Patent Publication Number: US-8529020-B2

Title: Liquid discharge recording head

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid discharge recording head such as an ink jet recording head. Such a head is applied to a liquid discharge recording apparatus such as an ink jet recording apparatus performing recording operation by discharging liquid. 
     2. Description of the Related Art 
     Conventionally, the ink jet recording apparatus has relatively low running cost and can be downsized and further readily support color image recording using plural colors of inks. Accordingly, the apparatus has widely been used for a computer-related output apparatus and commercialized. 
     In recent years, it is desired that a recording head with the wide recording width in line recording in order to realize high resolution image recording at further high speed. More specifically, the recording head of 4 to 12 inches are required. 
     For example, Japanese Patent Application Laid-Open No. 2007-296638 discusses a recording head with a wide recording width.  FIG. 10  illustrates an exploded perspective view of the recording head disclosed in Japanese Patent Application Laid-Open No. 2007-296638. In this recording head, a plurality of recording element substrates  1001  is arranged on a supporting plate  1200  in a staggered arrangement. An electric wiring board  1300  is disposed on the supporting plate  1200  and electrically connected to each recording element substrate  1001 . Further, the supporting plate  1200  is connected to an ink supplying member  1500  and forms an ink jet recording head. 
     However, according to the recording head with such a configuration, the electric wiring board is formed from a resin film typically including polyimide; the linear expansion by heat, or the amount of expansion and contraction, is considerably larger than that of a supporting plate made from ceramic. A configuration where a metal plate including SUS is cemented on an electric wiring board is also disclosed. However, the difference of linear expansion is not well resolved; the expansion and contraction about three times that of supporting plate made of ceramic occurs. In general, the amount of expansion of a component under a temperature difference relates to the coefficient of linear expansion of the component×the difference of temperature×the length of component. Thus, the recording head with a wide recording width has significantly large electric wiring board (large in the longitudinal direction). This configuration considerably enlarges the difference in expansion and contraction by heat around the ends of the recording head. 
     Therefore, the amounts of change in dimension by heat particularly increase between the recording element substrates at the longitudinal ends of the recording head and the electric wiring board. Accordingly, large tensile and compression stresses are applied to a component (for example, Au wire) connecting the recording element substrate and electric wiring board. A problem may thus arise in terms of securing electric connectivity and reliability of electric connection. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the problem of the conventional art. It is an object of the present invention to provide improved electric reliability of a recording head with a wide recording width. 
     In order to solve the problem described above, a liquid discharge recording head comprises: a recording element substrate including a plurality of recording elements and discharge ports for discharging liquid; an electric wiring board including an opening for disposing the recording element substrate, and a plurality of electrode terminals disposed at an edge of the opening and electrically connected to a plurality of electrodes provided at an edge of the recording element substrate; a supporting plate supporting the recording element substrate and the electric wiring board and including a material having a linear expansion coefficient lower than the linear expansion coefficient of the electric wiring board; and a cover plate including a material having a linear expansion coefficient lower than the linear expansion coefficient of the electric wiring board, stacked on the electric wiring board on the supporting plate and fixed to both the supporting plate and the electric wiring board. 
     The present invention can restrain variation in distance between the recording element substrate and the electric wiring board due to variation in temperature. As a result, electric reliability at longitudinal ends of the recording head with the wide recording width can be secured. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view illustrating a first exemplary embodiment of the present invention;  FIG. 1B  is a sectional view taken along the line  1 B- 1 B of  FIG. 1A . 
         FIG. 2A  is a perspective view of a recording element substrate used for the present invention;  FIG. 2B  is a sectional view taken along the line  2 B- 2 B of  FIG. 2A . 
         FIG. 3A  is a front view of the first exemplary embodiment of the present invention;  FIG. 3B  is a sectional view taken along the line  3 B- 3 B of  FIG. 3A . 
         FIG. 4A  is a front view of a reference head ( 1 ) for comparison with a recording head of the first exemplary embodiment;  FIG. 4B  is a sectional view taken along the line  4 B- 4 B of  FIG. 4A . 
