INK JET RECORDING HEAD AND BASE PLATE THEREFOR

Abstract: This specification discloses a base plate for an ink jet recording head provided with an electro-­ thermal converting member having a substrate (14), a pair of first electrodes (12) provided at a predetermined interval on the substrate, a pair of second electrodes (13) provided at an interval greater than the predetermined interval on the pair of first electrodes, and a heat generating resistance member (11) electrically connected to the respective ones of the pairs of electrodes in at least a portion thereof. The specification also discloses an ink jet recording head having such base plate.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an ink jet recording head and a base plate therefor. Related Background Art The ink jet recording method is a recording method whereby ink (recording liquid) is discharged from a discharge port provided in a recording head and the discharged ink is caused to adhere to a recording medium such as paper to thereby accomplish recording, and has numerous advantages such as very little noise being produced, the capability of high-speed recording and no necessity of using paper of special construction for recording, and recording heads of various types have heretofore been developed. Above all, a recording head of the type in which heat energy is caused to act on ink to discharge the ink from a discharge port has advantages such as good responsiveness to recording signals and the ease with which a number of discharge ports are disposed at high density. As a recording head of such type which utilizes heat energy as ink discharging energy, there is known a recording head of a construction in which electro-thermal converting elements having a heat generating resistance member layer and electrodes are arranged on a substrate, the converting elements having as required a protective film provided above the portion thereof which contacts liquid, and a top plate formed with liquid paths and a liquid chamber is joined thereto. The ink discharging energy in a recording head utilizing this system is generally imparted by an electro-thermal converting element having a pair of electrodes and a heat generating resistance member located between the electrodes. That is, when an electric current is applied to the electrodes to cause the heat generating resistance member to generate heat, the ink in the liquid path in contact with or near the heat generating resistance element is momentarily heated and bubbles are created there, and ink droplets are discharged from the discharge port by the change in volume resulting from the momentary expansion and contraction of volume caused by the creation of the bubbles. In the recording head using the electro-thermal converting element as described above, the other portions than the heat generating member are generally protected by an organic resin film to prevent the occurrence of leakage or short circuit of the electric current through the ink. In such case, the organic film has not been provided on the heat generating member of the heat generating portion by the reason that it adversely affects the heat conduction, or from the viewpoint of heat resisting property. Also, from the viewpoint of heat resisting property or the like, it has been necessary that actually the organic film be formed separately from the heat generating member of the heat generating portion. However, the separation of the organic film from the heat generating member of the heat generating portion has sometimes led to the problem that the electrodes connected to the heat generating member can no longer be protected and the reliability is reduced. As a countermeasure for this, it has been the practice to provide an intermediate area between the heat generating member and the electrodes and to form in this intermediate area the end of the organic protective film which is adjacent to the heat generating member. To achieve this, there is a method of widening the pattern width of the heat generating resistance member as disclosed, for example, in, Japanese Laid-Open Patent Application No. 033471/1983. However according to this method, in some cases, a so-called heat spot of high current density has been produced at the corner in which the pattern of the heat generating member is thinner, thereby adversely affecting the creation of bubbles. Also, in German Patent No. 3443563, there is proposed a construction in which the portions of the electrodes which are near the heat generating member are made thinner. However this is difficult to control during manufacture. Furthermore a method of using two layers and selectively etching the two layers has presupposed that the heat generating member and the two kinds electrodes can be selectively etched. This has severely limited the usable materials, the etching liquid and the etching method. Thus, there are still problems left to be solved in respect of a more ideal electro-thermal converting element in which the protection of the electro-thermal converting element and the prevention of leakage or short circuits are better accomplished and which does not adversely affect the creation of bubbles. SUMMARY OF THE INVENTION It is a primary object of the present invention to solve the above-noted problems. More specifically, it is an object of the present invention to provide an ink jet recording head having an electro-thermal converting member of a construction which can increase the degree of freedom