Patent Publication Number: US-2023138126-A1

Title: Liquid discharge head, liquid discharge apparatus, and bonded unit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-177761, filed on Oct. 29, 2021, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to a liquid discharge head, a liquid discharge apparatus, and a bonded unit. 
     Related Art 
     An inkjet image forming apparatus includes a liquid discharge head constructed of multiple components, such as a nozzle plate and a channel substrate, bonded to each other in layers. These components are bonded to each other with an adhesive such as a thermosetting adhesive. 
     SUMMARY 
     Embodiments of the present disclosure describe an improved liquid discharge head (or bonded unit) that includes a first component having a bonding face having a recess and a second component bonded to the bonding face of the first component. The recess includes a first recess to which an adhesive is applied and a second recess extending in an extending direction to connect the first recess and an outer peripheral end of the first component. The first recess includes an inner side face that is an interior of the first component, and the second recess includes a first wall face and a second wall face opposed to the first wall face. The first wall face and the second wall face define side walls of the second recess in a width direction orthogonal to the extending direction of the second recess. The extending direction of the second recess is inclined with respect to a perpendicular line perpendicular to the inner side face of the first recess. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG.  1    is an exploded perspective view of a liquid discharge head according to an embodiment of the present disclosure: 
         FIG.  2    is a cross-sectional view of the liquid discharge head illustrated in  FIG.  1    in a direction perpendicular to a nozzle array direction: 
         FIG.  3    is an enlarged view of a part of the liquid discharge head in  FIG.  2   : 
         FIG.  4    is a cross-sectional view of the liquid discharge head in the nozzle array direction; 
         FIG.  5    is a plan view of a nozzle plate bonded to an actuator substrate of the liquid discharge head: 
         FIG.  6    is a plan view illustrating a recess of the actuator substrate; 
         FIG.  7    is a cross-sectional view of the nozzle plate and the actuator substrate along line A-A in  FIG.  6   : 
         FIG.  8    is a plan view illustrating a recess of the actuator substrate according to Comparative Example 1 different from the present embodiment; 
         FIG.  9    is a plan view illustrating a recess of the actuator substrate according to Comparative Example 2 different from the present embodiment; 
         FIG.  10    is a plan view illustrating a recess of the actuator substrate according to another embodiment of the present disclosure; 
         FIG.  11    is a plan view illustrating a recess of the actuator substrate according to still another embodiment of the present disclosure: 
         FIG.  12    is a plan view illustrating a recess of the actuator substrate according to yet another embodiment of the present disclosure: 
         FIG.  13    is a plan view illustrating a recess of the actuator substrate according to still yet another embodiment of the present disclosure; 
         FIG.  14    is an exploded perspective view of a head module according to embodiments of the present disclosure; 
         FIG.  15    is an exploded perspective view of the head module viewed from a nozzle surface side thereof; 
         FIG.  16    is an exploded perspective view of a head, a base, and a cover of the head module; 
         FIG.  17    is a schematic view of a liquid discharge apparatus according to embodiments of the present disclosure; and 
         FIG.  18    is a plan view of a head unit of the liquid discharge apparatus. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     A liquid discharge head  200  according to an embodiment of the present disclosure is described below with reference to  FIGS.  1  to  4   . Identical reference numerals are assigned to identical components or equivalents and descriptions of those components are simplified or omitted as appropriate.  FIG.  1    is an exploded perspective view of the liquid discharge head  200 .  FIG.  2    is a cross-sectional view of the liquid discharge head  200  in a direction perpendicular to a nozzle array direction.  FIG.  3    is an enlarged cross-sectional view of a part of the liquid discharge head  200  illustrated in  FIG.  2   .  FIG.  4    is a cross-sectional view of the part of the liquid discharge head  200  in the nozzle array direction. 
     As illustrated in  FIGS.  1  and  2   , the liquid discharge head  200  includes a nozzle plate  201 , a channel substrate  202 , a diaphragm plate  203 , a piezoelectric element  211  serving as a pressure generator, a holding substrate  250 , and a frame  270  serving also as a common-chamber substrate. Hereinafter, the liquid discharge head  200  is also simply referred to as a head  200 . 
     In the present embodiment, the channel substrate  202 , the diaphragm plate  203 , and the piezoelectric element  211  construct an “actuator substrate  220 ” as an actuator member according to the present disclosure. Note that the actuator substrate  220  does not include the nozzle plate  201 , the holding substrate  250 , or the frame  270  that is bonded to the actuator substrate  220  after the actuator substrate  220  is formed as an independent component. 
