Patent Publication Number: US-6910761-B2

Title: Ink jet recording head and ink jet recording apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35USC 119 from Japanese Patent Application No. 2002-359728, the disclosure of which is incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an ink jet recording head and an ink jet recording apparatus. 
   2. Description of the Related Art 
   There is an ink jet recording system in which by rapidly vaporizing a predetermined amount of ink by heat, which heat is created by a heater resistor, an ink drop is then ejected from a orifice by such a resultant vapor bubble. In this system, the heater resistor tends to corrode due to the heat and the ink. In order to prevent this, an ink protection layer is interposed between the heater resistor and the ink. As a result of the ink protection layer, which covers the heater resistor, and through which the ink is heated, thermal conductivity with respect to the ink declines. In consideration of this defect, there is a measure in which a surface of a heater resistor is oxidized to form a surface oxidation film, and then, such a resultant surface oxidation film is utilized as an ink protection layer. This surface oxidation film is generally extremely thin, and thus, has good thermal conductivity with respect to the ink. An ink jet recording head is known, using heater resistors that are made from a material, such as TaSiO. Surfaces of the heater resistors are oxidized, so that such resultant oxidation surfaces each can serve as an ink protection layer (for example, refer to Japanese Patent Application Laid-Open (JP-A) No. 10-230605). 
   However, in a head structure in which heater resistors, each of which is made from, for example, TaSiO and has an oxidized surface layer serving as an ink protection layer, are used, major part of an insulating film layer is generally covered with the ink protection layers (or the oxidized surfaces) of the heater resistor and the remaining part or some part of the insulating film layer is not covered, i.e., it is exposed to the outside. The insulating film layer is ordinarily made from a silicon insulator, which is easily corroded by thermochemical reaction depending upon a composition of the ink. Therefore, some type of material to be used as the ink, which material does not corrode such a silicon insulator, must be selected from a limited number of such materials. As a result, the versatility of an ink jet recording head cannot be increased, so as to allow use of a wide variety of ink. 
   Further, to prevent the ink from corroding the silicon insulator, it is necessary to further provide an additional ink protection layer for covering the silicon insulator. In this case, as previously described, because the ink is heated purposely through this additional ink protection layer, thermal conductivity with respect to the ink declines. 
   SUMMARY OF THE INVENTION 
   In light of the above-described facts, a primary object of the present invention is to provide an ink jet recording head, which is simple in structure and easy to manufacture and which efficiently prevents ink from corroding an insulating film layer without further providing an additional ink protection layer. 
   Another object of the present invention is to provide an ink jet recording apparatus that can use ink, which is made from a large variety of materials. 
   In order to achieve the objects described above, according to an aspect of the present invention, there is provided an ink jet recording head for ejecting ink droplets to print an image, the print head comprising: a substrate; an insulating film layer disposed on the substrate; a plurality of partition walls for defining a plurality of bubbled-ink forming portions, the partition walls being disposed on the insulating film layer along a predetermined, first direction with a predetermined distance between them; a plurality of heater resistor portions disposed on the insulating film layer within the respective bubbled-ink forming portions, a surface of each heater resistor portion having an oxidation film which is formed by being thermally oxidized and which serves as an ink protection layer, each heater resistor portion being formed by a bubbled-ink forming area for heating and vaporizing ink and by extended portions which are connected to opposite ends, in the first direction, of the bubbled-ink forming area; and a plurality of pairs of electrodes, each pair of the electrodes being connected to a corresponding heater resistor portion, one electrode of each pair being a first electrode and being disposed at a lower surface side of the insulating film layer, the other electrode of each pair being a second electrode and being disposed on the heater resistor portion, wherein an upper surface of the insulating film layer is entirely covered with the partition walls and the heater resistor portions such that the upper surface of the insulating film layer is not in direct contact with ink. 
