BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially cut-out perspective view of main parts of a printing head according to a first embodiment of the present invention;
Each of FIGS. 2A, 2B, 2C, 2D, and 2E is an explanatory view of an ejecting process of a liquid at the printing head of FIG. 1;
FIG. 3 is an explanatory view of an inclination angle of an ejection port at the printing head of FIG. 1;
FIG. 4 is an explanatory view of an ejecting direction of the liquid at the printing head of FIG. 1;
Each of FIGS. 5A, 5B, and 5C is an explanatory view of landing positions of droplets ejected from the printing head of FIG. 1;
FIG. 6 is an exploded perspective view of the printing head of FIG. 1;
FIG. 7 is a schematic front view of an ink jet printing apparatus having the printing head of FIG. 1;
Each of FIGS. 8A, 8B, 8C, 8D, and 8E is an explanatory view of an ejecting process of a liquid at a printing head according to a second embodiment of the present invention;
Each of FIGS. 9A, 9B, 9C, 9D, and 9E is an explanatory view of an ejecting process of a liquid at a printing head of a conventional art;
Each of FIGS. 10A, 10B, and 10C is an explanatory view of landing positions of droplets ejected from the printing head of FIG. 9A;
FIG. 11 is an explanatory view of a printing example printed by a serial scan type ink jet printing apparatus using the printing head of FIG. 9A; and
Each of FIGS. 12A and 12B is an explanatory view of a printing example printed by a full line type ink jet printing apparatus using the printing head of FIG. 9A.
DESCRIPTION OF THE EMBODIMENTS
The present invention will now be described based on the drawings.
First Embodiment
FIG. 6 is an exploded perspective view of a printing head according to a first embodiment of the present invention. The printing head of the present embodiment is used in an ink jet printing apparatus as a printing head 110 for ejecting a liquid ink. Reference numeral 111 denotes an ejecting element equipped with an electro-thermal converter (air bubble generating device), a common liquid chamber, a flow path, an ejection port, etc., as described below, and 112 denotes a ceramic plate arranged with an electric wiring board as described below. The common liquid chamber in the ejecting element 111 is connected to a plurality of flow paths provided inside of flow path forming members. An ink is supplied to an ink supply port of the flow path forming members from an ink tank not shown. A plurality of nozzles are formed in alignment with flow paths, ejection ports, electro-thermal converters (air bubble generating devices), etc. The ink introduced into the common liquid chamber from the ink supply port is ejected from the ejection port of each nozzle.
FIG. 7 is a schematic front view of a full line type ink jet printing apparatus 120 capable of printing an image using the printing head 110. The printing apparatus 120 is provided with a conveying portion 121 that conveys a printing medium W such as paper in the conveying direction of an arrow Y1 and a feeding portion 122 that supplies the printing medium W to the conveying portion 121. Six printing heads 110 are removably mounted on the printing apparatus 120 of the present embodiment. Inks of yellow (Y), light magenta (LM), magenta (M), light cyan (LC), cyan (C), and black (K) from corresponding cartridges 123 are supplied to these printing heads 110. The six printing heads 110 are placed deviated in the conveying direction of the printing medium W. A nozzle alignment of each printing head 110 extends in an intersecting direction (perpendicular direction in the present embodiment) against the conveying direction of the printing medium W.
Reference numeral 124 denotes a recovering unit that conducts a recovering process to maintain a good ejecting state of the ink of the printing head 110. The recovering process may include, for example, a process for suction-ejecting or pressure-ejecting the ink that do not contribute to the printing of an image from the ejection port and a process for ejecting (preliminary-ejection) the ink that do not contribute to the printing of the image from the ejection port. The recovering process may further include a process for wiping an ejection port face (face where the ejection port is located) of the printing head 110. Reference numeral 125 denotes an operation panel portion for operating the printing apparatus 12.
FIG. 1 is a partially cut-out perspective view of a part near the nozzle of the printing head 110.
A plurality of heaters (electro-thermal converters) 2 for heating and foaming ink are placed on a heater board 1. Resistors such as tantalum nitride are used for the heaters 2 whose thickness, for example, is 0.01 to 0.5 μm, and whose sheet resistance value is 10 to 300 O per unit square. Electrodes (not shown) of aluminum for conduction are connected to the heaters 2. On the one side of the electrodes, switching transistors (not shown) for controlling the conduction with the heaters 2 are connected. The switch transistors are drive controlled by IC composed of circuits of gate devices for controlling, etc., and control the heaters 2 in accordance with signals from the printing apparatus.
The heaters 2 are formed at each of a plurality of flow paths 3. One end of each flow path 3 is communicated with a corresponding ejection port 4, and the other end of each flow path 3 is communicated with a common liquid chamber 5. The flow path 3 is surrounded by a heater board 1, nozzle walls 6, nozzle bank 7 of about 5-10 μm in thickness, and a top plate nozzle 8 of about 2 μm in thickness to form a tubular shape. In the present embodiment, the nozzle walls 6, the nozzle bank 7, and the top plate nozzle 8 are formed of photosensitive epoxy resin.