     The nozzle plate  201  has a plurality of nozzles  204  to discharge liquid. In the present embodiment, the nozzle plate  201  has two nozzle rows, in each of which the nozzles  204  are arranged in a row. 
     The channel substrate  202 , together with the nozzle plate  201  and the diaphragm plate  203 , defines an individual liquid chamber  206 , a fluid restrictor  207 , and a liquid inlet portion  208 . The individual liquid chamber  206  communicates with the nozzle  204 . The fluid restrictor  207  communicates with the individual liquid chamber  206 . The liquid inlet portion  208  communicates with the fluid restrictor  207 . 
     The liquid inlet portion  208  communicates with a common liquid chamber  210  defined by the frame  270  via a passage  209  and a flow path  210 A. Liquid is supplied to the common liquid chamber  210  from the outside of the head  200  via a supply port  272 . The passage  209  is a liquid supply inlet formed in the diaphragm plate  203 , through which the liquid is supplied from the common liquid chamber  210  to the individual liquid chamber  206 . 
     The flow path  210 A is a part of the common liquid chamber  210  defined by the holding substrate  250 . 
     As illustrated in  FIGS.  3  and  4   , the diaphragm plate  203  forms a deformable vibration portion  230  defining a part of the wall of the individual liquid chamber  206 . The piezoelectric element  211  and the individual liquid chamber  206  are disposed on opposite sides of the vibration portion  230 . The piezoelectric element  211  is attached onto a surface of the vibration portion  230  as a single unit. The vibration portion  230  and the piezoelectric element  211  construct a piezoelectric actuator. 
     The piezoelectric element  211  includes a lower electrode  213 , a piezoelectric layer (piezoelectric body)  212 , and an upper electrode  214  laminated in this order on the vibration portion  230 . The piezoelectric element  211  is coated with an insulating film  221 . The lower electrode  213  as a common electrode for a plurality of piezoelectric elements  211  is connected to a common-electrode power-supply wiring pattern  223  via a common wire  215 . The upper electrode  214  as an individual electrode for each piezoelectric element  211  is connected to a driver integrated circuit (IC)  240  via an individual wire  216 . The driver IC  240  is mounted on the actuator substrate  220  by, e.g., a flip-chip bonding, to cover an area between rows of the piezoelectric elements  211 . 
     As illustrated in  FIG.  1   , wires are led out from input/output (I/O) terminals, a power supply terminal, and an input terminal of drive waveforms (drive signals) of the driver IC  240  mounted on the actuator substrate  220  and connected to a connection terminal group  218 . Wires of a wiring member  260  such as a flexible printed circuit (FPC) or a flexible flat cable (FFC) are electrically connected to the respective connection terminals of the connection terminal group  218  by anisotropic conductive film (ACF) connection, solder connection, wire bonding, or the like. The other ends of the wires of the wiring member  260  are connected to a controller installed in an apparatus body of a liquid discharge apparatus such as a printer  500  illustrated in  FIG.  17   . The wiring member  260  is contained in the frame  270  and is led out to the outside of the head  200  through a wiring outlet  271 . Each connection terminal of the connection terminal group  218  is flatly disposed at an end of the actuator substrate  220 . 
     The holding substrate  250  is disposed on the actuator substrate  220 . The holding substrate  250  has a recess (vibration chamber)  251  that accommodates the piezoelectric element  211 . As described above, the holding substrate  250  defines the flow path  210 A which is a part of the common liquid chamber  210 . The holding substrate  250  is bonded to a surface of the actuator substrate  220  on which the diaphragm plate  203  is disposed with an adhesive. 
     In the liquid discharge head  200  having the above-described configuration, the driver IC  240  applies a voltage between the upper electrode  214  and the lower electrode  213  of the piezoelectric elements  211  to cause the piezoelectric layer  212  to expand in the direction of lamination of the electrodes, that is, in the direction of the electric field, and to contract in the direction parallel to the vibration portion  230 . At that time, the lower electrode  213  is constrained by the vibration portion  230 . For this reason, a tensile stress is generated at one side of the vibration portion  230  facing the lower electrode  213 , causing the vibration portion  230  to bend toward the other side of the vibration portion  230  facing the individual liquid chamber  206 . Accordingly, liquid in the individual liquid chamber  206  is pressurized and discharged from the nozzle  204 . 
     As described above, the nozzle plate  201 , the channel substrate  202 , the diaphragm plate  203 , the holding substrate  250 , and the frame  270  are laminated one on another and bonded to each other to construct the liquid discharge head  200 . At the time of bonding, these components are temporarily bonded to each other with a light curable adhesive, and subsequently bonded to each other with a final bonding adhesive. 
