Patent Publication Number: US-6217157-B1

Title: Liquid discharging head and liquid discharging apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid discharging head and a liquid discharging apparatus for discharging liquid by bubble generation for example by thermal energy, and more particularly to a liquid discharging head and a liquid discharging apparatus utilizing a movable separation membrane which is moved by the bubble. 
     The present invention is applicable to a printer for recording on various recording media such as paper, yarn, fiber, fabrics, leather, metal, plastics, glass, timber, ceramics etc., a copying machine, a facsimile apparatus having a communication system, a work processor having a printer unit, and an industrial recording apparatus combined in composite manner with various processing apparatus. In the present invention, the “recording” means not only forming a meaningful image such as a character or graphics on the recording medium but also forming a meaningless image such as a pattern. 
     2. Related Background Art 
     There is already known an ink jet recording method, so-called bubble jet recording method, for providing liquid such as ink with an energy such as heat to generate a state change involving a steep volume change (generation of a bubble), causing the liquid to be discharged through a discharge opening by the force based on such state change and depositing the liquid onto the recording medium to form an image. The recording head utilizing such bubble jet recording method is generally provided, as disclosed in the Japanese Patent Publication Nos. 61-59911 and 61-59914 (corresponding to the U.S. Pat. No. 4,723,129), with a discharge opening for discharging liquid, a liquid path communicating with the discharge opening, and a heat generating member (electrothermal converting member) positioned corresponding to the liquid path and serving as energy generating means for generating energy for discharging the liquid. 
     Such recording method is advantageous in various manners such as being capable of printing an image of high quality at a high speed and a low noise level, printing an image of a high resolution with a compact apparatus since the discharge openings can be arranged with a high density, and obtaining a color image in a simple manner. For this reason, the bubble jet recording method is recently utilized in various office equipment such as printer, copying machine, facsimile etc. and even in certain industrial applications such as fabric printing apparatus. 
     On the other hand, in the conventional bubble jet recording method, as the heat generating member repeats heating in direct or indirect contact with liquid, there may be formed, on the surface of the heat generating member, a deposit resulting from scorching of the liquid. Also, in case the liquid to be discharged is easily deteriorated by heat or cannot show sufficient bubble generation, satisfactory liquid discharge may not be achieved by the bubble formation by the aforementioned heat generating member. 
     On the other hand, the Japanese Patent Application Laid-Open No. 55-81172 proposed a method of separating a bubble generating liquid and a discharge liquid by a flexible membrane and generating a bubble in the bubble generating liquid by thermal energy thereby discharging the discharge liquid. In the configuration of the proposed method, the flexible membrane and the bubble generating liquid are so positioned that the flexible membrane is provided in a part of the nozzle, but the Japanese Patent Application Laid-Open No. 59-26270 discloses a configuration employing a large membrane separating the entire head into an upper part and a lower part. Such large membrane, being supported between two plate members constituting the liquid path, is so provided that the liquids in the two liquid paths are not mutually mixed. Also there are known configurations giving certain feature to the bubble generating liquid itself in consideration of the bubble generating characteristics, such as the one disclosed in the Japanese Patent Application Laid-Open No. 5-229122, employing liquid of a lower boiling point than that of the discharge liquid or the one disclosed in the Japanese Patent Application Laid-Open No. 4-329148, employing electrically conductive liquid as the bubble generating liquid. 
     SUMMARY OF THE INVENTION 
     The present inventors have found a novel issue, not known in the prior art, with respect to the displacement range of the movable separating membrane. The separating membrane in the liquid discharging head of the present invention is supported between a first liquid path wall and a second liquid path wall, and the movable area for each liquid path is limited by the liquid path walls. It is thus confirmed that the first and second liquid path walls define the displacement of the membrane and have significant influence on the characteristics of the head. Therefore the present inventors have concluded that it is important to define the displacement of the membrane by the membrane itself instead of the liquid path wall to achieve smooth membrane displacement thereby maintaining the highly reliable liquid discharging characteristics. 
     Therefore, the present inventors have made intensive investigation in order to provide a liquid discharging head excellent in durability and stability of liquid discharging regardless of the kind of the supplied liquid, while exploiting the effect of the separating function of the separating membrane. As a result, the present inventors have tried a membrane substantially free from elongation and having a recessed portion, and found that the amount of displacement of the recessed portion corresponds to the discharge amount of the liquid. Thus, it has been found that the stable discharge can be achieved regardless of the kind of the supplied liquid by defining the displacement amount of the recessed portion, as the discharge amount corresponds to the displacement amount of the recessed portion of the separating membrane. It has also been found that the durability of the separating membrane can be improved by defining the displacement amount of the recessed portion of the separating membrane in such a manner that such recessed portion does not elongate or contract at the maximum displacement. It has furthermore been found that the refiling of the discharge liquid can be improved by utilizing the self returning force of the membrane when the recessed portion is not given energy for the displacement. 
     From a different standpoint, in case various liquids are used as the discharge liquid, the amount of liquid discharged from the discharge opening for example by thermal energy fluctuates depending on the kind of the liquid. Such fluctuation tends to increase with the increase in the vicsocity of the liquid. However, a method of stabilizing the discharge amount in a given liquid discharging head, by varying the discharge energy according to the kind of the supplied liquid, is complex and is difficult to practice. Consequently it is important to provide a recording head capable, with a simple structure, of realizing stable liquid discharge regardless of the kind of the supplied liquid. 
     An object of the present invention, attained by such intensive investigation, is to provide a novel liquid discharging head and a novel liquid discharging apparatus, capable of improving the efficiency of liquid droplet discharge, excellent in the stability and durability of discharge and stabilizing and increasing the discharged droplet volume or discharge speed. 
     Another object of the present invention is to improve the discharge efficiency, discharge stability and durability in the liquid discharging head provided with a first liquid path for the discharge liquid communicating with a discharge opening, a second liquid path containing the bubble generating liquid in a suppiable or movable manner and including a bubble generating area, and a movable separating membrane for separating the first and second liquid paths, having a displacement area of the movable separating membrane at the upstream side with respect to the discharge opening. 
     Still another object of the present invention is to provide a liquid discharging head in which the discharge liquid and the bubble generating liquid are separated by a movable membrane, wherein the displacement of the movable separating membrane is stabilized at the pressure transmission to the discharge liquid by a displacement of the movable membrane by the pressure of bubble generation, thereby achieving excellent discharge efficiency, discharge stability and refilling efficiency. 
     Still another object of the present invention is to provide a liquid discharging head of the above-mentioned configuration, excellent in durability. 
     Still another object of the present invention is to provide a liquid discharging head of the above-mentioned configuration, capable of reducing the amount of deposit formed on the heat generating member and efficiently discharging the liquid without thermal influence thereto. 
     Still another object of the present invention is to provide a liquid discharging head having a wider freedom in selecting the discharge liquid, regardless of the viscosity, constituent material or composition thereof. 
     Still another object of the present invention is to provide a liquid discharging head in which the recessed portion of the movable separating membrane is made more easily deformable, thereby enabling to achieve a high density of the liquid path walls. 
     Still another object of the present invention is to provide a liquid discharging head comprising: 
     a discharge liquid path communicating with a discharge opening for discharging a discharge liquid and adapted to flow the discharge liquid; 
     a bubble generating liquid path including a bubble generating area for bubble generation and adapted to flow a bubble generating liquid; and 
     a movable separating membrane adapted for mutually and substantially separating the discharge liquid path and the bubble generating liquid path and having a recess, in a position corresponding to the bubble generating area, deviated so as to narrow the bubble generating liquid path; 
     wherein the recess has substantially non-displacing corner portions and is adapted to displace, excluding the corner portions, by a bubble generated in the bubble generating area. 
     Still another object of the present invention is to provide a liquid discharging head comprising: 
     a discharge liquid path communicating with a discharge opening for discharging a discharge liquid and adapted to flow the discharge liquid; 
     a bubble generating liquid path including a bubble generating area for bubble generation and adapted to flow a bubble generating liquid; and 
     a movable separating membrane adapted for mutually and substantially separating the discharge liquid path and the bubble generating liquid path and having a recess, in a position corresponding to the bubble generating area, deviated so as to narrow the bubble generating liquid path; 
     wherein the volume V 1  of the recess in a still state and the volume V 2  of the recess at the maximum displacement satisfy a relation: 
     
       
         V 2 &lt;V 1 . 
       