A movable valve 9 is provided in the flow path 3, and a free end 9A of the movable valve 9 is located near the ejection port 4, while the base end is located near the common liquid chamber 5. A supporting point at the base end of the movable valve 9 is attached to a valve supporting member 10, and the valve supporting member 10 is attached to the heater board 1 by a valve base 11 (see FIG. 2A). The top plate nozzle 8 is attached to a top plate 12 formed of Si, etc. At the top plate 12, an ink supply port not shown is formed by anisotropic etching, etc. A liquid ink is supplied into the common liquid chamber 5 from outside through the ink supply port, and the ink in the common liquid chamber 5 is supplied into each flow path 3.
An ejection port face F where the ejection ports 4 are located has a predetermined inclination of angle θ as follows.
As shown in FIG. 3, the ejection port face F is not perpendicular to the axis line (axis line of the nozzle) L1 of the flow path 3, but the normal line L2 of the ejection port face F and the axis line L1 incline at the angle θ. In other words, the ejection port face F is formed such that the normal line L2 intersects with the axis line L1 of the nozzle at the predetermined angle θ. The ejection port face F is inclined to face in the opposite direction (arrow Y2 direction) of the conveying direction Y1 of the printing medium W, i.e., to face in the relative moving direction of the printing head 110 with the printing medium W as a reference. Therefore, the ejection port face F is formed by inclining a face F0, which is perpendicular to the axis line L1, at the angle θ toward the relative moving direction (arrow Y2 direction) of the printing head 110. The size of the angle θ is established, as described below, taking into account the relative moving speed of the printing medium W and the printing head 10, etc.
FIGS. 2A to 2E are explanatory views of the ejecting process of droplets of the ink from the ejection port 4.
FIG. 2A illustrates a state before the ink in the flow path 3 is heated, i.e., a state of the heater 2 not energized. The ink near the ejection port 4 forms a meniscus M.
FIGS. 2B and 2C illustrate states of foam B generated with film boiling of ink, generated in the heated ink when the heater 2 is energized and heated. In this case, by the movable valve 9 shifting with the valve base 11 side as a supporting point, a propagation direction of the pressure based on the generation of the foam B is directed in the ejecting direction of the ink. The ink in the flow path 3 is ejected from ejection port 4 by the pressure generated by the foam and forms a liquid column such as the one shown in FIG. 2C as the foam B grows.
FIGS. 2D and 2E illustrate states of the foam B in the contraction process after the heating of the ink by the heater 2 has terminated. The ink near the ejection port 4 is drawn into the flow path 3 in accordance with the contraction of the foam B. Since the inertial force is acting in the ejecting direction at the tip portion of the liquid column, the liquid column is separated from the ink in the flow path 3. The separated liquid column forms main-droplet Dm and sub-droplet (satellite) Ds as a result of the surface tension of the ink and flies toward the printing medium.
The ejecting directions of such main-droplet Dm and sub-droplet Ds will be different as described below, since the ejection port face F is inclined at the predetermined angle θ.
As shown in FIGS. 2B and 2C, the meniscus M first starts to proceed in the ejection direction as the pressure generated by the foam propagates. This causes the ink near the ejection port 4 to be ejected from the ejection port 4 while maintaining the same contact angles a to the nozzle bank 7 and to the top plate nozzle 8 on the ejection port face F, as shown in FIG. 4. The angle defined by the ink ejection direction A1 and the axis line L1 of the flow path 3 will be the inclination angle θ of the ejection port face F as shown in FIG. 3. The ink near the ejection port 4 is ejected in the arrow A1 direction along the normal line L2 perpendicular to the ejection port face F, as shown in FIGS. 2B and 2C. The ink ejected in the arrow A1 direction will form the main-droplet Dm. On the other hand, as shown in FIGS. 2B and 2C, the ink located near the heater 2 is ejected in the arrow A2 direction along the axis line L1 direction of the flow path 3. The ink ejected in the arrow A2 direction will form the sub-droplet Ds.
As shown in FIG. 2D, the foam B enters into the contraction process, and the ink near the ejection port 4 is then drawn into the flow path 3 to form the main-droplet Dm and the sub-droplet Ds as shown in FIG. 2E. Since the directions of the main-droplet Dm and the sub-droplet Ds ejected by the foam are different, the main-droplet Dm flies in the arrow A1 direction (normal line L2 direction) at the angle θ with the axis line L1, and the sub-droplet Ds flies in the arrow A2 direction (axis line L1 direction), as shown in FIG. 2E.
The angle θ of the ejection port face F, i.e. the ejecting angle θ of the main-droplet Dm, is set in compliance with a configuration of the printing apparatus 120 having the printing head 110 or in compliance with control conditions. One example of a setting method of the angle θ will be described below based on FIGS. 5A, 5B, and 5C.
In this example, an ejecting speed of the main-droplet Dm is Vm, an ejecting speed of the sub-droplet Ds is Vs, a conveying speed of the printing medium W is Vf, and a distance between the ejection port 4 and the printing medium W is h. In a conventional printing head H in which an ejection port face is not inclined as shown in FIG. 10A, a deviation amount d in the landing positions of the main-droplet Dm and the sub-droplet Ds is shown by the following equation.