     A description is given below of the above-described bonding, for example, the actuator substrate  220  as a first component and the nozzle plate  201  as a second component are bonded to each other. 
     As illustrated in  FIG.  5   , recesses  10  are disposed at positions corresponding to four corners of the nozzle plate  201  on a surface of the actuator substrate  220  facing the nozzle plate  201  to temporarily bond the nozzle plate  201  to the actuator substrate  220 . In other words, the actuator substrate  220  has a bonding face to which the nozzle plate  201  is bonded, and the bonding face has the recesses  10 . The bonding face is a surface of the channel substrate  202  of the actuator substrate  220  facing the nozzle plate  201  (see  FIG.  2   ). An outer peripheral end of the actuator substrate  220  described later is an outer peripheral end of the channel substrate  202 . 
     When the actuator substrate  220  and the nozzle plate  201  are bonded to each other, a temporary bonding adhesive  90  is applied to a first recessed portion of the recess  10 , which is described later, and the final bonding adhesive is applied to a portion of the actuator substrate  220  to which the nozzle plate  201  is adhered, that is, a portion surrounded by the broken line in  FIG.  5   , excluding the recess  10 . The temporary bonding adhesive  90  is a light curable adhesive that is cured by light such as ultraviolet rays. 
     As the actuator substrate  220  and the nozzle plate  201  are bonded to each other, the temporary bonding adhesive  90  is held between the actuator substrate  220  and the nozzle plate  201  (see  FIG.  7    described later). In this state, the recess  10  is irradiated with light to cure the temporary bonding adhesive  90 . As a result, the actuator substrate  220  and the nozzle plate  201  are temporarily bonded to each other. Subsequently, these components (i.e., the actuator substrate  220  and the nozzle plate  201 ) are heated to cure the final bonding adhesive. As a result, the actuator substrate  220  and the nozzle plate  201  are permanently bonded to each other. 
     In the temporary bonding using the light curable temporary bonding adhesive  90 , the temporary bonding adhesive  90  applied to the recess  10  may be squeezed out of the actuator substrate  220 . In addition, the light may not sufficiently reach deep inside the recess  10 , that is, a far (inner) side from the outer peripheral end of the actuator substrate  220 , causing the insufficient temporary bonding. 
     The configuration of the recess  10  according to the present embodiment that solves the above situation is described below with reference to  FIG.  6   . In the present embodiment, since the recesses  10  at the four corners have the same shape, only the recess  10  at the upper right in  FIG.  5    is described. Hereinafter, the temporary bonding adhesive  90  is simply referred to as the adhesive  90 . 
     As illustrated in  FIG.  6   , the recess  10  includes a first recessed portion  11  as a first recess and a second recessed portion  12  as a second recess. The adhesive  90  is applied to the first recessed portion  11 . The second recessed portion  12  communicates with the first recessed portion  11  and extends to an outer peripheral end  220   a  of the actuator substrate  220 . In other words, the second recessed portion  12  extends in an extending direction to connect the first recessed portion  11  and the outer peripheral end  220   a  of the first component. The second recessed portion  12  is a light path to guide ultraviolet (UV) light L into the recess  10 . 
     As described above, the second recessed portion  12  serves as the light path, and the first recessed portion  11  to which the adhesive  90  is applied is farther from the outer peripheral end  220   a  than the second recessed portion  12 . Accordingly, the adhesive  90  is prevented from being squeeze out of the outer peripheral end  220   a  of the actuator substrate  220 . The second recessed portion  12  extends in an extending direction inclined with respect to an inner side face  11 A of the first recessed portion  11 , which is an interior of the first component. 
     The term “the extending direction of the second recessed portion is inclined with respect to the inner side face  11 A” means that center lines B 1  and B 2  connecting centers of the second recessed portion  12  in a width direction of the second recessed portion  12  form an angle with the inner side face  11 A, which are not perpendicular to the inner side face  11 A, and the center lines B 1  and B 2  are not parallel to the inner side face  11 A in the present embodiment. In other words, the extending directions B 1  and B 2  of the second recessed portion  12  is inclined with respect to a perpendicular line perpendicular to the inner side face  11 A of the first recessed portion  11 , which is indicated by line A-A in  FIG.  6   . Accordingly, the UV light L that enters the second recessed portion  12  is diffusely reflected in the first recessed portion  11 , and the entire adhesive  90  can be more uniformly irradiated with the UV light L. Thus, the adhesive  90  is cured in the first recessed portion  11 , and the actuator substrate  220  and the nozzle plate  201  can be temporarily bonded with preferable strength. 
