JP4219249B2 - Droplet discharge head and image forming apparatus - Google Patents

Description

  The present invention relates to a droplet discharge head and an image forming apparatus.

  An ink jet recording apparatus used as an image forming apparatus such as a printer, a facsimile machine, a copying apparatus, or a plotter has a nozzle for discharging ink droplets and an ink flow path (discharge chamber, pressure chamber, pressurized liquid chamber, liquid chamber) communicating with the nozzle. And an ink jet head as a droplet discharge head provided with pressure converting means for pressurizing ink by changing the pressure in the ink flow path.

As an ink jet head, for example, an electromechanical conversion element such as a piezoelectric element is used as a pressure conversion means for generating pressure to pressurize ink in a liquid chamber, and an elastic deformation that forms a wall surface of the liquid chamber by displacement of a drive means A so-called piezoelectric type is known in which an ink droplet is ejected by changing the volume / pressure of a liquid chamber by deforming a possible diaphragm.
JP-A-8-108534

  An example of such an ink jet head is shown in FIGS. 18 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber of the head, and FIG. 19 is a cross-sectional explanatory view along the lateral direction of the liquid chamber of the head.

  This ink jet head joins a liquid chamber substrate 211 and a nozzle plate 218 to supply ink to a pressurized liquid chamber 214 that communicates with a nozzle 213 that discharges ink droplets, and to the pressurized liquid chamber 214 via a communicating portion 220. The common liquid chamber 219 is formed, and the piezoelectric element 217 provided on the base substrate 212 is joined to the outside of the vibration plate 216 forming a part of the wall surface of the pressurized liquid chamber 214.

  The diaphragm 216 is elastically deformed as the piezoelectric element 217 is deformed. In order to efficiently change the displacement of the piezoelectric element 217 to change the volume of the pressurized liquid chamber 214, the diaphragm 216 is usually the pressurized liquid chamber 214. The rigidity is made smaller (= compliance is made larger) than the other surfaces constituting the structure. The common liquid chamber 219 is connected to an ink tank (not shown), and a support member 221 is provided between the liquid chamber substrate 211 and the base substrate 212.

  Here, when a voltage is applied to the piezoelectric element 217 from a drive circuit (not shown), the piezoelectric element 217 is deformed, and the diaphragm 216 is deformed so that the volume of the pressurized liquid chamber 214 is increased or decreased. When the volume of the pressurizing liquid chamber 214 is increased, the internal pressure of the pressurizing liquid chamber 214 decreases, so that the ink is replenished from the common liquid chamber 219 through the communication portion 220 to the pressurizing liquid chamber 214.

  Thereafter, driving is performed to increase the internal pressure of the pressurized liquid chamber 214. That is, when the piezoelectric element 217 is driven so as to reduce the volume of the pressurized liquid chamber 214, the internal pressure of the pressurized liquid chamber 214 increases, so that ink is pushed out from the nozzle 213 to become ink droplets 222. The recording can be performed by flying the ink droplets and attaching ink droplets to a recording medium (such as paper) (not shown).

  The head structure is not only a piezoelectric element, but also a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a shape memory alloy that uses a metal phase change caused by a temperature change. Some include actuators, electrostatic actuators using electrostatic force, and the like as pressure conversion means for ejecting ink.

  By the way, when ejecting droplets with an ink jet head as described above, it is necessary to increase the pressure of the pressurized liquid chamber. The pressure generated here propagates to the common liquid chamber at the same time as ink droplets are blown, but when this pressure is transmitted again to the pressure liquid chamber side, the pressure in the pressure liquid chamber fluctuates.

  In particular, in a head with a large number of nozzles, the pressure fluctuation when driving with multiple channels is large, causing resonance of the liquid chamber (mutual interference), and when the resonance frequency of this vibration matches the driving frequency for printing, There is a problem that the image quality deteriorates due to the droplet ejection.

In order to prevent this, it is necessary to increase the pressure attenuation efficiency in the common liquid chamber, but as a means for that, generally, the volume of the common liquid chamber is increased, as described in Patent Document 2. In addition, a damper portion for absorbing a pressure change in the liquid chamber is provided between the liquid chamber and the common liquid chamber.
Japanese Patent Laid-Open No. 06-191030

In order to reduce the pressure fluctuation when supplying ink from the outside to the common liquid chamber of the inkjet head, although the purpose is different, to absorb the fluctuation of the ink supply pressure in the ink supply path from the ink tank to the head. Some of them have dampers.
JP2000-158668

  However, in the head described in Patent Document 2, since the damper is provided for each individual liquid chamber, it is difficult to sufficiently reduce the rigidity of the damper portion, and it is difficult to perform effective pressure absorption. The configuration is also complicated. In particular, in recent years, the number of nozzles of the head tends to increase in order to cope with an increase in recording speed, and there is a problem that it is difficult to apply the configuration described in Patent Document 2.

  Further, what is described in Patent Document 3 is to reduce ink supply pulsation, and does not absorb pressure fluctuations in the common liquid chamber caused by driving of the head.

  The present invention has been made in view of the above problems, and a droplet discharge head capable of recording at high speed and high quality by efficiently attenuating pressure fluctuation while reducing resonance of a common liquid chamber, and the droplet An object of the present invention is to provide an image forming apparatus provided with an ejection head.

In order to solve the above problems, a liquid droplet ejection head according to the present invention includes:
In a droplet discharge head having a common liquid chamber for supplying a liquid to a plurality of liquid chambers each communicating with a plurality of nozzles,
The alignment direction of the liquid chamber when the X-direction, at least one surface of the wall along the X direction of the common liquid chamber is low have the pressure absorbing member surface stiffness than the other wall surface,
The member that forms the pressure absorber surface is configured such that when the pressure absorber surface is divided into three in the X direction, the average thickness of the three divided central portions is larger than the average thickness of both end portions.

