JP2008137255A - Inkjet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a decline in pattern accuracy caused by the distortion of a head. <P>SOLUTION: An inkjet head 10 is divided by bulkheads, and two or more pressure chambers communicating with a liquid material source by a common channel are arranged in the longitudinal direction. The surface of one side of the inkjet head is the 1st plate-like element which has a nozzle for discharging the liquid material filling the pressure chamber, and the surface of the other side is the 2nd plate-like elastically-deformable element wherein a pressure generating element 60 is arranged at the side opposite to each pressure chamber. The inkjet head has a Peltier element 300 which is used as a temperature gradient giving means for making the temperature of the end of the longitudinal direction lower than the one of the center part of the longitudinal direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet head of an ink jet apparatus that forms a pattern on a recording medium by ejecting droplets made of a liquid material such as ink using a pressure generating element such as a piezo element.

  An ink jet head that ejects ink using a conventional pressure generating element includes, for example, a nozzle plate in which a plurality of nozzles are arranged in the longitudinal direction and a pressure generating element in the longitudinal direction, as in the case of the nozzle, as disclosed in Patent Document 1. The diaphragms are arranged, and pressure chambers arranged between the nozzle plate and the diaphragm, each partitioned by a partition wall. The diaphragm is bent by the action of the pressure generating element to pressurize the pressure chamber, and a droplet made of a liquid material such as ink (hereinafter referred to as “droplet”) is discharged from the nozzle by the pressure.

JP 2002-234157 A

However, in the ink jet head having the above configuration (hereinafter referred to as “head”), if the diaphragm is bent and the pressure chamber is pressurized, the nozzle plate may also be bent. When the nozzle plate is bent, the volume change of the pressure chamber is suppressed, so that the discharge amount of the droplet is reduced.
The end of the head in the longitudinal direction has a relatively high rigidity because a cavity such as a pressure chamber is not formed. On the other hand, in the central part, since there are many areas occupied by the cavity (pressure chamber) between the nozzle plate and the diaphragm, the structure is low in rigidity and easily bent. Therefore, the above-described decrease in the discharge amount is greater in the central portion than in the end portion of the head, and the discharge amount may vary in the longitudinal direction of the head. The variation has been a cause of a decrease in the accuracy (quality) of the pattern formed on the recording medium.

  In order to solve the above problems, the head of the present invention is partitioned by a partition, and a plurality of pressure chambers communicating with a liquid material supply source are arranged in a longitudinal direction in a common flow path, and one surface is the pressure chamber Is a first plate-like member in which a nozzle for discharging the liquid material filled therein is formed, and the other surface is an elastically deformable second member in which a pressure generating element is arranged opposite to each of the pressure chambers. The head is a plate-like member having a temperature gradient applying means for lowering the temperature at the end in the longitudinal direction as compared with the temperature at the center in the direction.

When the pressure chamber is pressurized by the pressure element, the first plate-shaped member tends to bend in the direction of being pressurized with the end portion as a fulcrum. For this reason, the amount of change in the volume of the pressure chamber in the central portion is reduced and the discharge amount is also reduced.
On the other hand, the viscosity of the liquid material generally increases as the temperature decreases. Therefore, when the temperature of the liquid material is lowered, the ratio of the discharge amount to the pressurization amount of the pressure element is lowered. Therefore, as described above, by lowering the temperature of the end of the head as compared with the temperature of the central portion, the difference in the discharge amount due to the bending of the first plate-like member is compensated, and the discharge amount in the longitudinal direction is compensated. Variations can be suppressed and the accuracy of the pattern formed on the recording medium can be improved.

Preferably, the temperature gradient applying means includes at least one of a cooling means for cooling the end portion and a heating means for heating the center portion.
With this configuration, either the cooling of the end portion or the heating of the central portion can be performed, so that a temperature gradient can be applied in the longitudinal direction of the head. In addition, since both the cooling of the end portion and the heating of the central portion can be performed simultaneously to form a steep gradient, it is possible to cope with the case where the rigidity of the first plate member is insufficient.