   According to another aspect of the present invention, there is provided an ink jet recording apparatus which is provided with an ink jet recording head for ejecting ink droplets to print an image, the ink jet recording head comprising: a substrate; an insulating film layer disposed on the substrate; a plurality of partition walls for defining a plurality of bubbled-ink forming portions, the partition walls being disposed on the insulating film layer along a predetermined, first direction with a predetermined distance between them; a plurality of heater resistor portions disposed on the insulating film layer within the respective bubbled-ink forming portions, a surface of each heater resistor portion having an oxidation film which is formed by being thermally oxidized and which serves as an ink protection layer, each heater resistor portion being formed by a bubbled-ink forming area for heating and vaporizing ink and by extended portions which are connected to opposite ends, in the first direction, of the bubbled-ink forming area; a plurality of pairs of electrodes, each pair of the electrodes being connected to a corresponding heater resistor portion, one electrode of each pair being a first electrode and being disposed at a lower surface side of the insulating film layer, the other electrode of each pair being a second electrode and being disposed on the heater resistor portion, the second electrode including a first terminal and a second terminal, between which the bubbled-ink forming area is positioned when viewed in top plan view, the first terminal being electrically connected to the first electrode; and an ejection nozzle including a plurality of nozzles at positions corresponding to the plurality of heater resistor portions, 
   wherein an upper surface of the insulating film layer is entirely covered with the partition walls and the heater resistor portions such that the upper surface of the insulating film layer is not in direct contact with ink. 
   The foregoing and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention, as illustrated in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective sectional view showing part of an ink jet recording head according to a first embodiment of the invention. 
       FIG. 2A  is a sectional view of the head part of  FIG. 1  viewed in a direction perpendicular to a direction in which heater resistor portions are disposed. 
       FIG. 2B  is a sectional view of the head part of  FIG. 1  viewed in the direction in which the heater resistor portions are disposed. 
       FIG. 3A  is a partial plan view of the head part of FIG.  1 . 
       FIG. 3B  is a view similar to  FIG. 3A  of another example of the head part. 
       FIG. 4A  is a partial sectional view of an ink jet recording head according to a second embodiment of the invention, viewed in a direction perpendicular to a direction in which heater resistor portions are disposed. 
       FIG. 4B  is a partial sectional view of the head part of  FIG. 4A  viewed in the direction in which the heater resistor portions are disposed. 
       FIG. 5A  is a partial sectional view of an ink jet recording head according to a third embodiment of the invention, viewed in a direction in which heater resistor portions are disposed. 
       FIG. 5B  is a view similar to  FIG. 5A  of another example of the head part of FIG.  5 A. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An ink jet recording head according to a first embodiment of the present invention will be described in detail below on the basis of  FIGS. 1 ,  2 A,  2 B,  3 A and  3 B. 
   The ink jet recording head includes a substrate  8 , a first insulating film layer  12  and a second insulating film layer  16 , which are disposed in this order. Between the first insulating film layer  12  and the second insulating film layer  16  are provided first electrode layer portions  14 , which are separated from one another and disposed at predetermined intervals in a predefined first direction. Heater resistor portions  18 , which are provided in the same manner as the first electrode layer portions  14 , are disposed on the second insulating film layer  16 . Second electrode layer portions  20  are spaced apart from one another and respectively disposed on the heater resistor portions  18 . Partition walls  22  are each provided between two of the second electrode layer portions  20  in the first direction. Non-illustrated nozzles serving as ink discharge openings are spaced apart from one another and disposed in the first direction. 
   The first electrode layer portions  14 , which are formed from aluminum, serve as negative poles. The second insulating film layer  16  is formed from a silicone oxide film. Dimensions (or film thicknesses) at portions thereof between the first electrode layer portions  14  and the heater resistor portions  18  are approximately 1 to 2 m. 
   The heater resistor portions  18 , which are formed from TaSiO through sputtering processing or the like, have thicknesses of approximately 0.1 m. The heater resistor portions  18  are thermally oxidized, so that surfaces thereof are changed into tantalum insulating films (surface oxidation films)  24 . The tantalum insulating films  24  have sufficient mechanical strength and corrosion resistance to serve as ink protection layers. They are very thin and have thicknesses of about 0.01 m and good thermal conductivity with respect to ink. The thermal oxidization for forming the tantalum insulating films  24  is carried out at a temperature of about 400° C. after the second electrode layer portions are formed, so that other materials on the substrate, e.g., the first electrode layer portions  14  are not adversely affected. 
   As the second electrode layer portions  20  are directly contacted with ink, they are formed of a metal material having a relatively small resistivity and excellent corrosion resistance to ink. For example, they are formed by sputtering or plating of Ni, Au or the like. 
   The partition walls  22  are spaced apart to provide bubbled-ink forming portions  10  therebetween. In each of the bubbled-ink forming portions  10 , a pair of terminals  20   a  and  20   b , which form the second electrode layer portion  20 , are opposed to each other, between which a rectangular-shaped part of the heater resistor portion  18  is positioned, said rectangular-shaped part constituting a bubbled-ink forming area  28 . One of the terminals  20   a  (left hand side in  FIG. 2B ) is connected via a through-hole  26  to the first electrode layer portion  14 , which is a negative electrode, and the other terminal  20   b  is a positive electrode. Thus, a so-called turnover structure is formed in which a positive electrode is disposed on an upper surface of a insulating film layer and a negative electrode is disposed on a lower surface of the insulating film layer. 