  Moreover, it is preferable that the member which forms a pressure absorber surface has at least two types of thickness of a thin part and a thick part. In this case, as for the member which forms a pressure absorber surface, it is preferable that the both ends of a X direction are a thin part, and a center part is a thick part. And it is preferable that the member which forms a pressure absorber surface comprises a laminated structure, and the number of lamination | stacking differs in a thin part and a thick part.

Moreover, members for forming the pressure absorbing member surface is preferably made of Ni.

The droplet discharge head according to the present invention is
Droplet discharge having a common liquid chamber for supplying a liquid to a plurality of liquid chambers in which a plurality of nozzles communicate with each other, and having a plurality of pressure conversion means for changing the pressure in the liquid chamber on a base substrate In the head
The alignment direction of the liquid chamber when the X-direction, at least one surface of the wall along the X direction of the common liquid chamber is low have the pressure absorbing member surface stiffness than the other wall surface,
The member forming the pressure absorber surface is characterized in that when the pressure absorber surface is divided into three parts in the X direction, the average rigidity of the three divided central parts is higher than the average rigidity of both end parts. Drop ejection head.

According to the liquid droplet ejection head according to the present invention, when the arrangement direction of the liquid chambers is the X direction, at least one of the wall surfaces along the X direction of the common liquid chamber has lower rigidity than the other wall surfaces. When the pressure absorber surface is divided into three parts in the X direction, the member forming the pressure absorber surface has a structure in which the average thickness of the three divided central portions is thicker than the average thickness of both end portions , or When the liquid chamber alignment direction is the X direction, at least one of the wall surfaces along the X direction of the common liquid chamber is a pressure absorber surface having lower rigidity than the other wall surfaces, and this pressure absorber surface is formed. When the pressure absorber surface is divided into three parts in the X direction, the average rigidity of the central portion divided into three is higher than the average rigidity of both ends , so that the resonance frequency is maintained while maintaining the rigidity of the pressure absorber surface. Of the head can be suppressed Can be made different resonance frequency dynamic frequency and pressure absorbing body surface, stable ejection characteristics can be obtained even during high-speed driving. Since the image forming apparatus according to the present invention includes the droplet discharge head according to the present invention, high-quality recording can be performed at high speed.

  An image forming apparatus according to the present invention includes the droplet discharge head according to the present invention.

  According to the droplet discharge head according to the present invention, one wall surface of the common liquid chamber is used as a pressure absorber surface, and a member forming the pressure absorber surface has a structure in which the thickness is not uniform or has a portion having different rigidity. Since it is configured, it is possible to suppress the decrease in the resonance frequency while maintaining the rigidity of the pressure absorber surface, and the head drive frequency and the resonance frequency of the pressure absorber surface can be made different, which is stable even at high speed drive The droplet ejection characteristics can be obtained. Since the image forming apparatus according to the present invention includes the droplet discharge head according to the present invention, high-quality recording can be performed at high speed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. An ink jet head according to a first embodiment of a droplet discharge head of the present invention will be described with reference to FIGS. 1 is an exploded perspective view of the head, FIG. 2 is a cross-sectional view of the head along the longitudinal direction of the liquid chamber, and FIG. 3 is a lateral view of the head along the AA line of FIG. It is sectional explanatory drawing of the arrangement direction of a nozzle. Here, FIG. 3 is shown with the upper limit inverted, unlike the others.

  This inkjet head is bonded to the flow path forming substrate (liquid chamber substrate) 1 formed of a single crystal silicon substrate, the diaphragm 2 bonded to the lower surface of the flow path forming substrate 1, and the upper surface of the flow path forming substrate 1. A pressure plate 6 having a nozzle plate 3 and a frame member 14 which will be described later, and a nozzle 5 for ejecting ink droplets communicate with each other, and an ink supply path serving as a fluid resistance portion in the pressure chamber 6 A common liquid chamber 8 for supplying ink through a (communication portion) 7 is formed.

  Then, a laminated piezoelectric element 12 as a driving means is bonded to the outer side of the diaphragm 2 (on the opposite side to the liquid chamber 6) corresponding to each pressurized liquid chamber 6, and the laminated piezoelectric element 12 is a base substrate. 13 and fixed.

  The frame member 14 is formed with a dug portion for forming the common liquid chamber 8 together with the flow path forming substrate 1 and an ink supply port (communication pipe) 9 for supplying ink to the common liquid chamber 8 from the outside. The communication tube 9 is connected to an ink supply source such as an ink cartridge (not shown).

  Further, an FPC cable 18 is connected to the piezoelectric element 12 by solder bonding, ACF (anisotropic conductive film) bonding or wire bonding in order to give a drive signal. The FPC cable 18 is selectively connected to each piezoelectric element 12. A drive circuit (driver IC) 19 for applying a drive waveform is mounted.

  Here, the flow path forming substrate 1 is obtained by anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110) using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), thereby providing each pressurized liquid chamber. 6 and a groove portion constituting the ink supply path (communication pipe) 7 are formed.

  The diaphragm 2 is formed from a nickel metal plate and is manufactured by an electroforming method. The nozzle plate 3 forms a nozzle 5 having a diameter of 10 to 30 μm corresponding to each pressurized liquid chamber 6 and is bonded to the flow path forming substrate 1 with an adhesive. Note that the nozzle 5a (see FIG. 3) corresponding to the end of the common liquid chamber 8 in the longitudinal direction or the pressurized liquid chamber corresponding to the nozzle 5a at both ends is not used for image formation, but is used for sucking out bubbles. It can also be a dummy nozzle provided.

  The nozzle plate 3 may be made of a metal such as stainless steel or nickel, a combination of a metal and a resin such as a polyimide resin film, silicon, or a combination thereof. Further, a water repellent film is formed on the nozzle surface (surface in the ejection direction: ejection surface) by a known method such as a plating film or a water repellent coating in order to ensure water repellency with ink. A sealant 20 is filled between the periphery of the nozzle plate 3 and the head frame 14. The sealant 20 also serves as an adhesive.