Preferably, the cooling means and / or the heating means is a Peltier element.
Since the Peltier element operates by energization, it can be cooled and / or heated without providing a refrigerant pipe or the like separately. Therefore, a temperature gradient can be applied to the head without complicating the configuration.

The heating means may be an electric heater.
Since the electric heater also operates by energization, a temperature gradient can be applied to the head without complicating the configuration.

Preferably, the apparatus further comprises discharge amount measuring means for measuring the amount of liquid material discharged from the nozzle at the end portion and the amount of liquid material discharged from the nozzle at the center portion. The temperature gradient is set so that the discharge amounts are substantially the same.
Since the head can be cooled and / or heated in accordance with the change in the ejection amount due to the bending of the first plate member, the variation in the ejection amount can be further suppressed and the pattern formed on the recording medium can be improved.

Preferably, the temperature gradient applying means is arranged over the entire area in the longitudinal direction of the head.
With such a configuration, it is possible to compensate for the difference in the discharge amount due to the bending of the first plate-like member over the entire area in the longitudinal direction of the head. Therefore, it is possible to further suppress the variation in the ejection amount and further improve the pattern formed on the recording medium.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. The embodiment of the present invention separately incorporates a means for imparting a temperature gradient to the head, and the internal configuration of the head is not substantially different from the conventional one. First, the configuration of the head and the deflection of the head will be described with reference to FIGS.

  FIG. 1 shows a part of a target head 10 according to the present embodiment, a nozzle plate 20, a pressure chamber substrate 30, and a second plate member as a first plate member which is a main member constituting the head. It is a perspective view divided and shown in the diaphragm 40 as. The vibration plate 40 and the nozzle plate 20 are joined to the upper surface and the lower surface of the pressure chamber substrate 30 in which the pressure chamber 52, the common flow path 54, and the like are formed to form the head 10. The number of pressure chambers 52 and the like is 120 to 360 in the X-axis direction. The illustrated structure is continuously formed so as to be symmetric with respect to the center line 56. Accordingly, the actual number of pressure chambers 52 is 240 to 720. The X-axis direction is the longitudinal direction.

  The pressure chamber substrate 30 is a silicon substrate having a predetermined thickness. The pressure chamber substrate 30 is selectively removed by etching so that a portion of the pressure chamber substrate 30 penetrates to the back surface, and the remaining portion is the partition wall 50. The region is sandwiched from above and below by a diaphragm 40 and a nozzle plate 20, which will be described later, and serves as a pressure chamber 52, a common channel 54, and the like.

  The vibration plate 40 is an elastically deformable plate member, and is formed by laminating an elastic film 42 and an insulator film 44 for electrically insulating the lower electrode film 62 of the piezoelectric element 60 as a pressure generating element. Has been. Piezo elements 60 are arranged at positions corresponding to the respective pressure chambers 52 via lower electrode films 62 that are common electrodes.

  The piezo element 60 includes a ferroelectric thin film 64, an upper electrode 66, and the like, and a lead electrode 68 is drawn from the upper electrode 66. The lead electrode 68 is electrically connected to a head control mechanism (not shown), and can apply a voltage independently to each piezo element 60. A voltage can be applied to the piezo element 60 to bend the diaphragm 40 in the direction of decreasing the volume of the pressure chamber 52, and a voltage can be applied in the opposite direction to reduce the volume of the diaphragm 40 to the pressure chamber 52. It can be bent in the direction of increasing.

  The nozzle plate 20 is a plate-like member in which the nozzles 21 are arranged so as to correspond to the respective pressure chambers 52. When the vibration plate 40 bends in a direction to reduce the volume of the pressure chamber 52, ink as a liquid material filled in the pressure chamber 52 is ejected as droplets from the nozzle. Further, when the vibration plate 40 bends in the direction of increasing the volume of the pressure chamber 52, ink is filled into the pressure chamber 52 from an ink tank (not shown) via the common flow path.

  Unlike the diaphragm 40, the pressure chamber substrate 30 and the nozzle plate 20 are made of an inelastic material in order to accurately replace the operation (vertical movement) of the diaphragm 40 with the volume change of the pressure chamber 52. However, when a large number of droplets are ejected continuously, the nozzle plate 20 may be slightly bent. The degree of the bending differs between the central portion and the end portion of the head 10. FIG. 2 shows a state in which the nozzle plate 20 is bent.