     
     Still another object of the present invention is to provide a liquid discharging apparatus comprising: 
     a liquid discharging head including a discharge liquid path communicating with a discharge opening for discharging a discharge liquid and adapted to flow the discharge liquid; a bubble generating liquid path including a bubble generating area for bubble generation and adapted to flow a bubble generating liquid; and a movable separating membrane adapted for mutually and substantially separating the discharge liquid path and the bubble generating liquid path and having a recess, in a position corresponding to the bubble generating area, deviated so as to narrow the bubble generating liquid path; wherein the recess has substantially non-displacing corner portions and is adapted to displace, excluding the corner portions, by a bubble generating in the bubble generating area; and transport means for transporting a recording medium for forming a record by receiving the discharge liquid discharge from the liquid discharging head. 
     Still another object of the present invention is to provide a liquid discharging apparatus comprising: 
     a liquid discharging head including a discharge liquid path communicating with a discharge opening for discharging a discharge liquid and adapted to flow the discharge liquid; a bubble generating liquid path including a bubble generating area for bubble generation and adapted to flow a bubble generating liquid; and a movable separating membrane adapted for mutually and substantially separating the discharge liquid path and the bubble generating liquid path and having a recess, in a position corresponding to the bubble generating area, deviated so as to narrow the bubble generating liquid path; wherein the volume V 1  of the recess in a still state and the volume V 2  of the recess at the maximum displacement satisfy a relation V 2 &lt;V 1 ; and 
     transport means for transporting a recording medium for forming a record by receiving the discharge liquid discharge from the liquid discharging head. 
     According to the present invention, the movable separating membrane, for separating the first liquid path in which the discharge liquid is supplied and the second liquid path in which the non-discharged bubble generating liquid is supplied, is provided with a recessed portion so as to oppose to the bubble generating area and the fulcrum of the recessed portion is positioned at a non-displacing corner to constantly stabilize the initial state of the recessed portion and the shape thereof at the maximum displacement, thereby achieving stable liquid discharge. 
     Also by maintaining a relationship V 2 &lt;V 1  between the volume V 1  of the recessed portion in a still state and the volume V 2  thereof at the maximum displacement, the pressure by bubble generation acts only on the displacement of the recessed portion substantially without causing elongation or contraction of the movable separating membrane even at the maximum displacement, thereby realizing stable discharge and improved durability. Besides, with the contraction of the bubble, the recessed portion of the movable separating membrane promptly returns to the initial state by the self returning force provided by the non-displacing corner portion, thereby improving the refilling of the discharge liquid. 
     Furthermore, the recessed portion is provided with an inflection portion between a corner part and a bottom part, having a thickness smaller than that of the bottom part of the recessed portion, whereby the recessed portion is rendered more easily deformable and the pressure by bubble generation is more easily transmitted to the first liquid path at the side of the discharge opening thereof. Thus the liquid in the first liquid path can be efficiently discharged from the discharge opening by the bubble generation. 
     Furthermore, by providing the movable separating membrane with a part of a smaller thickness between the corner part and the bottom part of the recessed portion, the movable separating membrane can be made more easily deformable and the liquid in the first liquid path can be efficiently discharged from the discharge opening by the bubble generation. Furthermore, with such more easily deformable recessed portion, there can be provided a liquid discharging head sufficiently allowing to increase the density of the liquid paths. 
     Furthermore, by selecting the height h 2  from the bottom part of the recessed portion to the inflection part thereof equal to or larger than the height hi from the heat generating member to the bottom part of the recessed portion, the pressure by bubble generation is transmitted to the movable separating membrane before it escapes to the upstream and downstream sides of the second liquid path. Consequently the pressure by bubble generation can be efficiently transmitted to the movable separating membrane, thus improving the discharge efficiency. 
     Furthermore, the pressure by bubble generation can be sufficiently and efficiently to the entire bottom part of the recessed portion by maintaining a relationship W 1 ≧WH≧W 2  among the distance W 1  between the corner parts of the recessed portion, the width W 2  of the bottom part thereof and the width WH of the heat generating member. It is furthermore made possible to efficiently transmit the pressure by bubble generation to the entire bottom part of the recessed portion by maintaining a relationship W 1 ≧W 3 ≧WH wherein W 3  is the distance between the inflection parts, present between the corner part and the bottom part of the recessed portion. 
     Furthermore, the pressure by bubble generation can be satisfactorily and efficiently transmitted to the entire bottom part of the recessed portion by maintaining a relationship S 1 ≧SH≧S 2  wherein S 1  is the area defined by connecting the corners of the recessed portion and projected in a direction toward the heat generating member, S 2  is the area of the bottom part of the recessed portion and SH is the area of the heat generating member. It is furthermore possible to more efficiently transmit the pressure by bubble generation to the entire bottom part of the recessed portion by maintaining a relationship S 1 ≧S 3 ≧SH wherein S 3  is the area formed by connecting the inflection parts, present between the corner part and the bottom part, of the recessed portion. 
     Furthermore, it is possible to supply the bubble generating liquid from a guide path at the generation or extinction of the bubble by adopting a configuration in which the liquid in the second liquid path flows in the guide path provided in the substrate. It is furthermore possible to obtain uniform pressure balance in the second liquid path by adjusting the cross section of the guide path, thereby enabling parallel displacement of the movable separating membrane more securely and more stably. Furthermore, a configuration having guide path which divide the entire liquid paths into plural blocks enables uniform liquid flow in the second liquid paths. Also a configuration having a bubble reservoir in a part of the second liquid path allows to eliminate bubbles from the liquid supplied through the guide path and to utilize the liquid with reduced bubble content, thereby more easily attaining desired bubble discharging characteristics. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A,  1 B,  1 C,  1 D, E and  1 F are cross-sectional views along the liquid path showing are embodiment of the liquid discharging head of the present invention; 
     FIGS. 2A,  2 B,  2 C,  2 D,  2 E and  2 F are magnified cross-sectional views in the vicinity of the recessed portion of the movable separating membrane shown in FIGS. 1A to  1 F; 
     FIG. 3 is a partially broken perspective view of the liquid discharging head shown in FIGS. 1A to  1 F and  2 A to  2 F; 
     FIGS. 4A and 4B are magnified cross-sectional views along the liquid path showing the recessed portion of the movable separating membrane of the liquid discharging head of the present invention, respectively in an initial state and in a state at the maximum displacement; 
     FIGS. 5A and 5B are similar views showing a reference example not provided with the corner part at the fulcrum of the recessed portion of the movable separating membrane, respectively in an initial state and in a state at the maximum displacement of the recessed portion; 
     FIG. 6 is a cross-sectional view, parallel to the heat generating member, showing the liquid path of the liquid discharging head of the present invention; 
     FIGS. 7A and 7B are magnified cross-sectional views along the liquid path showing the volume of the recessed portion of the movable separating membrane of the liquid discharging head of the present invention, respectively in an initial state and in a state at the maximum displacement; 
     FIGS. 8A and 8B are cross-sectional views showing a configuration of the liquid discharging head of the present invention, respectively with a protective film to be explained later and without such protective film; 
     FIG. 9 is a wave form chart showing a voltage to be applied to the electrical resistance layer shown in FIGS. 8A and 8B; 
     FIGS. 10A and 10B are views showing a process for preparing the movable separating membrane of the liquid discharging head of the present invention; 
     FIGS. 11A and 11B are views showing another process for preparing the movable separating membrane of the liquid discharging head of the present invention; 
     FIGS. 12A,  12 B,  12 C,  12 D,  12 E and  12 F are cross-sectional views along the liquid path showing another embodiment of the liquid discharging head of the present invention; 
     FIGS. 13A,  13 B,  13 C,  13 D,  13 E and  13 F are magnified cross-sectional views in the vicinity of the recessed portion of the movable separating membrane shown in FIGS. 12A to  12 F; 
     FIG. 14 is a partially broken perspective view of the liquid discharging head shown in FIGS. 12A to  12 F and  13 A to  13 F; 
     FIGS. 15A and 15B are magnified cross-sectional views along the liquid path showing the recessed portion of the movable separating membrane in another embodiment of the liquid discharging head of the present invention, respectively in an initial state and in a state at the maximum displacement; 
     FIG. 16 is a cross-sectional view, parallel to the heat generating member, showing the liquid path in another embodiment of the liquid discharging head of the present invention; 
     FIGS. 17A and 17B are views showing a process for preparing the movable separating membrane in another embodiment of the liquid discharging head of the present invention; 
     FIGS. 18A,  18 B,  18 C,  18 D and  18 E are cross-sectional views along the liquid path showing another embodiment of the movable separating membrane of the liquid discharging head of the present invention; 
     FIGS. 19A and 19B are cross-sectional views perpendicular to the liquid path showing another embodiment of the movable separating membrane of the liquid discharging head of the present invention; 
     FIGS. 20A,  20 B,  20 C,  20 D,  20 E and  20 F are magnified cross-sectional views in the vicinity of the recessed portion of the movable separating membrane in another embodiment of the liquid discharging head of the present invention; 
     FIGS. 21A,  21 B,  21 C,  21 D,  21 E and  21 F are magnified cross-sectional views in the vicinity of the recessed portion of the movable separating membrane in still another embodiment of the liquid discharging head of the present invention; 
     FIGS. 22A,  22 B,  22 C,  22 D,  22 E and  22 F are magnified cross-sectional views, along a line  22 A to  22 F— 22 A to  22 F in FIG. 1A, of the vicinity of the movable separating membrane in another embodiment of the present invention; 
     FIGS. 23A,  23 B,  23 C,  23 D,  23 E and  23 F are magnified cross-sectional views of the vicinity of the movable separating membrane shown in another embodiment of the present invention shown in FIGS. 12A to  12 F; 
     FIGS. 24A,  24 B,  24 C,  24 D,  24 E and  24 F are magnified cross-sectional views of the vicinity of the movable separating membrane, seen from the side of the discharge opening, in another embodiment of the present invention shown in FIGS. 12A to  12 F; 
     FIGS. 25A,  25 B,  25 C and  25 D are views showing positional relationship between the heat generating member and the movable separating membrane in another embodiment of the present invention; 
     FIGS. 26A,  26 B,  26 C and  26 D are views showing positional relationship between the heat generating member and the movable separating membrane in still another embodiment of the present invention; 
     FIGS. 27A,  27 B,  27 C,  27 D,  27 E and  27 F are cross-sectional views along the liquid path, showing another embodiment of the liquid discharging head of the present invention; 
     FIGS. 28A,  28 B,  28 C and  28 D are plan views and a cross-sectional view showing an example of the second liquid path in another embodiment of the liquid discharging head of the present invention; 
     FIG. 29 is a cross-sectional view showing the principal parts of another embodiment of the liquid discharging head of the present invention; 
     FIG. 30 is a cross-sectional view showing the entire structure of the liquid discharging head shown in FIG. 29; 
     FIG. 31 is a cross-sectional view showing another embodiment of the liquid discharging head of the present invention; 
     FIG. 32A is a plan view of an element board in another embodiment of the liquid discharging head of the present invention; FIG. 32B is a partial magnified view of the board shown in FIG. 32A; and FIG. 32C is a magnified partial plan view of still another embodiment; 
     FIG. 33 is a schematic perspective view showing the principal parts of an ink jet recording apparatus, constituting the liquid discharging apparatus in which the liquid discharging head of the present invention is mounted; and 
     FIG. 34 is a schematic perspective view showing the principal parts of the liquid discharging apparatus constituting another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now the present invention will be clarified in detail by preferred embodiments thereof with reference to the attached drawings. 
     FIGS. 1A to  1 F are cross-sectional views along the liquid path showing an embodiment of the liquid discharging head of the present invention, while FIGS. 2A to  2 F are magnified cross-sectional views in the vicinity of the recessed portion of the movable separating membrane shown in FIGS. 1A to  1 F, and FIG. 3 is a partially broken perspective view of the liquid discharging head shown in FIGS. 1A to  1 F and  2 A to  2 F. 
     In the present embodiment, as shown in FIGS. 1A to  1 F, a first liquid path  3  communicating with a discharge opening  1  is filled with first liquid supplied from a first common liquid chamber  143 , while a second liquid path  4  containing a bubble generating area  7  is filled with bubble generating liquid which generates a bubble upon receiving thermal energy by a heat generating member  2 . Between the first liquid path  3  and the second liquid path  4  there is provided a movable separating membrane  5  for mutually separating the first and second liquid paths. The movable separating membrane  5  is provided, in a portion thereof opposed to the bubble generating area  7 , with a recessed portion  8  having corner parts  8   a  at the fulcrums thereof, thus forming an expansion in the first liquid path  3 . The movable separating membrane  5  is fixed to an orifice plate  9  to prevent mixing of two liquids. In the second liquid path  4 , the bubble generating area  7  is constituted by the vicinity of the projected area of the heat generating member  2 . 
