according to the steps shown in Fig. 2. First, the surface of Si wafer was thermally oxidized to form an SiO₂ coating with a thickness of 3 µm, thereby obtaining a substrate. Next, on the surface of the substrate where the SiO₂ coating was formed, a Ta layer with a thickness of 3000 Å as the heat-generating resistor layer and an Al layer with a thickness of 5000 Å as the electrode layer were laminated by sputtering in this order. Next, the Ta layer and the Al layer were subjected successively to patterning by the photolithographic steps to form return electrodes and heat-generating resistors (50 µm x 150 µm) with Ta layers exposed between a pair of electrodes at an arrangement density of 8 dots/mm as shown in Fig. 1B. Next, a photosensitive polyimide resin [Photoneece (produced by Toray)] was spin coated to a thickness of about 2 µm, and further the resin was removed from the principal part of the heat-generating resistor except for the vicinity of the boundary with the electrodes and from on the portion which becomes the electrode take-out portion. Here, under the state with the surface-exposed portion of the heat-generating resistor previously formed being dipped in an aqueous solution containing boric acid at 0.5 mol/liter and sodium tetraborate at 0.05 mol/liter, the electrode end portion exposed at the electrode take-out portion was connected to the anode of a power source of 200 V to effect the anodic oxidation treatment for 20 seconds. After completion of the anodic oxidation, the head was taken out from the reaction liquid, thoroughly washed and dried, followed by bonding of a ceiling plate comprising a glass having a flow passage and a liquid chamber as shown in Fig. 1(B) with an epoxy adhesive while effecting registration so that the heat-generating resistor may be arranged at the predetermined position within the flow passage, and then the heat-generating resistor of the bonded product was cut at the downstream side with a dicing saw to form an orifice, thus completing an ink jet recording head of the present invention. Further, by repeating the above procedure, a large number of ink jet recording heads of the present invention were prepared and durability test was conducted under the recording conditions shown below for evaluation thereof, and the results of Weibull plot are shown by (1) in Fig. 5. Driving voltage=1.2 x foaming voltage Driving frequency: 3 KHz Pulse width: 2 µsec The results shown by (2) in Fig. 5 are those of the same evaluation conducted for comparative purpose with the use of a recording head of the prior art having the same constitution as the recording head obtained in the above Example except for providing no organic resin protective layer, namely with the protective layer consisting only of electrodes and an anodically oxidized coating formed by anodic oxidation of the surface of the heat-generating resistor. In the recording head by use of the base plate for ink jet recording of this Example, a protective layer comprising an anodically oxidized coating was provided at the principal portion of the surface of the heat-generating resistor constituting the electricity-heat converter, whereby oxidation of the heat-generating resistor with heat, or the reaction of the heat-generating resistor with ink by leak current could be effectively prevented. Further, a homogeneous organic insulating film was provided on the electricity-heat convertor extending from the portion other than the anodically oxidized coating over the electrodes, whereby the boundary portion between the heat-generating resistor and the electrodes at which no protective layer having good protective performance has been deemed to be formed with difficulty was covered with this organic insulating film to be effectively protected, and its reliability could be improved to great extent. Example 2 (Type B) Preparations of a base plate for ink jet recording head and an ink jet recording head of the present invention by use of said base plate were practiced in the following manner by performing formation of an electricity-heat converter according to the steps shown in Fig. 3. First, the surface of Si wafer was thermally oxidized to form an SiO₂ coating with a thickness of 3 µm, thereby obtaining a substrate. Next, on the surface of the substrate where the SiO₂ coating was formed, a Ta layer with a thickness of 3000 Å as the heat-generating resistor layer and an Al layer with a thickness of 5000 Å as the electrode layer were laminated by sputtering in this order. Next, the Ta layer and the Al layer were subjected successively to patterning by the photolithographic steps to form return electrodes and heat-generating resistors (50 µm x 150 µm) with Ta layers exposed between a pair of electrodes at an arrangement density of 8 dots/mm as shown in Fig. 1B. Next, a photosensitive polyimide resin [Photoneece (produced by Toray)] was spin coated to a thickness of about 2 µm, and further the resin was removed from on the principal part of the heat-generating resistor except for the vicinity of the boundary with the electrodes and from on the portion which becomes the electrode take-out portion. Here, under the state with the surface-exposed portion of the heat-generating resistor previously formed being dipped in an aqueous solution containing boric acid at 0.5 mol/liter and sodium tetraborate at 0.05 mol/liter, the electrode end portion exposed at the electrode take-out portion was connected to the anode of a power source of 200 V to effect the anodic oxidation treatment for 20 seconds. After completion of the anodic oxidation, the head was taken out from the reaction liquid, thoroughly washed and dried, followed by spin coating of the same photosensitive polyimide resin as described above on the entire surface of the substrate where the heat-generating resistor and the electrodes