JP4999149B2 - Liquid ejection head and image forming apparatus - Google Patents

Description

  The present invention relates to a liquid discharge head and an image forming apparatus, and in particular, the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, and the liquid in the pressure chamber is pressurized by a pressure generating unit. The present invention relates to a liquid discharge head and an image forming apparatus for discharging the liquid from a nozzle communicating with the pressure chamber.

  The ink is supplied to a plurality of pressure chambers from a common flow path in which ink is stored, the ink in the pressure chamber is pressurized by pressure generating means represented by a piezoelectric element, and the ink is ejected from a nozzle communicating with the pressure chamber. Inkjet printing heads (inkjet heads) are conventionally known.

In such a print head, a structure in which an air damper is provided in the head is widely employed in order to prevent fluid crosstalk. Fluid crosstalk is a phenomenon in which sound waves generated from an arbitrary pressure chamber during ink discharge pass through a common flow path and enter other pressure chambers, adversely affecting other ink discharges. Sound waves having a resonance frequency of 200 to 300 kHz are the main cause of fluid crosstalk. For example, Patent Document 1 discloses a structure in which an air damper is provided in a common flow path, and fluid crosstalk is prevented by attenuating sound waves by deformation of the air damper.
JP 2003-127363 A

  However, the conventional print head has the following problems.

First, as representing the performance of the air damper, there is a damper acoustic capacitance C _d. Damper acoustic capacitance C _d represents the deformability of the damper. To prevent fluid crosstalk is excellent damper acoustic capacitance C _d is large damper. Damper acoustic capacitance C _d is the case of the beam structure fixed at both ends of the damper, in proportion to the fifth power of the damper width W, is inversely proportional to the cube of the damper thickness t. In other words, to widen the damper width W, reducing the damper thickness t, it leads to increasing the damper acoustic capacitance C _d. However, in recent years, with the increase in the density of nozzles, a sufficient space for installing an air damper cannot be obtained, and the damper width W has become narrower. As a result, a situation where not enough damper acoustic capacitance C _d, are no longer prevent fluid crosstalk. Of course, by reducing the damper thickness t, it is possible to increase the damper acoustic capacitance C _d. However, if the damper thickness t is reduced, the damper is easily broken and the risk of ink leakage increases. As described above, there is a problem in the method using the air damper, and it is desirable from the viewpoint of cost that fluid crosstalk can be prevented by a method other than the air damper.

  As a method other than the air damper, it can be considered that the sound wave generated when ink is ejected in the common flow path is attenuated. However, attenuation of sound waves in the common channel cannot be expected. This is because the sound wave attenuation constant in the ink (liquid) is small, and the scale of the common flow path is small, so that the sound wave travels only a short distance and is on the order of several millimeters at most. That is, the sound wave hardly attenuates in the common flow path, and fluid crosstalk cannot be prevented.

  Therefore, it is conceivable to configure so that the sound wave is released to the head main body (for example, the common flow path partition wall) rather than attenuating the sound wave in the common flow path. Since the head main body is solid, the attenuation is larger than that of ink (liquid), and the length scale is several tens of millimeters, so that the sound wave travels a long distance. Therefore, the sound wave is more easily attenuated than ink (liquid). However, in actuality, it is difficult to escape the sound waves in the common flow path to the head body side. This is because the sound wave reflectance between the liquid and the solid is very high.

Here, as shown in FIG. 15, a case is considered in which a sound wave propagating through the ink in the common flow channel hits the head body (solid) perpendicularly. When Z ₁ is the acoustic impedance of the ink (liquid) and Z ₃ is the acoustic impedance of the head body (solid), the energy transmittance T ₀ is expressed by the following equation (1).

For example, when Z ₁ = 1.5 × 10 ⁶ [Ns / m ³ ] (acoustic impedance of liquid) and Z ₃ = 45.7 × 10 ⁶ [Ns / m ³ ] (acoustic impedance of SUS347), from equation (1) The energy transmittance T ₀ = 13%. That is, a little less than 90% of the energy of the sound wave is reflected by the head body, and the reflected wave causes crosstalk.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a liquid discharge head and an image forming apparatus that can prevent fluid crosstalk.

In order to achieve the above object, according to a first aspect of the present invention, the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, and the liquid in the pressure chamber is pressurized by pressure generating means. A liquid discharge head that discharges the liquid from a nozzle that communicates with the pressure chamber, and a crosstalk that attenuates a sound wave that has propagated in the common flow path when liquid is discharged to the partition of the common flow path A prevention member is provided, and the crosstalk prevention member is at least two layers of a first member that contacts the liquid in the common flow path and a second member that is joined to the side opposite to the liquid side of the first member. is configured, the first member, Z ₁ and the acoustic impedance of the liquid in the common flow _path, Z ₂ the acoustic impedance of the first _member, the acoustic impedance of the second member when the Z _3, following Formula Z ₁ <Meets the relationship Z 2 _{<Z 3,} and the acoustic impedance Z ₁ of the _liquid, the relationship between the acoustic impedance Z ₃ of the acoustic impedance Z ₂ and the second member of the first member, the following equation 0.72 × _{(Z 1} × _Z ³⁾ to provide a ^{_{1/2 ≦ Z 2 <1.39 × (}} Z 1 × Z 3) the liquid discharge head is characterized by being composed to ^1/2 less than Suyo.