     As shown in FIG. 3, the heat generating member  2  is provided in an array of plural units on an element board  10 , on which plural second liquid paths  4  are provided respectively corresponding to the heat generating members  2 . A support member  11  supporting the movable separating membrane  5  serves also as a wall for defining and forming the second liquid paths  4 . The movable separating membrane  5  is provided with plural recessed portions  8 , respectively corresponding to the bubble generating areas  7  positioned in the vicinity of the bubble generating areas  7  which are in the vicinity of the projected areas of the heat generating members  2 . The first liquid path  3  is provided in plural units, so as to respectively contain the recessed portions  8 . In FIG. 3, however, the positions of walls  28  for defining the first liquid paths are represented by broken lines. 
     The present invention is based on the movement of the movable separating membrane  5 , and the movable separating membrane  5  itself is provided with the recessed portion  8  which is displaced toward the first liquid path  3  by the growth of a bubble generated on the surface of the heat generating member  2 . 
     In an initial state shown in FIGS. 1A and 2A, the liquid in the first liquid path  3  is retracted to the vicinity of the discharge opening  1  by the capillary force. In the present embodiment, the discharge opening  1  is provided at the downstream position, in the liquid flow direction in the first liquid path  3 , with respect to the projected area of the heat generating member  2  onto the first liquid path  3 . 
     When thermal energy is given to the heat generating member  2  (consisting of a heat-generating resistance member of 40×105 μm in the present embodiment) in this state, the heat generating member  2  is rapidly heated whereby the surface thereof in contact with the second liquid in the bubble generating area heats the liquid and generates a bubble therein (FIGS.  1 B and  2 B). A bubble  6  thus formed is based on a film boiling phenomenon as described in the U.S. Pat. No. 4,723,129 and is generated with an extremely high pressure over the entire area of the heat generating member. The generated pressure is transmitted as a pressure wave in the second liquid in the second liquid path  4  and acts on the movable separating membrane  5 , whereby the recessed portion  8  thereof is deformed to initiate the discharge of the first liquid in the first liquid path  3 . However the corner parts  8   a  formed at the fulcrums of the recessed portion  8  are not involved in such deformation. 
     The bubble generated on the entire surface of the heat generating member  2  rapidly grows to assume a film shape (FIGS.  1 C and  2 C). The expansion of the bubble  6  with an extremely high pressure in the initial stage of generation causes a further deformation of the recessed portion  8  of the movable separating membrane  5 , whereby the first liquid in the first liquid path  3  is further discharged from the discharge opening  1 . 
     With the further growth of the bubble  6  thereafter, the deformation proceeds to such a level that the central part of the recessed portion  8 , excluding the corner parts  8   a  of the membrane  5 , enters the first liquid path  3  (FIGS.  1 D and  2 D). 
     When the bubble  6  starts to contract thereafter, the recessed portion  8  of the movable separating membrane  5  starts to return to the position before deformation (FIGS.  1 E and  2 E). 
     Subsequently, the recessed portion  8  of the movable separating membrane  5  promptly returns to the initial state shown in FIGS. 1F and 2F by the self returning force exerted by the non-deformed corner parts  8   a,  whereby the liquid refilling in the first liquid path  3  is accelerated. Also, with the extinction of the bubble, the recessed portion  8  of the movable separating membrane  5  displaces into the second liquid path  4 , thereby reducing the volume thereof and also reducing the refilling amount of the bubble generating liquid, whereby the refilling is completed promptly. Also, as the corner parts  8   a  of the recessed portion  8  have a function of suppressing the rebounding movement immediately after the displacement by bubble generation, the recessed portion  8  immediately returns to the initial state after displacement, thereby enabling high-speed drive. 
     FIGS. 4A and 4B are magnified cross-sectional views along the liquid path showing the recessed portion  8  of the movable separating membrane  5  of the liquid discharging head of the present invention, respectively in the initial state and in a state at the maximum displacement, while FIGS. 5A and 5B are similar views showing a reference example not provided with the corner parts at the fulcrums of the recessed portion  8  of the movable separating membrane  5 , respectively in the initial state and in the state at maximum displacement of the recessed portion, and FIG. 6 is a cross-sectional view, parallel to the heat generating member, showing the liquid path of the liquid discharging head of the present invention. 
     In case the fulcrums  26  of the recessed portion do not have the corner parts as shown in FIGS. 5A and 5B and the bottom part  27  of the recessed portion assumes an inverted shape at the maximum displacement as shown in FIG. 5B, the recessed portion deforms with the fulcrums  26  as the inflection points. 
     On the other hand, in case the fulcrums of the recessed portion have the corner parts  8   a,  such corner parts  8   a  have an effect, in the initial state shown in FIG. 4A, of defining the initial shape always in a constant shape. Also at the maximum displacement shown in FIG. 4B, the shape is always constant because the deformation is not concentrated locally but is spread over a wide area in the vicinity of the corner parts. Thus the corner parts  8   a  define the shape at the initial state and at the maximum displacement, thereby achieving very stable liquid discharge and improving durability. The displacement governing area of the corner parts  8   a  will also be understood from FIG.  6 . 
     FIGS. 7A and 7B are magnified cross-sectional views along the liquid path showing the volume of the recessed portion 8 of the movable separating membrane  5  in the liquid discharging head of the present invention, respectively in an initial state and in a state at the maximum displacement. 
     In this embodiment, the driving conditions are so selected as to satisfy a condition V 2 &lt;V 1 , wherein V 1  is the volume of the recessed portion in the initial state shown in FIG.  7 A and V 2  is that at the maximum displacement shown in FIG.  7 B. 
     Under the condition V 2 &lt;V 1 , the movable separating member in the recessed portion  8  does not show elongation or contraction even at the maximum displacement. Consequently V 1  and V 2  remain always constant, thereby stabilizing the liquid discharge. The volume V 1  of the recessed portion means a volume defined between the face of the movable separating membrane  5  at the side of the first liquid path and the bottom part  8   b  of the recessed portion  8  in the initial state, and the volume V 2  means a volume surrounded by faces in contact with the inflection parts 8 c  of the recessed portion  8  and the bottom part  8   b  thereof at the maximum displacement. Also the “inflection part” used in the present specification and the appended drawings means, in the recessed portion of the movable separating membrane, a part showing the largest deformation at the maximum displacement. 
     The configuration of the present embodiment allows to employ different liquids for the discharge liquid and the bubble generating liquid and to discharge the discharge liquid only. Consequently, it is possible to satisfactorily discharge highly viscous liquid such as polyethylene glycol in which a sufficient discharging force cannot be obtained in the conventional configuration because of insufficient bubble generation under the application of heat, by supplying such liquid in the first liquid path  103  and supplying the second liquid path  104  with liquid capable of satisfactory bubble generation (for example a mixture of ethanol: water =4:6 with a viscosity of 1-2 cp). 
     Also as the bubble generating liquid, there can be selected liquid which does not generate a deposit such as kogation on the surface of the heat generating member under the influence of heat, in order to stabilize the bubble generation and ensuring satisfactory liquid discharge. 
     Furthermore, the configuration of the liquid discharging head of the present invention can discharge various liquid such as highly viscous liquid with an even higher discharge efficiency and an even higher discharging power, because of the effects explained in the foregoing embodiment. 
     Furthermore, liquid susceptible to heat can be discharged without thermal damage with a high discharge efficiency and a high discharging power as explained above, by supplying such liquid as the discharge liquid in the first liquid path  103  and supplying the second liquid path  104  with liquid stabler to heat capable of satisfactory bubble generation as the bubble generating liquid. 
     In the following there will be explained the configuration of an element board  110  provided with the heat generating members  102  for giving heat to the liquid. 
     FIGS. 8A and 8B are longitudinal cross-sectional views showing a configuration of the liquid discharging head of the present invention, respectively with a protective film to be explained later and without such protective film. 
     As shown in FIGS. 8A and 8B, on an element board  110 , there are provided a second liquid path  104 , a movable separating membrane  105  constituting a partition wall, a movable member  131 , a first liquid path  103 , and a grooved member  132  provided with a groove constituting the first liquid path  103 . 
     The element board  110  is composed by forming, on a substrate  110   f  such as of silicon, a silicon oxide film or a silicon nitride film  110   e  for the purpose of electrical insulation and heat accumulation, on which patterned are an electrical resistance layer  110   d  for example of hafnium boride (HtB 2 ), tantalum nitride (TaN) or tantalum-aluminum (TaAl) constituting the heat generating member of a thickness of 0.01 to 0.2 μm, and a wiring electrode  110   c  for example of aluminum of a thickness of 0.1 to 1.0 μm. A voltage is applied to the electrical resistance layer  110   d  from the two wiring electrodes  110   c  to generate heat by the current in the electrical resistance layer  110   d.  On the electrical resistance layer  110   d  between the wiring electrodes  110   c,  there are formed a protective layer  110   b  for example of silicon oxide or silicon nitride of a thickness of 0.1 to 0.2 μm and an anticavitation layer  110   a  for example of tantalum of a thickness of 0.1 to 0.6 μm to protect the electrical resistance layer  110   d  from various liquids such as the ink. 
     As the pressure or impact wave generated at the generation or extinction of the bubble is very strong and significantly deteriorates the service life of the hard and fragile oxide film, the anticativation layer  110   a  is composed of a metal such as tantalum (Ta). 
     There may also be adopted a configuration dispensing with the above-mentioned protective layer by the combination of the liquid, configuration of the liquid paths and the resistance material, as exemplified in FIG.  8 B. An example of the material for the resistance layer not requiring such protective layer is iridium-tantalum-aluminum alloy. The present invention is particularly advantageous for the configuration without the protective layer, since the liquid for bubble generation can be selected for this purpose, separately from the discharge liquid. 
     Therefore, the heat generating member  102  in the above-described embodiment may be constructed with the electrical resistance layer (heat generating part)  110   d  only between the wiring electrodes  110   c  or with a protective layer for protecting the electrical resistance layer  110   d.    
     In the present embodiment, the heat generating member  102  is provided with a heat generating part constituted by a resistance layer capable of heat generation in response to an electrical signal, but the present invention is not limited to such configuration and there may be employed any heat generating part capable of generating, in the bubble generating liquid, a bubble sufficient for discharging the discharge liquid. For example there may be employed a photothermal converting member for generating heat by receiving light such as from a laser, or a heat generating part for generating heat by receiving a high frequency radio wave. 
     The aforementioned element board  110  may be provided, in addition to the electrothermal converting members composed of the electrical resistance layer  110   d  constituting the heat generating parts and the wiring electrodes  110   c  for supplying the electrical resistance layer  110   d  with electrical signals, integrally with functional elements such as transistors, diodes, latches, shift registers etc. for selectively driving such electrothermal converting elements by a semiconductor process. 
     For discharging the liquid by driving the heat generating part of the electrothermal converting member provided on the aforementioned element board  110 , a rectangular pulse is applied to the electrical resistance layer  110   d  through the wiring electrodes  110   d  thereby causing rapid heat generation in the electrical resistance layer  110   d.    
     FIG. 9 is a wave form chart showing the voltage to be applied to the electrical resistance layer  110   d  shown in FIGS. 8A and 8B. In the liquid discharging head of the above-described embodiment, the heat generating member is driven by applying an electrical signal of a voltage of 24 V, a pulse duration of 7 μsec and a current of 150 mA with a frequency of 6 kHz to discharge liquid ink from the discharge opening by the aforementioned functions. However the conditions of the driving signal in the present invention are not limited to those mentioned above but there may be employed any drive signal capable of appropriate bubble generation in the bubble generating liquid. 
     In the present invention, as explained in the foregoing, the liquid can be discharged with a discharging power and a discharge efficiency higher than in the conventional liquid discharging head. The bubble generating liquid can be of liquid of the aforementioned properties, such as methanol, ethanol, n-propanol, isopropanol, n-hexane, n-heptane, n-octane, toluene, xylene, methylene dichloride, trichlene, fleon TF, fleon BF, ethylether, dioxane, cyclohexane, methyl acetate, ethyl acetate, acetone, methylethylketone, water and mixtures thereof. 
     The discharge liquid may be composed of various liquid regardless of the bubble generating property or the thermal properties. There may also be employed liquid of low bubble generating property that cannot be easily discharged in the conventional configuration, liquid subject to deterioration by heat or highly viscous liquid. However the discharge liquid is desirably not hindering the liquid discharging operation, bubble generating operation or the function of the movable separating membrane by the discharge liquid itself or by a reaction with the bubble generating liquid. 
     The discharge liquid for recording may also be composed of highly viscous ink. Other examples of the discharge liquid include pharmaceuticals or perfumes which are susceptible to heat. 
     The recording operation was conducted by the combinations of the bubble generating liquid and the discharge liquid in the following compositions. As a result, records of high quality could be obtained by satisfactorily discharging not only the liquid of a viscosity in excess of 10 cp that could not be satisfactorily discharged in the conventional liquid discharging head but also the liquid of a viscosity as high as 150 cp. 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Bubble generating liquid 1 
                 ethanol 
                 40 
                 wt. % 
               