  2A to 2D are schematic cross-sectional views in which the head 10 is cut along a longitudinal direction (X-axis direction shown in FIG. 1) along a plane perpendicular to the Y-axis (see FIG. 1, the same applies hereinafter). is there. As shown in FIG. 2A, pressure chambers 52 having an upper surface formed of the diaphragm 40, a lower surface formed of the nozzle plate 20, and a side surface formed of the partition walls 50 are arranged at equal intervals. A piezo element 60 is disposed on the upper surface of each pressure chamber 52, and the nozzle 21 is formed on the lower surface. Although 11 nozzles 21 are illustrated, 240 to 720 nozzles are actually formed as described above. The pressure chamber substrate end portion 206 also functions as the partition wall 50, but is formed wider (longer in the longitudinal direction) than the partition wall 50 in other regions (for example, the central portion), and the nozzle plate 20 and the diaphragm 40. Are strongly coupled to the pressure chamber substrate 30.

  FIG. 2B shows the force applied to the nozzle plate 20 when the droplet 200 is ejected from the group of nozzles 21 formed in the head central portion 202. When the diaphragm 40 is bent in the direction in which the pressure chamber 52 is compressed by the piezo element 60, a force is applied to bend the central portion of the nozzle plate 20 in the direction of the arrow by the filled ink. As a result, the nozzle plate 20 bends downward as long as it does not peel from the partition wall 50.

  Next, FIG. 2C shows the force applied to the nozzle plate 20 when the droplet 200 is ejected from the group of nozzles 21 formed on the head end portion 204. Similar to the case where the droplet 200 is ejected from the central portion described above, a force acts to deflect the head end portion 204 in the direction of the arrow. However, even when the same force is applied, the degree of deflection of the nozzle plate 20 at the head center portion 202 and the head end portion 204 is different. The pressure chamber substrate end portion 206 has a high rigidity and is difficult to be deformed because the three substrates are combined in a wide area. Therefore, the head end portion 204 has little deflection of the nozzle plate 20.

  FIG. 2D schematically shows a state in which the nozzle plate 20 bends when a voltage is simultaneously applied to all the piezo elements 60 to operate the diaphragm 40 and the droplets 200 are simultaneously ejected from all the nozzles 21. It is shown as an example. The force generated in each pressure chamber 52 is indicated by an arrow.

  The magnitude of the force is the same in the head central portion 202 and the head end portion 204, but the degree of deformation of the nozzle plate 20 is larger in the head central portion 202. Therefore, the nozzle plate 20 bends downward in an arc shape. Therefore, even when the same voltage is applied to the piezo element 60, the variation in the pressure chamber volume of the head central portion 202 is reduced, and the ejection amount of the droplet 200 is also reduced. That is, the ejection amount may vary between the head center portion 202 and the head end portion 204. In the present invention, a temperature gradient is applied to the head 10 and the above-described variation is suppressed by utilizing the temperature dependence of the ink viscosity.

(First embodiment)
FIG. 3 shows the head 10 according to the first embodiment of the present invention. It is a figure which shows typically the external appearance seen from the Y-axis direction. The head 10 according to the present embodiment is characterized in that a Peltier element 300 as a temperature gradient applying unit is attached (arranged) to a side surface (a surface perpendicular to the Y axis) of the end portion. When energized, the Peltier element 300 dissipates heat absorbed by one surface (hereinafter referred to as “front surface”) from the other surface (hereinafter referred to as “back surface”). Therefore, when the surface is stuck, the sticking area can be cooled.

  As shown in the drawing, the surface of the Peltier element 300 is attached to both ends of the head 10, and when the pattern is formed, the element is energized from the power supply 302 to cool the end. A temperature gradient is generated in the entire head 10 due to heat conduction of the members forming the head 10. That is, the temperature gradually decreases from the center of the head to the end of the head. Since the Peltier element 300 is electrically driven, precise temperature control is possible, and an arbitrary temperature gradient can be set only by providing the wiring 304 that is electrically connected to the power source provided in the ink jet apparatus.