     The inner side face  11 A is one of side faces of the first recessed portion  11  on the side opposite to a portion communicating with the second recessed portion  12 . In other words, the inner side face  11 A is a surface farthest from the portion between the first recessed portion  11  and the second recessed portion  12  communicating with each other among the side faces defining the first recessed portion  11  in the present embodiment. Alternatively, a face  11 B, which is another of the side faces of the first recessed portion  11 , disposed on a line extended from the center line B 1  or B 2  of the second recessed portion  12 , in particular, the center line B 1  which is closest to the first recessed portion  11  may be defined as an inner side face, and the center line B 1  or B 2  may be inclined with respect to the face  11 B. That is, in the present embodiment, the center line B 1  or B 2  indicating the extending direction of the second recessed portion  12  is inclined with respect to a perpendicular line, which is indicated by line A-A or line C in  FIG.  6   , perpendicular at least one of the inner side face  11 A (i.e., a third wall face) of the first recessed portion  11  opposite to the portion communicating with the second recessed portion  12  or the face  11 B (i.e., a fourth wall face adjacent to the third wall face with an angle with the third wall face) on the extended line extended from the center line B 1 . Hereinafter, the direction of the center lines B 1  and B 2  connecting the centers of the second recessed portion  12  in the width direction also is referred to as the extending directions B 1  and B 2  of the second recessed portion  12 . The inner side face  11 A is parallel to the outer peripheral end  220   a  of the actuator substrate  220 . Further, in the present embodiment, the extending directions B 1  and B 2  of the second recessed portion  12  are inclined with respect to the outer peripheral end  220   a . The extending directions B 1  and B 2  of the second recessed portion  12  and the width direction of the second recessed portion  12  are along the bonding face of the actuator substrate  220  to which the nozzle plate  201  is adhered. 
     As described above, the recess  10  according to the present embodiment prevents the adhesive  90  from being squeezed out and facilitates the adhesive  90  applied in the first recessed portion  11  being sufficiently cured. As a result, as illustrated in  FIG.  7   , the actuator substrate  220  as the first component and the nozzle plate  201  as the second component are temporarily bonded to construct a bonded unit  300 . 
     In the present embodiment, the second recessed portion  12  is narrower adjacent to the outer peripheral end  220   a  of the actuator substrate  220  than adjacent to the first recessed portion  11  in the width direction of the second recessed portion  12 . That is, an inclination angle of a wall face  12 A of the second recessed portion  12  on one side changes at an inflection point  12   a  as a boundary, so that the second recessed portion  12  is narrower in the width direction adjacent to the outer peripheral end  220   a  than adjacent to the first recessed portion  11 . In other words, the second recessed portion  12  has a narrow part close to the outer peripheral end  220   a  and a wider part closer to the first recessed portion  11  than the narrow part, and the wider part has a width larger than a width of the narrow part in the width direction. Thus, the configuration of the second recessed portion  12  that is narrow adjacent to the outer peripheral end  220   a  further prevents the adhesive  90  from being squeezed. In addition, the configuration of the second recessed portion  12  that is wide adjacent to the first recessed portion  11  facilitates light that enters the second recessed portion  12  being diffused in the recess  10  to sufficiently cure the adhesive  90 . 
     Further, the wall face  12 A of the second recessed portion  12  on one side in the width direction deeply extends from the outer peripheral end  220   a  toward the first recessed portion  11  as compared with a wall face  12 B on the other side. That is, the wall face  12 A (i.e., a first wall face) extending toward the first recessed portion  11  is longer than the wall face  12 B (i.e., a second wall face) by a certain distance. 
     In other words, the second recessed portion  12  includes the first wall face  12 A and the second wall face  12 B opposed to the first wall face  12 A. The first wall face  12 A and the second wall face  12 B define side walls of the second recessed portion  12  in the width direction orthogonal to the extending direction of the second recessed portion  12 . The first wall face  12 A and the second wall face  12 B extend from the outer peripheral end  220   a  toward the first recessed portion  11 , and the first wall face  12 A is longer than the second wall face  12 B. Thus, the wall face  12 A on one side, which is longer than the wall face  12 B, guides light incident from the second recessed portion  12  into the first recessed portion  11  along the wall face  12 A to facilitate the adhesive  90  in the first recessed portion  11  being cured. 
     In the present embodiment, an inclined face  11 C inclined with respect to each of the inner side face  11 A and the face  11 B is disposed between the inner side face  11 A and the face  11 B to connect the inner side face  11 A and the face  11 B. The inclined face  11 C is continuous with the inner side face  11 A and face  11 B. In other words, the first recessed portion  11  has a shape such that a corner where the inner side face  11 A and the face  11 B intersect with each other is chamfered by the inclined face  11 C. 