         FIG. 5A  is a front view of a reference head ( 2 ) for comparison with the recording head of the first exemplary embodiment;  FIG. 5B  is a sectional view taken along the line  5 B- 5 B of  FIG. 5A . 
         FIG. 6A  is a front view of a reference head ( 3 ) for comparison with the recording head of the first exemplary embodiment;  FIG. 6B  is a sectional view taken along the line  6 B- 6 B of  FIG. 6A . 
         FIG. 7  is a sectional view illustrating a modification of the first exemplary embodiment. 
         FIG. 8A  is a perspective view of a second exemplary embodiment of the present invention;  FIG. 8B  is a sectional view taken along the line  8 B- 8 B of  FIG. 8A . 
         FIG. 9A  is a perspective view of a third exemplary embodiment of the present invention;  FIG. 9B  is a sectional view taken along the line  9 B- 9 B of  FIG. 9A . 
         FIG. 10  is an exploded perspective view of a recording head disclosed in Japanese Patent Application Laid-Open No. 2007-296638. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
       FIG. 1A  is a perspective appearance view of an ink jet recording head illustrating this exemplary embodiment.  FIG. 1B  is a sectional view of the recording head taken along the line  1 B- 1 B illustrated in  FIG. 1A . 
     In  FIGS. 1A and 1B , the ink jet recording head of this embodiment includes a plurality of recording element substrates  101  and an electric wiring board  119  for providing electric signals to the recording element substrates  101  from outside. Discharge energy generating elements  111  (see  FIG. 2B ) for discharging recording liquid are formed in the recording element substrate  101 . 
     This ink jet recording head further includes a supporting plate  103  for fixedly supporting the recording element substrates  101  and the electric wiring board  119 , and an ink supplying member  105  having a recording liquid supplying reservoir for storing the recording liquid to be supplied to each recording element substrate  101 . The surface of the electric wiring board  119  on the supporting plate  103  is covered with a cover plate  117  for restraining deformation of the electric wiring board  119  due to variation in temperature. 
     The ink supplying member  105  and the supporting plate  103  are fixed by adhesive (not shown); the supporting plate  103  and each recording element substrate  101  are fixed by the adhesive. Further, the electric wiring board  119  and the cover plate  117  are fixed to supporting plate  103  by the adhesive  106 . Likewise, the electric wiring board  119  and the cover plate  117  are also fixed by the adhesive  106 . 
       FIG. 2A  is a perspective appearance view of the recording element substrate  101 .  FIG. 2B  is a sectional view taken along the line  2 B- 2 B illustrated in  FIG. 2A . More specifically, the recording element substrate  101  includes a Si substrate  107 , for example, formed from a thin film 0.5 to 1 mm thick. A recording liquid supplying port  109  is formed in the Si substrate  107  as an ink flow path; the port  109  is a through slot formed in a shape of a long groove. Electricity-heat transducing elements  111 , which are discharge energy generating elements such as heaters, and electric wiring such as of Al are formed at both sides of the recording liquid supplying port  109  by a film formation technique. A flow path forming member  116  is formed on the Si substrate  107 . A plurality of liquid discharge ports  115  is formed in the flow path forming member  116 . The ports  115  correspond to the respective electricity-heat transducing elements  111  and are arranged in rows. Each liquid discharge port  115  communicates with the recording liquid supplying port  109  via a flow path  113 . 
     Next, the configuration of the ink jet recording head of this embodiment will hereinafter be described. 
     The ink jet recording head of this embodiment includes a recording element unit and an ink supplying unit. 
     In the recording element unit, the eight recording element substrates  101  are arranged and fixed in a predetermined positional accuracy on the main surface of the supporting plate  103 . The supporting plate  103  is, for example, made of alumina (Al 2 O 3 ) material 0.5 to 10 mm thick. The material of the supporting plate  103  is not limited to alumina. Instead, the material may be what has a coefficient of linear expansion lower than that of the electric wiring board  119  and high stiffness. For example, the material may be silicon (Si), aluminum nitride (AlN), zirconia, silicon nitride (Si 3 N 4 ), silicon carbide (SiC), molybdenum (Mo) and tungsten (W). 
     The plurality of recording element substrates  101 , which mainly include silicon (Si) material, are arranged such that parts of the ends of groups of the discharge ports, which are provided on the respective recording element substrates  101  and form the rows, overlap each other in the discharge port arrangement direction. Accordingly, the groups of discharge ports corresponding to one row of the recording head of this embodiment are adapted such that the discharge ports of two rows of the recording element substrate  101  are arranged in the staggered arrangement. The parts of ends of discharge ports of the recording element substrates  101  are thus arranged in the overlapping manner. This configuration can thereby correct a malfunction concerning an image due to a positional deviation in arrangement. 