  In the ink jet head configured as described above, when a drive pulse voltage of 20 to 50 V is selectively applied to the piezoelectric element 12, the piezoelectric element 12 to which the pulse voltage is applied uses the stacking direction (d33 direction). ), The diaphragm 2 is deformed in the direction of the nozzle 5, the ink in the pressurized liquid chamber 6 is pressurized by the volume / volume change of the pressurized liquid chamber 6, and ink droplets are ejected (jetted) from the nozzle 5. Is done.

  As the ink droplets are ejected, the liquid pressure in the pressurized liquid chamber 6 decreases, and a slight negative pressure is generated in the pressurized liquid chamber 6 due to the inertia of the ink flow at this time. Under this state, when the voltage application to the piezoelectric element 12 is turned off, the diaphragm 2 returns to the original position and the pressurized liquid chamber 6 becomes the original shape, so that further negative pressure is generated. To do. At this time, the ink is filled into the pressurized liquid chamber 6 from the ink supply port 9 through the common liquid chamber 8 and the ink supply path (communication portion) 7 which is a fluid resistance portion. Therefore, after the vibration of the ink meniscus surface of the nozzle 5 is attenuated and stabilized, a pulse voltage is applied to the piezoelectric element 12 to discharge the ink droplet for the next ink droplet discharge.

  In the above description, the nozzles are shown facing upward (other than FIG. 3). However, when ejecting ink toward a member that forms an image, such as paper, the direction of ejecting ink is vertically downward. In many cases, even in the present invention, ink droplets fly toward the image forming member from the vertical direction of the image forming member (such as paper) that is conveyed horizontally during image formation, that is, when ink is ejected.

  Next, the structure of the common liquid chamber of this ink jet head will be described with reference to FIGS. FIG. 4 is an enlarged cross-sectional explanatory view of a main portion along the liquid chamber arrangement direction for explaining the common liquid chamber portion of the head, and shows the common liquid chamber and the ink supply port portion extracted. FIG. 5 is an explanatory plan view of the pressure absorber portion, and FIG. 6 is an explanatory plan view showing another example of the pressure absorber portion.

  In this head, the common liquid chamber 8 is formed by the frame member 14 and the pressure absorber 21 (the member forming the pressure absorbing surface) 21 having a rigidity lower than that of the frame member 14, so that the liquid chambers are arranged in the X direction. At this time, at least one of the wall surfaces along the X direction of the common liquid chamber 8 is a pressure absorber surface 21a for absorbing pressure with lower rigidity than the other wall surfaces.

  Here, as shown in FIG. 4, the pressure absorber 21 forming the pressure absorber surface 21a is not uniform in thickness in the X direction, and is thick on the average near the center and thin near both ends. It has a configuration. Specifically, when the pressure absorber surface 21a is divided into three parts in the X direction, the average thickness of the central part divided into three parts is thicker than the average thickness of both end parts, and the thick part 23 is provided in the center part. A thin portion 22 is formed in the portion. In this example, an example of three equal parts is shown as three divisions. However, as will be described later, the central part may be divided into three to form the thick part 23. At this time, the thick portion 23 has higher rigidity than the thin portion 22, and the pressure absorber 21 has a plurality of portions having different rigidity.

  In this case, the pressure absorber 21 is provided on the first layer 21A to be the thin portion 22 forming the diaphragm 2, and the second layer forming the thick portion 23 together with the first layer 21A. A laminated structure with the layer 21B is employed. As described above, the thickness of the pressure absorber 21 can be easily made non-uniform, and a part of the plurality of layers can be formed of the same layer as the diaphragm 2. The pressure absorber 21 can be formed at the same time in the diaphragm forming step, and the manufacturing process can be simplified.

  Here, there is a step in the thickness at the boundary between the thin portion 22 and the thick portion 23, but such a step is not provided. For example, the thickness from the thick portion to the thin portion is continuously increased. In this case, the thickness of the pressure absorber 21 can be made non-uniform, and a structure having portions with different rigidity can be obtained. In addition, the area distribution in which the thin wall portion 22 and the thick wall portion 23 are provided is not limited to three equal parts as described above, and an optimal distribution and position are determined according to the material and size of the pressure absorber. Just decide.

  Further, as shown in FIG. 5, the thin portion 21A and the thick portion 21B of the pressure absorber 21 may have the same width in the direction orthogonal to the X direction (the width Uy in the short direction of the thin portion 21A). Alternatively, as shown in FIG. 6, the width of the thick portion 21B can be made smaller than the width Uy in the short direction of the thin portion 21A.

  In this way, by adopting a configuration in which the thickness of the pressure absorber is not uniform, the structural vibration of the common liquid chamber is complicated, and generation of a large vibration mode at a low frequency can be suppressed. It is possible to prevent the resonance frequencies of the common liquid chamber 8 from overlapping.

  In addition, the structure of the pressure absorber having a plurality of parts having different rigidity complicates the structural vibration of the common liquid chamber, and can suppress the generation of a large vibration mode at a low frequency, and is common with the drive frequency. It is possible to prevent the resonance frequencies of the liquid chambers 8 from overlapping. In addition, as a structure which a pressure absorber has a several part from which rigidity differs, it can also achieve by making material differ partially, for example besides changing thickness partially.

  That is, in order to prevent the pressure vibration propagating from the pressure chamber to the common liquid chamber during droplet discharge from propagating to other pressure chambers, it is necessary to increase the pressure attenuation efficiency in the common liquid chamber. A part of the wall surface of the chamber is made of a member having a low rigidity or a structure, and the pressure fluctuation is attenuated by vibration of the wall surface itself, or the wall surface of the common liquid chamber is coated with a member having low elasticity such as rubber. A method of attenuating pressure fluctuations by deformation of the surface of the surface can be considered. Among these, the method of attenuating the pressure fluctuation by the vibration of the wall surface itself is particularly excellent in terms of ease of manufacturing (cost and construction difficulty) and good damping efficiency.