     The inclined face  11 C further diffuses the UV light L in the first recessed portion  11 . Although the relation between the inner side face  11 A and the face  11 B has been described above, the inner side face  11 A is also continuous with a face  11 D via an inclined face on the other side. The faces  11 B and  11 D (i.e., continuous faces) are continuous with the second recessed portion  12 . That is, the face  11 B is connected to the first wall face  12 A, and the face  11 D is connected to the second wall face  12 B. 
     The extending direction B 1  or the extending direction B 2  of the second recessed portion  12  is preferably inclined with respect to the perpendicular line of each side face (i.e., the inner side face  11 A, the face  11 B, or the face  11 D) of the first recessed portion  11 . Thus, the UV light is diffusely reflected in the first recessed portion  11  to cure the adhesive  90  in the first recessed portion  11 . All the side faces of the first recessed portion  11  described above do not include a narrow chamfered face, for example, corresponding to the corner between the inner side face  11 A and the face  11 B, such as the inclined face  11 C described above. However, the extending directions B 1  or B 2  of the second recessed portion  12  may be inclined with respect to a perpendicular line perpendicular to the inclined face  11 C or the like. The side faces of the first recessed portion  11  extend in a direction in which the first component and the second component are bonded to each other, that is, in the direction perpendicular to the surface of the paper on which  FIG.  6    is drawn. However, the direction may not be strictly perpendicular. 
     A description is given below of experiment results indicating the effect of the recess  10  according to the present embodiment that prevents the adhesive  9 ) from being squeezed out and facilitates the adhesive  90  being cured. In the experiment, the effect is compared between “the present embodiment” including the recess  10  having the configuration illustrated in  FIG.  6    and, “Comparative Example 1” and “Comparative Example 2” including recesses having configurations different from the present embodiment. As illustrated in FIG.  8 , a recess  10 ′ in Comparative Example 1 does not includes the second recessed portion  12 , and the portion to which the adhesive  90  is applied is open on two sides of the outer peripheral end of the actuator substrate  220 . As illustrated in  FIG.  9   , in a recess  10 ′ in Comparative Example 2, the extending direction of the portion corresponding to the second recessed portion  12  according to the present embodiment is perpendicular to the inner side face  11 A′ farthest from the outer peripheral end  220   a  of the actuator substrate  220 . 
     In the present embodiment, Comparative Example 1, and Comparative Example 2, the adhesive  90 , which is UV curable (also referred to as the UV adhesive  90 ), was applied to the first recessed portion  11 , the actuator substrate  220  and the nozzle plate  201  were bonded to each other, and the UV adhesive  90  in the first recessed portion was irradiated with the UV light L. After a predetermined time elapsed to cure the UV adhesive  90 , an “average cured proportion of the UV adhesive  90 ” and an “occurrence rate of the squeezed out UV adhesive  90 ” were measured. In each of the present embodiment, Comparative Example 1, and Comparative Example 2, the number of samples N was 24. 
     Specifically, the experiment was performed as follows. First, in each of the present embodiment, Comparative Example 1, and Comparative Example 2, the UV adhesive  90  was applied to the actuator substrate  220  in a circular shape with substantially the same amount and the same diameter as viewed from above as illustrated in  FIGS.  6 ,  8 , and  9   . Then, the actuator substrate  220  and the nozzle plate  201  were bonded to each other, and the UV adhesive  90  was irradiated with the UV light L. After the predetermined time elapsed to cure the UV adhesive  90 , the bonded portion was visually observed from the nozzle plate  201  side to confirmed whether the UV adhesive  90  was squeezed out. The occurrence rate of the squeezed out UV adhesive was calculated by dividing the number of samples in which the UV adhesive  90  was squeezed out by the number of samples N (i.e.,  24 ). 
     Thereafter, the actuator substrate  220  was separated from the nozzle plate  201 . The bonded portion of the actuator substrate  220  to which the UV adhesive  90  was applied was cleaned to remove the uncured UV adhesive  90 . An image of the actuator substrate  220  was captured in the direction in which the nozzle plate  201  was bonded, that is, in the direction perpendicular to the surface of the paper on which  FIG.  6    is drawn to measure the shape of the cured UV adhesive  90 . An area of the circular shape was defined as 100%, and a proportion of an area where the UV adhesive remains was calculated. The proportions were averaged over 24 samples to calculate the average cured proportion of the UV adhesive  90 . The experiment results conducted by the above-described method are illustrated in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 AVERAGE CURED 
                 OCCURRENCE RATE 
               
