Patent Publication Number: US-2010118089-A1

Title: Droplet discharging head with a through hole having a protrusion on a surface, droplet discharging device and a functional-film forming device

Description:
This is a Continuation of application Ser. No. 11/677,160 filed Feb. 21, 2007. The disclosure of the prior application is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     Several aspects of the present invention relate to a droplet discharging head, a droplet discharging device and a functional-film forming device. 
     2. Related Art 
     A droplet discharging device with an inkjet head is increasingly used as a functional-film forming device for industrial use, in addition to its use for printing letters and images by means of an image forming device such as an inkjet printer. Specifically, a functional-film forming device is used for discharging liquid materials including organic and inorganic materials in order to form, for example, a functional film such as a semiconductor film, a conductive film or an insulating film on a substrate. 
     JP-A-2002-127430 is an example of related art, disclosing a technology that concerns an inkjet head to improve the landing precision of ink. 
     However, when viscosity increases in a liquid material discharged from the droplet discharging device, the straight moving property of the discharged droplet deteriorates, thus reducing its landing precision. 
     SUMMARY 
     An advantage of the present invention is to provide a droplet discharging head, a droplet discharging device and a functional-film forming device that are capable of enhancing the landing precision. 
     A droplet discharging head according to a first aspect of the invention includes a first through hole having an outlet for discharging of a liquid material and a second through hole having an inlet for injection of the liquid material. The second through hole is provided with protrusions on its surface. 
     A droplet discharging head according to a second aspect of the invention includes (1) a base body that includes a cavity for holding of a liquid material and a nozzle portion for discharging of the liquid material from the cavity, the cavity and the nozzle portion having been formed in the base body, and (2) a control portion that is placed on the cavity and controls the discharging of the liquid material. The nozzle portion includes a first through hole with an outlet for discharging of the liquid material and a second through hole with an inlet for injection thereof. The second through hole has a plurality of protrusions formed on its surface. 
     This enhances, through the rectifying effect of the protrusions, the straight moving property of the liquid material flowing in the nozzle portion, thereby improving the landing precision of the droplets discharged from the outlet even in cases where the liquid material being discharged has a relatively high viscosity, as in the case of an organic solvent, a high polymer material, or the like. 
     In the above droplet discharging head, it is preferable that the sectional area of the protrusions be larger toward the outlet than toward the inlet. This enhances the rectifying effect. 
     In the above droplet discharging head, it is preferable that the second through hole have a tapered shape. 
     In the above droplet discharging head, it is preferable that the second through hole have a columnar shape. 
     A droplet discharging head according to a third aspect of the invention has a through hole that includes an outlet for discharging of a liquid material and an inlet for injection thereof. The through hole has protrusions on its surface, the protrusions each having a larger sectional area toward the outlet than toward the inlet. 
     A droplet discharging head according to a fourth aspect of the invention has (1) a base body that includes a cavity for holding of a liquid material and a nozzle portion for discharging of the liquid material from the cavity, the cavity and the nozzle portion having been formed in the base body, and (2) a control portion that is placed on the cavity and controls the discharging of the liquid material. The nozzle portion has an outlet for discharging of the liquid material and an inlet for injection thereof and is provided with protrusions on its surface, the protrusions each having a larger sectional area toward the outlet than toward the inlet. 
     This enhances, through the rectifying effect of the protrusions, the straight moving property of the liquid material flowing in the nozzle portion, thereby improving the landing precision of the droplets discharged from the outlet even in cases where the liquid material being discharged has a relatively high viscosity, as in the case of an organic solvent, a high polymer material, or the like. The protrusions provided at the outlet fixes the form of the droplets at the time when they are discharged so that their straight moving property is enhanced. 
     In the above droplet discharging head, it is preferable that the protrusions be formed in such a manner that their cross sections perpendicular to the flow path of the liquid material are symmetric in shape with respect to the lines passing through the center of the flow path. 
     In the above droplet discharging head, the protrusions may be formed in such a manner that their cross sections have a shape that includes an acute angle 
     In the above droplet discharging head, the rectifying effect can be improved by forming each of the protrusions in a straight line running from its end at the inlet through to its other end at the outlet. 