  According to the present invention, since the energy transmittance of the sound wave in the first member and the second member constituting a part of the common flow path partition is improved, the sound wave generated at the time of liquid ejection is transmitted to the head main body side (common flow path partition side). Thus, fluid crosstalk can be prevented.

Invention of Claim 2 is the liquid discharge head of Claim 1, Comprising: The said common flow path is arrange | positioned on the opposite side to the said nozzle side of the said pressure chamber, The said crosstalk prevention member is It is provided in the partition on the opposite side to the said pressure chamber side of the said common flow path, It is characterized by the above-mentioned.

The aspect of claim 2 is excellent in refilling property, and can efficiently release sound waves generated in the pressure chamber during liquid ejection to the head body side (common flow path partition wall side), thereby reliably preventing fluid crosstalk. can do.

The invention according to claim 3, a liquid discharge head according to claim 1 or claim 2, wherein the second member is the a liquid tank which liquid is stored, the first member, A supply flow path that communicates the liquid tank and the common flow path is formed.

According to the third aspect of the present invention, fluid crosstalk can be prevented and the liquid tank can be arranged efficiently.

A fourth aspect of the present invention is the liquid ejection head according to the third aspect , wherein a filter member is provided in at least a part of the supply flow path.

According to the fourth aspect of the present invention, foreign matters can be prevented from entering the common flow path from the liquid tank.

The invention according to claim 5 is the liquid discharge head according to claim 4 , wherein the flow path area of the portion of the supply flow path where the filter member is provided is larger than that of other portions of the supply flow path. It is characterized by having a large structure.

According to the fifth aspect of the present invention, pressure loss due to the filter member can be reduced.

A sixth aspect of the present invention is the liquid discharge head according to the first or second aspect , wherein the first member is provided with a heater wiring.

According to the sixth aspect of the present invention, it is possible to prevent a discharge failure caused by the thickening of the liquid in the common flow path.

A seventh aspect of the present invention is the liquid discharge head according to the first or second aspect , wherein the first member is provided with a Peltier element.

The aspect of claim 7 is an aspect suitable for the case where the second member is a circuit board, and prevents ejection failure caused by thickening of the liquid in the common flow path and prevents deterioration of the circuit element. be able to.

The invention according to claim 8 is the liquid discharge head according to claim 1 or 2 , wherein a liquid circulation path is formed in the first member.

According to the aspect of the eighth aspect, the liquid circulation path can be efficiently incorporated into the liquid discharge head.

The invention according to claim 9 is the liquid discharge head according to claim 1 or 2 , wherein the first member is provided with a wiring member for driving the pressure generating means. It is characterized by.

According to the ninth aspect, high-density wiring can be mounted.

According to a tenth aspect of the present invention, the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, and the liquid in the pressure chamber is pressurized by a pressure generating unit and communicates with the pressure chamber. A liquid discharge head for discharging the liquid from a nozzle, wherein a partition wall of the common flow path is provided with a crosstalk preventing member for attenuating a sound wave propagated in the common flow path during liquid discharge, The crosstalk preventing member includes at least two layers of a first member that contacts the liquid in the common flow path and a second member that is bonded to the opposite side to the liquid side of the first member, and the first member Where Z _{1 is} the acoustic impedance of the liquid in the common channel, Z _{2 is} the acoustic impedance of the first member, and Z ₃ is the acoustic impedance of the second member , the following formula: Z ₁ <Z ₂ < Z ₃ of relationship Is configured to satisfy, wherein the first member, wherein the heater wire is provided.
According to an eleventh aspect of the present invention, the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by a pressure generating unit, and communicates with the pressure chamber. A liquid discharge head for discharging the liquid from a nozzle, wherein a partition wall of the common flow path is provided with a crosstalk preventing member for attenuating a sound wave propagated in the common flow path during liquid discharge, The crosstalk preventing member includes at least two layers of a first member that contacts the liquid in the common flow path and a second member that is bonded to the opposite side to the liquid side of the first member, and the first member Where Z _{1 is} the acoustic impedance of the liquid in the common channel, Z _{2 is} the acoustic impedance of the first member, and Z ₃ is the acoustic impedance of the second member , the following formula: Z ₁ <Z ₂ < Z ₃ of relationship It is configured to satisfy, wherein the first member, characterized in that the Peltier element is provided.
According to a twelfth aspect of the present invention, the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by a pressure generating unit, and communicates with the pressure chamber. A liquid discharge head for discharging the liquid from a nozzle, wherein a partition wall of the common flow path is provided with a crosstalk preventing member for attenuating a sound wave propagated in the common flow path during liquid discharge, The crosstalk preventing member includes at least two layers of a first member that contacts the liquid in the common flow path and a second member that is bonded to the opposite side to the liquid side of the first member, and the first member Where Z _{1 is} the acoustic impedance of the liquid in the common channel, Z _{2 is} the acoustic impedance of the first member, and Z ₃ is the acoustic impedance of the second member , the following formula: Z ₁ <Z ₂ < Z ₃ of relationship It is configured to satisfy, wherein the first member, wherein the liquid circulation path is formed.
According to a thirteenth aspect of the present invention, the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by a pressure generating unit, and communicates with the pressure chamber. A liquid discharge head for discharging the liquid from a nozzle, wherein a partition wall of the common flow path is provided with a crosstalk preventing member for attenuating a sound wave propagated in the common flow path during liquid discharge, The crosstalk preventing member includes at least two layers of a first member that contacts the liquid in the common flow path and a second member that is bonded to the opposite side to the liquid side of the first member, and the first member Where Z _{1 is} the acoustic impedance of the liquid in the common channel, Z _{2 is} the acoustic impedance of the first member, and Z ₃ is the acoustic impedance of the second member , the following formula: Z ₁ <Z ₂ < Z ₃ of relationship It is configured to satisfy, wherein the first member, wherein the wire member for driving the pressure generating means.
In order to achieve the above object, an invention according to claim 14 provides an image forming apparatus comprising the liquid discharge head according to any one of claims 1 to 13. To do.