     Further, the electric wiring board  119 , which is for providing electric inputs to the electricity-heat transducing elements  111  of the recording element substrate  101  from outside, is formed with openings corresponding to the fixed positions of the recording element substrates  101 . The recording element substrate  101  is cemented to the supporting plate  103  so as to fit into the opening. As shown in  FIGS. 1B and 2A , electrodes  120  formed on the ends of the surface of the recording element substrate  101  and the electrode terminal  124  formed on the surface of the electric wiring board  119 , are connected to each other by an electrically connecting part such as bonding wire  121 . The electrically connecting part is sealed with a sealing agent  122  in order to prevent corrosion owing to recording liquid. 
     As shown in  FIGS. 1A and 1B , the ink supplying unit includes the ink supplying member  105 , a filter (not shown), a joint rubber (not shown) and a flow path plate (not shown). More specifically, the ink supplying member  105  is formed from a structural base member by injection molding using resin material. 
     Here, the cover plate  117  according to this embodiment has a longitudinal dimension longer than that of the electric wiring board  119  and a thickness of 0.1 to 0.3 mm. The cover plate  117  is formed from a Ti material (α=5 ppm/° C.) whose coefficient of linear expansion is smaller than that of the electric wiring board  119 . Such a cover plate  117  is cemented to the electric wiring board  119  so as to cover the entire top part of the electric wiring board  119 . Here, as shown in  FIG. 1A , the cover plate  117  and the supporting plate  103  are directly cemented to the recording head at both the longitudinal ends thereof. 
     According to this configuration, the electric wiring board  119  is cemented between the supporting plate  103  of alumina and the cover plate  117  of Ti, whose linear expansion coefficients are smaller than that of the electric wiring board  119 . The expansion and contraction of the electric wiring board  119  due to variation in temperature is restrained to those of the material having a small linear expansion coefficient. In particular, with respect to electricity, it can be adapted such that the cover plate  117  and the supporting plate  103  are cemented to the recording head at both longitudinal ends thereof while sandwiching the wiring element, as with this embodiment. This configuration can restrain the expansion and contraction of the electric wiring board at the around both the longitudinal ends of the recording head which the expansion of the electric wiring board significantly affects. 
     The recording head of this embodiment and reference recording heads as comparative examples have been made. The length of the electrically connecting part at the end of each recording head has been measured. Three reference recording heads have been made. That is, three heads modified as follows have been prepared with respect to the recording head of this embodiment: (1) the recording head without the cover plate  117 ; (2) the recording head with the cover plate  117  which has been made of Ti but not cemented to the supporting plate  103 ; (3) the recording head with the cover plate  117  which has been made of polyimide (α≅20 ppm/° C.) and cemented to both of the electric wiring board  119  and the supporting plate  103 . 
       FIG. 3A  is a front view of the recording head of this embodiment;  FIG. 3B  is a sectional view taken along the line  3 B- 3 B of  FIG. 3A . Front views of the reference recording heads ( 1 ) to ( 3 ) are illustrated in  FIGS. 4A ,  5 A and  6 A; sectional views thereof taken along the lines  4 B- 4 B,  5 B- 5 B and  6 B- 6 B are illustrated in  FIGS. 4B ,  5 B and  6 B, respectively. 
     Each recording head to be measured includes the supporting plate  103  of alumina (183 mm wide in longitudinal dimension) and the electric wiring board  119  of flexible film wiring board (161 mm wide in longitudinal dimension). The supporting plate  103  and the electric wiring board  119  are cemented by a thermosetting epoxy resin  106  (about 50-100 μm thick). The longitudinal dimension width of the cover plate  117  of this embodiment is 171 mm; the longitudinal dimension width of the recording head ( 2 ) is 161 mm; and longitudinal dimension width of the recording head ( 3 ) is 171 mm. As well as the recording heads, the supporting plates  103  and the electric wiring boards  119  are cemented by the thermosetting epoxy resin  106 . 
     The measurement temperature was an ambient temperature (23° C.) and a high-temperature environment (150° C.). The lengths L of electric wiring parts at the ends of the recording heads have been measured at both the temperatures. The electric wiring part indicates a part between an electrode formed at the end of the surface of the recording element substrate  101  and an electrode terminal formed at the surface of the electric wiring board  119  ( FIG. 3B ). 
     Table 1 represents the results of the respective types of recording heads. These results show that the expansion and contraction of the electric wiring board of this embodiment has been restrained. Therefore, according to this embodiment, the amount of distance variation owing to temperatures between the recording element substrate  101  and the electric wiring board  119  can be restrained; the recording head having high electric reliability can be obtained. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 HEAD TYPE 
               