   There is no electrode between any two adjacent heater resistor portions  18 . Each of the heater resistor portions  18  is heated by applying pulsed electric current, which flows from the positive electrode ( 20   b ) to the negative electrode ( 20   a ). 
   In each of the bubbled-ink forming portions  10 , as shown in  FIG. 3A , the heater resistor portion  18  includes the bubbled-ink forming area  28 , which has the same width as the second electrode layer portion  20  (forming the terminal pair  20   a  and  20   b ), and extended portions  30 , which are symmetrically disposed about and connected to the bubbled-ink forming area  28  when seen from above (see FIG.  3 A). The extended portions  30  and the partition walls  22  are partly overlapped as seen from above. 
   Namely, each of the partition walls  22  is disposed in straddling relation to two adjacent extended portions  30 . Spaces each defined by two of the partition walls  22  and one heater resistor portion  18  between the two serve as the bubble-ink forming portions  10 . Incidentally, because the extended portions  30  do not reach a high temperature and do not contribute to the above-noted bubble formation due to a reason described below, it is unnecessary to use high heat resistant resin as a material constituting the partition walls  22 . 
   The second insulating film layer  16  is totally covered by the heater resistor portions  18  and the partition walls  22  and is not exposed. Thus, the ink does not contact the second insulating film layer  16 , and the second insulating film layer  16  is not corroded by the ink. 
   When the surface of the second insulating film layer  16  is uneven, the surfaces of the heater resistor portions  18  reflect such an uneven surface and are correspondingly uneven. Due to such unevenness of the surfaces, lives of the heater resistor portions  18  are shortened. In consideration thereof, it is preferable that at least face portions, which contact the heater resistor portions  18 , of the second insulating film layer  16  are made flat and smooth by using, for example, a known method which is employed in a conventional LSI manufacturing process. If the surface of the second insulating film layer  16  is made even, the surfaces of the heater resistor portions  18  become even, and lives thereof can be lengthened. 
   Further, as shown in  FIG. 2A , a relation of W 2 &lt;W 1 &lt;W 3  is set where the width of the first electrode layer portion  14  is W 1 , the width of the second electrode layer portion  20  is W 2 , and the width of the heater resistor portion  18  (which includes the extended portions  30 ) is W 3 . 
   Due to this structure, the following operation and effects are obtained. Specifically, when the second insulating film layer  16  is formed over the first electrode layer portions  14 , a stepped or undulating surface of the second insulating film layer  16  is formed, representing presence and absence of the first electrode layer portions  14 . In each of the bubbled-ink forming areas  28 , the surface of the heater resistor portion  18  is affected by such an uneven surface of the second insulating film layer  16  and becomes likewise uneven. The life of the heater resistor portion  18  is thereby shortened. However, because the width W 2  of the second electrode layer portion  20  is narrower than the width W 1  of the first electrode layer portion  14 , no noticeable surface unevenness at the bubbled-ink forming area  28  of the heater resistor portion  18  is generated. Thus, in each bubbled-ink forming area  28 , the surface of the heater resistor portion  18  can be substantially flat even if the surface of the second insulating film layer  16  is not flat. Accordingly, the life of the heater resistor portion  18  can be extended. Further, because intervals between the heater resistor portions  18  depend on the widths of the heater resistor portions  18 , high-density disposition of the heater resistor portions  18  can be carried out. 
   For example, in a case in which the ink jet recording head has 600 dpi resolution, intervals between the heater resistor portions  18  in the above-described first direction are about 42 m. In this case, it is preferable that the width W 3  of the heater resistor portion  18  including the extended portions  30  is about 38 m, that the width W 1  of the first electrode layer portion  14  is about 32 m, that the width W 2  of the second electrode layer portion  20  is about 26 m, and that the width or a length, in the above-noted first direction, of a part of the extended portion  30  that is overlapped with or covered by the partition wall  22  is about 3 m or more. 
   Further, each of the terminal pairs formed by the second electrode layer portions  20  can be of any shape, when seen from above. Shapes such as in the embodiments shown in  FIGS. 3A and 3B  are preferable. If terminals of each terminal pair have tapered parts (parts thickened toward ends), a width of each of which gradually increases or diverges towards the other tapered part, it is preferable in view of manufacturing that each tapered part presents an obtuse angle at the boundary thereof, as shown in FIG.  3 B. 