were provided, and subsequently according to the photolithographic steps, the organic insulating film was patterned so that the principal portion of the anodically oxidized coating provided on the heat-generating resistor surface and the portion which became the electrode take-out portion were exposed to have a double layer structure of the anodically oxidized coating and the organic insulating film formed on at least the brim portion on the electrode sides of the anodically oxidized coating, and also said organic insulating film may extend from the brim portion of the anodically oxidized coating via the boundary portion between the electrodes and the heat-generating resistor over the electrodes. Finally, a ceiling plate comprising a glass having a flow passage and a liquid chamber as shown in Fig. 1B was bonded with an epoxy adhesive while effecting registration so that the heat-generating resistor may be arranged at the predetermined position within the flow passage, and further the heat-generating resistor of the bonded product was cut at the downstream side with a dicing saw to form an orifice, thus completing an ink jet recording head of the present invention. Further, by repeating the above procedure, a large number of ink jet recording heads of the present invention were prepared and durability test was conducted under the recording conditions shown below for evaluation thereof, and the results of Weibull plot are shown by (1) in Fig. 6. Driving voltage=1.2 x foaming voltage Driving frequency: 3 KHz Pulse width: 2 µsec The results shown by (2) in Fig. 6 are those of the same evaluation conducted for comparative purpose with the use of a recording head of the prior art having the same constitution as the recording head obtained in the above Example except for providing no organic resin protective layer, namely with the protective layer consisting only of electrodes and an anodically oxidized coating formed by anodic oxidation of the surface of the heat-generating resistor. In the recording head by use of the base plate for ink jet recording of this Example, a protective layer comprising an anodically oxidized coating was provided at the principal portion of the surface of the heat-generating resistor constituting the electricity-heat convertor, whereby oxidation of the heat-generating resistor with heat, or the reaction of the heat-generating resistor with ink by leak current could be effectively prevented. Further, an organic insulating film extending from the brim portion on the electrode side of the anodically oxidized coating on the heat-generating resistor surface of the electricity-heat convertor to over electrodes was further provided, whereby the boundary portion between the heat-generating resistor and the electrodes at which no protective layer having good protective performance has been deemed to be formed with difficulty was covered with this organic insulating film to be effectively protected, and moreover at the boundary portion between the anodically oxidized coating and the organic insulating film, these were provided overlappingly to exclude sufficiently the danger of lowering in protective performance at the boudary between the protective layers of different kinds, and its reliability could be improved to great extent. Example 3 (Type C) Preparation of an ink jet recording head of the present invention was practiced in the following manner by performing formation of an electricity-heat convertor according to the steps shown in Fig. 4. First, the surface of Si wafer was thermally oxidized to form an SiO₂ coating with a thickness of 3 µm, thereby obtaining a substrate. Next, on the surface of the substrate where the SiO₂ coating was formed, a Ta layer with a thickness of 3000 Å as the heat-generating resistor layer and an Al layer with a thickness of 5000 Å as the electrode layer were laminated by sputtering in this order. Next, the Ta layer and the Al layer were subjected successively to patterning by the photolithographic steps to form return electrodes and heat-generating resistors (50 µm x 150 µm) with Ta layers exposed between a pair of electrodes at an arrangement density of 8 dots/mm as shown in Fig. 1B. Here, under the state with the surface-exposed portion of the heat-generating resistor previously formed being dipped in an aqueous solution containing boric acid at 0.5 mol/liter and sodium tetraborate at 0.05 mol/liter, the electrode end portion exposed at the electrode take-out portion was connected to the anode of a power source of 200 V to effect the anodic oxidation treatment for 20 seconds. After completion of the anodic oxidation, the head was taken out from the reaction liquid, thoroughly washed and dried, followed by spin coating of a photosensitive polyimide resin Photoneece (produced by Toray)] to a thickness of about 2 µm, which was further subjected to patterning according to the photolithographic steps, so that the principal portion of the anodically oxidized coating provided on the heat-generating resistor surface and the portion which became the electrode take-out portion were exposed, and also the organic insulating layer covering from the brim portion on the electrode side of the anodically oxidized coating formed on the heat-generating resistor surface via the boundary portion between electrodes and the heat-generating resistor to over a part of the electrodes could be formed. Finally, a ceiling plate comprising a glass having a flow passage and a liquid chamber as shown in Fig. 1B was bonded with an epoxy adhesive while effecting registration so that the heat-generating resistor may be arranged at the predetermined position within the flow passage, and further the heat-generating resistor of the bonded product was cut at the downstream side with a dicing saw to form an orifice, thus completing an ink