  However, when the rigidity of the wall surface of the common liquid chamber is lowered and the vibration easily occurs, there arises a problem that pressure fluctuation of the common liquid chamber occurs due to resonance of the wall surface itself.

  Specifically, as shown in FIG. 7, when the pressure absorber 21 with a part of the wall surface of the common liquid chamber formed of the thin wall portion 22 to reduce the rigidity is used and driven at a drive frequency of 4 kHz, The vibration mode of the wall surface of the common liquid chamber is as shown in FIG. Further, the vibration mode of the wall surface of the common liquid chamber when driven at a driving frequency of 16.8 kHz without lowering the rigidity of the wall surface of the common liquid chamber is as shown in FIG. In addition, the area of the wall surface of the common liquid chamber of the example shown in FIG. 8 or FIG. 9 is the same, and the wall surface of different rigidity is comprised by changing the thickness of the part which forms a wall surface.

  As can be seen from FIGS. 8 and 9, the resonance frequency when the pressure absorber is configured by reducing the rigidity of the wall surface area of the common liquid chamber is in a lower frequency band than the frequency when the rigidity is not lowered. Transition to. Accordingly, when the cycle of ejecting ink droplets is shortened, that is, when the drive frequency of the head is increased, the resonance frequency of the wall surface of the common liquid chamber may overlap. Usually, a frequency band of several kHz to several tens of kHz is used as the driving frequency of the inkjet head, and this driving frequency is lower than the resonance frequency of the wall surface of the common liquid chamber, but the resonance frequency is lower on the wall surface with reduced rigidity. Therefore, the resonance frequency may overlap the drive frequency band of the recording head.

  At the resonance point of the common liquid chamber wall surface, the pressure of the common liquid chamber itself greatly fluctuates with the vibration of the wall surface. Therefore, when the rigidity of the wall surface of the common liquid chamber is lowered and used as a pressure absorber, the pressure change of the common liquid chamber wall 10 shows a large pressure fluctuation value at the resonance frequency as shown in FIG.

  As described above, the pressure absorber that should originally attenuate the pressure of the common liquid chamber is provided with the pressure absorber itself, and conversely, the pressure fluctuation of the common liquid chamber is increased. In order to avoid this, it is necessary to set the driving frequency of the recording head in a band that does not overlap with the resonance frequency, which restricts the driving condition of the recording head.

  In particular, the number of nozzles of the recording head tends to increase in order to cope with the higher speed of the ink jet recording apparatus. However, as the number of nozzles increases, that is, the number of individual liquid chambers increases, the length of the common liquid chamber ( The length of the liquid chamber arrangement direction) becomes longer, and as a result, the length of the pressure absorber must also be increased. By reducing the length of the pressure absorber, the rigidity is further reduced, and the resonance point of the common liquid chamber wall surface is further shifted to the lower frequency side, so that the drive frequency of the recording head does not overlap the resonance frequency. In order to achieve this, it is necessary to further tighten the drive condition setting. In particular, in a head having a large number of nozzles and a long common liquid chamber length, such as a line-type head, a problem occurs because the generated pressure fluctuation is large.

  On the other hand, the pressure absorber 21 including the thick portion 23 is not used as a pressure absorber that is the thin portion 22 as in the present invention, but the resonance frequency is reduced while obtaining the pressure damping effect. Can be suppressed. Therefore, stable droplet ejection characteristics can be obtained even during high-speed driving.

  Here, the evaluation result of the frequency characteristic of the pressure change of the common liquid chamber provided with the pressure absorber according to the present invention is shown in FIG. This frequency characteristic is a frequency characteristic when the region of 35% of both ends of the length in the X direction of the pressure absorber surface 21a is the thin portion 22 and the remaining central portion 30% is the thick portion 23 in FIG. . As can be seen from a comparison between FIG. 11 and the frequency characteristics of the common liquid chamber pressure change in the structure in which the entire pressure absorber surface of FIG. 10 described above is a thin wall portion, the whole of the pressure absorber of FIG. However, although the rigidity is low, the pressure absorber according to the present invention can obtain a higher pressure damping effect.

  In the present embodiment, as shown in FIG. 4, the pressure absorber 21 has a structure in which both ends in the X direction are supported, but the thickness in the vicinity of the support portions at both ends is reduced, that is, the rigidity is increased. By lowering, the amount of deformation of the entire pressure absorber 21 can be increased. Thereby, even if the thickness of the pressure absorber 21 is partially increased and the function as the pressure absorber 21 of the portion is lowered, the deterioration of the function when viewed as a whole can be suppressed to the minimum.

  Further, since both ends of the common liquid chamber 8 are most susceptible to pressure fluctuation when pressure resonance occurs in the common liquid chamber 8, the thin wall portion 22 having a high pressure absorption effect is provided in a place where the pressure fluctuation amount is large. By providing, an efficient pressure damping effect can be obtained.

  Further, the pressure absorber 21 is composed of two types of thicknesses, a thin portion 22 and a thick portion 23, and has a structure in which both end portions in the X direction are thin portions 22 and a central portion is a thick portion 23. The structure is simplified, the manufacturing is easy, and the pressure damping effect can be enhanced.

  In addition, the pressure absorber 21 has a laminated structure, and the layer constituting the thin portion 22 is further layered to form the thick portion 23, so that pressure absorbers having different thicknesses can be formed by a simpler construction method. It becomes possible to form. In the present embodiment, the thin portion 21 has one layer and the thick portion 22 has two layers, but other structures, for example, the thin portion 21 has one layer and the thick portion has three layers. You can also do it.