   The width W 2  of the second electrode layer portion  20  corresponds to the width of connection between each of the terminals  20   a  and  20   b  and the heater resistor portion  18  (see FIGS.  3 A and  3 B). 
   Operation of the above-described first embodiment will be described below. 
   The bubbled-ink forming portion  10  is filled with ink, which has been introduced through an ink inlet opening (not illustrated). Pulsed electric current, which is applied, flows from the positive electrode ( 20   b ) to the negative electrode ( 20   a ), so that the bubbled-ink forming area  28  of the heater resistor portion  18  is instantaneously heated to a high temperature. A certain amount of ink positioned at the bubbled-ink forming area  28  is vaporized by heat of the heater resistor portion  18  into a vapor bubble. The vapor bubble expands, and force of the expanding vapor bubble in a direction perpendicular to the surface of the bubbled-ink forming area  28  of the heater resistor portion  18  ejects ink through the corresponding non-illustrated nozzle. For the following reasons, the extended portions  30  at both sides of the heater resistor portion  18  are not heated to a high temperature, and thus, do not contribute to such a vapor bubble formation. 
   Therefore, although the ink protection layers are the surface oxidation films of the heater resistor portions  18 , it is possible to prevent corrosion of the second insulating film layer  16  by ink without adding any further ink protection layers. As a result, a variety of ink materials can be used and an ink jet recording head and an ink jet recording apparatus, with high versatility, can be provided. 
   Now, detailed description will be given of the reason why the extended portions  30  do not reach high temperatures. 
   Even though each of the heater resistor portions  18  totally and evenly generates heat, heat tends to be conducted and dissipated to the outside at a peripheral part of the heater resistor portion, whereby the temperature of this peripheral part is lower than that of a central part of the heater resistor portion. The tantalum insulating films  24  are extremely thin and have high thermal conductivity with respect to ink, and therefore, the above-described tendency is increased. Thus, the extended portions  30  of the heater resistor portion  18  do not reach a higher temperature than the rectangular-shaped part of the heater resistor portion  18 . 
   Further, when the heater resistor portion  18  has pulsed electric current applied thereto to generate heat, the current, which flows through the heater resistor portion  18 , takes the shortest route between the two terminals due to extremely high electrical current density. The extended portions  30  of the heater resistor portion  18  have low electrical current density distribution. Therefore, the rectangular-shaped part, which constitutes the bubbled-ink forming area  28 , of the heater resistor portion  18  easily reach a high temperature, whereas the extended portions  30  do not easily reach a high temperature. 
   Furthermore, TaSiO has a negative (resistance) temperature coefficient. When the rectangular-shaped part of the heater resistor portion, which constitutes the bubbled-ink forming area  28 , is heated to a high temperature, a value of electrical resistance of the rectangular-shaped part decreases and an amount of electrical current flowing therethrough becomes large, as compared to the extended portions  30 . As just described, the rectangular-shaped part, which constitutes a bubbled-ink forming area  28 , of the heater resistor portion  18  easily reaches a high temperature, whereas the extended portions  30  are maintained at a low predefined temperature. 
   As a multiplier effect of the above-described facts, the extended portions  30  of the heater resistor portion  18  do not reach a high temperature, and do not contribute to formation of ink bubbles. Thus, the partition walls are not adversely affected. 
   In practice, the inventors have conducted reliability testing for an ink jet recording head according to the present invention. In this testing, only the rectangular-shaped part of the heater resistor portion  18  has had troubles based on either wear-out failure or overcurrent failure, though the number of occurences of such troubles are small, whereas the extended portions  30  have had no trouble. 
   Next, with reference to  FIGS. 4A and 4B , an ink jet recording head according to a second embodiment of the present invention will be described.  FIGS. 4A and 4B  are similar to  FIGS. 2A and 2B , respectively. Components which are the same as those explained in the first embodiment are denoted by the same reference numerals, and redundant explanation will be omitted where appropriate. 
   The structure of the second embodiment is similar to that of the first embodiment except in that the heater resistor portions  18  are formed on top surfaces of the second electrode layer portions  20 . In other words, the second electrode layer portions  20  and the heater resistor portions  18  are formed and laminated in this order. 
   Operation of the ink jet recording head according to the second embodiment will be described below. 