  According to the present invention, since the energy transmittance of the sound wave in the first member and the second member constituting a part of the common flow path partition is improved, the sound wave generated at the time of liquid ejection is transmitted to the head main body side (common flow path partition side). Thus, fluid crosstalk can be prevented.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram showing an outline of an ink jet recording apparatus as an image forming apparatus according to the present invention. As shown in FIG. 1, the inkjet recording apparatus 10 includes a printing unit 12 having a plurality of printing heads 12K, 12C, 12M, and 12Y provided for each ink color, and each printing head 12K, 12C, 12M, and 12Y. An ink storage / loading unit 14 for storing ink to be supplied to the paper, a paper feeding unit 18 for supplying the recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle surface of the printing unit 12 An adsorption belt conveyance unit 22 that is arranged opposite to the (ink ejection surface) and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, a print detection unit 24 that reads a printing result by the printing unit 12, and a print And a paper discharge unit 26 for discharging the printed recording paper (printed matter) to the outside.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  In the case of an apparatus configuration using roll paper, a cutter 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is arranged on the print surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least a portion facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 is flat. It is configured to make.

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, an adsorption chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The recording paper 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blowing method of spraying clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip transport mechanism instead of the suction belt transport unit 22 is also conceivable, when the print area is transported by a roller / nip, the roller comes into contact with the print surface of the paper immediately after printing, so that the image blurs. There is a problem that it is easy. Therefore, as in this example, suction belt conveyance that does not contact the image surface in the printing region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 12 is a so-called full-line type head in which line-type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper transport direction (sub-scanning direction). Each of the print heads 12K, 12C, 12M, and 12Y constituting the printing unit 12 has a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10. It is composed of a line type head.

  Printing corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side (left side in FIG. 1) along the conveyance direction (paper conveyance direction) of the recording paper 16 Heads 12K, 12C, 12M, and 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the print heads 12K, 12C, 12M, and 12Y while the recording paper 16 is conveyed.

  Thus, according to the printing unit 12 in which the full line head that covers the entire width of the paper is provided for each ink color, the recording paper 16 and the printing unit 12 are relatively moved in the paper transport direction (sub-scanning direction). It is possible to record an image on the entire surface of the recording paper 16 by performing this operation only once (that is, by one sub-scan). Accordingly, high-speed printing is possible as compared with a shuttle type head in which the print head reciprocates in a direction (main scanning direction) orthogonal to the paper transport direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank has a pipeline that is not shown. The print heads 12K, 12C, 12M, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means, etc.) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. doing.

  The print detection unit 24 includes an image sensor (line sensor or the like) for imaging the droplet ejection result of the print unit 12, and means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor. Function as.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor includes a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test patterns printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by blocking the paper holes by pressurization. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined uneven surface shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with sorting means (not shown) for switching the paper discharge path in order to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. ing. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

  Since the print heads 12K, 12C, 12M, and 12Y provided for each ink color have the same structure, the print head is represented by reference numeral 50 in the following.

[Print head structure]
FIG. 2 is a plan view showing the ink ejection surface of the print head 50. In the print head 50 of this example, the nozzles 51 that eject ink droplets are arranged in a two-dimensional shape (matrix shape) in a main scanning direction and an oblique direction that is not orthogonal to the main scanning direction. Projection nozzle rows projected so as to be aligned along the main scanning direction are arranged at regular intervals with a constant nozzle pitch P, and high density of the dot pitch printed on the recording paper surface is achieved. Yes.