  As described above, the configuration of the thin portion 22 and the thick portion 23 of the pressure absorber 21 can provide a high pressure damping effect if the length of the thin portion 21 in the X direction is increased. However, the pressure absorber surface 21a, That is, the pressure fluctuation due to the vibration of the pressure absorber 21 occurs at a low frequency. Conversely, if the length of the thin portion 21 in the X direction is shortened, the vibration of the pressure absorber surface 21a is improved, but the pressure damping effect is reduced.

  Therefore, in carrying out the present invention, it is necessary to sufficiently examine the size and thickness of the pressure absorber, the elastic modulus of the material, and the like, and to select the size and member for obtaining the optimum structure.

Therefore, 32 types of print heads as shown in Table 1 with different structures of the pressure absorber and the head were prepared, and the following evaluation was performed by an ejection test.
Evaluation A: Mutual interference evaluation: Is the pressure absorber functioning sufficiently?
Evaluation B: Frequency-dependent evaluation ... Is the resonance of the pressure absorber affecting the injection characteristics?

  In the evaluation A, a head was actually mounted on the printer, an evaluation chart was printed, and a determination was made based on whether or not an image abnormality occurred in the print sample (no abnormality = ◯, there was an abnormality = ×). In Evaluation B, the ink droplets were ejected while changing the drive frequency with the head alone, and the droplet ejection characteristics (ink droplet ejection speed, ink droplet ejection volume, ejection bending, etc.) at that time were observed, and the characteristics depended on the frequency. (No frequency dependence = ◯, Frequency dependence = ×).

The following items were selected as structural factors that would affect these evaluations. The positions of Ud, Uy, and Ux are as shown in FIGS.
Thin portion 22 thickness Ud (m)
Length in the short direction of the thin portion 22 Uy (m)
The length Ux (μm) in the longitudinal direction (X direction) of the thin portion 22
Young's modulus of thin-walled portion E (Pa)

Considering the above as variables,
K = Ud ^a × Uy ^b × Ux ^c × E ^d
Then, a to d were considered as fitting parameters, and by optimizing this, it was considered to index the performance of the pressure absorber with one parameter K.
As a result, it was found that if a = 2, b = −2.5, c = −3.5, and d = 2/3, the phenomenon can be expressed well.

The results are shown in Table 1. From this, it can be seen that if the value of K falls within the range of 2 × 10 ^{10 to} 9 × 10 ¹⁰ , good results can be obtained for both evaluations A and B.

  That is, in the member 21 forming the pressure absorber surface, the thickness of the thin portion 22 is Ud (m), the length of the thin portion 22 in the short direction is Uy (m), and the length of the thin portion 22 in the X direction is Ux ( m) When the Young's modulus of the thin-walled portion 22 is E (Pa), the rigidity of the pressure absorber and the resonance frequency of the pressure absorber are optimized by satisfying the relationship of the following equation (1). Thus, it is possible to reliably obtain stable injection characteristics even at high speed.

  Here, when the head becomes larger (long) and the pressure absorber area further increases with the increase in the number of nozzles, if a soft member such as a resin is used as a member for forming the pressure absorber, the low frequency band Many resonances of the pressure absorber occur. In addition, since a soft member having a large area is difficult to process, it is preferable to use a hard material for the member of the pressure absorber even if the rigidity is somewhat high. However, even a highly rigid member can obtain a sufficient pressure absorbing effect.

  Therefore, the pressure resonance characteristics of the common liquid chamber were examined using a head having a nozzle number exceeding 200 bits and changing the member forming the pressure absorber. The result is shown in FIG.

  Here, as a simple index representing the degree of pressure resonance, the head driving frequency band is assumed to be 1 to 16 kHz, and the comparison is made by the sum of pressure fluctuation values when pressure resonance occurs. For example, in the characteristic of FIG. 11, there are resonance points at 4 kHz, 10 kHz, and 10.8 kHz, and the pressure fluctuation values are 0.8, 1.1, and 0.5, respectively, so 0.8 + 1.1 + 0.5 = 2.4 can be calculated. Here, this is referred to as a “pressure resonance index”.

  As can be seen from FIG. 12, when the Young's modulus of the pressure absorber is 100 MPa or less, the pressure resonance index increases rapidly. That is, the pressure fluctuation in the common liquid chamber tends to affect the droplet discharge characteristics. Therefore, it is preferable to use a member having a Young's modulus of 100 Pa or more as the member forming the pressure absorber 21.

  As described above, by using a member having a Young's modulus of 100 Pa or more as a member for forming the pressure absorbing surface, the resonance frequency is lowered due to the increase in the area of the pressure absorber, which is generated by increasing the number of nozzles and the head size. Stable ejection characteristics can be obtained even with a long head having a large number of nozzles.

  Ni is suitable as such a member. That is, Ni has a Young's modulus of about 150 MPa, satisfies the above-described requirements as a member for forming a pressure absorber surface, and is excellent in workability.

  Further, the length Ux occupied by the thin portion 22 is important in the X-direction length Tx of the pressure absorber 21. If the ratio of the thin portion 22 is reduced, a sufficient pressure absorbing effect cannot be obtained. This is because the structural damping capacity of the thin wall portion 22 changes and the thick wall portion 23 becomes longer, so that the pressure of the entire common liquid chamber cannot be sufficiently absorbed. Conversely, when the proportion of the thin portion 22 is increased, the vibration of the pressure absorber becomes a problem as described above.

  Therefore, a print head in which the ratio between the X-direction length Ux of the thin wall portion 22 and the entire length Tx of the pressure absorber 21 is prepared, and the ejection characteristics are evaluated. The results are shown in Table 2.

  From this result, it can be seen that the ratio of Ux to Tx (Ux / Tx) is preferably set in the range of 0.25 to 0.45.