               
                   
                 PROPORTION OF UV 
                 OF SQUEEZED OUT 
               
               
                   
                 ADHESIVE [%] 
                 UV ADHESIVE [%] 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 PRESENT 
                 100 
                 0 
               
               
                 EMBODIMENT 
               
               
                 COMPARATIVE 
                 91 
                 16.7 
               
               
                 EXAMPLE 1 
               
               
                 COMPARATIVE 
                 70 
                 0 
               
               
                 EXAMPLE 2 
               
               
                   
               
            
           
         
       
     
     As illustrated in Table 1, in the present embodiment, the average cured proportion of the UV adhesive  90  was highest, i.e., 100%, and the occurrence rate of the squeezed out UV adhesive  90  was lowest, i.e., 0%. In Comparative Example 1, the cured proportion was 91%, which was relatively high, but the occurrence rate of the squeezed out UV adhesive  90  was 16.7%, that is, the UV adhesive  90  was squeezed out. Since the recess  10 ′ does not include the second recessed portion  12  as illustrated in  FIG.  8   , the UV light L is likely to be widely diffused in the recess  10 ′, but the UV adhesive  90  is likely to be squeezed out. In Comparative Example 2, the UV adhesive  90  was not squeezed out, but the cured proportion was low, i.e., 70%. In Comparative Example 2, as illustrated in  FIG.  9   , although the passage portion corresponding to the second recessed portion  12  prevents the UV adhesive  90  from being squeezed out, the UV light L may not be sufficiently diffused in the portion corresponding to the first recessed portion  11  since the extending direction of the passage portion is perpendicular to the inner side face  11 A′, and the UV adhesive  90  may not be sufficiently cured. 
     As described above, the configuration of the recess  10  according to the present embodiment, specifically, the configuration in which the recess  10  includes the second recessed portion  12  extending in the extending direction inclined with respect to the inner side face  11 A prevents the UV adhesive  90  from being squeezed out and facilitates the UV adhesive  90  being sufficiently cured. 
     As illustrated in  FIG.  7   , the inner side face  11 A has asperities which undulate in the vertical direction in  FIG.  7   . Accordingly, the UV light L can be further diffused in the first recessed portion  11 . Alternatively, the inner side face  11 A may have asperities which undulate in the width direction (the vertical direction in  FIG.  6    and the direction perpendicular to the surface of the paper on which  FIG.  7    is drawn), or other faces of the first recessed portion  11  and the second recessed portion  12  (e.g., the faces  11 B,  11 C, and  11 D, the first wall face  12 A, or the second wall face  12 B) may have asperities. With such a configuration, light can be further diffused in the recess  10 . 
     Modifications of the recess  10  are described below. 
     In the recess  10  illustrated in  FIG.  10   , for example, an extending direction B of the second recessed portion  12  is substantially parallel to the outer peripheral end of the actuator substrate  220  extending in the left-and-right direction in  FIG.  10    (and perpendicular to the outer peripheral end  220   a  of the actuator substrate  220 ). On the other hand, the first recessed portion  11  is inclined with respect to the outer peripheral end  220   a  of the actuator substrate  220 . As a result, the extending direction B of the second recessed portion  12  is inclined with respect to the inner side face  11 A of the first recessed portion  11 . 
     The shape of the first recessed portion  11  is not limited to a rectangle, and as illustrated in  FIG.  11   , inner side faces  11 A 1  and  11 A 2  are inclined with respect to the outer peripheral end  220   a  of the actuator substrate  220 . As a result, the extending direction B of the second recessed portion  12  is inclined with respect to the inner side faces  11 A 1  and  11 A 2 . 
     In  FIG.  12   , the one wall face  12 A of the second recessed portion  12  is inclined with respect to the inner side face  11 A, but the other wall face  12 B is substantially perpendicular to the inner side face  11 A. Also in this case, the extending direction B of the second recessed portion  12  is inclined with respect to the inner side face  11 A. 
     Also in the above embodiments, the configuration in which the extending direction B of the second recessed portion  12  is inclined with respect to the inner side face  11 A facilitates the UV adhesive  90  being sufficiently cured. 
     The extending direction of the entire second recessed portion  12  is not necessarily inclined with respect to the inner side face  11 A. For example, in  FIG.  13   , the extending direction B 2  of the second recessed portion  12  adjacent to the outer peripheral end  220   a  is substantially perpendicular to the inner side face  11 A, but the extending direction B 1  of the second recessed portion  12  adjacent to the first recessed portion  11  is inclined with respect to the inner side face  11 A. Accordingly, the UV adhesive  90  applied to the first recessed portion  11  can be sufficiently cured. In particular, the configuration in which the extending direction B 1  of the second recessed portion  12  adjacent to the first recessed portion  11  is inclined with respect to the inner side face  11 A is more effective to cure the UV adhesive  90  than the configuration in which the extending direction B 2  is inclined with respect to the inner side face  11 A. 