  3 is a cross-sectional view taken along line 3-3 in FIG. As shown in FIG. 3, the nozzle 51 is formed on the lower wall side of the pressure chamber 52 filled with ink. The diaphragm 56 constitutes the upper wall of the plurality of pressure chambers 52, and a common liquid chamber 55 in which ink is stored is located on the opposite side of the diaphragm 56 from the pressure chamber 52 side. The common liquid chamber 55 is a main aspect of the common flow path in the present invention, and may be divided into a main flow and a tributary. A supply port (through hole) 53 for supplying ink from the common liquid chamber 55 to each pressure chamber 52 is formed in the vibration plate 56.

  According to such a print head 50, the common liquid chamber 55 is disposed on the opposite side of the pressure chamber 52 from the nozzle 51 side with the diaphragm 56 interposed therebetween, so that the pressure from the common liquid chamber 55 through the supply port 53 is increased. Ink can be efficiently supplied to the chamber 52. That is, the head structure is excellent in refillability.

  On the opposite side of the diaphragm 56 from the pressure chamber 52 side, a piezoelectric element 58 (pressure generating means) including individual electrodes 57 is disposed at a position corresponding to each pressure chamber 52. In this example, the diaphragm 56 is made of a conductive member such as SUS, and also serves as a common electrode for the plurality of piezoelectric elements 58. The diaphragm 56 may be made of a non-conductive member, and a conductive layer may be formed on the surface on the piezoelectric element 58 side. On the piezoelectric element 58 side of the diaphragm 56, a protective cover 60 is provided so as to surround each piezoelectric element 58 so as to ensure a certain gap around each piezoelectric element 58. Thereby, electrical insulation with respect to the ink in the common liquid chamber 55 is ensured, and displacement of the piezoelectric element 58 is not restricted.

  When a driving signal (driving voltage) is applied to the piezoelectric element 58, the diaphragm 56 is deformed so as to bend toward the pressure chamber 52 due to the displacement of the piezoelectric element 58. As a result, the ink in the pressure chamber 52 is pressurized and an ink droplet is ejected from the nozzle 51.

  In such a print head 50, the upper wall 63 of the common liquid chamber 55 is composed of two layers, that is, an intermediate layer 64 (first member) and a surface layer 66 (second member). A sound wave generated in the pressure chamber 52 propagates to the common liquid chamber 55 through the supply port 53 and enters the other pressure chambers 52 to adversely affect the fluid crosstalk. A specific method for preventing fluid crosstalk will be described in detail later.

[Configuration of ink supply system]
FIG. 4 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10. The ink tank 70 is a base tank that supplies ink to the print head 50 and is installed in the ink storage / loading unit 14 described with reference to FIG. In the form of the ink tank 70, there are a system that replenishes ink from a replenishment port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink decreases. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type. The ink tank 70 shown in FIG. 4 is equivalent to the ink storage / loading unit 14 shown in FIG. 1 described above.

  As shown in FIG. 4, a filter 72 is provided between the ink tank 70 and the print head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm). Although not shown in FIG. 4, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the ink jet recording apparatus 10 is provided with a cap 74 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 76 as a means for cleaning the nozzle surface. The maintenance unit including the cap 74 and the cleaning blade 76 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  The cap 74 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap 74 is raised to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the print head 50, thereby covering the nozzle surface with the cap 74.

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the piezoelectric element 58 operates.

  Prior to this state, the piezoelectric element 58 is operated (within the range of viscosity that can be discharged by the operation of the piezoelectric element 58), and preliminary discharge is performed toward the cap 74 (ink receiver) to discharge the deteriorated ink. (Purge, idle discharge, spit out) are performed.

  Further, when air bubbles are mixed in the ink in the print head 50 (pressure chamber 52), the ink cannot be ejected from the nozzle 51 even if the piezoelectric element 58 is operated. In such a case, the cap 74 is applied to the print head 50, and the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with the suction pump 77, and the suctioned and removed ink is sent to the collection tank 78. . In this suction operation, the deteriorated ink having increased viscosity (solidified) is sucked out when the initial ink is loaded into the print head 50 or when the ink is used after being stopped for a long time. In addition, since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is desirable to perform preliminary ejection when the increase in ink viscosity is small.

  The cleaning blade 76 is made of an elastic member such as rubber, and can slide on the nozzle surface of the print head 50 by a blade moving mechanism (not shown). When ink droplets or foreign matters adhere to the nozzle surface, the nozzle surface is wiped by sliding the cleaning blade 76 on the nozzle surface to clean the nozzle surface. When the nozzle surface is cleaned by the blade moving mechanism, preliminary discharge is performed in order to prevent foreign matters from being mixed into the nozzle 51 by the blade.

[Method of preventing fluid crosstalk]
Next, a method for preventing fluid crosstalk will be described.