  That is, when the X-direction length of the thin portion 22 is Ux (μm) and the X-direction length of the entire pressure absorber surface is Tx (μm), by satisfying the relationship of the following equation (2), Since the structure of the absorber can be optimized, pressure absorption and resonance can be more reliably suppressed, and the injection characteristics can be stabilized.

Next, another embodiment according to the present invention will be described with reference to FIG.
In this embodiment, the pressure absorber 21 is configured to include the second thick portion 24 in a part of the thin portion 22 region.

  Thus, by providing the second thick portion 24, the resonance frequency of the common liquid chamber wall surface is further shifted to the higher frequency side, and the generation of resonance points in the head driving frequency band can be further suppressed.

  Further, by providing the second thick portion 24, the strength of the thin portion 22 is increased, and there is an effect that the processing of the head becomes easier. As an example, the pressure change characteristics of the common liquid chambers with and without the second thick part 24 were compared. The result is shown in FIG.

  From this result, it can be seen that the head provided with the second thick part 24 can obtain better characteristics with less pressure change compared to the head not provided with the second thick part 24.

  In this way, by providing the second thick portion in the thin portion of the pressure absorber, the resonance frequency of the pressure absorber can be further separated from the driving frequency, so that stable injection characteristics are more effective. Can get to. Further, since the strength of the pressure absorber is increased, handling during assembly is facilitated, and manufacturing workability is improved.

  Here, by making the thickness of the second thick part 24 the same as that of the thick part 23, the thick part 23 and the second thick part 24 can be formed simultaneously, and the processing is simplified. And the manufacturing cost can be reduced.

Next, still another embodiment according to the present invention will be described with reference to FIG.
In this embodiment, the pressure absorber 21 is provided on a part of the wall surface forming the common liquid chamber 8 of the frame member 14. In this case, a damper chamber 25 is formed on the back side of the pressure absorber 21 so that the pressure absorber 21 can be displaced, and the damper chamber 25 communicates with the atmosphere through an atmosphere communication path (not shown). It is preferable. Even if it does in this way, the effect similar to each said embodiment is acquired except the effect by forming a part of pressure absorber 21 with the diaphragm 2. FIG.

  As described above, according to the droplet discharge head according to the present invention, one wall surface of the common liquid chamber is used as a pressure absorber surface, and the members forming the pressure absorber surface have a non-uniform thickness or are rigid. Since it has a configuration having a plurality of different parts, it is possible to suppress a decrease in the resonance frequency while maintaining rigidity, and to make the drive frequency of the head different from the resonance frequency of the pressure absorber surface. In addition, stable droplet ejection characteristics can be obtained.

  In particular, the droplet discharge head according to the present invention is preferably applied to a line type recording head. That is, the line type recording head has a large number of bits and the length of the pressure absorber in the X direction becomes long, and the resonance of the pressure absorber itself, which is a problem of the present invention, is generated remarkably. Therefore, by applying the present invention, it becomes possible to absorb the pressure change while maintaining the rigidity, and it is possible to obtain stable droplet discharge characteristics even with a full-line long head.

Next, specific examples of the present invention will be described.
Example 1
A laminated piezoelectric element as a pressure converting means is joined to a support substrate (base substrate 11) made of SUS using an anaerobic adhesive, and a groove is formed on the piezoelectric element using a dicing saw. The piezoelectric element 12 separated so as to correspond to the above was formed. The actuator unit was formed by joining the FPC 18 serving as an energizing member to the side surface of the grooved piezoelectric element 12 using solder.

  On the other hand, the nozzle plate 3 and the diaphragm 2 manufactured by the electroforming method and the silicon flow channel plate (liquid chamber substrate) 1 manufactured by the etching method are positioned and laminated with high accuracy, and each interface is formed with an epoxy adhesive. Joined. Then, the upper surface of the piezoelectric element 12 of the actuator unit was joined to the back surface of the diaphragm 2 with an epoxy adhesive.

  The resin frame member 14 forming the common liquid chamber 8 having a length in the longitudinal direction of 35 mm, a length in the short direction of 1 mm, and a depth of 2 mm is anaerobically bonded to the rear surface of the diaphragm 2 and the end surface of the base substrate 11. The ink jet head was manufactured by bonding with an agent.

  At this time, the opening serving as the common liquid chamber 8 of the frame member 14 is closed by the diaphragm 2. Therefore, this diaphragm 2 has a laminated structure by Ni electroforming having a thickness of 3 μm and 27 μm, and the portion closing the common liquid chamber 8 is one layer (12 mm in the end of the common liquid chamber in the longitudinal direction). The thin portion 22 was formed with a thickness of 3 μm, and the central portion was the thick portion 23 formed with one layer and two layers (thickness 3 μm + 27 μm = 30 μm).

  The ink jet head having the nozzle 5 for 200 bits thus manufactured was mounted on a printer and a printing test was performed.

  As a result, even when multi-printing was performed in which ink was ejected from all nozzles, a good result was obtained that did not cause poor image quality.

  For comparison, if an inkjet head with all the diaphragms closing the common liquid chamber made of one thin layer (3 μm) is manufactured and mounted on the printer in the same way, and a print test is performed, poor image quality There has occurred.

  Thereby, it was confirmed that the droplet ejection characteristics of the present invention are improved.

(Example 2)
A laminated piezoelectric element as a pressure converting means is joined to a support substrate (base substrate 11) made of SUS using an anaerobic adhesive, and a groove is formed on the piezoelectric element using a dicing saw. The piezoelectric element 12 separated so as to correspond to the above was formed. The actuator unit was formed by joining the FPC 18 serving as an energizing member to the side surface of the grooved piezoelectric element 12 using solder.

  On the other hand, the nozzle plate 3 and the diaphragm 2 manufactured by the electroforming method and the silicon flow channel plate (liquid chamber substrate) 1 manufactured by the etching method are positioned and laminated with high accuracy, and each interface is formed with an epoxy adhesive. Joined. Then, the upper surface of the piezoelectric element 12 of the actuator unit was joined to the back surface of the diaphragm 2 with an epoxy adhesive.