     The configurations of the recesses  10  illustrated in  FIGS.  10  to  13    can be combined. For example, the first recessed portion  11  having the shape illustrated in  FIG.  11    and the second recessed portion  12  illustrated in  FIG.  13    may be combined. 
     A head module  100  according to the present embodiment including the above-described liquid discharge head  200  is described below with reference to  FIGS.  14  to  16   .  FIG.  14    is an exploded perspective view of the head module  100 .  FIG.  15    is an exploded perspective view of the head module  100  viewed from a nozzle surface side, on which the plurality of nozzles  204  is disposed, of the head module  100 .  FIG.  16    is an exploded perspective view of the head  200 , a base  102 , and a cover  103  of the head module  100 . 
     The head module  100  includes a plurality of heads  200  as liquid discharge heads to discharge liquid, the base  102 , the cover  103 , a heat radiator  104 , a manifold  105 , a printed circuit board (PCB)  106 , and a module case  107 . In the present embodiment, the head module  100  includes eight heads  200  as an example, but embodiments of the present disclosure are not limited thereto. The PCB  106  and the piezoelectric element of the head  200  are connected via the flexible wiring member  260 . 
     In the present embodiment, the plurality of heads  200  are mounted with a space therebetween onto the base  102 . The head  200  is inserted into an opening  121  in the base  102 , and the peripheral end of the nozzle plate  201  of the head  200  is bonded to the cover  103  bonded and secured to the base  102  to attach the head  200  to the base  102 . A flange  70   a  provided outside the head  200  is bonded and secured to the base  102 . The head  200  is secured to the base  102  by, but not limited to, bonding, swaging, crimping, riveting, screwing, or the like. 
     An example of a liquid discharge apparatus according to the present embodiment is described below with reference to  FIGS.  17  and  18   .  FIG.  17    is a schematic view of the liquid discharge apparatus.  FIG.  18    is a plan view of a head unit of the liquid discharge apparatus illustrated in  FIG.  17   . 
     The printer  500  as a liquid discharge apparatus includes a loading device  501 , a guide conveyor  503 , a printing device  505 , a drying device  507 , and an ejection device  509 . The loading device  501  carries a continuous medium  510  such as continuous paper or a continuous sheet into the printer  500 . The guide conveyor  503  guides and conveys the continuous medium  510  from the loading device  501  to the printing device  505 . The printing device  505  discharges liquid onto the continuous medium  510  to form (print) an image. The drying device  507  dries the continuous medium  510 . The ejection device  509  carries out the continuous medium  510 . 
     The continuous medium  510  is fed from a winding roller  511  of the loading device  501  to the downstream side. Then, the continuous medium  510  is guided and conveyed with rollers of the loading device  501 , the guide conveyor  503 , the drying device  507 , and the ejection device  509 , and wound around a take-up roller  591  of the ejection device  509 . In the printing device  505 , the continuous medium  510  is conveyed on a conveyance guide  559  so as to face ahead unit  550 . The head unit  550  discharges liquid onto the continuous medium  510  to form an image. 
     As illustrated in  FIG.  18   , the head unit  550  includes two head modules  100 A and  100 B according to the present embodiment on a common base  552 . The head module  100 A includes head arrays  1 A 1 ,  1 A 2 ,  1 B 1 , and  1 B 2 . Each of the head arrays  1 A 1 ,  1 A 2 ,  1 B 1 , and  1 B 2  includes multiple liquid discharge heads  200  (two heads  200  in the present embodiment) arranged in a head array direction perpendicular to a conveyance direction of the sheet P indicated by arrow D in  FIG.  18   . The head module  100 B includes head arrays  1 C 1 ,  1 C 2 ,  1 D 1 , and  1 D 2 . Each of the head arrays  1 C 1 ,  1 C 2 ,  1 D 1 , and  1 D 2  includes multiple liquid discharge heads  200  arranged in the head array direction perpendicular to the conveyance direction of the sheet P. The head arrays  1 A 1  and  1 A 2  of the head module  100 A discharge liquid of the same color. Similarly, the head arrays  1 B 1  and  1 B 2  of the head module  100 A are grouped as one set and discharge liquid of the same desired color. The head arrays  1 C 1  and  1 C 2  of the head module  100 B are grouped as one set and discharge liquid of the same desired color. The head arrays  1 D 1  and  1 D 2  of the head module  100 B are grouped as one set and discharge liquid of the same desired color. 
     The head module according to the present disclosure can be formed together with functional parts and mechanisms as a single unit (integrated unit) to construct a liquid discharge unit. For example, the head module may be combined with at least one of the configurations of a head tank, a carriage, a supply unit, a maintenance unit, a main scanning moving unit, or a liquid circulation device. 
     Examples of the “single unit” include a combination in which the head module and one or more functional parts and mechanisms are secured to each other through, e.g., fastening, bonding, or engaging, and a combination in which one of the head module and the functional parts and mechanisms is movably held by another. Further, the head module, the functional parts, and the mechanisms may be detachably attached to each other. 