  The ink ejected from the nozzles 21 has a pattern forming material dissolved or dispersed in a volatile solvent. The viscosity of the solvent generally has a negative correlation with the liquid temperature, and the viscosity increases as the liquid temperature decreases. When droplets are discharged from the same nozzle 21 with the same force, the discharge amount decreases as the viscosity increases. Therefore, when the temperature gradient as described above is applied, the discharge amount variation in the longitudinal direction of the head is compensated by compensating (canceling) the decrease in the discharge amount at the center of the head due to the deflection of the nozzle plate 20 that occurs during pattern formation. It can suppress and can form a highly accurate pattern.

Further, when a relatively wide pattern is formed by discharging a large number of droplets on the substrate, the landed droplets naturally dry from the droplets outside the droplet group, but the liquid discharged from the head 10 Since the temperature of the droplet at the center of the head is relatively higher than the outside of the droplet group, the natural drying of the landed droplet group proceeds more uniformly. Therefore, a pattern with improved film thickness uniformity can be obtained.
Furthermore, it is possible to cope with the reduction in the nozzle interval (pitch) due to the higher density of the head 10, the lowering of the ratio of the partition wall 50 in the pressure chamber substrate 30 and the lowering of the rigidity of the head 10 that may occur in the future. .

  In FIG. 3, one of the side surfaces of the head 10 is illustrated, but a Peltier element 300 may be attached to the opposite side to cool from both sides. Further, although each Peltier element 300 is connected to an individual power source 302, both Peltier elements 300 may be operated by one power source 302.

(Second Embodiment)
FIG. 4 shows a head 10 according to a second embodiment of the present invention. It is a figure which shows typically the external appearance seen from the Y-axis direction similarly to the said 1st Embodiment.
In the head 10 according to the present embodiment, the Peltier element 300 is attached to the side surface (surface perpendicular to the Y axis) of the head end portion, and the Peltier element 300 is also attached to the center of the head. The surface of the Peltier element 300 at the head end is affixed similarly to the first embodiment, and the affixed area is cooled. On the other hand, the back surface of the Peltier element 300 at the center of the head is affixed to heat the affixed area. In other words, since the head 10 of the present embodiment can heat the center of the head while cooling the head end, it is possible to set a steeper temperature gradient than the head 10 that only cools the head end. . As a result, even when the head 10 having a higher density is used, the deflection of the nozzle plate 20 can be corrected, and a higher definition pattern can be formed.

(Third embodiment)
FIG. 5 shows a head 10 according to a third embodiment of the present invention. It is a figure which shows typically the external appearance seen from the Y-axis direction similarly to the said 1st Embodiment.
The head 10 of the present embodiment is characterized in that the Peltier element 300 is attached to an area other than the head end. The side surface of the head 10 is divided into seven blocks in the longitudinal direction, and the Peltier element 300 is attached to six blocks excluding the central block. In addition, each Peltier element 300 at the target position across the center is combined and controlled (driven) independently.

  Rather than using the thermal conductivity of the head 10, the temperature gradient can be set more finely than the head that cools only the head end portion by providing a temperature gradient applying means in the entire longitudinal direction. As a result, it is possible to further suppress fluctuations in the discharge amount of the droplets due to the deflection of the nozzle plate 20, and to form a higher definition pattern.

(Fourth embodiment)
FIG. 6 shows a head 10 according to a fourth embodiment of the present invention including other elements constituting the ink jet apparatus. The head 10 moves along the head driving shaft 602 and can eject droplets at an arbitrary position. A Peltier element is disposed at least at the head end, and a temperature gradient can be applied in the same manner as in the first to third embodiments.
The recording medium transport unit 604 mounts the recording medium 606 and moves in the vertical direction of the head drive shaft 602 along the transport unit drive shaft 608. The droplet weight measurement unit 610 can measure the weight of droplets ejected from the head 10.