  FIG. 5 is a cross-sectional view of the main part showing the periphery of the upper wall 63 of the common liquid chamber 55 of the print head 50. In the drawing, reference numeral 62 represents an ink layer stored in the common liquid chamber 55. As described above, the upper wall 63 of the common liquid chamber 55 has a two-layer configuration of the intermediate layer 64 (first member) and the surface layer 66 (second member). The upper wall 63 of the common liquid chamber 55 may be composed of three or more layers. The surface layer 66 is composed of, for example, an ink tank, a build-up substrate, a head fixing member, and the like.

The thickness L of the intermediate layer 64 is expressed by the following equation (2) when the wavelength of the sound wave passing through the intermediate layer 64 is λ and n is a non-negative integer (that is, n = 0, 1, 2,...).
[Equation 2]
L = λ × (2n + 1) / 4 (2)
It is configured to satisfy. The energy transmittance T _{1 at} this time is expressed by the following equation (3) when the acoustic impedance of the ink layer 62 is Z ₁ , the acoustic impedance of the intermediate layer 64 is Z ₂ , and the acoustic impedance of the surface layer 66 is Z _3.

It is represented by The relationship between the acoustic impedance _{Z 1,} Z 2, _{Z 3} has the following formula (4)
[Equation 4]
Z ₁ <Z ₂ <Z ₃ or Z ₃ <Z ₂ <Z ₁ (4)
When configured to satisfy the above, the energy transmittance T ₁ of the present embodiment is equal to or higher than the conventional energy transmittance T ₀ described above. That is, by configuring so as to satisfy the formulas (2) and (4), the energy transmittance is improved as compared with the conventional case, and as a result, the ink propagates from the pressure chamber 52 into the common liquid chamber 55 during ink ejection. The energy of the sound wave thus generated can be released to the partition wall 63 (intermediate layer 64 and surface layer 66) side of the common liquid chamber 55, and fluid crosstalk can be prevented.

For example, similarly to the example described above, Z ₁ = 1.5 × 10 ⁶ [Ns / m ³ ] (acoustic impedance of liquid) and Z ₃ = 45.7 × 10 ⁶ [Ns / m ³ ] (acoustic impedance of SUS347) in some cases, an intermediate layer 64 between the ink layer 62 (liquid) and the surface layer 66 (SUS347), for example, try to determine the energy transmittance _{T 1} of the case of arranging the glass. When the intermediate layer 64 is not present, the energy transmittance T ₀ is 13% as described above.

First, the speed of sound in the glass is 5100 [m / s], and if the crosstalk frequency to be handled is 300 [kHz], the wavelength λ of the sound wave passing through the glass is 17 [mm]. Therefore, from the formula (2), the glass thickness L = 4.25 [mm]. That is, as the intermediate layer 64, glass having a thickness of 4.25 [mm] may be disposed between the ink layer 62 and the surface layer 66. The acoustic impedance Z ₂ of the glass is ^{13.2 × 10 6 [Ns / m} 3], which satisfies the equation (4).

In this way, the energy transmittance T ₁ when the glass configured as described above is arranged as the intermediate layer 64 is T ₁ = 4 / 4.92 = 0.81 (81%) from the equation (3). T ₁ is more than 80%. Therefore, the energy transmittance is greatly improved as compared with the prior art, and as a result, the energy of the sound wave generated by the ink ejection can be released to the partition wall 63 (intermediate layer 64 and surface layer 66) side of the common liquid chamber 55. And fluid crosstalk can be prevented.

The acoustic impedances Z ₁ , Z ₂ , and Z ₃ of the ink layer 62, the intermediate layer 64, and the surface layer 66 are expressed by the following equation (5)
[Equation 5]
Z ₂ ≈ (Z ₁ × Z ₃ ) ^1/2 ... (5)
It is preferable that it is comprised so that it may satisfy | fill. When satisfying formula (5), sonic energy transmittance T ₁ becomes largest, the effect of preventing the fluid crosstalk increases.

For example, when Z ₁ = 1.5 × 10 ⁶ [Ns / m ³ ] (liquid acoustic impedance) and Z ₃ = 103 × 10 ⁶ [Ns / m ³ ] (tungsten acoustic impedance), the acoustic impedance Z ₂ = by selecting the material is ^{12.4 × 10 6 [Ns / m} 3] as the intermediate layer 64, the energy transmission factor T ₁ is the largest. Therefore, as the material close to the acoustic impedance (12.4 × 10 ⁶ [Ns / m ³ ]) that maximizes the energy transmittance T ₁ , glass with Z ₂ = 13.2 × 10 ⁶ [Ns / m ³ ] is used as the intermediate layer 64. Is selected, the energy transmittance T _{1 is} 99.5%, and almost 100% of the energy is transmitted.

In order to set the energy transmittance T ₁ to 90% or more, it is configured to satisfy the following equation (6), and in order to set it to 95% or more, the following equation (7) is satisfied. Good.