               
                   
                 water 
                 60 
                 wt. % 
               
               
                 Bubble generating liquid 2 
                 water 
                 100 
                 wt. % 
               
               
                 Bubble generating liquid 3 
                 isopropyl 
                 10 
                 wt. % 
               
               
                   
                 alcohol 
               
               
                   
                 water 
                 90 
                 wt. % 
               
               
                 Discharge liquid 1 
               
               
                   
                 carbon black 
                 5 
                 wt. % 
               
               
                   
                 (pigment ink; ca. 15 cp) 
               
               
                   
                 styrene-acrylic acid-ethyl 
                 1 
                 wt. % 
               
               
                   
                 actylate copolymer 
               
               
                   
                 (oxidation degree 140; 
               
               
                   
                 weight-averaged molecular 
               
               
                   
                 weight 8000) 
               
               
                   
                 monoethanolamine 
                 0.25 
                 wt. % 
               
               
                   
                 glycerin 
                 6.9 
                 wt. % 
               
               
                   
                 thiodiglycol 
                 5 
                 wt. % 
               
               
                   
                 ethanol 
                 3 
                 wt. % 
               
               
                   
                 water 
                 16.75 
                 wt. % 
               
               
                 Discharge liquid 2 
               
               
                   
                 polyethyleneglycol 200 
                 100 
                 wt. % 
               
               
                 Discharge liquid 3 
               
               
                   
                 polyethyleneglycol 600 
                 100 
                 wt. % 
               
               
                   
               
            
           
         
       
     