  The head 10 of the present embodiment divides the head 10 into several blocks in the longitudinal direction immediately before ejecting droplets onto the recording medium 606, and the amount of droplets ejected from the nozzles arranged in the blocks. , And a temperature gradient is set by controlling the voltage applied to the Peltier device 300 based on the measurement result. Since the temperature gradient is applied based on the actually measured values, fluctuations in the droplet discharge amount due to the deflection of the nozzle plate can be further suppressed, and a higher definition pattern can be formed.

(Modification 1)
In each of the embodiments described above, the Peltier element 300 is attached to the head 10 (a surface perpendicular to the Y axis). However, the surface on which the Peltier element 300 can be arranged is not limited to the above-described surface. FIG. 7 shows a mode of arrangement on another surface.

FIG. 7A shows a mode in which the Peltier element 300 is arranged (attached) on a surface perpendicular to the Z-axis of the head 10. FIG. 7 (b) shows a mode of arrangement (pasting) on a plane perpendicular to the X-axis. As in the above-described embodiments, the Peltier device 300 is connected to the power supply 302 via the wiring 304, and cools the sticking surface.
As described above, since each substrate constituting the head 10 has thermal conductivity, even when arranged on the above-described surface, a temperature gradient is imparted to the head 10 and fluctuations in the discharge amount of droplets can be suppressed. Further, it is possible to improve the cooling capacity by arranging on two or all three of the three surfaces including the surface perpendicular to the Y axis.

(Modification 2)
In each of the above embodiments, the Peltier element 300 is used as means for providing a temperature gradient. However, the means is not limited to the Peltier element, and other means may be used. As a cooling means, a mode in which a refrigerant is circulated around the head end portion or a mode in which cold air is blown is also possible. Moreover, as a heating means, the aspect which arrange | positions an electric heater in the center part of a head is also possible.

The perspective view which shows a head. The figure which shows the aspect which a nozzle plate bends. 1 is a diagram showing a head according to a first embodiment of the present invention. The figure which shows the head concerning the 2nd Embodiment of this invention. The figure which shows the head concerning the 3rd Embodiment of this invention. The figure which shows the head concerning the 4th Embodiment of this invention. The figure which shows the aspect of arrangement | positioning of the Peltier device in a modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Head, 20 ... Nozzle plate, 21 ... Nozzle, 30 ... Pressure chamber substrate, 40 ... Diaphragm, 42 ... Elastic film, 44 ... Insulator film, 50 ... Partition, 52 ... Pressure chamber, 54 ... Common flow path, 56 ... head center line, 60 ... piezo element, 62 ... lower electrode film, 64 ... ferroelectric thin film, 66 ... upper electrode, 68 ... lead electrode, 200 ... droplet, 202 ... head central portion, 204 ... head end 206, pressure chamber substrate end, 300 ... Peltier element, 302 ... power supply, 304 ... wiring, 602 ... head drive shaft, 604 ... recording medium transport unit, 606 ... recording medium, 608 ... transport unit drive shaft, 610 ... Droplet weight measurement unit.

Claims (6)

A plurality of pressure chambers, which are separated by a partition wall and communicate with a liquid material supply source in a common flow path, are arranged in the longitudinal direction, and a nozzle for discharging the liquid material filled in the pressure chamber is formed on one surface. An ink jet head that is an elastically deformable second plate member in which a pressure generating element is disposed on the opposite side of each of the pressure chambers.
An ink jet head, comprising: a temperature gradient imparting unit configured to lower a temperature at an end portion in the longitudinal direction as compared with a temperature at a central portion in the direction.   The inkjet head according to claim 1, wherein the temperature gradient applying unit includes at least one of a cooling unit that cools the end portion and a heating unit that heats the central portion.   The inkjet head according to claim 1, wherein the cooling unit and / or the heating unit is a Peltier element.   The inkjet head according to claim 1, wherein the heating unit is an electric heater.   There is further provided a discharge amount measuring means for measuring the amount of the liquid material discharged from the nozzle at the end portion and the amount of the liquid material discharged from the nozzle at the center portion, and both the discharge amounts are substantially the same. The inkjet head according to claim 1, wherein a temperature gradient is set so that   The inkjet head according to claim 1, wherein the temperature gradient applying unit is disposed over the entire area in the longitudinal direction of the inkjet head.

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