jet recording head of the present invention. Further, by repeating the above procedure, a large number of ink jet recording heads of the present invention were prepared and durability test was conducted under the recording conditions shown below for evaluation thereof, and the results of Weibull plot are shown by (1) in Fig. 7. Driving voltage=1.2 x foaming voltage Driving frequency: 3 KHz Pulse width: 2 µsec The results shown by (2) in Fig. 7 are those of the same evaluation conducted for comparative purpose with the use of a recording head of the prior art having the same constitution as the recording head obtained in the above Example except for providing no organic resin protective layer, namely with the protective layer consisting only of electrodes and an anodically oxidized coating formed by anodic oxidation of the surface of the heat-generating resistor. In the recording head by use of the base plate for ink jet recording of this Example, a protective layer comprising an anodically oxidized coating was provided at the principal portion of the surface of the heat-generating resistor constituting the electricity-heat convertor, whereby oxidation of the heat-generating resistor with heat, or the reaction of the heat-generating resistor with ink by leak current could be effectively prevented. Besides, an organic insulating film extending from the brim portion on the electrode side of the anodically oxidized coating on the heat-generating resistor surface of the electricity-heat convertor to over electrodes was further provided, whereby the boundary portion between the heat-generating resistor and the electrodes at which no protective layer having good protective performance has been deemed to be formed with difficulty was covered with this organic insulating film to be effectively protected, and moreover these protective performances were exhibited to give better protective function at the brim portion on the electrode side of the anodically oxidized coating on the heat-generating resistor surface covered with the protective layer comprising a double layer structure of the anodically oxidized coating and the organic insulating film and on the electrode surfaces, and its reliability could be improved to great extent. In the present invention, since a protective layer comprising an anodically oxidized coating at the principal portion on the heat-generating resistor surface constituting the electricity-heat converter, the reaction of the heat-generating resistor and ink by leak current can be prevented. Further, since a homogeneous organic insulating film extending from the portion other than the anodically oxidized coating on the heat-generaing resistor surface of the electricity-heat converter to over the electrodes is provided to protect effectively the boundary between the heat-generating resistor and the electrodes, at which a protective layer has been deemed to be formed with difficulty, by coverage with the organic insulating layer, whereby its reliability could be improved to great extent. Further, in the anodic oxidation treatment in Examples of Type A and Type B in the present invention, the conditions which can well afford oxidation of only one kind of heat-generating resistor is to be set, whereby its control can be easily done. Further, in Type B and Type C, an organic insulating film extending from the brim portion on the electrode side of the anodically oxidized coating on the heat-generating resistor surface of the electricity-heat convertor to over electrodes is provided, whereby the boundary portion between the heat-generating resistor and the electrodes at which no protective layer having good protective performance has been deemed to be formed with difficulty is covered with this organic insulating film to be effectively protected, and moreover at the boundary portion between the anodically oxidized coating and the organic insulating film, these are provided overlappingly to exclude sufficiently the danger of lowering in protective performance at the boundary between the protective layers of different kinds, and its reliability could be improved to great extent. Besides, in Type C, an organic insulating film extending from the brim portion on the electrode side of the anodically oxidized coating on the heat-generating resistor surface of the electricity-heat convertor to over electrodes is further provided, whereby the boundary portion between the heat-generating resistor and the electrodes at which no protective layer having good protective performance has been deemed to be formed with difficulty is covered with this organic insulating film to be effectively protected, and moreover these protective performances are exhibited to give better protective function at the brim portion on the electrode side of the anodically oxidized coating on the heat-generating resistor surface and on the electrode surfaces, covered with the protective layer comprising a double layer structure of the anodically oxidized coating and the organic insulating film, and its reliability could be improved to great extent. Further, in the anodic oxidation treatment in the present invention, by calling attention on the heat-generating resistor material, for example, even the conditions not sufficient for coatability of the anodically oxidized film in view of the electrode material can be also used, whereby its control can be easily done and freedom in selection of materials is also great. In the present invention, an organic insulating film was provided even onto a part of the heat-generating resistor between electrodes, but since no extreme elevation of temperature occurs by thermal conductivity of electrodes in the vicinity of electrodes, no inconvenience is caused in durability, except for an organic insulating film which is particularly weakly resistant to heat.

