1. Technical Field
The present invention relates to a liquid ejecting head and a liquid ejecting apparatus, and in particular, relates to a liquid ejecting head and a liquid ejecting apparatus that are used effectively when ink containing flat plate-like particles is discharged.
2. Related Art
As a representative example of liquid ejecting heads that are mounted on liquid ejecting apparatuses and discharge liquid through nozzles, known are ink jet recording heads that discharge ink droplets through the nozzles by using pressures generated by displacement of piezoelectric actuators, for example. The ink jet recording heads of this type have the following configuration generally. That is, the piezoelectric actuators are provided at one surface side of a flow path formation substrate on which pressure generation chambers communicating with the nozzles are formed, and the piezoelectric actuators are deformed to pressurize ink in the pressure generation chambers. With this, ink droplets are discharged through the nozzle.
Among such ink jet recording heads, there is an ink jet recording head that discharges metallic ink containing a metal pigment of flat plate-like particles in order to produce a printed matter having metal glossiness (for example, see JP-A-2007-46034).
In the ink jet recording head that discharges the metallic ink, when flow with the discharge is generated on a flow path in the head, even if viscosity of the metallic ink is equivalent to that of normal ink, a large number of flat plate-like particles as the metal pigment contained in the metallic ink disturb the flow in the flow path on a region in the vicinity of a wall surface of the flow path. Due to this, a thick boundary layer is formed. It is considered that the thick boundary layer is formed for the following manner. That is, the velocity gradient of the fluid on the region in the vicinity of the wall surface is increased. Then, the flat plate-like particles receive an asymmetric force due to the velocity gradient to move in the different direction from the flow direction as a rotational movement, for example. Because of this, the flow is further disturbed.
As a result of the formation of the thick boundary layer, there arises a problem that the wall surface resistance is increased and the discharge becomes unstable. The problem is described in detail as follows.
Then, a driving signal as illustrated in
However, when the piezoelectric actuators are driven with the driving signal S12 as illustrated in
It is to be noted that the above-mentioned problem occurs not only on the ink jet recording head but on the liquid ejecting heads for ejecting liquids other than ink as long as the liquids contain the flat plate-like particles as the pigment.
An advantage of some aspects of the invention is to provide a liquid ejecting head and a liquid ejecting apparatus that are capable of realizing liquid discharge stability even when liquid containing a pigment of flat plate-like particles is discharged and a drawing operation before main discharge is performed.
A liquid ejecting head according to an aspect of the invention includes a pressure generation chamber to which liquid containing a flat plate-like particle is filled, a pressure generation unit that generates pressure change on the liquid in the pressure generation chamber with supply of a driving signal, and a nozzle plate on which a nozzle for discharging the liquid in the pressure generation chamber with the pressure change is formed. In the liquid ejecting head, the nozzle includes at least a first nozzle portion that is formed at a side of a discharge surface of the liquid and a second nozzle portion that communicates with the first nozzle portion and is formed at a side of the pressure generation chamber, and the nozzle satisfies an expression of φ2/φ1≧1.4 when an opening diameter of the first nozzle portion at the side of the discharge surface is assumed to be φ1 and an opening diameter of the second nozzle portion at the side of the pressure generation chamber is assumed to be φ2.
According to the aspect of the invention, a boundary layer in the vicinity of the inner circumferential surface of the nozzle from the side of the pressure generation chamber to the side of the discharge end is made thinner so as to realize the smooth flow on the center portion. As a result, the metallic ink containing the flat plate-like particle as the pigment can be discharged preferably even when the metallic ink is drawn to the side of the pressure generation chamber once, and then, discharged.
In the aspect of the invention, it is preferable that a relation between the opening diameters φ1 and φ2 satisfy an expression of φ2/φ1≧1.6. Further, it is preferable that the flat plate-like particle satisfy an expression of b/a≧0.03 when the dimension of a diagonal line on a surface of the flat plate-like particle is assumed to be “a” and the thickness of the flat plate-like particle is assumed to be “b”.
A liquid ejecting apparatus according to another aspect of the invention includes the above-mentioned liquid ejecting head.