     With the aforementioned liquid that has conventionally considered difficult to discharge, the low discharge speed in such liquid increases the fluctuation in the direction of discharge, thus deteriorating the landing accuracy of the dot on the recording sheet. Also the discharge amount fluctuates because of the unstable discharge, and, because of these facts, a high-quality image was difficult to obtain. In the configuration of the above-described embodiment, the bubble generation can be achieved sufficiently and stably by the use of the bubble generating liquid. There can therefore be attained improvement in the landing accuracy of the liquid droplet and stabilization in the ink discharge amount, thus resulting in a significant improvement in the quality of the recorded image. 
     In the following there will be explained the method for producing the liquid discharging head of the present invention. 
     The head is basically prepared by forming a wall of the second liquid path on the element board, then mounting thereon the movable separating membrane thereon and mounting thereon a grooved member provided with a groove constituting the first liquid path. Otherwise it is prepared, after forming the wall of the second liquid path, by adhering thereon the grooved member on which the movable separating membrane is mounted in advance. 
     There will also be explained in detail the method of preparing the second liquid path. 
     At first, on an element substrate (silicon wafer), there was formed an electrothermal converting element including the heat generating member consisting for example of hafnium boride or tantalum nitride with an apparatus similar to that employed in the semiconductor manufacture, and the surface of the element substrate was then rinsed in order to improve the adhesion with photosensitive resin in a next step. Further improvement in adhesion can be achieved by surface modification of the element substrate for example with ultraviolet light-ozone, followed by spin coating for example of a silane coupling agent (A189 manufactured by Japan Unicar Co.) diluted to 1 wt. % with ethyl alcohol. 
     Then the substrate surface with thus improved adhesion was rinsed and laminated with an ultraviolet-sensitive resin film (Dry Film Ordil SY-318 manufactured by Tokyo Ohka Co.). 
     Then a photomask was placed on the dry film, and the portions to be left as the second liquid path walls were irradiated with the ultraviolet light through the photomask. The exposure was executed with an apparatus MPA-600 manufactured by Canon Inc., with an exposure amount of ca. 600 mJ/cm 2 . 
     Then the dry film was developed with a developer (BMRC-3 manufactured by Tokyo Ohka Co.) consisting of a mixture of xylene and butyl cellosolve acetate to dissolve the unexposed portions, thereby leaving the portions hardened by exposure as the second liquid path walls. Further, the residue remaining on the substrate surface was eliminated by processing with an oxygen plasma ashing apparatus (MAS-800 manufactured by Alcantec Co.) for about 90 seconds, and the exposed portions were completely hardened by ultraviolet irradiation of 100 mJ/cm 2  for 2 hours at 150° C. 
     Through the above-described process, the second liquid path walls could be formed uniformly, with sufficient precision, on the plural heater boards (element boards) prepared by dividing the above-mentioned silicon substrate. More specifically, the silicon substrate was cut into respective heater boards  1  with a dicing machine (AWD-4000 manufactured by Tokyo Seimitsu Co.) equipped with a diamond blade of a thickness of 0.05 mm. The separated heater board was fixed on an aluminum base plate with an adhesive material (SE4400 manufactured by Toray Co.). 
     The printed circuit board adhered in advance to the aluminum base plate and the heater board were connected with aluminum wires of a diameter of 0.05 mm. 
     Then, on the heater board thus obtained, a jointed member of the grooved member and the movable separating membrane was positioned and adhered by the above-described process. More specifically, the grooved member provided with the movable separating membrane and the heater board are mutually positioned and fixed with a pressing spring, then the ink/bubble generating liquid supply member is adhered to the aluminum base plate, and the gaps between the aluminum wires and among the grooved member, heater board and ink/bubble generating liquid supply member were sealed with a silicone sealant (TSE399 manufactured by Toshiba Silicone Co.). 
     The above-described process allowed to prepare the second liquid paths with sufficient precision, without positional aberration with respect to the heaters of the heater board. In particular, the positional precision between the first liquid path and the movable member can be improved by adhering the grooved member and the movable separating membrane in advance. Such highly precise manufacturing technology stabilizes the discharge, thereby improving the print quality, and allows collective manufacture on the wafer, thereby enabling mass production with a low cost. 
     In the second embodiment, the second liquid paths are formed with the ultraviolet-setting dry film, but they can also be obtained by laminating a resin having absorption band in the ultraviolet region, particularly in the vicinity of 248 nm, then hardening the resin and directly eliminating the resin corresponding to the second liquid paths with an excimer laser. 
     Also the first liquid paths etc. were prepared by adhering a grooved top plate, provided with an orifice plate having the discharge openings, grooves constituting the first liquid paths and a recess constituting a first common liquid chamber commonly communicating with plural first liquid paths and serving the supply the first liquid to such liquid paths, to the jointed member of the aforementioned substrate and the movable separating membrane. The movable separating membrane is fixed by being sandwiched between the grooved top plate and the second liquid path walls. The movable separating membrane need not necessarily be fixed to the substrate but may be fixed to the grooved top plate and then to the substrate. 
     The movable separating membrane  105  is preferably composed of a resinous material with satisfactory heat resistance, solvent resistance and molding property and capable of forming a thin film, represented by recent engineering plastics such as polyimide, polyethylene, polypropylene, polyamide, polyethylene terephthalate, melamine resin, phenolic resin, polybutadiene, polyurethane, polyethyletherketone, polyethersulfone, polyallylate, silicone rubber, polysulfone, fluorinated resin etc., compounds thereof, or a metal with satisfactory durability, heat resistance and solvent resistance such as silver, nickel, gold, iron, titanium, aluminum, platinum, tantalum, stainless steel, phosphor bronze or compounds thereof, or silicone or compounds thereof. 
     FIGS. 10A and 10B illustrate the process for preparing the movable separating membrane, and FIGS. 11A and 11B illustrate another process for preparation. 
     At first, as shown in FIG. 10A, a mold  22  corresponding to the recessed portion of the movable separating membrane was formed with a metal or a resinous material on a silicon mirror wafer  21 . Then a releasing agent was coated on the mold  22 , and liquid polyimide resin was spin coated thereon to form a film  23  as shown in FIG.  10 B. 
     Then the film  23  was peeled off from the mirror wafer  11  and was positioned and fixed on the substrate on which the aforementioned second liquid path was formed, thereby obtaining the movable separating membrane. 
     However the movable separating membrane can also be prepared by other methods. For example, the movable separating membrane can be formed by preparing a commercially available thin film  24  and molds  25  for forming the recessed portion as shown in FIG. 11A, and pressing the thin film  24  between the molds  25  as shown in FIG.  11 B and causing plastic deformation by heat. 
     FIGS. 12A to  12 F are cross-sectional views, along the liquid path, showing another embodiment of the liquid discharging head of the present invention, while FIGS. 13A to  13 F are magnified cross-sectional views of the vicinity of the recessed portion of the movable separating membrane shown in FIGS. 12A to  12 F, and FIG. 14 is a partially broken perspective view of the liquid discharging head shown in FIGS. 12A to  12 F and  13 A to  13 F. 
     In the present embodiment, as shown in FIGS. 12A to  12 F, a first liquid path  3  communicating with a discharge opening  1  is filled with first liquid supplied from a first common liquid chamber  143 , while a second liquid path  4  containing a bubble generating area  7  is filled with bubble generating liquid which generates a bubble upon receiving thermal energy by a heat generating member  2 . Between the first liquid path  3  and the second liquid path  4  there is provided a movable separating membrane  5  for mutually separating the first and second liquid paths. The movable separating membrane  5  is provided, in a portion thereof opposed to the bubble generating area  7 , with a recessed portion  8  having corner parts  8   a  at the fulcrums thereof, thus forming an expansion in the first liquid path  3 . The movable separating membrane  5  is fixed to an orifice plate  9  to prevent mixing of two liquids. In the second liquid path  4 , the bubble generating area  7  is constituted by the vicinity of the projected area of the heat generating member  2 . 
     As shown in FIGS. 13A to  13 F, the recessed portion  8  of the movable separating membrane  5  is provided with inflection parts  8   c  between the corner parts  8   a  and the bottom part  8   b,  and the thickness (W 8   c ) of the inflection parts  8   c  is made smaller than that (W 8   b ) of the bottom part  8   b.  The “inflection part” used in the present specification and in the appended drawings means a part showing largest deformation in the recessed portion of the movable separating membrane at the maximum displacement thereof. 
     As shown in FIG. 14, the heat generating member  2  is provided in an array of plural units on an element board  10 , on which plural second liquid paths  4  are provided respectively corresponding to the heat generating members  2 . A support member  11  supporting the movable separating membrane  5  serves also as a wall for defining and forming the second liquid paths  4 . The movable separating membrane  5  is provided with plural recessed portions  8 , respectively corresponding to the bubble generating areas  7  positioned in the vicinity of the bubble generating areas  7  which are in the vicinity of the projected areas of the heat generating members  2 . The first liquid path  3  is provided in plural units, so as to respectively contain the recessed portions  8 . In FIG. 14, however, the positions of walls  28  for defining the first liquid paths are represented by broken lines. 
     The present invention is based on the movement of the movable separating membrane  5 , and the movable separating membrane  5  itself is provided with the recessed portion  8  which is displaced toward the first liquid path  3  by the growth of a bubble generated on the surface of the heat generating member  2 . 
     In an initial state shown in FIGS. 12A and 13A, the liquid in the first liquid path  3  is retracted to the vicinity of the discharge opening  1  by the capillary force. In the present embodiment, the discharge opening  1  is provided at the downstream position, in the liquid flow direction in the first liquid path  3 , with respect to the projected area of the heat generating member  2  onto the first liquid path  3 . 
     When thermal energy is given to the heat generating member  2  (consisting of a heat-generating resistance member of 40×105 μm in the present embodiment) in this state, the heat generating member  2  is rapidly heated whereby the surface thereof in contact with the second liquid in the bubble generating area heats the liquid and generates a bubble therein (FIGS.  12 B and  13 B). A bubble  6  thus formed is based on a film boiling phenomenon as described in the U.S. Pat. No. 4,723,129 and is generated with an extremely high pressure over the entire area of the heat generating member. The generated pressure is transmitted as a pressure wave in the second liquid in the second liquid path  4  and acts on the movable separating membrane  5 , whereby the recessed portion  8  thereof is deformed, starting from the thinner inflection parts  8   c,  to initiate the discharge of the first liquid in the first liquid path  3 . However the corner parts  8   a  formed at the fulcrums of the recessed portion  8  are not involved in such deformation. 
     The bubble generated on the entire surface of the heat generating member  2  rapidly grows to assume a film shape (FIGS.  12 C and  13 C). The expansion of the bubble  6  with an extremely high pressure in the initial stage of generation causes a further deformation of the recessed portion  8  of the movable separating membrane  5 , whereby the first liquid in the first liquid path  3  is further discharged from the discharge opening  1 . 
     When the further growth of the bubble  6  thereafter, the deformation proceeds to such a level that the entire recessed portion  8 , excluding the vicinity of the corner parts  8   a  of the membrane  5 , enters the first liquid path  3  (FIGS.  12 D and  13 D). Since the above-described displacement of the recessed portion  8  from the initial state to the maximum displacement is facilitated by the inflection parts  8   c  thinner than other parts of the recessed portion  8 , the pressure caused by bubble generation can be efficiently guided to the discharge opening, thereby improving the discharge efficiency. 