of materials usable for a protective film, etc., and a base plate for use in such recording head. It is also an object of the present invention to provide an ink jet recording head of higher durability in which the protective film is not in contact with a high temperature portion, and a base plate for use in such recording head. According to the present invention, a base plate for an ink jet recording head comprising a substrate, a pair of first electrodes mutually spaced apart by a predetermined distance on said substrate and a heat generating resistance layer electrically connected to and carried on said pair of first electrodes and a second electrode, is characterized in that there is a pair of second electrodes which sandwich the said heat generating resistance layer between themselves and that said pair of second electrodes interpose a portion of said heat generating resistance layer positioned between said pair of first electrodes, second electrodes being mutually spaced apart by a distance which is greater than the said distance by which the first electrodes are mutually spaced apart. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 to 4 show the characteristic portions of embodiments of the ink jet recording head of the present invention. Figure 2A is the plane view of the structure of Figure 2B. Figure 5 is a schematic view showing a form of the ink jet recording head to which the present invention is applied. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will herein after be described with respect to an embodiment thereof. Figure 1 schematically shows the characteristic portions of the typical ink jet recording head of the present invention. As shown in Figure 1, in the present invention, pairs of first and second electrodes 12 and 13 respectively have been provided above and below a heat generating resistance member layer 11 on a substrate 14. That is, the recording head has been made into a construction in which the heat generating resistance layer 11 is partly interposed between the pairs of first and second electrodes 12 and 13. Also, the second electrodes, 13 are mutually spaced apart a greater distance than the mutual spacing apart of the first electrodes 12. In the present invention, the portion of the heat generating resistance member 11 between the opposed electrodes which is electrically connected to the electrodes is energised to generate heat energy for discharging ink from a discharge port and cause the discharged ink to fly. That is, an electro-thermal converting member 15 has been constructed of the electrodes 12, 13 and the heat generating resistance member 11. The characteristic portions of the ink jet recording head of the present invention could typically be made in the following manner. A layer (Ta) providing the first electrodes 12 has been laminated on a substrate 14 (Si) whose surface has been made non-conductive, by the sputtering method, and has been made into a counter-polar shape by the use of the photolithographic process or the like. Then, the heat generating resistance layer 11 (Ta alloy) and a layer (Al) providing the second electrodes 13 have likewise been laminated by sputtering, and patterning has been made with the second electrodes 13 being separated more from the heat generating resistance member portion than the first electrodes 12. Also, the heat generating resistance layer 11 has been pattern-formed by the photolithographic technique so as to assume a desired shape of heat generating resistance member between the first electrodes. Thereafter, an organic protective material 16 such as photosensitive resin (polyimide) has been laminated by spin coat, whereafter patterning has been made and the heat generating portion and the other portion of a part of the first electrode have been protected by an organic protective film 16 as shown in Figures 2A and 2B. As the material of the organic protective film 16, use could be made of a material chemically stable and excellent in the property of intimate contact with the ground, for example, photosensitive polyimide resin such as PIQ produced by Hitachi Kasei Co., Ltd., PYRALIN produced by Du Pont, Inc., JSR-CBR produced by Nippon Synthetic Rubber Co., Ltd. or Photoneece produced by Toray Co., Ltd. As regards the width of the pattern, the widths of the respective layers needed not be equal and uniform. In the present invention, the structure as shown in Figure 4 has also led to a good result. That is, the structure shown in Figure 4 differs from the structure described in connection with Figures 2A and 2B in that an inorganic protective film 17 is provided between the organic protective film 16 and the second electrodes 13. In this case, the inorganic protective film 17 is provided by attaching SiO₂ to a thickness of the order of 1 µm by the sputtering method. Finally, the body of the ink jet recording head of the present invention is shown in Figure 5. In Figure 5, the reference numeral 15 designates electro-thermal converting elements, the reference numeral 18 denotes a liquid chamber, the reference numeral 19 designates liquid paths, the reference numeral 20 denotes discharge ports, the reference numeral 21 designates a supply port, the reference numeral 22 denotes a top plate, the reference numeral 23 designates a liquid path wall, and the reference numeral 24 denotes a base plate for the ink jet recording head. As shown in Figure 5, the liquid paths 19 and the discharge ports 20 communicating with the liquid paths 