According to the aspect of the invention, liquid such as the metallic ink containing the flat plate-like particle can be discharged onto a medium preferably so as to contribute to the excellent printing of a printed matter or the like required to have constant glossiness preferably, for example.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, an embodiment of the invention is described in detail with reference to the accompanying drawings.
A driving force of a driving motor 6 is transmitted to the carriage 3 through a plurality of gears (not illustrated) and a timing belt 7. With this, the carriage 3 on which the recording head units 1A and 1B are mounted is moved along the carriage shaft 5. On the other hand, a platen 8 is provided on the apparatus main body 4 along the carriage shaft 5 and a recording sheet S as a recording medium, such as paper, which has been fed by a paper feeding roller (not illustrated in
As illustrated in
A nozzle plate 20 is made to adhere fixedly to one surface of the flow path formation substrate 11 at the opening surface side with an adhesive, a thermal welding film, or the like. Nozzles 21 communicating with the vicinity of the ends of the pressure generation chambers 12 at the side opposite to the ink supply paths 14 are bored on the nozzle plate 20. The nozzle plate 20 can be formed by a glass ceramic, a silicon single crystal substrate, a stainless steel, or the like preferably.
Each nozzle 21 in the embodiment is constituted as a two-stage nozzle having a first nozzle portion 21A and a second nozzle portion 21B as the nozzle portion and a portion in the vicinity thereof are illustrated in an enlarged manner as an example in
Returning to
Further, the first electrode 60, a piezoelectric layer 70, a second electrode 80 are formed on the adhesion layer 56 in a lamination manner so as to constitute each piezoelectric element 300. The piezoelectric layer 70 is a thin film having the thickness of equal to or smaller than 2 μm, preferably 0.3 to 1.5 μm. The piezoelectric element 300 corresponds to a pressure generation unit in the embodiment. The piezoelectric element 300 indicates a portion including the first electrode 60, the piezoelectric layer 70, and the second electrode 80. In general, each piezoelectric element 300 is configured such that one of the electrodes included in the piezoelectric element 300 is set as a common electrode and the other thereof and the piezoelectric layer 70 are patterned for each pressure generation chamber 12. In the embodiment, the first electrode 60 is set as the common electrode to the piezoelectric elements 300 and the second electrodes 80 are set as individual electrodes of the piezoelectric elements 300. There arises no problem even if these electrodes are inversed for convenience of driving circuits and wirings. The piezoelectric elements 300 and a vibrating plate that is displaced by driving of the piezoelectric elements 300 are collectively referred to as an actuator device. In the above-mentioned example, the elastic film 50, the adhesion layer 56, the first electrode 60, and the insulating film provided if necessary act as the vibrating plate. It is needless to say that the vibrating plate is not limited thereto. For example, the elastic film 50 and the adhesion layer 56 may not be provided. Alternatively, the piezoelectric elements 300 themselves may also serve as the vibrating plate substantively.
Lead electrodes 90 are connected to the second electrodes 80 as the individual electrodes of the piezoelectric elements 300. The lead electrodes 90 are drawn from the vicinity of the end portions of the second electrodes 80 at the side of the ink supply paths 14 so as to extend onto the elastic film 50 or the insulating film provided if necessary. The lead electrodes 90 are made of gold (Au), for example.
The protection substrate 30 is bonded onto the flow path formation substrate 11 on which the piezoelectric elements 300 are formed with an adhesive 35. That is to say, the protection substrate 30 is bonded onto the first electrode 60, the elastic film 50, the insulating film provided if necessary, and the lead electrodes 90. The protection substrate 30 has the manifold portion 31 constituting at least a part of the manifold 100. In the embodiment, the manifold portion 31 penetrates through the protection substrate 30 in the thickness direction and is formed over the width direction of the pressure generation chambers 12. As described above, the manifold portion 31 communicates with the communicating portion 13 of the flow path formation substrate 11 so as to constitute the manifold 100 as the ink chamber common to the respective pressure generation chambers 12. Further, the communicating portion 13 of the flow path formation substrate 11 may be divided for the respective pressure generation chambers 12 and only the manifold portion 31 may be constituted as the manifold. Further, only the pressure generation chambers 12 may be provided on the flow path formation substrate 11, for example. In this case, the ink supply paths 14 communicating the manifold 100 and the respective pressure generation chambers 12 may be provided on a member (for example, the elastic film 50, the insulating film provided if necessary, or the like) interposed between the flow path formation substrate 11 and the protection substrate 30.