D={(1/Vs)−(1/Vm)}×h×Vf
In this case, the deviation amount d is generated in accordance with the ejecting speeds of the ink Vm and Vs, distance h, and conveying speed Vf, and the landing positions of the main-droplet Dm and the sub-droplet Ds cannot be made coincident.
On the other hand, according to the printing head 110 of the present embodiment, the landing positions of the main-droplet Dm and the sub-droplet Ds can be made coincident by setting the angle θ so as to satisfy conditions of the equation below.
[(1/Vs)−{1/(Vm·cos θ)}]×h×Vf=h·tan θ
The equation above is rearranged to derive the equation below.
(1/Vs)−{1/(Vm·cos θ)}=tan θ/Vf
High-quality image can be printed by setting the angle θ so as to satisfy the equation such as this to make coincident the landing positions of the main-droplet Dm and the sub-droplet Ds on the printing medium W.
Second Embodiment
The printing head 110 of the first embodiment described above is a so-called edge shooter type, and the ejecting direction of the ink and the supplying direction of the ink into the nozzle approximately coincide. However, the present invention can also be applied to a so-called side shooter type printing head. In the side shooter type printing head, the ejecting direction of the ink and the supplying direction of the ink into the nozzle are different.
FIGS. 8A to 8E are sectional views of main parts of the side shooter type printing head applying the present invention, and identical elements are designated with identical reference numerals in the above embodiment and will not be described.
The ejection port 4 is formed at a location of the top plate 12 facing the heater 2. The nozzle is formed by the heater 2, the flow path between the heater 2 and the ejection port 4, the ejection port 4, etc. The ejection port face F where the ejection port 5 is formed is inclined at the predetermined angle θ against the axis line L1 of the nozzle, as described in the above embodiment. The ink in the common liquid chamber 5 is supplied into the nozzle from the arrow C direction in FIG. 8E.
The printing head of the present example is capable of ejecting the ink utilizing the thermal energy of the heater 2, in the same way as the printing head in the above embodiment. As shown in FIGS. 8A to 8E, the ink in the nozzle is foamed by the heat of the heater 2, and the droplets of the ink can be ejected from the ejection port 4 by utilizing the foam energy of the air bubbles B at this time. Since the ejection port face F is inclined at the angel θ, the main-droplet Dm and the sub-droplet Ds ejected from the ejection port 4 are ejected in the same directions as stated in the above embodiment. In other words, the main-droplet Dm flies in the arrow A1 direction (normal line direction of the ejection port face) at the angle θ with the axis line L1, and the sub-droplet Ds flies in the arrow A2 direction (axis line L1 direction).
Thus, as in the embodiment above, high-quality image can be printed by making coincident the landing positions of the main-droplet Dm and the sub-droplet Ds on the printing medium W.
Other Embodiments
In addition to a printing head that ejects ink, the present invention can be applied to a printing head (liquid ejecting head) capable of ejecting various liquids used directly or indirectly for image printing. In addition, the ejecting method of the liquid of the printing head may be a method using an electro-thermal converter (heater), as well as a method using a piezo-element, etc. Furthermore, the movable valve 10 does not always have to be provided in an edge shooter type printing head such as the one described in the first embodiment.
The present invention can also be applied to the full line type ink jet printing apparatus shown in FIG. 7 as well as to the serial scan type ink jet printing apparatus described above. In either printing apparatus, as mentioned above, the ejection port only needs to be provided with a predetermined inclination angle in association with the relative moving direction of the head and the printing medium. In other words, the face (ejection port face F) on which the ejection port is formed only needs to be inclined such that the ejection port inclines and opens in the direction (arrow Y2) in which the head relatively moves against the printing medium. As a result, the axis line (L1) of the nozzle and the normal line (L2) of the ejection port face (F) where the ejection port is located are not coincident, but intersect at the predetermined angle instead.
In the foregoing embodiments, the nozzle walls 6, the nozzle bank 7, and the top plate nozzle 8 defining peripheral surfaces of the ejection port are made of the same material, and their physical characteristics are the same. However, among those peripheral surfaces, at least the top plate nozzle 8 in the arrow Y1 direction and the nozzle bank 7 in the arrow Y2 direction may be formed of the same material. Their physical characteristics may include at least one of wettability to liquid or surface roughness. In addition, as long as the physical characteristics are the same, the materials forming the peripheral parts of the ejection port may be different. Furthermore, an orifice plate in which an ejection port is formed may be attached to the aperture of the liquid flow path. Additionally, physical characteristics (including wettability to liquid) of the material forming the peripheral parts of the ejection port may be different, and in that case, the inclination angle of the ejection port only needs to be optimally set considering the difference in ejecting directions of the main-droplet and the sub-droplet resulting from the physical characteristics.
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 No. 2006-116101, filed Apr. 19, 2006, which is hereby incorporated by reference herein in its entirety.
Patent Application
20070247493