[Equation 6]
0.72 × (Z ₁ × Z ₃ ) ^1/2 ≦ Z ₂ ≦ 1.39 × (Z ₁ × Z ₃ ) ^1/2 (6)
[Equation 7]
0.80 × (Z ₁ × Z ₃ ) ^1/2 ≦ Z ₂ ≦ 1.26 × (Z ₁ × Z ₃ ) ^1/2 ... (7)
As described above, according to the present embodiment, the upper wall 63 of the common liquid chamber 55 has a two-layer structure of the intermediate layer 64 and the surface layer 66, and further satisfies the above equations (2) and (4). By configuring in this way, the energy transmittance of the sound wave is improved. Thereby, sound waves generated during ink ejection can be released to the head body side (upper wall 63 side of the common flow channel 55), and fluid crosstalk can be prevented.

[First Modification]
FIG. 6 is a cross-sectional view of a main part showing a first modification of the print head 50. In the first modification, the surface layer 66 also serves as the ink tank 70, and the supply flow path 80 is formed in the intermediate layer 64. Ink is stored inside the ink tank 70 (surface layer 66), and the ink is supplied to the common liquid chamber 55 via the supply flow path 80. With such a configuration, fluid crosstalk can be prevented and the ink tank 70 can be arranged efficiently.

[Second Modification]
FIG. 7 is a cross-sectional view of a main part showing a second modification of the print head 50. In the second modification, a filter member 82 is provided in the supply flow path 80 of the first modification shown in FIG. 6, and the flow path area of the part where the filter member 82 is disposed is another part. It is widely configured compared to Thereby, fluid crosstalk can be prevented and pressure loss due to the filter member 72 can be reduced.

  FIG. 8 is a perspective view schematically showing a method for producing the intermediate layer 64 shown in FIG. When the thickness of the intermediate layer 64 in FIG. 7 is L, as shown in FIG. 8, a filter member 82 is provided inside by sandwiching the filter film 84 between the intermediate layers 64A and 64B having a thickness of L / 2. An intermediate layer 64 can be formed. The ratio of the thicknesses of the intermediate layers 64A and 64B is not limited to this example.

[Third Modification]
FIG. 9 is a cross-sectional view of a main part showing a third modification of the print head 50. In the third modification, the heater wiring 86 is provided inside the intermediate layer 64. Thereby, fluid crosstalk can be prevented, and the heater for adjusting the ink temperature (for adjusting the head temperature) can be efficiently arranged.

  A plurality of heater wires 86 may be provided. The surface layer 66 may be a build-up substrate or a head fixing member, or may also serve as an ink tank as in the first and second modifications. The position at which the heater wiring 86 is disposed is not particularly limited, and may be disposed on the ink layer 62 (common liquid chamber 55) side or on the surface layer 66 side. For example, by disposing the heater wiring 86 on the ink layer 62 side, the ink layer 62 can be efficiently warmed and ink thickening can be suppressed. When the surface layer 66 also serves as an ink tank, the heater wiring 86 is arranged on the surface layer (ink tank) 66 side, so that the ink stored in the ink tank can be efficiently warmed. Further, when the heater wiring 86 is disposed on both sides of the intermediate layer 64 (the ink layer 62 side and the surface layer 66 side), the ink located on both sides of the intermediate layer 64 can be warmed more efficiently.

  FIG. 10 is a perspective view schematically showing a method for producing the intermediate layer 64 shown in FIG. As shown in FIG. 10, the intermediate layer 64 having the heater wiring 86 therein can be formed by sandwiching the heater wiring 86 between two intermediate layers 64A and 64B having a width smaller than that of the intermediate layer 64. Further, when the heater wiring 86 is formed on the surface of the intermediate layer 64, for example, a method such as sputtering may be used.

[Fourth Modification]
FIG. 11 is a cross-sectional view of a main part showing a fourth modification of the print head 50. In the fourth modification, a Peltier element 88 is provided inside the intermediate layer 64. The Peltier element 88 has a size that can be accommodated in the intermediate layer 64, and the Peltier element can be efficiently disposed in the intermediate layer 64.

  The Peltier element 88 has a property that one surface is heated and the opposite surface is cooled. For this reason, by using the Peltier element 88 disposed in the intermediate layer 64, one of the ink layer 62 and the surface layer 66 can be heated and the other can be cooled. For example, when the surface layer 66 is composed of a build-up substrate, a circuit element such as a switch IC on the substrate can be cooled by applying a voltage to the Peltier element 88 so that the surface layer 66 side is cooled. Thus, deterioration of the circuit element can be prevented. Further, at this time, the ink layer 62 located on the opposite side of the surface layer 66 can be warmed, so that it is possible to prevent ejection failure due to ink thickening.

  As described above, in the fourth modified example, fluid crosstalk can be prevented similarly to the first to third modified examples described above, and further, deterioration of circuit elements and defective discharge can be prevented.