     Alternatively, each of the protrusions may be formed in such a manner that its end at the inlet and its other end at the outlet are in a positional relationship that is out of alignment by an angle of 90 degrees. 
     In the above droplet discharging head, it is preferable that the control portion be a piezoelectric element that changes the volume of the cavity. 
     In the above droplet discharging head, it is preferable that the control portion be a heater that heats the cavity. 
     A droplet discharging device according to a fifth aspect of the invention is provided with the above droplet discharging head. 
     A functional-film forming device according to a sixth aspect of the invention is provided with the above droplet discharging head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a sectional view schematically showing the structure of a droplet discharging head according to one embodiment of the invention. 
         FIG. 2  is a schematic showing the structure of a droplet discharging device according to one embodiment of the invention. 
         FIG. 3A  is a schematic showing a section, being parallel to the flow path of droplets, of a nozzle portion in a droplet discharging head according to a first embodiment of the invention. 
         FIG. 3B  is a plan view schematically showing the nozzle portion when it is observed from the direction a shown in  FIG. 3A . 
         FIG. 4A  is a schematic showing a section, being parallel to the flow path of droplets, of a nozzle portion in a droplet discharging head according to a modification of the first embodiment. 
         FIG. 4B  is a plan view schematically showing the nozzle portion when it is observed from the direction a shown in  FIG. 4A . 
         FIG. 5A  is a schematic showing a section, being parallel to the flow path of droplets, of a nozzle portion of a droplet discharging head according to a second embodiment of the invention. 
         FIG. 5B  is a plan view schematically showing the nozzle portion when it is observed from the direction a shown in  FIG. 5A . 
         FIG. 6A  is a schematic showing a section, being parallel to the flow path of droplets, of a nozzle portion of a droplet discharging head according to a modification of the second embodiment. 
         FIG. 6B  is a plan view schematically showing the nozzle portion when it is observed from the direction a shown in  FIG. 6A . 
         FIG. 7A  is a sectional view schematically showing another example of the structure of the droplet discharging head according to one embodiment of the invention. 
         FIG. 7B  is a sectional view schematically showing details of a control portion according to the above example. 
         FIG. 8A  is a sectional view schematically showing another example of the shape of an inner nozzle hole  102  of a droplet discharging head according to one embodiment of the invention. 
         FIG. 8B  is a plan view schematically showing the inner nozzle hole  102  of the above example when it is observed from the direction a shown in  FIG. 8A . 
         FIG. 9A  is a schematic showing a section, being parallel to the flow path of droplets, of a nozzle portion of a droplet discharging head according to a fourth embodiment of the invention. 
         FIG. 9B  is a plan view schematically showing the nozzle portion of the fourth embodiment when it is observed from the direction a shown in  FIG. 9A . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the invention will be described. 
     First Embodiment 
       FIG. 1  schematically shows the structure of a droplet discharging head  10  according to a first embodiment of the invention in its sectional view. 
     As shown in  FIG. 1 , the droplet discharging head  10  is provided with a nozzle plate  11 , a flow path substrate  12 , a diaphragm  13 , a piezo (piezoelectric element)  14  and an electrode  19 . For example, a nozzle portion  100  is formed in the nozzle plate  11  while a cavity  17  and a reservoir  18  are formed in the flow path substrate  12 . The nozzle plate  11  and the flow path substrate  12  may be formed either separately or integrally. 
     Here, the nozzle portion  100  represents part of a base body having a structure to discharge a liquid material, which includes the nozzle plate  11 , and mainly refers to the part which the liquid material lastly passes through before it is discharged. It does not always take the form of a through hole, but in  FIG. 1  it forms a through hole. 
     On the other hand, the cavity  17  represents part of a base body having a structure to hold a liquid material, which includes the flow path substrate  12 , and mainly refers to the part that is changed in volume by the electrostrictive effect of the piezoelectric element. 
     The droplet discharging head  10  is placed, for example, in a head unit portion (represented by A in  FIG. 2 ) of a droplet discharging device shown in  FIG. 2 . The droplet discharging device is used not only for the discharging of image forming inks but also for the discharging of functional-film forming inks employed in a variety of industrial uses including, for example, the discharging of organic solvents onto silicon substrates or the discharging of high polymer materials. Functional-film forming inks including organic solvents and high polymer materials typically are liquid materials having a high viscosity as compared to image forming inks. 