     The term “liquid discharge apparatus” used in the present disclosure includes an apparatus including the head module or the liquid discharge unit to drive the liquid discharge head to discharge liquid. The term “liquid discharge apparatus” used here includes, in addition to apparatuses to discharge liquid to materials onto which liquid can adhere, apparatuses to discharge the liquid into gas (air) or liquid. 
     The “liquid discharge apparatus” may further include devices relating to feeding, conveying, and ejecting of the material onto which liquid can adhere and also include a pretreatment device and an aftertreatment device. 
     The “liquid discharge apparatus” may be, for example, an image forming apparatus to form an image on a sheet by discharging ink, or a three-dimensional apparatus to discharge fabrication liquid to a powder layer in which powder material is formed in layers to form a three-dimensional object. 
     The “liquid discharge apparatus” is not limited to an apparatus that discharges liquid to visualize meaningful images such as letters or figures. For example, the liquid discharge apparatus may be an apparatus that forms meaningless images such as meaningless patterns or an apparatus that fabricates three-dimensional images. 
     The above-described term “material onto which liquid can adhere” represents a material on which liquid is at least temporarily adhered, a material on which liquid is adhered and fixed, or a material into which liquid is adhered to permeate. Specific examples of the “material onto which liquid can adhere” include, but are not limited to, a recording medium such as a paper sheet, recording paper, a recording sheet of paper, a film, or cloth, an electronic component such as an electronic substrate or a piezoelectric element, and a medium such as layered powder, an organ model, or a testing cell. The “material onto which liquid can adhere” includes any material to which liquid adheres, unless particularly limited. 
     Examples of the “material onto which liquid can adhere” include any materials to which liquid can adhere even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic. 
     The term “liquid discharge apparatus” may be an apparatus to relatively move the liquid discharge head and the material onto which liquid can adhere. However, the liquid discharge apparatus is not limited to such an apparatus. For example, the liquid discharge apparatus may be a serial head apparatus that moves the liquid discharge head or a line head apparatus that does not move the liquid discharge head. 
     Examples of the liquid discharge apparatus further include: a treatment liquid applying apparatus that discharges a treatment liquid onto a paper sheet to apply the treatment liquid to the surface of the paper sheet, for reforming the surface of the paper sheet, and an injection granulation apparatus that injects a composition liquid, in which a raw material is dispersed in a solution, through a nozzle to granulate fine particle of the raw material. 
     Liquid to be discharged through the nozzles of the liquid discharge head is not limited to a particular liquid as long as the liquid has a viscosity or surface tension to be discharged from the liquid discharge head. However, preferably, the viscosity of the liquid is not greater than 30 mPa·s under ordinary temperature and ordinary pressure or by heating or cooling. Examples of the liquid include a solution, a suspension, or an emulsion including, for example, a solvent, such as water or an organic solvent, a colorant, such as dye or pigment, a functional material, such as a polymerizable compound, a resin, or a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, and an edible material, such as a natural colorant. Such a solution, a suspension, or an emulsion can be used for, e.g., inkjet ink; surface treatment liquid; a liquid for forming an electronic element component, a light-emitting element component, or an electronic circuit resist pattern; or a material solution for three-dimensional fabrication. 
     Examples of an energy source for generating energy to discharge liquid include a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal actuator that employs a thermoelectric conversion element, such as a thermal resistor, and an electrostatic actuator including a diaphragm and a counter electrode. 
     The terms “image formation,” “recording,” “printing,” “image printing,” and “fabricating” used in the present embodiments may be used synonymously with each other. 
     Although the several embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and various modifications and changes can be made without departing from the scope of the present disclosure. 
     In the above-described embodiments, examples of the first component and the second component of the liquid discharge head are the actuator substrate  220  and the nozzle plate  201 , respectively, but the present disclosure is not limited thereto. Examples of the first component and the second component include a channel substrate, a diaphragm plate, a common-chamber substrate, a frame, and other components of the liquid discharge head to be bonded to each other. Further, the present disclosure is not limited to the liquid discharge head in which the first component and the second component are bonded to each other, and can be applied to other bonded units in which a first component and a second component are bonded to each other. 
     In the above-described embodiment, the recess is disposed only on the first component, but the recess may be disposed on both the first component and the second component. 
     As described above, according to the present disclosure, the components can be appropriately bonded to each other. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.