[Fifth Modification]
FIG. 12 is a cross-sectional view of a main part showing a fifth modification of the print head 50. In the fifth modification, a liquid circulation path 90 is formed inside the intermediate layer 64. The temperature adjustment liquid flowing in the liquid circulation path 90 is not particularly limited, and may be water or ink, for example. A pump (not shown) for circulating the temperature adjusting liquid is configured to also serve as another pump (for example, the suction pump 77 shown in FIG. 4 or the ink channel circulation pump (not shown)). May be. With this configuration, fluid crosstalk can be prevented and a temperature control liquid circulation path can be efficiently incorporated.

[Sixth Modification]
FIG. 13 is a cross-sectional view of a main part showing a sixth modification of the print head 50. In the sixth modification, the internal wiring 92 is formed corresponding to each piezoelectric element 58 so as to penetrate the intermediate layer 64, and the surface layer 66 is constituted by a build-up substrate. One end of the internal wiring 92 is electrically connected to the individual electrode 57 of the piezoelectric element 58 through the protective cover 60, and the other end of the internal wiring 92 is an electrode (not shown) formed on the surface layer (build-up substrate) 66. Electrically connected. In this way, the individual electrode 57 of the piezoelectric element 58 is drawn out to the surface layer (build-up substrate) 66 through the internal wiring 92 in a direction substantially perpendicular to the vibration plate 56 on which the piezoelectric element 58 is disposed, whereby the vibration plate Compared with the case where the wiring is drawn out along the top 56, the electrical wiring can be mounted at a high density.

  The internal wiring 92 provided in the intermediate layer 64 may be used for wiring other than the piezoelectric element 58, for example, a temperature sensor or a pressure sensor. Further, although the internal wiring 92 of this modification is configured to penetrate the intermediate layer 64 in the vertical direction, the internal wiring 92 may be disposed in the horizontal direction of the intermediate layer 64. In this case, the surface layer 66 can be made of a material other than the buildup substrate.

[Other Embodiments]
FIG. 14 is a cross-sectional view of a main part showing another embodiment of the print head 50. The print head 50 shown in FIG. 3 has a common liquid chamber 55 arranged on the opposite side of the pressure chamber 52 from the nozzle 51 side (with the diaphragm 56 in between), whereas the print head shown in FIG. In the head 50, a common liquid chamber 55 is disposed on the same side as the nozzle 51 side of the pressure chamber 52. In such a configuration of the print head 50, the bottom wall of the common liquid chamber 55 has a two-layer configuration of an intermediate layer 64 and a surface layer 66. Even in such a print head 50, fluid crosstalk can be prevented by configuring the print head 50 so as to satisfy the expressions (2) and (4).

  The liquid ejection head and the image forming apparatus of the present invention have been described in detail above. However, the present invention is not limited to the above examples, and various improvements and modifications are made without departing from the gist of the present invention. Of course it is also good.

1 is an overall configuration diagram showing an outline of an inkjet recording apparatus. FIG. 3 is a plan view illustrating an ink discharge surface of a print head. It is sectional drawing which follows the 3-3 line in FIG. It is the schematic which showed the structure of the ink supply system. FIG. 4 is a cross-sectional view of a main part showing the periphery of an upper wall of a common liquid chamber of the print head. FIG. 5 is a cross-sectional view of a main part showing a first modification of a print head. It is principal part sectional drawing which showed the 2nd modification of the print head. FIG. 8 is a perspective view schematically showing a method for producing the intermediate layer shown in FIG. 7. It is principal part sectional drawing which showed the 3rd modification of the print head. FIG. 10 is a perspective view schematically showing a method for producing the intermediate layer shown in FIG. 9. It is principal part sectional drawing which showed the 4th modification of the print head. It is principal part sectional drawing which showed the 5th modification of the print head. It is principal part sectional drawing which showed the 6th modification of the print head. It is principal part sectional drawing which showed other embodiment of the print head. It is explanatory drawing of the structure of the conventional head.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device 50 ... Print head 51 ... Nozzle 52 ... Pressure chamber 53 ... Supply port 58 ... Piezoelectric element 55 ... Common liquid chamber 62 ... Ink layer 63 ... Upper wall 64 ... Intermediate layer , 66 ... surface layer, 70 ... ink tank, 80 ... supply flow path, 82 ... filter member, 86 ... heater wiring, 88 ... Peltier element, 90 ... liquid circulation path, 92 ... internal wiring

Claims (14)