            
           
           
               
               
               
               
               
            
               
                   
                 RECORDING 
                 REFERENCE 
                 REFERENCE 
                 REFERENCE 
               
               
                   
                 HEAD OF THIS 
                 RECORDING 
                 RECORDING 
                 RECORDING 
               
               
                   
                 EMBODIMENT 
                 HEAD (1) 
                 HEAD (2) 
                 HEAD (3) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 VARIATION AMOUNT OF L/μm 
                 8 
                 25 
                 25 
                 27 
               
               
                   
               
            
           
         
       
     
     Although this embodiment has been described such that the material of the cover plate  117  is Ti, the material is not limited to Ti. Instead, any material having a low coefficient of linear expansion may be applied. For example, ceramic and metal materials, such as alumina (Al 2 O 3 ), silicon (Si), aluminum nitride (AlN), zirconia, silicon nitride (Si 3 N 4 ), silicon carbide (SiC), molybdenum (Mo) and tungsten (W), may be adopted. That is, the linear expansion coefficients of the cover plate  117  and the supporting plate  103  can be lower than the linear expansion coefficient of the electric wiring board  119 . A large difference between the linear expansion coefficients of the cover plate  117  and the supporting plate  103  creates distortion, thereby causing possibility of exerting an influence on the electrically connecting part. Accordingly, a configuration can be selected where the linear expansion coefficients of the cover plate  117  and the supporting plate  103  are substantially the same as each other. 
     As to the fixation by cementing between the cover plate  117  and the supporting plate  103  at the longitudinal end of the recording head, the longitudinal dimensions of the cover plate  117  and the electric wiring board  119  can be the same as each other, as shown in  FIG. 7 . In this case, the electric wiring board  119  is provided with an opening at an area in proximity to the longitudinal end of the recording head. The cover plate  117  and the supporting plate  103  are cemented to each other through the opening. This configuration can maintain flatness over the entire area of the cover plate  117 . 
     A second exemplary embodiment of the present invention will be described with reference to  FIGS. 8A and 8B . 
       FIG. 8A  illustrates an ink jet recording head pertaining to the second exemplary embodiment of the present invention;  FIG. 8B  is a corresponding sectional view taken along the line  8 B- 8 B of  FIG. 8A . As to elements which can be configured as with the first exemplary embodiment, identical symbols will be assigned to the corresponding parts and description thereof will be omitted. 
     In this embodiment, the cover plate is disposed only in proximity to a longitudinal end of the recording head. 
     As shown in  FIGS. 8A and 8B , in this embodiment, the cover plate  118  is smaller than that in the first exemplary embodiment and disposed in the proximities of each end of the electric wiring board  119 . Further, the cover plate  118  is cemented to the top surface of the electric wiring board  119  and the supporting plate  103 . 
     In general, a plane including the surface (surface where the discharge port is formed) of the recording element substrate  101  is periodically cleaned by wiping with a rubber blade for the sake of secure recording without a deterioration of the recording quality in the ink jet recording head. 
     In the present invention, the cover plate is formed from a ceramic or a metallic material having a linear expansion coefficient lower than the linear expansion coefficient of the electric wiring board  119 . Accordingly, it is concerned that the rubber blade is damaged or deteriorates in durability at the cleaning process. 