  In addition, the resin frame member 14 forming the common liquid chamber 8 having a longitudinal length of 63 mm, a lateral length of 2.5 mm, and a depth of 3 mm is anaerobically formed on the back surface of the diaphragm 2 and the end surface of the base substrate 11. The ink jet head was manufactured by bonding with an adhesive.

  At this time, the opening serving as the common liquid chamber 8 of the frame member 14 is closed by the diaphragm 2. Therefore, the diaphragm 2 has a three-layer Ni electroforming laminated structure with thicknesses of 3 μm, 15 μm, and 15 μm, and the portion that closes the common liquid chamber 8 is 1 in the longitudinal direction of the common liquid chamber and the area of the end 20 mm. The thin portion 22 is formed by two layers (thickness 3 μm + 15 μm = 18 μm), and the central portion is the thick portion 23 formed by one to three layers (thickness 3 μm + 15 μm + 15 μm = 33 μm).

  The inkjet head having the nozzle 5 for 360 bits thus manufactured was mounted on a printer and a printing test was performed.

  As a result, even when multi-printing was performed in which ink was ejected from all nozzles, a good result was obtained that did not cause poor image quality.

  For comparison, if an inkjet head with all the diaphragms closing the common liquid chamber made of one thin layer (3 μm) is manufactured and mounted on the printer in the same way, and a print test is performed, poor image quality There has occurred.

  Thereby, it was confirmed that the droplet ejection characteristics of the present invention are improved.

  Next, an example of an ink jet recording apparatus equipped with an ink jet head which is a liquid droplet ejection head according to the present invention will be described with reference to FIGS. FIG. 23 is a perspective explanatory view of the recording apparatus, and FIG. 24 is a side explanatory view of a mechanism portion of the recording apparatus.

  This ink jet recording apparatus includes a carriage movable in the main scanning direction inside the recording apparatus main body 111, a recording head comprising the ink jet head according to the present invention mounted on the carriage, an ink cartridge for supplying ink to the recording head, and the like. A paper feed cassette (or a paper feed tray) 114 on which a large number of sheets 113 can be stacked from the front side is detachably attached to the lower part of the apparatus main body 111. In addition, the manual feed tray 115 for manually feeding the paper 113 can be opened, the paper 113 fed from the paper feed cassette 114 or the manual feed tray 115 is taken in, and the printing mechanism unit 112 takes the required After the image is recorded, it is discharged to a discharge tray 116 mounted on the rear side.

  The printing mechanism 112 holds a carriage 123 slidably in the main scanning direction by a main guide rod 12 and a sub guide rod 122 which are guide members horizontally mounted on left and right side plates (not shown). (Y), cyan (C), magenta (M), black (Bk) each head is composed of an ink jet head that is a liquid droplet ejection head according to the present invention for ejecting ink droplets of each color, and a plurality of ink ejection openings are mainly used. They are arranged in a direction crossing the scanning direction and mounted with the ink droplet ejection direction facing downward. Also, each ink cartridge 125 for supplying each color ink to the head 124 is replaceably mounted on the carriage 123.

  The ink cartridge 125 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the inkjet head below, and a porous body filled with ink inside, and the capillary force of the porous body Thus, the ink supplied to the inkjet head is maintained at a slight negative pressure.

  Further, although the heads 124 of the respective colors are used here as the recording heads, a single head having nozzles for ejecting ink droplets of the respective colors may be used.

  Here, the carriage 123 is slidably fitted to the main guide rod 121 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the sub guide rod 122 on the front side (upstream side in the paper conveyance direction). is doing. In order to move and scan the carriage 123 in the main scanning direction, a timing belt 130 is stretched between a driving pulley 128 and a driven pulley 129 that are rotationally driven by a main scanning motor 127. The carriage 123 is reciprocally driven by forward and reverse rotations of the main scanning motor 127.

  On the other hand, in order to convey the sheet 113 set in the sheet cassette 114 to the lower side of the head 124, the sheet 113 is guided from the sheet feeding cassette 114 to the sheet feeding roller 131 and the friction pad 132. A guide member 133, a transport roller 134 that reverses and transports the fed paper 113, a transport roller 135 that is pressed against the peripheral surface of the transport roller 134, and a tip that defines the feed angle of the paper 113 from the transport roller 134 A roller 136 is provided. The transport roller 134 is rotationally driven by a sub-scanning motor 137 through a gear train.

  A printing receiving member 139 is provided as a paper guide member that guides the paper 113 fed from the transport roller 134 on the lower side of the recording head 124 corresponding to the movement range of the carriage 123 in the main scanning direction. On the downstream side of the printing receiving member 139 in the paper conveyance direction, a conveyance roller 141 and a spur 142 that are rotationally driven to send the paper 113 in the paper discharge direction are provided, and paper discharge that further feeds the paper 113 to the paper discharge tray 116. A roller 143 and a spur 144, and guide members 145 and 146 forming a paper discharge path are disposed.

  At the time of recording, the recording head 124 is driven according to the image signal while moving the carriage 123, thereby ejecting ink onto the stopped sheet 113 to record one line. Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the sheet 113 reaches the recording area, the recording operation is terminated and the sheet 113 is discharged. In this case, the inkjet head, which is a droplet discharge head according to the present invention constituting the head 124, can absorb pressure fluctuations in the common liquid chamber and suppress resonance, so that there is no mutual interference and stable enemy discharge. Since it has characteristics, a high-quality image can be recorded.