     When the bubble  6  starts to contract thereafter, the recessed portion  8  of the movable separating membrane  5  starts to return to the position before deformation (FIGS.  12 E and  13 E). 
     Subsequently, the recessed portion  8  of the movable separating membrane  5  promptly returns to the initial state shown in FIGS. 12F and 13F by the self returning force exerted by the non-deformed corner parts  8   a,  whereby the liquid refilling in the first liquid path  3  is accelerated. Also, with the extinction of the bubble, the recessed portion  8  of the movable separating membrane  5  displaces into the second liquid path  4 , thereby reducing the volume thereof and also reducing the refilling amount of the bubble generating liquid, whereby the refilling is completed promptly. Also, as the corner parts  8   a  of the recessed portion  8  have a function of suppressing the rebounding movement immediately after the displacement by bubble generation, the recessed portion  8  immediately returns to the initial state after displacement, thereby enabling high-speed drive. 
     FIGS. 15A and 15B are magnified cross-sectional views along the liquid path showing the recessed portion  8  of the movable separating membrane  5  in the liquid discharging head of the other embodiment of the present invention, respectively in the initial state and in a state at the maximum displacement, while FIG. 16 is a cross-sectional view, parallel to the heat generating member, of the liquid discharging head of the other embodiment of the present invention. 
     In case the fulcrums  2  of the recessed portion do not have the corner parts as shown in FIGS. 5A and 5B and the bottom part  27  of the recessed portion assumes an inverted shape at the maximum displacement as shown in FIG. 5B, the recessed portion deforms with the fulcrums  26  as the inflection points. 
     On the other hand, in case the fulcrums of the recessed portion have the corner parts  8   a,  such corner parts  8   a  have an effect, in the initial state shown in FIG. 15A, of defining the initial shape always in a constant shape. Also at the maximum displacement shown in FIG. 15B, the shape is always constant because the deformation is not concentrated locally but is spread over a wide area in the vicinity of the corner parts. Thus the corner parts  8   a  define the shape at the initial state and at the maximum displacement, thereby achieving very stable liquid discharge and improving durability. The displacement governing area of the corner parts  8   a  will also be understood from FIG.  16 . 
     Besides, the presence of the thinner inflection part  8   c  between the corner part  8   a  and the bottom part  8   b  of the recessed portion facilitates the deformation of the recessed portion, thereby allowing to efficiently guide the pressure by bubble generation to the discharge opening and improving the discharge efficiency. In the liquid discharging head employing the separating membrane, as such membrane is sandwiched between the liquid path walls for forming the first and second liquid paths respectively above and below the separating membrane, it becomes less deformable with a higher density of the nozzles since the movable separating membrane present between the liquid path walls becomes narrower. However the more easily deformable recessed portion allows to provide a liquid discharging head capable of sufficiently adapting to the nozzles arranged at a high density. 
     Furthermore, the configuration of the present embodiment allows to employ different liquids for the discharge liquid and the bubble generating liquid and to discharge the discharge liquid only. Consequently, it is possible to satisfactorily discharge highly viscous liquid such as polyethylene glycol in which a sufficient discharging force cannot be obtained in the conventional configuration because of insufficient bubble generation under the application of heat, by supplying such liquid in the first liquid path  103  and supplying the second liquid path  104  with liquid capable of satisfactory bubble generation (for example a mixture of ethanol: water=4:6 with a viscosity of 1 to 2 cp). 
     Also as the bubble generating liquid, there can be selected liquid which does not generate a deposit such as kogation on the surface of the heat generating member under the influence of heat, in order to stabilize the bubble generating and ensuring satisfactory liquid discharge. Furthermore, the configuration of the liquid discharging head of the present invention can discharge various liquid such as highly viscous liquid with an even higher discharge efficiency and an even higher discharging power, because of the effects explained in the foregoing embodiment. 
     Furthermore, liquid susceptible to heat can be discharged without thermal damage with a high discharge efficiency and a high discharging power as explained above, by supplying such liquid as the discharge liquid in the first liquid path  103  and supplying the second liquid path  104  with liquid stabler to heat capable of satisfactory bubble generation as the bubble generating liquid. 
     FIGS. 17A and 17B illustrate another example of the process for producing the movable separating membrane. At first, as shown in FIG. 17A, there were prepared a commercially available thin film  24  for forming the movable separating membrane and a male mold  25  and a female mold  26  for forming the recessed portion, and, the film  24  was pressed to the female mold  26  as shown in FIG.  17 B and was subjected to plastic deformation by heat to obtain the movable separating membrane with the recessed portion. 
     FIGS. 18A to  18 E are cross-sectional views, transversal to the liquid path, showing still other embodiment of the movable separating membrane of the present invention. FIG. 18A shows a separating membrane with a semi-oval recessed portion, while FIG. 18B shows a separating membrane a V-shaped recessed portion, wherein a thinner inflection part  8   c  is provided between each corner part  8   a  and bottom part  8   b.  FIGS. 18C to  18 E show separating membranes with a trapezoidal recessed portion. In FIG. 18C a thinner part is formed by a curved notch. In FIG. 18D, the entire rising part is made thinner than other parts, and, in FIG. 18E, the entire rising part and a part of the bottom are made thinner than other parts. Also these configurations facilitate deformation of the recessed portion of the movable separating membrane, thereby efficiently guiding the pressure by bubble generation to the discharge opening and improving the discharge efficiency. 
     FIGS.  19 A and l 9 B are cross-sectional views, perpendicular to the liquid path, showing still other embodiments of the movable separating membrane of the present invention. In the illustrated cross section perpendicular to the liquid path, thinner inflection parts  8   c  are provided between the corner parts  8   a  and the bottom part  8   b  to obtain effects similar to those in the above-described embodiments. 
     FIGS. 20A to  20 F are magnified cross-sectional views of the vicinity of the recessed portion of the movable separating membrane in another embodiment of the present invention. 
     In this embodiment, as shown in FIG. 20A, the recessed portion of the movable separating membrane  5  is so formed as to satisfy a condition h 2 ≧h 1 , wherein h 1  is the height from the heat generating member  2  to the bottom part  8   b  of the recessed portion in the still state and h 2  is the height from bottom part  8   b  of the recessed portion to the inflection part  8   c  thereof in the still state. For example if h 2  is 20 μm, h 1  is preferably within a range of 5 to 10 μm. The “inflection part” used in the present specification and the appended drawings means, in the recessed portion of the movable separating membrane, a part showing the largest deformation at the maximum displacement. 
     In an initial state shown in FIG. 20A, the liquid in the first liquid path  3  is retracted to the vicinity of the discharge opening  1  by the capillary force. In the present embodiment, the discharge opening  1  is provided at the downstream position, in the liquid flow direction in the first liquid path  3 , with respect to the projected area of the heat generating member  2  onto the first liquid path  3 . 
     When thermal energy is given to the heat generating member  2  (consisting of a heat-generating resistance member of 40×105 μm in the present embodiment) in this state, the heat generating member  2  is rapidly heated whereby the surface thereof in contact with the second liquid in the bubble generating area heats the liquid and generates a bubble therein (FIG.  20 B). A bubble  6  thus formed is based on a film boiling phenomenon as described in the U.S. Pat. No. 4,723,129 and is generated with an extremely high pressure over the entire area of the heat generating member. The generated pressure is transmitted as a pressure wave in the second liquid in the second liquid path  4  and acts on the movable separating membrane  5 . As the height h 2  from the bottom part  8   b  of the recessed portion  8  to the inflection part  8   c  thereof is selected equal to or larger than the height h 1  from the heat generating member  2  to the bottom part  8   b  of the recessed portion  8 , the pressure by bubble generation is transmitted to the movable separating membrane  5  before it can escape to the upstream and downstream sides of the second liquid path  4 , so that the pressure can be efficiently transmitted to the movable separating membrane  5 . The transmission of the pressure by bubble generation to the movable separating membrane causes deformation of the recessed portion  8  thereof, thereby initiating the discharge of the first liquid in the first liquid path  3 . However the corner parts  8   a  formed at the fulcrums of the recessed portion  8  are not involved in such deformation. 
     The bubble generated on the entire surface of the heat generating member  2  rapidly grows to assume a film shape (FIG.  20 C). The expansion of the bubble  6  with an extremely high pressure in the initial stage of generation causes a further deformation of the recessed portion  8  of the movable separating membrane  5 , whereby the first liquid in the first liquid path  3  is further discharged from the discharge opening  1 . 
     With the further growth of the bubble  6  thereafter, the deformation proceeds to such a level that the entire recessed portion  8 , excluding the vicinity of the corner parts  8   a  of the membrane  5 , enters the first liquid path  3  (FIG.  20 D). 
     When the bubble  6  starts to contract thereafter the recessed portion  8  of the movable separating membrane  5  starts to return to the position before deformation (FIG.  20 E). 
     Subsequently, the recessed portion  8  of the movable separating membrane  5  promptly returns to the initial state shown in FIG. 20F by the self returning force exerted by the non-deformed corner parts  8   a,  whereby the liquid refilling in the first liquid path  3  is accelerated. 
     Also, with the extinction of the bubble, the recessed portion  8  of the movable separating membrane  5  displaces into the second liquid path  4 , thereby reducing the volume thereof and also reducing the refilling amount of the bubble generating liquid, whereby the refilling is completed promptly. Also, as the corner parts  8   a  of the recessed portion  8  have a function of suppressing the rebounding movement immediately after the displacement by bubble generation, the recessed portion  8  immediately returns to the initial state after displacement, thereby enabling high-speed drive. 
     FIGS. 21A to  21 F are magnified cross-sectional views of the vicinity of the recessed portion of the movable separating membrane in still another embodiment of the present invention. 
     In this embodiment, as shown in FIG. 21A, the recessed portion  8  of the movable separating membrane  5  has an inflection part  8   c  between the corner part  8   a  and the bottom part  8   b,  with a thickness smaller in the inflection part  8   c  than in the bottom part  8   b.  Also as shown in FIG. 20A, the recessed portion of the movable separating membrane  5  is so formed as to satisfy a condition h 2 ≧h 1 , wherein h 1  is the height from the heat generating member  2  to the bottom part  8   b  of the recessed portion in the still state and h 2  is the height from bottom part  8   b  of the recessed portion to the inflection part  8   c  thereof in the still state. For example if h 2  is 20 μm, h 1  is preferably within a range of 5 to 10 μm. Other configurations are same as those in the foregoing embodiment. 
     In an initial state shown in FIG. 21A, the liquid in the first liquid path  3  is retracted to the vicinity of the discharge opening  1  by the capillary force. In the present embodiment, the discharge opening  1  is provided at the downstream position, in the liquid flow direction in the first liquid path  3 , with respect to the projected area of the heat generating member  2  onto the first liquid path  3 . 