     A liquid material, being brought from an external feeding unit into the droplet discharging head  10  via a material inlet (not illustrated), fills the space forming the reservoir  18 , the cavity  17  and the nozzle portion  100 . Subsequently, electric signals, being propagated from the electrode  19  to the piezo  14 , causes a flexure to occur in the piezo  14  and the diaphragm  13 , increasing the pressure inside the cavity  17  for a moment, thereby causing droplets to be discharged from the nozzle hole of the nozzle portion  100 . 
       FIGS. 3A and 3B  schematically show the shape of the nozzle portion  100  in the droplet discharging head  10  in its sectional views,  FIG. 3A  showing a section that is parallel to the flow path of the liquid material and  FIG. 3B  representing a plan view observed from the direction a shown in  FIG. 3A . 
     As shown in  FIGS. 3A and 3B , the nozzle portion  100  includes an outer nozzle hole (first through hole)  101  and an inner nozzle hole (second through hole)  102 . The outer nozzle hole  101  has a droplet outlet  103  for discharging of droplets toward outside. The inner nozzle hole  102  has a droplet inlet  104  that leads to the cavity  17 . 
     On the inside wall of the inner nozzle hole  102 , protrusions  105  are formed. The protrusions  105  have an advantageous effect of rectifying the liquid material flowing in the inner nozzle hole  102 . 
     The protrusions  105  are formed in such a manner that the areas of their cross sections shown in  FIG. 3B  are the larger, the nearer the cross sections are to the droplet outlet  103 . In addition, as the figure shows, the end portions b of the cross sections have a triangular shape with an acute angle (preferably 60° or less). 
     The protrusions  105  are arranged in such a manner that their positions divide the inner circumference of the inner nozzle hole  102  into quarters. The number of the protrusions  105  is not limited to four, but it is preferable that the cross section of the inner nozzle hole  102 , which is perpendicular to the flow path of the liquid material, have a symmetric shape with respect to the lines passing through the center of the flow path. 
     Meanwhile, a broken line  106  in  FIG. 3B  shows a cross section of the outer nozzle hole  101 . In  FIG. 3B , the protrusions  105  are placed in the inner nozzle hole  102  without overlapping the outer nozzle hole  101 . 
     The nozzle portion  100  according to the first embodiment can be formed by electroforming using nickel, cobalt, manganese or alloys of those metals. Alternatively, the nozzle plate  11  and the flow-path forming substrate  12  may be integrally formed by photolithography using a silicon substrate. Whereas it is preferable that the protrusions  105  be 10 to 20 μm thick, those with thinner shapes are more easily formed by electroforming while thicker ones are more easily formed by photolithography. 
       FIGS. 4A and 4B  are sectional views showing the shape of the nozzle portion  100  in the droplet discharging head  10  according to a modification of the first embodiment.  FIG. 4A  is a schematic showing its section that is parallel to the flow path of the liquid material, and  FIG. 4B  is a plan view of its cross section observed from the direction a shown in Fig. A. 
     The nozzle portion  100  shown in  FIGS. 3A and 3B  and the nozzle portion  100  shown in  FIGS. 4A and 4B  are of different shapes. 
     In the example of  FIGS. 4A and 4B , the protrusions  105  are formed in such a way that their cross sections being perpendicular to the flow path each has a constant dimension. Furthermore, the end portions b of the cross sections each has a quadrangular shape, as shown therein. The protrusions  105  are arranged in such a manner that their positions divide the inner circumference of the inner nozzle hole  102  into quarters, but the number of the protrusions  105  is not limited to four. It is preferable that a cross section of the inner nozzle hole  102 , being perpendicular to the flow path of the liquid material, be of a symmetric shape with respect to the lines passing through the center of the flow path. Meanwhile, the broken line  106  in  FIG. 4B  shows the cross section of the outer nozzle hole  101 . In  FIG. 4B , the protrusions  105  are located in the inner nozzle hole  102  without overlapping the outer nozzle hole  101 . The protrusions  105  shown in  FIGS. 4A ,  4 B have a shape that allows them to be formed more easily by photolithography, as compared with the protrusions in  FIGS. 3A ,  3 B. 