19 have been formed correspondingly to the electrothermal converting elements 15 of the base plate 24 for the ink jet recording head. Also, the liquid paths 19 have been communicated with the liquid chamber 18. Actually, these discharge ports 20, liquid paths 19 and liquid chamber 18 have been formed by joining the top plate 22 to the liquid path wall (preferably made of photosensitive resin) formed on the base plate 24 for the ink jet recording head. The top plate 22 has been formed with the supply port 21, through which ink has been supplied into the liquid chamber 18, i.e., into the recording head. When an ink jet recording head was made with the aforedescribed substrate used as the base plate of the ink jet recording head of such a construction and discharge of liquid was effected, stable liquid droplets could be formed for a long time and the durability was satisfactory. The present invention has been shown with respect to an example in which the electrodes, the heat generating resistance member layer and the inorganic protective layer have been formed by the sputtering method, whereas these could be formed not only by the sputtering method, but also by numerous film forming means. Particularly, the vacuum deposition method is suitable for elimination of dust and for making the layers minute and thus, it is preferable. Of course, for the formation of the organic protective film, use can be made of not only the abovementioned spin coat, but also other numerous film forming means including the roll coat. It should be noted that the materials of the substrate, the first and second electrodes, the heat generating resistance member layer, the protective films, etc. are not limited to the above-mentioned materials. The materials used for these portions may be any other materials as long as they ensure the functions of the respective portions to be fully performed. To obtain the advantages as previously described, the first electrode 12 could be provided only near the heat generating resistance member, as shown in Figure 3. In addition, the form of the ink jet recording head formed by the use of the substrate of the present invention is not limited to the form shown in Figure 5, because the substrate of the present invention can be used in most ink jet recording heads utilizing heat energy. With the construction shown and described, the first electrodes can first be formed and therefore there are few limitations in making them and there is therefore a wide choice in the material that can be selected. For example, it is easy to form the first electrodes of the same material as the heat generating resistance member layer which constitutes the heat generating resistance member. This is particularly important in the case of a form in which no inorganic insulating film is provided on the heat generating resistance member. To prevent the corrosion by the battery effect, it is necessary to select materials having similar oxidation-reduction potentials for the heat generating resistance member and the first electrodes, and in the present invention, the selection which satisfies such a condition becomes easy. If only similar materials are employed for the portions which contact the ink, the occurrence of corrosion by the battery effect can be prevented. Also, if in some portion of the first electrodes the current density is reduced and the heat generation temperature thus becomes lower in the heat generating resistance member and if the surface is protected so that this low temperature portion is at the end of the organic resin film, then deterioration of the durability of the organic film by heat is avoided (see Figure 2B).

Claims: A base plate for an ink jet recording head comprising a substrate (14), a pair of first electrodes (12) mutually spaced apart by a predetermined distance on said substrate (14) and a heat generating resistance layer (11) electrically connected to and carried on said pair of first electrodes (12), and a second electrode characterized in that there is a pair of second electrodes (13) between which the said heat generating resistance layer (11) extends and that said pair of second electrodes expose a portion of said heat generating resistance layer (11) positioned between said pair of first electrodes (12), second electrodes (13) being mutually spaced apart by a distance which is greater than the said distance by which the first electrodes are mutually spaced apart. An ink jet recording head having the base plate according to claim 1, wherein said heat generating resistance layer, said pair of first electrodes and said pair of second electrodes together form part of a liquid path (19) and in use act as an electro-thermal converting member (15) for generating heat which creates bubbles in ink in the liquid path (19). An ink jet recording head according to claim 2, wherein said pair of first electrodes and said heat generating resistance layer are made from the same material and protective films (16, 17) are provided on at least said pair of second electrodes (13). An ink jet recording head according to claim 2 or 3, wherein a plurality of said liquid paths (19) are provided and said electro-thermal converting members (15) are provided within each of said liquid paths (19). An ink jet recording head according to claim 3, wherein said protective film is an organic protective film (16).

Inventors: SHIOZAKI, ATSUSHI
Applicants: CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J2
IPC codes: B41J2