     When thermal energy is given to the heat generating member  2  (consisting of a heat-generating resistance member of 40×105 μm in the present embodiment) in this state, the heat generating member  2  is rapidly heated whereby the surface thereof in contact with the second liquid in the bubble generating area heats the liquid and generates a bubble therein (FIG.  21 B). A bubble  6  thus formed is based on a film boiling phenomenon as described in the U.S. Pat. No. 4,723,129 and is generated with an extremely high pressure over the entire area of the heat generating member. The generated pressure is transmitted as a pressure wave in the second liquid in the second liquid path  4  and acts on the movable separating membrane  5 . As the height h 2  from the bottom part  8   b  of the recessed portion  8  to the inflection part  8   c  thereof is selected equal to or larger than the height h 1  from the heat generating member  2  to the bottom part  8   b  of the recessed portion  8 , the pressure by bubble generation is transmitted to the movable separating membrane  5  before it can escape to the upstream and downstream sides of the second liquid path  4 , so that the pressure can be efficiently transmitted to the movable separating membrane  5 . The transmission of the pressure by bubble generation to the movable separating membrane causes deformation of the recessed portion  8  thereof, thereby initiating the discharge of the first liquid in the first liquid path  3 . However the corner parts  8   a  formed at the fulcrums of the recessed portion  8  are not involved in such deformation. 
     The bubble  6  generated on the entire surface of the heat generating member  2  rapidly grows to assume a film shape (FIG.  21 C). The expansion of the bubble  6  with an extremely high pressure in the initial stage of generation causes a further deformation of the recessed portion  8  of the movable separating membrane  5 , whereby the first liquid in the first liquid path  3  is further discharged from the discharge opening  1 . 
     With the further growth of the bubble  6  thereafter, the deformation proceeds to such a level that the entire recessed portion  8 , excluding the vicinity of the corner parts  8   a  of the membrane  5 , enters the first liquid path  3  (FIG.  21 D). 
     When the bubble  6  starts to contract thereafter, the recessed portion  8  of the movable separating membrane  5  starts to return to the position before deformation (FIG.  21 E). 
     Subsequently, the recessed portion  8  of the movable separating membrane  5  promptly returns to the initial state shown in FIG. 21F by the self returning force exerted by the non-deformed corner parts  8   a,  whereby the liquid refilling in the first liquid path  3  is accelerated. Also, with the extinction of the bubble, the recessed portion  8  of the movable separating membrane  5  displaces into the second liquid path  4 , thereby reducing the volume thereof and also reducing the refilling amount of the bubble generating liquid, whereby the refilling is completed promptly. Also, as the corner parts  8   a  of the recessed portion  8  have a function of suppressing the rebounding movement immediately after the displacement by bubble generation, the recessed portion  8  immediately returns to the initial state after displacement, thereby enabling high-speed drive. 
     FIGS. 22A to  22 F are magnified cross-sectional views, along a line  22 A to  22 F- 22 A to  22 F in FIG. 1A, of the recessed portion of the movable separating membrane in another embodiment, and show states respectively corresponding to those shown in FIGS. 1A to  1 F. 
     As shown in FIG. 22A, the distance between the corner parts is represented by W 1 , that between the inflection parts by W 3 , the width of the bottom part by W 2  and that of the heat generating member by WH. If WH is larger than W 1 , the pressure by bubble generation cannot be efficiently transmitted to the movable separating membrane, so that an unnecessarily large pressure is required for deforming the recessed portion. On the other hand, if WH is smaller than W 2 , the pressure by bubble generation cannot be sufficiently transmitted to the entire bottom part of the recessed portion. Consequently, the recessed portion is desirable so designed as to satisfy a relation W 1 ≧WH≧W 2  in order to improve the discharge efficiency. 
     The pressure by bubble generation can be more efficiently transmitted to the movable separating membrane by satisfying a relation W 1 ≧W 3 ≧WH, more preferably W 1 ≧W 3 ≧WH≧W 2 . The “inflection part” used in the present specification or in the appended drawings means a part, in the recessed portion of the movable separating membrane, showing the largest deformation at the maximum displacement. 
     FIGS. 23A to  23 F are magnified cross-sectional views of the vicinity of the recessed portion of the movable separating membrane in still another embodiment of the liquid discharging head of the present invention. In this embodiment, as shown in FIG. 23A, the recessed portion  8  of the movable separating membrane  5  has an inflection part  8   c  between the corner part  8   a  and the bottom part  8   b,  with a thickness smaller in the inflection part  8   c  than in the bottom part  8   b.  Other configurations are same as those in the foregoing embodiment. 
     In an initial state shown in FIG. 23A, the liquid in the first liquid path  3  is retracted to the vicinity of the discharge opening  1  by the capillary force. In the present embodiment, the discharge opening  1  is provided at the downstream position, in the liquid flow direction in the first liquid path  3 , with respect to the projected area of the heat generating member  2  onto the first liquid path  3 . 
     When thermal energy is given to the heat generating member  2  (consisting of a heat-generating resistance member of 40×105 μm in the present embodiment) in this state, the heat generating member  2  is rapidly heated whereby the surface thereof in contact with the second liquid in the bubble generating area heats the liquid and generates a bubble therein (FIG.  23 B). A bubble  6  thus formed is based on a film boiling phenomenon as described in the U.S. Pat. No. 4,723,129 and is generated with an extremely high pressure over the entire area of the heat generating member. The generated pressure is transmitted as a pressure wave in the second liquid in the second liquid path  4  and acts on the movable separating membrane  5 , whereby the recessed portion  8  of the movable separating membrane  5  deforms starting from the thinner inflection parts  8   c  to initiate the discharge of the first liquid in the first liquid path  3 . However the corner parts  8   a  formed at the fulcrums of the recessed portion  8  are not involved in such deformation. 
     The bubble  6  generated on the entire surface of the heat generating member  2  rapidly grows to assume a film shape (FIG.  23 C). The expansion of the bubble  6  with an extremely high pressure in the initial stage of generation causes a further deformation of the recessed portion  8  of the movable separating membrane  5 , whereby the first liquid in the first liquid path  3  is further discharged from the discharge opening  1 . 
     With the further growth of the bubble  6  thereafter, the deformation proceeds to such a level that the entire recessed portion  8 , excluding the vicinity of the corner parts  8   a  of the membrane  5 , enters the first liquid path  3  (FIG.  23 D). Since the displacement of the recessed portion  8  from the initial state to the maximum displacement explained above is facilitated by the thinner inflection parts  8   c  of the recessed portion  8 , the pressure by bubble generation can be efficiently transmitted toward the discharge opening, thereby improving the discharge efficiency. 
     When the bubble  6  starts to contract thereafter, the recessed portion  8  of the movable separating membrane  5  starts to return to the position before deformation (FIG.  23 E). 
     Subsequently, the recessed portion  8  of the movable separating membrane  5  promptly returns to the initial state shown in FIG. 23F by the self returning force exerted by the non-deformed corner parts  8   a,  whereby the liquid refilling in the first liquid path  3  is accelerated. Also, with the extinction of the bubble, the recessed portion  8  of the movable separating membrane  5  displaces into the second liquid path  4 , thereby reducing the volume thereof and also reducing the refilling amount of the bubble generating liquid, whereby the refilling is completed promptly. Also, as the corner parts  8   a  of the recessed portion  8  have a function of suppressing the rebounding movement immediately after the displacement by bubble generation, the recessed portion  8  immediately returns to the initial state after displacement, thereby enabling high-speed drive. 
     FIGS. 24A to  24 F are magnified cross-sectional views, seen from the side of the discharge opening in FIGS. 12A to  12 F, of the recessed portion of the movable separating membrane in another embodiment, and show states respectively corresponding to those shown in FIGS. 12A to  12 F. As shown in FIG. 24A, the distance between the corner parts is represented by W 1 , that between the inflection parts by W 3 , the width of the bottom part by W 2  and that of the heat generating member by WH. If WH is larger than W 3 , the pressure by bubble generation cannot be efficiently transmitted to the movable separating membrane, so that an unnecessarily large pressure is required for deforming the recessed portion. On the other hand, if WH is smaller than W 2 , the pressure by bubble generation cannot be sufficiently transmitted to the entire bottom part of the recessed portion. Consequently, the recessed portion is desirable so designed as to satisfy a relation W 1 ≧WH≧W 2  in order to improve the discharge efficiency, in addition to the aforementioned effect of forming thinner inflection parts. The pressure by bubble generation can be more efficiently transmitted to the movable separating membrane by satisfying a relation W 1 ≧W 3 ≧WH, more preferably W 1 ≧W 3 ≧WH≧W 2 . 
     FIGS. 25A to  25 D show the positional relationship between the heat generating member and the movable separating membrane in another embodiment, wherein FIG. 25A is a magnified cross-sectional view of the liquid discharging head along the liquid path thereof; FIG. 25B is a plan view of the heat generating member; FIG. 25C is a plan view of the movable separating membrane; and FIG. 25D is a plan view showing the heat generating member and the movable separating membrane in superposed state. As shown in FIG. 25A, the area defined by connecting the corner parts  8   a,  in the projection of the recessed portion toward the heat generating member, is taken as S 1 , the area of the bottom part  8   b  of the recessed portion is taken as S 2 , the area defined by connecting the inflection parts of the recessed portion is taken as S 3 , and the area of the heat generating member  2  is taken as SH. If SH is larger than S 1 , the pressure by bubble generation cannot be efficiently transmitted to the movable separating membrane, so that an unnecessarily large pressure is required for deforming the recessed portion. On the other hand, if SH is smaller than S 2 , the pressure by bubble generation cannot be sufficiently transmitted to the entire bottom part of the recessed portion. Consequently, the recessed portion is desirable so designed as to satisfy a relation S 1 ≧SH≧S 2  in order to improve the discharge efficiency. In the foregoing description, SH is the area of the entire heat generating member, but is more preferably an area showing effective film boiling (called effective bubble generating area) on the surface of the heat generating member  2 . 
     The pressure by bubble generation can be more efficiently transmitted to the movable separating membrane by satisfying a relation S 1 ≧S 3 ≧SH, more preferably S 1 ≧S 3 ≧SH≧S 2 . The “inflection part” used in the present specification or in the appended drawings means a part, in the recessed portion of the movable separating membrane, showing the largest deformation at the maximum displacement. 
     FIGS. 26A to  26 D show the positional relationship between the heat generating member and the movable separating membrane in another embodiment, wherein FIG. 26A is a magnified cross-sectional view of the liquid discharging head along the liquid path thereof; FIG. 26B is a plan view of the heat generating member; FIG. 26C is a plan view of the movable separating membrane; and FIG. 26D is a plan view showing the heat generating member and the movable separating membrane in superposed state. As shown in FIG. 26A, the area defined by connecting the corner parts  8   a,  in the projection of the recessed portion toward the heat generating member, is taken as S 1 , the area of the bottom part  8   b  of the recessed portion is taken as S 2 , the area defined by connecting the inflection parts of the recessed portion is taken as S 3 , and the area of the heat generating member  2  is taken as SH. If SH is larger than S 1 , the pressure by bubble generation cannot be efficiently transmitted to the movable separating membrane, so that an unnecessarily large pressure is required for deforming the recessed portion. On the other hand, if SH is smaller than S 2 , the pressure by bubble generation cannot be sufficiently transmitted to the entire bottom part of the recessed portion. Consequently, the recessed portion is desirable so designed as to satisfy a relation S 1 ≧SH≧S 2  in order to improve the discharge efficiency, in addition to the aforementioned effect of forming thinner inflection parts. The pressure by bubble generation can be more efficiently transmitted to the movable separating membrane by satisfying a relation S 1 ≧S 3 ≧SH, more preferably S 1 ≧S 3 ≧SH≧S 2 . In the foregoing description, SH is the area of the entire heat generating member, but is more preferably an area showing effective film boiling (called effective bubble generating area) on the surface of the heat generating member  2 . 