     The first embodiment of the invention allows the straight moving property of the liquid material flowing in the nozzle portion  100  to be enhanced by the rectifying effect of the protrusions  105  provided on the inside wall of the inner nozzle hole  102 . Consequently, the embodiment allows the landing precision of droplets discharged from the droplet outlet  103  to be improved even in cases where the droplets being discharged are made of a liquid material with a relatively high viscosity, as in the case of an organic solvent or a high polymer material. It is also effective for discharging of smaller droplets. 
     The droplet discharging head  10  according to the first embodiment employs the piezo  14  as a control portion for discharging of the liquid material from the nozzle hole. However, the control portion is not limited to the piezo alone. Any other portion may be employed if it discharges a liquid material. For example, as shown in  FIGS. 7A and 7B , the control portion may be one using a heater  20 . In this case, as shown in  FIG. 7B , the heater  20  heats the cavity  17 , creating a bubble  21  in the liquid material in the cavity  17 , thereby causing droplets  22  to be discharged from the droplet outlet  103 . 
     Second Embodiment 
       FIGS. 5A and 5B  show the shape of the nozzle portion  100  of the droplet discharging head  101  in its sectional views.  FIG. 5A  is a schematic of its section that is parallel to the flow path of the liquid material and  FIG. 5B  is a plan view of its cross section observed from the direction a shown in  FIG. 5A . 
     In the second embodiment, the protrusions  105  are provided on the inside wall of the outer nozzle hole  101  in the nozzle portion  100 . The protrusions  105  are formed in such a way that the area of each of their cross sections is the larger, the nearer the cross sections are to the droplet outlet  103 . The end portions b have a triangular shape with an acute angle (preferably 60° or less). 
     Furthermore, the protrusions  105  are arranged in such a manner that their positions divide the inner circumference of the outer nozzle hole  101  into quarters. The number of the protrusions  105  is not limited to four, but it is preferable that their cross sections perpendicular to the flow path of the liquid material in the droplet discharging head  10  be of a symmetric shape with respect to the lines passing through the center of the flow path of the liquid material. 
     The nozzle portion  100  can be formed by electroforming with a metal such as nickel, cobalt, manganese or an alloy of those metals, in the same way as in the first embodiment. Alternatively, it may be integrally formed on a silicon substrate forming the nozzle plate  11  by means of photolithography. Whereas it is preferable that the protrusions  105  have a thickness of 10 to 20 μm, those with thinner shapes are more easily formed by electroforming while thicker ones are more easily formed by photolithography. 
     Furthermore,  FIGS. 6A and 6B  show, in sectional views, the shape of the nozzle portion  100  in the droplet discharging head  10  according to a modification of the second embodiment.  FIG. 6A  shows its section that is parallel to the flow path of the liquid material, while  FIG. 6B  is its plan view observed from the direction a shown in  FIG. 6A . 
     The nozzle portion  100  in  FIGS. 5A and 5B  and the nozzle portion  100  in  FIGS. 6A and 6B  are of different shapes. 
     In the example of  FIGS. 6A and 6B , the protrusions  105  are formed in such a manner that each of their cross sections being perpendicular to the flow path has a constant dimension. Furthermore, as shown in  FIG. 6B , the end portion b of each of the cross sections is in a quadrangular shape. The protrusions  105  are arranged in such a way that their positions divide the inner circumference of the outer nozzle hole  101  into quarters, but the number of the protrusions  105  is not limited to four. It is preferable that the cross section of the outer nozzle hole  101 , being perpendicular to the flow path of the liquid material, have a symmetric shape with respect to the lines passing through the center of the flow path of the liquid material. The shape of the protrusions  105  shown in  FIGS. 6A and 6B  facilitates their formation by photolithography, as compared with the shape of those in  FIGS. 5A and 5B . 
     The second embodiment of the invention allows the straight moving property of the liquid material to be enhanced, because its flow in the nozzle portion  100  is rectified by the protrusions  105  provided on the inside wall of the outer nozzle hole  101 . Thus, the embodiment allows the landing precision of droplets discharged from the droplet outlet  103  to be improved even in cases where the liquid material being discharged has a relatively high viscosity or elasticity, as in the case of an organic solvent or a high polymer material. It is also effective for discharging of smaller droplets. In addition, provision of the protrusions  105  at the droplet outlet  103  enhances the straight moving property of droplets, because the droplets are rectified at the droplet outlet  103  at the time when they are discharged. 