     In this case, it is effective to adopt a configuration without cover plate in the wiping area, as with this embodiment. 
     Thus, in this embodiment, the cover plate  118  is partially disposed at the longitudinal end of the recording head. Accordingly, the configuration, where the cover plate  118  is not wiped when the surface of the recording element substrate is wiped, can be adopted. This configuration can also restrain the expansion and contraction of the wiring board as with the above embodiment. Therefore, the reliability of electric connection can be improved between the recording element substrate and the electric wiring board. 
     In this embodiment, the cover plate  118  and the supporting plate  103  are not cemented at both widthwise ends of the recording head. This configuration can relieve stress generated at the electric wiring board under heating, into the widthwise direction of the recording head. The amount of expansion in the widthwise direction of the recording head is small. Accordingly, an influence thereof on the electrically connecting part is also small. 
     If the cover plate  118  and the supporting plate  103  are cemented to each other all around the edges without any allowance, the stress to be generated under heating cannot be relieved into anywhere, thereby causing possibility of peeling the cemented fixation. The configuration of this embodiment can relieve the stress without any influence on the electrically connecting part. 
     A third exemplary embodiment of the present invention will be described with reference to  FIGS. 9A and 9B . 
       FIG. 9A  illustrates an ink jet recording head pertaining to the third exemplary embodiment of the present invention;  FIG. 9B  is a corresponding sectional view taken along the line  9 B- 9 B of  FIG. 9A . As to elements which can be configured as with the first exemplary embodiment, identical symbols will be assigned to the corresponding parts and description thereof will be omitted. 
     This embodiment adopts a configuration where the cover plate and the supporting plate are cemented to each other not only at both the ends of the recording head, but also through openings provided in the electric wiring board separately from the openings for arranging the recording element substrates. 
     As shown in  FIG. 9 , as with the first exemplary embodiment, the cover plate  117  and the electric wiring board  119  are cemented to each other. The cover plate  117  and the supporting plate  103  are directly cemented to each other at both the longitudinal ends of the recording head. In particular, according to this embodiment, some areas without disposition of wiring are formed in the electric wiring board  119 . The openings  123  are formed in these areas. 
     The number, positions and dimensions of openings  123  are arbitrarily determined according to the wiring pattern and the dimension and length of the electric wiring board. The cover plate  117  and the supporting plate  103  are directly cemented through the openings  123 . The cover plate  118  and the supporting plate  103  are thus intermittently fixed along the widthwise edges of the recording head. This configuration can thereby provide paths for relieving the stress, as with the descriptions of the above embodiments. 
     Therefore, in this embodiment, the cemented fixation area between the cover plate  117  and the supporting plate  103  is larger than that of the first embodiment. Accordingly, the expansion and contraction of the electric wiring board  119  is further restrained, thereby allowing reliability to be improved in electric connection between the recording element substrate  101  and the electric wiring board  119 . 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application Nos. 2009-134074, filed on Jun. 3, 2009, and 2010-072951, filed on Mar. 26, 2010, which are hereby incorporated by reference herein in their entirety.