A piezoelectric element holding portion 32 is provided on the protection substrate 30 on a region opposed to the piezoelectric elements 300. The piezoelectric element holding portion 32 may have a space so as not only to inhibit the motion of the piezoelectric elements 300. It is sufficient that the piezoelectric element holding portion 32 may have a space so as not to inhibit the motion of the piezoelectric elements 300 and the space may be sealed or may not be sealed.
As a material of the protection substrate 30, a material having substantially the same coefficient of thermal expansion as that of the flow path formation substrate 11, for example, a glass, a ceramic material, or the like is used preferably. In the embodiment, the protection substrate 30 is formed by using the silicon single crystal substrate that is the same material as the flow path formation substrate 11.
Further, a through-hole 33 is provided on the protection substrate 30. The through-hole 33 penetrates through the protection substrate 30 in the thickness direction thereof. Portions in the vicinity of the ends of the lead electrodes 90 drawn from the respective piezoelectric elements 300 are exposed in the through-hole 33.
A driving circuit 120 that is controlled by a controller (not illustrated) and drives the piezoelectric elements 300 is fixed onto the protection substrate 30. For example, a circuit substrate, a semiconductor integrated circuit (IC), or the like can be used as the driving circuit 120. The driving circuit 120 and the lead electrodes 90 are electrically connected to each other through a connection wiring 121 formed by a conductive wire such as a bonding wire.
A compliance substrate 40 is bonded onto the protection substrate 30 having the above-mentioned configuration. The compliance substrate 40 is constituted by a sealing film 41 and a fixing plate 42. The sealing film 41 is made of a material having flexibility and low rigidity and one surface of the manifold portion 31 is sealed by the sealing film 41. Further, the fixing plate 42 is made of a relatively hard material. A region of the fixing plate 42, which is opposed to the manifold 100, corresponds to an opening 43 on which the fixing plate 42 is completely removed in the thickness direction. Therefore, one surface of the manifold 100 is sealed only by the sealing film 41 having flexibility.
In the recording head 10, ink is taken from an ink introduction port connected to an external ink supply unit (not illustrated) and inner portions from the manifold 100 to the nozzles 21 are filled with the ink. Thereafter, a voltage is applied to between the first electrode 60 and the respective second electrodes 80 corresponding to the respective pressure generation chambers 12 in accordance with a driving signal (for example, driving signal S12) from the driving circuit 120. The elastic film 50, the adhesion layer 56, the first electrode 60, and the piezoelectric layers 70 are deformed in a deflection manner with the voltage application. With this, vibration with the deformation is transmitted to the ink in the respective pressure generation chambers 12 through the elastic film 50 functioning as the vibrating portion. As a result, the pressures in the respective pressure generation chambers 12 are increased and ink droplets containing the flat plate-like particles as the pigment are discharged through the nozzles 21. The nozzles 21 in the embodiment are configured as the two-stage nozzles as described above such that the expression of φ2/φ1≧1.4 is satisfied. Therefore, the metallic ink containing the flat plate-like particles as the pigment can be discharged preferably even when the metallic ink is discharged with the driving signal S12 as illustrated in
Table 1 indicates a result of examination about the number of discharge unstable nozzles when the metallic ink containing the plate-like particles having various shapes is discharged by the liquid ejecting head according to the embodiment for three types of pigment shape parameters (b/a).
A parameter of the nozzle shape is set to φ2/φ1. Further, the pigment shape parameter (b/a) indicates a ratio of the thickness dimension “b” relative to the diagonal line dimension “a” of the surface when a flat plate-like particle 36A is considered to have a rectangular parallelepiped shape as illustrated in
The evaluation conditions of the discharge characteristic in this case are as follows. That is, an ink droplet velocity is set to 6 m/s and a discharge frequency is set to 1 kHz. The evaluation of continuous discharge stability is made by discharging ink through all the nozzles 21 for 30 seconds continuously and examining whether or not abnormality (velocity lowering, deterioration in landing accuracy) occurs.