     Third Embodiment 
     The protrusions  105  are formed only in the inner nozzle hole  102  in the first embodiment, and only in the outer nozzle hole  101  in the second embodiment, but the protrusions  105  may be provided along the entire length of the inside wall of the nozzle portion  100 , all through the outer nozzle hole  101  and the inner nozzle hole  102 . 
     In a third embodiment, as well, the protrusions  105  are formed in such a way that the area of each of their cross sections is the larger, the nearer the cross sections are to the droplet outlet  103 , as in the examples of  FIGS. 3A and 3B  as well as  FIGS. 5A and 5B . Or, the protrusions  105  are formed in such a manner that their cross sections perpendicular to the flow path are of a constant dimension, as in the examples of  FIGS. 4A and 4B  as well as  FIGS. 6A and 6B . The end portions b of the cross sections may each has a triangular shape with an acute angle (preferably 60° or less), as in the examples of  FIGS. 3A and 3B  as well as  FIGS. 5A and 5B , or a quadrangular shape, as in the examples of  FIGS. 4A and 4B  as well as  FIGS. 6A and 6B . End portions having a curved section are also effective. 
     The number of the protrusions  105  may be any, but it is preferable that the cross section of the nozzle portion  100 , being perpendicular to the flow path of the liquid material, be in a symmetric shape with respect to the lines passing through the center of the flow path of the liquid material. 
     The protrusions  105  are allowed to have a higher rectifying effect if they are made to form straight lines running from the droplet outlet  103  through to the droplet inlet  104 . That means, it is preferable that the protrusions  105  provided in the outer nozzle hole  101  and the protrusions  105  provided in the inner nozzle hole  102  be arranged in alignment with each other. 
     Alternatively, the protrusions  105  may be each formed in such a manner that an end thereof at the droplet outlet  103  and another end thereof at the droplet inlet  104  are in a positional relationship that is out of alignment by an angle of 90 degrees. That is, the protrusions  105  provided in the outer nozzle hole  101  and the protrusions  105  provided in the inner nozzle hole  102  are arranged to be in a positional relationship forming an angle of 90 degrees with each other. 
     In each of the embodiments described above, the outer nozzle hole  101  and the inner nozzle hole  102  are each in a columnar shape, but their shapes are not limited to columnar shapes. For example, as shown in  FIGS. 8A and 8B , the inner nozzle hole  102  may have a tapered shape. In this case, the inner nozzle hole  102  gradually becomes smaller in diameter from the cavity  17  toward the droplet outlet  103 . Therefore, it is not necessary here that the protrusions  105  are formed in such a way that their cross sections perpendicular to the flow path grows larger in diameter toward the droplet outlet  103 . 
     Fourth Embodiment 
     A fourth embodiment of the invention is a modification of the first embodiment.  FIGS. 9A and 9B  show the shapes of sections of the nozzle portion  100  in the droplet discharging head  10  according to the fourth embodiment.  FIG. 9A  is a schematic of its section that is parallel to the flow path of the liquid material, and  FIG. 9B  is a plan view showing its cross section observed from the direction a shown in  FIG. 9A . 
     The nozzle portion  100  shown in  FIGS. 9A and 9B  have protrusions  105  of a shape that is different from the shape of the protrusions in the nozzle portion  100  of the first embodiment shown in  FIGS. 3A and 3B . Namely, the protrusions  105  in  FIGS. 9A and 9B  stick out to overlap the broken line  106  that represents the cross section of the outer nozzle  101 . That means that the protrusions  105  are arranged in such a manner that their cross sections perpendicular to the flow path form together an internal diameter that is smaller than the internal diameter of the outer nozzle  101 . This reduces the shift in volume occurring at the border between the outer nozzle  101  and the inner nozzle  102 , thereby further enhancing the stability of the discharging of droplets. 
     The entire disclosure of Japanese Patent Application Nos: 2006-052466, filed Feb. 28, 2006 and 2006-302546, filed Nov. 8, 2006 are expressly incorporated by reference herein.