  A recovery device 147 for recovering defective ejection of the head 124 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 123. The recovery device 147 includes a cap unit, a suction unit, and a cleaning unit. The carriage 123 is moved to the recovery device 147 side during printing standby, and the head 124 is capped by the capping unit, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting ink that is not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  When a discharge failure occurs, the discharge port of the head 124 is sealed with a capping unit, bubbles and the like are sucked out from the discharge port with the suction unit through the tube, and ink or dust adhering to the discharge port surface is removed by the cleaning unit. And the defective discharge is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

  Thus, since this image forming apparatus is equipped with the inkjet head which is the droplet ejection head according to the present invention, stable droplet ejection characteristics can be obtained by high-speed driving.

  Note that the image forming apparatus according to the present invention can also be applied to a printer, a facsimile machine, a copying machine, a multi-function machine thereof, and the like. Further, the present invention can also be applied to a droplet discharge head or a droplet discharge device that discharges a liquid other than ink, such as a DNA sample, a resist, or a pattern material, or an image forming apparatus that includes these. Further, the pressure conversion means (actuator means) of the droplet discharge head according to the present invention is not limited to a piezoelectric actuator, and an electrostatic actuator, a thermal actuator, an actuator using a shape memory alloy, or the like is used. Can do.

FIG. 3 is an exploded perspective view of a droplet discharge head according to the present invention. It is sectional explanatory drawing in alignment with the liquid chamber longitudinal direction of the head. It is sectional explanatory drawing of the common liquid chamber part along the nozzle arrangement direction of the head. It is principal part expanded sectional explanatory drawing along the row direction of the liquid chamber of the common liquid chamber part of the head. It is a plane explanatory view of a pressure absorber. It is a plane explanatory view showing other examples of the pressure absorber. It is principal part expanded sectional explanatory drawing along the row direction of the liquid chamber of the common liquid chamber part of a comparative example. It is explanatory drawing of the vibration mode of the wall surface of a common liquid chamber when driving a comparative example with the drive frequency of 4 kHz. It is explanatory drawing of the vibration mode of the wall surface of a common liquid chamber when driving a comparative example with the drive frequency of 16.8 kHz. It is explanatory drawing of the pressure fluctuation characteristic of the common liquid chamber of a comparative example. It is explanatory drawing of the pressure fluctuation characteristic of the common liquid chamber provided with the pressure absorber which concerns on this invention. It is explanatory drawing of the pressure resonance characteristic of the Young's modulus of a pressure absorber, and a common liquid chamber. It is a plane explanatory view of a pressure absorber used for explanation of other embodiments of the present invention. It is explanatory drawing of the pressure change characteristic of the common liquid chamber with which it uses for operation | movement description of the same embodiment. It is sectional explanatory drawing in alignment with the liquid chamber longitudinal direction of the head used for description of further another embodiment of this invention. 1 is an explanatory perspective view illustrating an example of an image forming apparatus according to the present invention. It is side surface explanatory drawing used for description of the mechanism part of the apparatus. It is sectional explanatory drawing in alignment with the liquid chamber longitudinal direction used for description of the conventional droplet discharge head. It is sectional explanatory drawing in alignment with the liquid chamber transversal direction where it uses for description of the head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Flow path (liquid chamber) board | substrate 2 ... Vibration board 3 ... Nozzle board 5 ... Nozzle hole 6 ... Pressurized liquid chamber 7 ... Ink supply path 8 ... Common liquid chamber 9 ... Ink supply port 11 ... Base board 12 ... Piezoelectric element DESCRIPTION OF SYMBOLS 13 ... Base board 14 ... Frame member 18 ... FPC cable 19 ... Drive circuit (driver IC)
20 ... Sealant 21 ... Pressure absorber 22 ... Thin part 23 ... Thick part 24 ... Second thick part 25 ... Damper chamber

Claims (9)

In a droplet discharge head having a common liquid chamber for supplying a liquid to a plurality of liquid chambers each communicating with a plurality of nozzles,
The alignment direction of the liquid chamber when the X-direction, at least one surface of the wall along the X direction of the common liquid chamber is low have the pressure absorbing member surface stiffness than the other wall surface,
The member forming the pressure absorber surface is characterized in that when the pressure absorber surface is divided into three in the X direction, the average thickness of the three divided central portions is larger than the average thickness of both end portions. . 2. The droplet discharge head according to claim 1 , wherein the member forming the pressure absorber surface has at least two kinds of thicknesses, a thin portion and a thick portion. 3. The droplet discharge head according to claim 2 , wherein the members forming the pressure absorber surface are thin portions at both ends in the X direction and thick portions at the center portion. 4. 4. The liquid droplet ejection head according to claim 2 , wherein the member forming the pressure absorber surface has a laminated structure, and the number of laminated layers is different between the thin portion and the thick portion. Discharge head. In the liquid droplet ejecting head according to any one of claims 1 to 4, the droplet discharge head member for being Ni to form the pressure absorbing member surface. In the liquid droplet ejecting head according to any one of claims 1 to 5, at least a part of members forming the diaphragm and the pressure absorbing member surface to form at least one surface of the liquid chamber is integrally formed of the same layer A droplet discharge head characterized by comprising: Droplet discharge having a common liquid chamber for supplying a liquid to a plurality of liquid chambers in which a plurality of nozzles communicate with each other, and having a plurality of pressure conversion means for changing the pressure in the liquid chamber on a base substrate In the head
The alignment direction of the liquid chamber when the X-direction, at least one surface of the wall along the X direction of the common liquid chamber is low have the pressure absorbing member surface stiffness than the other wall surface,
The member forming the pressure absorber surface is characterized in that when the pressure absorber surface is divided into three parts in the X direction, the average rigidity of the three divided central parts is higher than the average rigidity of both end parts. Drop ejection head. In the liquid droplet ejecting head according to any one of claims 1 to 7, a droplet discharge head, wherein the head is a line type recording head. An image forming apparatus for forming an image on a recording medium includes a liquid droplet ejection head, an image forming apparatus characterized by comprising a liquid droplet ejection head according to any one of claims 1 to 8.

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