   The ink jet recording head of the second embodiment operates in the same manner as the ink jet recording head of the first embodiment. However, in the second embodiment, upper and side surfaces of each of the second electrode layer portions  20  are fully covered by the heater resistor portions  18  such that the second electrode layer portions  20  do not contact the ink. The second electrode layer portions  20  can be made of aluminum, which is not corrosion-resistant to ink. As compared to Ni and Au, Al is a low-cost material and has good workability as well. Thus, production cost can be reduced. Further, because the ink jet recording head does not use harmful materials such as Ni, it is environmentally friendly. 
   Next, with reference to  FIGS. 5A and 5B , an ink jet recording head according to a third embodiment of the present invention will be described. Elements which are the same as those explained in the first and the second embodiments are denoted by the same reference numerals, and redundant explanations will be omitted where appropriate. 
   The structure of the third embodiment is similar to those of the first and the second embodiments, except in that the second insulating film layer  16  comprises two second insulating film layers  16 A and  16 B, and in that a third electrode layer portion  32  is formed between the first electrode layer portion  14  and the heater resistor portion  18 . 
     FIG. 5A  is a cross sectional view showing a bubbled-ink forming portion  10  of the third embodiment in which one second insulating film layer  16 A is formed between the heater resistor portion  18  and the third electrode layer portion  32  and the other second insulating film layer  16 B is formed between the third electrode layer portion  32  and the first electrode layer portion  14 .  FIG. 5B  is a cross sectional view showing a variant example of the bubbled-ink forming portion  10  of the third embodiment in which the one second insulating film layer  16 A is formed between the second electrode layer portion  20  and the third electrode layer portion  32  and the other second insulating film layer  16 B is formed between the third electrode layer portion  32  and the first electrode layer portion  14 . 
   As described above, the second insulating film layer  16  comprises the two insulating film layers  16 A and  16 B. Since the second insulating film layer  16  tends to be relatively thick, there is a case in which connection between the second electrode layer portion  20  and the first electrode layer portion  14  cannot be implemented through only one through-hole. In consideration thereof, the second electrode layer portion  20  and the third electrode layer portion  32  are connected through a through-hole  26  and the third electrode layer portion  32  and the first electrode layer portion  14  are connected through another through-hole  27 . Namely, the second electrode layer portion  20  and the first electrode layer portion  14  are connected through the third electrode layer portion  32 . 
   Next operation of the ink jet recording head according to the third embodiment will be described. 
   The ink jet recording head of the third embodiment operates in a manner similar to those of the first and the second embodiment. However, in the third embodiment, because the second insulating film layer  16 , which comprises the two insulating film layers  16 A and  16 B, is relatively thick, it is difficult for the heat of the heater resistor portion  18  to be transmitted to the first electrode layer portion  14 , which is made of Aluminum which has good thermal conductivity. Thus, the efficiency of thermal conductivity with respect to the ink can be improved 
   Note that the present invention is not limited to the embodiments described above. 
   For example, in the embodiment described above, the heater resistor portions  18 , which have the surface oxidation films each serving as an ink protection layer, are formed from TaSiO. However, the present invention is not limited to such a configuration. Any other materials, whose surface oxidation film can serve as an ink protection layer, can be used. For example, CrSiO or the like is usable. 
   Further, in the embodiment described above, the second electrode layer  20  is an single layer. However, the present invention is not limited to such a configuration. The second electrode layer can be formed as a laminated structure comprising a plurality of layers. 
   Still further, in the embodiment described above, each end of the extended portions  30  has a linear shape. However, the present invention is not limited to such a configuration. If at least part of each of the extended portions is covered by an associated partition wall, an objective insulating film layer is covered by the partition walls and the extended portions, and this objective insulating film layer is not exposed to the outside, then the ends of the extended portions may have any appropriate shape. 
   Furthermore, in the embodiments described above, the first electrode layer portions  14  are negative and one end terminals of the terminal pairs constituting the second electrode layer portions  20  are positive. However, the invention is not limited to such a configuration. The first electrode layer portions can be positive and the one end terminals of the terminal pairs of the second electrode layer portions  20  can be negative. 
   Moreover, in the embodiments described above, one terminal of the terminal pair is connected to the first electrode layer portion  14  through the through-hole  26 . However, the present invention is not limited to such a configuration. Any other appropriate structure in which electrodes are not provided between adjacent heater resistor portions can be employed. 
   It is to be understood that the present invention is by no means limited to the specific embodiments as illustrated and described herein, and that various modifications thereof may be made which fall within the scope of the present invention as defined in the appended claims.