     FIGS. 27A to  27 F are cross-sectional views showing another embodiment of the liquid discharging head of the present invention. The present embodiment is same in the basic working principle as the embodiment shown in FIGS. 1A to  3 , but is different in that guide paths  9 ,  10  for enabling liquid flow are provided at the upstream and downstream sides of the bubble generating area  7 . 
     FIG. 27A shows a state of bringing the bubble generating liquid in the bubble generating area to an initial stable state by moving the bubble remaining in the liquid path and constituting a cause of instability and the extremely heated liquid by means of forced flow means to be explained later, prior to the bubble generating step by the heat generating member  2 , in order to achieve stable bubble generation. The bubble generating liquid, supplied from the guide path  9 , is discharged from the guide path  10  through the bubble generating area  7  so that the bubble generating area  7  can be brought to the initial stable state at any time. Therefore, stable discharge can be attained by such initializing operation after a prolonged pause or after heat accumulation or bubble generation by a high-duty drive. 
     FIGS. 27B to  27 F show steps of generation and extinction of the bubble  6  in the bubble generating area  7  by the heat generating member  2 . In these states, when energy is given to the heat generating member  2  it heats the second liquid (bubble generating liquid) to generate a bubble therein (FIG.  27 B). The pressure generated by bubble generation is transmitted as a pressure wave in the second liquid (bubble generating liquid) in the second liquid path  4  and acts on the movable separating membrane  5 , whereby the recessed portion  8  of the movable separating membrane  5  deforms to initiate the discharge of the first liquid (discharge liquid) in the first liquid path  3 . 
     The bubble  6  rapidly grows to assume a film shape (FIG.  27 C). The expansion of the bubble  6  with an extremely high pressure in the initial state of generation causes a further deformation of the recessed portion  8  of the movable separating membrane  5 , whereby the first liquid (discharge liquid) in the first liquid path  3  is further discharged from the discharge opening  1 . With the further growth of the bubble  6  thereafter, the deformation process to such a level that the entire recessed portion  8 , excluding the vicinity of the corner parts  8   a  of the membrane  5 , enters the first liquid path  3  (FIG.  27 D). 
     When the bubble  6  starts to contract thereafter, the recessed portion  8  of the movable separating membrane  5  starts to return to the position before deformation (FIG.  27 E). Subsequently, the recessed portion  8  of the movable separating membrane  5  promptly returns to the initial state shown in FIG. 27F by the self returning force exerted by the non-deformed corner parts  8   a,  whereby the liquid refilling in the first liquid path  3  is accelerated. Also, with the extinction of the bubble, the recessed portion  8  of the movable separating membrane  5  displaces into the second liquid path  4 , thereby reducing the volume thereof and also reducing the refilling amount of the bubble generating liquid, whereby the refilling is completed promptly. 
     The present embodiment can stabilize the discharge amount since the movable separating membrane  5  having the recessed portion  8  is substantially free from elongation. It is particularly important, however, that the displacement volume of the movable separating membrane  5  is small with respect to the maximum volume of the bubble  6 , so that the discharge amount is stabilized with respect to the variation in the volume of the bubble. In the state shown in FIG. 27D, if the displacement volume of the movable separating membrane  5  is extremely different from the maximum volume of the bubble  6 , the stress on the membrane  5  may become very high, detrimentally affecting the service life thereof. In the present embodiment, however, the guide paths  9 ,  10  are provided at the upstream and downstream sides of the bubble generating area  7  and are adapted to discharge the second liquid (bubble generating liquid) so as to absorb the excessive volume of the bubble  6 , thereby realizing high stability and high durability. Also the durability problem of the membrane, encountered in case the membrane displacement cannot follow the abrupt volumic change at the contraction of the bubble can be solved by the pressure adjusting and relaxing function of these guide paths, whereby high stability and high durability can be realized. In particular, the present embodiment realizes highly stable discharge, because the guide paths are balanced at the upstream and downstream sides to enable well balanced displacement of the movable separating membrane  5 . 
     Also in the present embodiment, liquid path resistances  11 ,  12  are provided at the junctions with the guide paths  9 ,  10  in order to prevent unnecessary dissipation of the pressure of the bubble generating area  7  into the guide paths  9 ,  10 . 
     FIGS. 28A to  28 D show still another embodiment, in which the liquid path resistances, provided as in the foregoing embodiment, are made mutually different at the upstream and downstream sides. FIG. 28D is a cross-sectional view showing a state of bubble generation in the configuration shown in FIG.  28 A. 
     In FIG. 28A, the liquid path resistances  13 ,  14  are so formed as to facilitate the liquid flow in the downstream direction but to hinder it in the upstream direction. Consequently, at the generation of the bubble  6  by the heat generating member  2 , the bubble  6  grows at the upstream side in such a direction as to push up the movable separating membrane  5  but at the downstream side toward the downstream guide path  10 , whereby the movable separating membrane  5  shows a larger displacement at the upstream side (FIG.  28 D). As a result, there is generated a flow of the discharge liquid (first liquid) from the upstream side to the downstream side, thereby improving the refilling efficiency for the discharge (first) liquid. The configurations shown in FIGS. 28B and 28C can also improve the discharge characteristics by differentiating the balance of the liquid path resistances  15 ,  16 ,  17 ,  18 . 
     FIGS. 29 and 30 are longitudinal cross-sectional views of other embodiments of the liquid discharging head of the present invention. As shown in these drawings, there are provided a second liquid path  20  including holes provided in the element substrate  19 , a movable separating membrane  5  constituting a partition wall, and a grooved member  21  provided with a groove constituting the first liquid path  3 . The holes in the substrate  19  can be formed for example by sand blasting or etching. The holes in the substrate, formed at the upstream nd downstream sides of the bubble generating area  7 , are used as guide paths  22 ,  23  for enabling the flow of the bubble generating liquid. 
     FIGS. 29 and 30 are longitudinal cross-sectional views showing an embodiment of the liquid discharging head utilizing holes in the element substrate. In this embodiment, the guide paths  22 ,  23  are connected to a second liquid path  20 , provided in a base plate  24  on which the element substrate  19  is adhered. The bubble generating liquid can be circulated or made to flow by forced flow means, such as a pump (not shown), connected to the second liquid path  20 . On the other hand, the first liquid is supplied by the first liquid path  3 , positioned opposite to the guide paths  22 ,  23  and separated by the movable separating membrane  5 . Consequently the entire configuration is simple and highly reliable in preventing the mutual mixing of the liquids. Also the pressure from the liquid paths  22 ,  23  can be accommodated since the cross section of the liquid paths can be selected sufficiently large. 
     FIG. 31 is a schematic lateral cross-sectional view showing another embodiment of the liquid discharging head of the present invention. In this embodiment, the second liquid path in the head is constructed as a circulating structure including a pump  25  serving as forced flow means. In this embodiment, a bubble reservoir  27  is provided at the upstream side of the second liquid path  26  for eliminating a bubble etc. eventually contained in the second liquid (bubble generating liquid), thereby stabilizing the bubble generation and the liquid discharge. 
     FIG. 32A is a schematic view showing another embodiment of the liquid discharging head of the present invention, and FIG. 32B is a magnified view thereof. In this embodiment, second liquid paths  28  provided on an element substrate  31  are divided in the unit of  10  nozzles, whereby the second liquid (bubble generating liquid) can be made to flow with a uniform flow rate at the center and at the ends of the head. In order that the liquid in the second liquid paths  28  has a uniform flow rate over the nozzles, the liquid path resistance R 1  from a supply inlet (guide path  29 ) to the entrance of each nozzle and the liquid path resistance R 2  at the entrance are so selected that R 1 +R 2  is constant in each nozzle. FIG. 32C shows an embodiment in which an exit (guide path  30 ) is provided for every two heat generating members  2  and two second liquid paths  32 . There is thus realized a head showing uniform liquid path resistance to each nozzle and little fluctuation in the characteristics between the nozzles. 
     FIG. 33 is a schematic perspective view showing the principal parts of an ink jet recording apparatus, constituting the liquid discharging apparatus in which the liquid discharging head is mounted. 
     Referring to FIG. 33, there is shown an ink jet head cartridge  601  in which the liquid discharging head of the aforementioned configuration and an ink tank are integrated or the ink tank is made detachable. The head cartridge  601  is mounted on a carriage  607 , engaging with a spiral groove  606  of a lead screw  605 , which is rotated through transmission gears  603 ,  604  by the forward or reverse rotation of a driving motor  602 , and the cartridge is reciprocated, together with the carriage  607  in directions a and b, along a guide member  608  and by the rotation of the motor  602 . A printing sheet P, fed by an unrepresented feeding device on a platen roller  609 , is pressed thereto by a pressure plate  610  along the moving direction of the carriage. 
     In the vicinity of an end of the lead screw  605 , there are provided photocouplers  611 ,  612  constituting home position detection means, which detects the presence of a lever  607   a  of the carriage  607  for switching, for example, the driving direction of the motor  602 . 
     There are also shown a support member  613  for supporting a cap member  614  for covering the front face, having the discharge openings, of the aforementioned liquid discharge head; ink suction means  615  for sucking ink, which remains in the cap member  614  by idle discharge from the head  601  and for executing suction recovery of the head  601  through an aperture in the cap member; a cleaning blade  617  and a moving member  618  for moving the blade  617  in a direction perpendicular to the moving direction of the carrier  607 , wherein the blade  617  and the moving member  618  are supported by a main body support member  619 . The blade  617  is not limited to the above-described configuration but may assume other known forms. There is also shown a lever  620  for starting the suction operation at the suction recovery. It is moved by the movement of a cam  621  engaging with the carriage  607 , whereby the driving force from the motor  602  is controlled by known transmission means such as a clutch. 
     A control unit for supplying signals to the heat generating members  202  in the head  601  and for controlling various mechanisms is provided in the main body of the apparatus and is therefore not illustrated. The ink jet recording apparatus  600  of the above-described configuration executes recording on the printing sheet P, fed by the unrepresented feeding device on the platen  609 , by the reciprocating motion of the head  601  over the entire width of the sheet P. 
     FIG. 34 is a schematic perspective view showing the principal parts of another embodiment of the liquid discharging apparatus in which the liquid discharging head is mounted. This embodiment will be explained by an ink discharging recording apparatus, utilizing ink as the discharge liquid. A carriage HC of the apparatus supports a head cartridge in which a liquid tank  90  containing ink and a liquid discharging head unit  200  are detachably mounted, and executes reciprocating motion in the transversal direction of a recording medium  150  such as paper transported by recording medium transporting means. 
     Unrepresented signal supply means supplies the liquid discharging means in the carriage with drive signals, in response to which the liquid discharging head discharges the recording liquid to the recording medium. 
     The liquid discharging apparatus of this embodiment is further provided with a motor  111  for driving the recording medium transport means and the carriage, gears  112 ,  113  for transmitting the power from the motor to the carriage, a carriage shaft  85  etc. There is also provided a circulating pump  114  for circulating the liquid by sending the liquid to the head and receiving the liquid therefrom, and is connected, through tubes  115 , to the aforementioned guide paths connected to the liquid path of the head. Such recording apparatus and the liquid discharging process executed therein provided satisfactory images by liquid discharge onto various recording media.