By referring to Table 1, the following is found. That is, for each pigment shape parameter (b/a), as the nozzle shape (φ2/(φ1) is larger, that is, the opening diameter (φ2 of the nozzle portion 21B is larger relative to the opening diameter (φ1 of the nozzle portion 21A, the number of discharge unstable nozzles is reduced and the metallic ink can be discharged stably.
Based on the result of Table 1, evaluation of the discharge stability for the respective combinations is illustrated in Table 2. In Table 2, double circles indicate “very preferable”, circles indicate “preferable”, and crosses indicate “unavailable”. The evaluation is made by setting the range where stable printing can be expected on the discharge evaluation to “the number of discharge unstable nozzles≦10” as a reference in consideration of the number of discharge unstable nozzles and recording quality in the actual printing in the recording head 10 that discharges the metallic ink containing the flat plate-like particles having the respective shapes.
The evaluation results of Table 1 and Table 2 are illustrated in
Therefore, according to the embodiment having a configuration in which the relation between the opening diameter of the first nozzle portion 21A and the opening diameter of the second nozzle portion 21B satisfies the expression φ2/φ1≧1.4, a sufficient stable discharge characteristic is obtained even when the metallic ink containing the flat plate-like particles is used. In this case, it is needless to say that the range of φ2/φ1≧1.6 is more preferable. It is to be noted that measurement values described in the specification also include errors at some degree.
The embodiment of the invention has been described thus far. The basic configuration of the invention is not limited to the above-mentioned configuration. For example, the nozzles 21 in the above-mentioned embodiment are formed such that the inner circumferential surfaces of the second nozzle portions 21B are in parallel with the ink discharge direction and are continuous to the first nozzle portions 21A through stair-like step portions. However, the invention is not limited to the stair-like shapes. The inner circumferential surfaces of the second nozzle portions 21B may have tapered shapes inclined with respect to the discharge direction, or the like, as long as the relation between the opening diameters of the first nozzle portions 21A at the side of the discharge surface and the opening diameters of the second nozzle portions 21B at the side of the pressure generation chambers has a predetermined dimensional relation as in the above-mentioned embodiment.
Further, as illustrated in
The nozzles 21 in the above-mentioned embodiment are formed on the nozzle plate 20. However, the nozzles 21 are not limited thereto and may be formed by a plurality of members.
Further, the recording apparatus I in the above-mentioned embodiment includes the piezoelectric actuators using thin film-type piezoelectric elements as the pressure generation unit that generates pressure change on the pressure generation chambers 12. However, the invention is not required to be limited thereto. For example, thick film-type piezoelectric actuators formed by a method of bonding a green sheet, or the like, piezoelectric actuators using longitudinal vibration-type piezoelectric elements in which piezoelectric materials and electrode formation materials are alternately laminated to be expanded and contracted in the axial direction, or the like, can be also used.
The embodiment as illustrated in
Further, in the above-mentioned embodiment, the ink jet recording apparatus has been described as an example of a liquid ejection apparatus. However, the invention is widely applied to liquid ejection apparatuses including liquid ejecting heads that discharge liquids containing the flat plate-like particles. It is needless to say that the invention can be also applied to a liquid ejection apparatus including a liquid ejecting head that ejects liquid other than ink. As other liquid ejecting heads, various recording heads to be used for an image recording apparatus such as a printer, a color material ejecting head to be used for manufacturing color filters of a liquid crystal display and the like, an electrode material ejecting head to be used for forming electrodes of an organic EL display, a field emission display (FED), and the like, a bioorganic compound ejecting head to be used for manufacturing a bio chip, and the like can be exemplified.
The entire disclosure of Japanese Patent Application No. 2012-184258 filed Aug. 23, 2012 is expressly incorporated by reference herein.
Number | Date | Country | Kind |
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2012-184258 | Aug 2012 | JP | national |