Claims: A base plate for an ink jet recording head, said base plate having on it an electro-thermal transducer (2, 3) protected by an organic insulating film (12) and by a protective oxide film (13) formed by anodic oxidation and positioned so as to correspond to a heat generation region of the transducer, characterised in that the organic insulating film (12) is continuous with the protective oxide film (13) 50 as to define therewith an unbroken protective layer for the transducer (2, 3). A base plate according to claim 1, wherein the organic insulating film (12) covers margins of the heat generation region of the transducer. A base plate according to claim 2, wherein the organic insulating film (12) covers the periphery of the heat generation region of the transducer. A base plate according to claim 2 or 3, wherein the electro-thermal transducer comprises a heat generating resistor (2) on the base plate (1) a pair of electrodes (3) electrically connected to the heat generating resistor (2) the protective oxide film (13) being the result of anodic oxidation of the surface of the heat generating resistor between the electrodes, and the organic insulating film (12) being provided on the electrodes (3) and on at least a part of the heat-generating resistor between the electrodes. A base plate according to claim 4, wherein the organic insulating film (12) where it covers margins of the heat generation region makes direct physical contact with the heat generating resistor (2) and the protective oxide film (13) is at regions of the heat generating resistor (2) not covered by the organic insulating film (12). A base plate according to claim 4, wherein the organic film where it covers margins of the heat generation region of the transducer makes physical contact partly directly with the heat generating resistor (2) and partly with a protective oxide film on the heat generating resistor. A base plate according to claim 4, wherein the organic insulating film where it covers margins of the heat generation region makes physical contact with a protective oxide film that covers the heat generating resistor (2). A base plate according to any of claims 4 to 7, wherein the surfaces of the electrodes are also provided with a protective oxide film (12) which is the result of anodic oxidation. A base plate as claimed in claim 8, wherein the resistor is a film of tantalum. A base plate according to claim 9, wherein the electrodes are of aluminium, magnesium, titanium or tantalum. A base plate according to any preceding claim, wherein a heat resisting layer is provided between the substrate and the electro-thermal transducer. A base plate according to claim 11, which is of silicon and has a surface layer of silicon dioxide. A base plate according to any preceding claim, wherein the organic insulating film is a polymerisation product of a photosensitive polyimide resin. An ink jet recording head comprising a base plate as claimed in any preceding claim, means defining with the base plate an ink channel leading to an orifice through which the ink is to be discharged, the protective oxide film and the organic insulating film forming an interior surface of the ink channel. Ink jet recording apparatus having an ink jet recording head comprising: a liquid chamber; a liquid path communicating the liquid chamber with an orifice; and a base plate as claimed in any of claims 1 to 13, of which the organic insulating film and the protective oxide film forming part of an inner wall of the liquid path, the arrangement being such that recording is brought about when the electro-thermal transducer is driven by a recording signal to bring about discharge of ink from an orifice by means of thermal energy so as to cause the ink to be emitted onto a recording medium. Ink jet recording apparatus according to claim 11, wherein the ink jet recording head is driven by a recording signal having a pulse width of 2u sec and has a driving voltage 1.2 times a foaming voltage. A method for making a base plate for an ink jet recording head, said method comprising: providing a substrate(1); depositing a layer of resistive material (2) on the substrate (1); depositing electrically conductive material (3) on the resistive layer (2) and patterning the conductive material (3) to form a pair of electrodes on the resistive layer (2) spaced apart to define therebetween a heat generation region of an electro-thermal transducer (2, 3); characterised in that the method further comprising the steps of: forming at the heat generation region of the transducer an anodically oxidised film (13); and forming an organic insulating film (12) that is continuous with the protective oxide film (13) to define therewith an unbroken protective layer for the transducer (2, 3). A method according to claim 17, wherein the surface layers of the electrodes (3) are formed with a protective oxide film (13) by anodic oxidation before the organic insulating film (12) is deposited. A method according to claim 17 or 18, comprising the steps of depositing a photo-sensitive resin to form the organic insulating film (12), said resin covering the electrodes (3) and the heat generation region, patterning the resin with light, and selectively removing unexposed resin to reveal the protective oxide film (13) at the heat generation region. A method for making a base plate for an ink jet recording head comprising: providing a substrate (1); depositing a layer of resistive material (2) on the substrate (1); depositing electrically conductive material (3) on the resistive layer (2) and patterning the conductive material to form a pair of electrodes on the resistive layer, said electrodes (3) being spaced apart to define therebetween a heat generation region of an electro- thermal transducer (2,3); characterised in that the method further comprises the steps of: depositing a photosensitive resin (13) over the electrodes (3) and the electroconductive region and selectively exposing the photosensitive resin (3) to a pattern of light so as to produce an organic insulating film (12) covering the electrodes (3) and extending onto at least part of the heat-generation region between the electrodes (3); and anodically oxidising the resistive material (2) exposed at the heat generation region to form a protective oxide film that defines with the organic insulating film an unbroken protective layer for the transducer (2,3).

Inventors: KOMURO, HIROKAZU, MASUDA, KAZUAKI, SATO, KOICHI, SHIOZAKI, ATSUSHI
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J2
IPC codes: B41J2