A liquid in which the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by pressure generating means, and the liquid is discharged from a nozzle communicating with the pressure chamber An ejection head,
The partition wall of the common flow path is provided with a crosstalk prevention member that attenuates sound waves propagated in the common flow path during liquid discharge, and the crosstalk prevention member is in contact with the liquid in the common flow path. It is composed of at least two layers of a first member and a second member joined to the opposite side of the first member to the liquid side,
When the acoustic impedance of the liquid in the common channel is Z ₁ , the acoustic impedance of the first member is Z ₂ , and the acoustic impedance of the second member is Z ₃ , the first member has the following formula Z ₁ <meets the relationship Z 2 _{<Z 3,} and the acoustic impedance Z ₁ of the _liquid, the relationship between the acoustic impedance Z ₃ of the acoustic impedance Z ₂ and the second member of the first member, the following equation 0.72 × ^{_{(Z 1 × Z 3) 1/2}} ≦ Z 2 <1.39 × (Z 1 × Z 3) the liquid discharge head is characterized by being composed to ^1/2 less than Suyo. The common flow path is disposed on the opposite side of the pressure chamber from the nozzle side,
The cross-talk preventing member, the liquid discharge head according to claim 1, characterized in that provided on the opposite side of the partition wall between the pressure chamber side of the common flow channel. The second member is a liquid tank in which the liquid is stored;
Wherein the first member, the liquid ejection head according to claim 1 or claim 2, characterized in that supply channels communicating the common flow path and the liquid tank is formed. The liquid discharge head according to claim 3 , wherein a filter member is provided in at least a part of the supply flow path. 5. The liquid discharge head according to claim 4 , wherein a flow passage area of a portion of the supply flow passage where the filter member is provided is configured to be larger than other portions of the supply flow passage. Wherein the first member, the liquid ejection head according to claim 1 or claim 2, characterized in that the heater wire is provided. Wherein the first member, the liquid ejection head according to claim 1 or claim 2, characterized in that the Peltier element is provided. Wherein the first member, the liquid ejection head according to claim 1 or claim 2, characterized in that the liquid circulation path is formed. Wherein the first member, the liquid ejection head according to claim 1 or claim 2, characterized in that the wiring member for driving the pressure generating means.   A liquid in which the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by pressure generating means, and the liquid is discharged from a nozzle communicating with the pressure chamber An ejection head,
  The partition wall of the common flow path is provided with a crosstalk prevention member that attenuates sound waves propagated in the common flow path during liquid discharge, and the crosstalk prevention member is in contact with the liquid in the common flow path. It is composed of at least two layers of a first member and a second member joined to the opposite side of the first member to the liquid side,
  The first member defines an acoustic impedance of the liquid in the common flow path as Z ₁ , The acoustic impedance of the first member is Z ₂ , The acoustic impedance of the second member is Z ₃ When Z ₁ <Z ₂ <Z ₃ Configured to satisfy the relationship
  The liquid discharge head according to claim 1, wherein the first member is provided with a heater wiring.   A liquid in which the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by pressure generating means, and the liquid is discharged from a nozzle communicating with the pressure chamber An ejection head,
  The partition wall of the common flow path is provided with a crosstalk prevention member that attenuates sound waves propagated in the common flow path during liquid discharge, and the crosstalk prevention member is in contact with the liquid in the common flow path. It is composed of at least two layers of a first member and a second member joined to the opposite side of the first member to the liquid side,
  The first member defines an acoustic impedance of the liquid in the common flow path as Z ₁ , The acoustic impedance of the first member is Z ₂ , The acoustic impedance of the second member is Z ₃ When Z ₁ <Z ₂ <Z ₃ Configured to satisfy the relationship
  A liquid ejection head, wherein the first member is provided with a Peltier element.   A liquid in which the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by pressure generating means, and the liquid is discharged from a nozzle communicating with the pressure chamber An ejection head,
  The partition wall of the common flow path is provided with a crosstalk prevention member that attenuates sound waves propagated in the common flow path during liquid discharge, and the crosstalk prevention member is in contact with the liquid in the common flow path. It is composed of at least two layers of a first member and a second member joined to the opposite side of the first member to the liquid side,
  The first member defines an acoustic impedance of the liquid in the common flow path as Z ₁ , The acoustic impedance of the first member is Z ₂ , The acoustic impedance of the second member is Z ₃ When Z ₁ <Z ₂ <Z ₃ Configured to satisfy the relationship
  A liquid discharge head, wherein a liquid circulation path is formed in the first member.   A liquid in which the liquid is supplied to a plurality of pressure chambers from a common flow path in which the liquid is stored, the liquid in the pressure chamber is pressurized by pressure generating means, and the liquid is discharged from a nozzle communicating with the pressure chamber An ejection head,
  The partition wall of the common flow path is provided with a crosstalk prevention member that attenuates sound waves propagated in the common flow path during liquid discharge, and the crosstalk prevention member is in contact with the liquid in the common flow path. It is composed of at least two layers of a first member and a second member joined to the opposite side of the first member to the liquid side,
  The first member defines an acoustic impedance of the liquid in the common flow path as Z ₁ , The acoustic impedance of the first member is Z ₂ , The acoustic impedance of the second member is Z ₃ When Z ₁ <Z ₂ <Z ₃ Configured to satisfy the relationship
  The liquid ejection head according to claim 1, wherein the first member is provided with a wiring member for driving the pressure generating means. An image forming apparatus comprising the liquid discharge head according to any one of claims 1 to 13 .

Images