JP2007015178A - Liquid discharge head and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To permit excellent refill and stable discharge of an ink. <P>SOLUTION: The liquid discharge head comprises a plurality of discharge openings which discharge a liquid, a plurality of pressure chambers communicating with the discharge openings, a piezoelectric element provided on the side opposite to the sides of the pressure chambers where the discharge openings are formed and deforming the pressure chambers, a common liquid chamber supplying the liquid to the pressure chambers on the side opposite to the side where the discharge openings of the pressure chambers are formed, and a heat dissipation element formed nearly vertically to a surface where the piezoelectric element is arranged so as to make at least its part rise through the common liquid chamber nearly vertically to the surface where the piezoelectric element is arranged, including a member having at least electrical conductivity and thermal conductivity and dissipating heat generated by the piezoelectric element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus and an image forming apparatus, and more particularly to a liquid ejecting head and an image forming apparatus that eject liquid from an ejection port using displacement of a piezoelectric element.

  In general, in an ink jet recording apparatus, a number of nozzles of a head are based on dot pattern data (also referred to as “dot data” or “print data”) obtained by developing print image data input from a host computer. Then, ink droplets are ejected at predetermined timings, and printing is performed when these ink droplets land and adhere to a medium such as recording paper.

2. Description of the Related Art Conventionally, heads mounted on an ink jet recording apparatus have been provided with various cooling means. For example, in patent document 1, in order to control the temperature in a head, the air blower is provided in the head unit. In Patent Document 2, a radiator is attached to the drive circuit in order to cool the head drive circuit.
Japanese Unexamined Patent Publication No. Sho 62-113562 JP 2000-294705 A

  However, this type of head is provided with a large number of ejection elements such as piezoelectric elements, and heat generation by the ejection elements may cause a problem. For example, when the piezoelectric element is excessively heated, the displacement characteristics of the piezoelectric element are deteriorated, and ink ejection may become unstable, leading to a decrease in image quality. In addition, the piezoelectric element is deteriorated and the life is shortened. In particular, when high-viscosity ink is used, a higher driving voltage is applied to each ejection element compared to the case of ejecting general viscosity ink, so that the amount of heat generated by each ejection element increases. On the other hand, it is also required to realize a head with excellent refilling property that can discharge high-viscosity ink with a short discharge cycle (high discharge frequency).

  Furthermore, in a line head having a nozzle row having a length corresponding to the width direction of the medium, since high-speed throughput is important, each discharge element is often forced to continuously drive, and the amount of heat generated by the entire head increases. . In addition, there are nozzles that eject ink locally and nozzles that eject little ink, the amount of heat generated by each ejection element is different, changes occur in the ejection characteristics of the head, and image unevenness occurs. May occur.

  In Patent Document 1, only the temperature of the entire head is controlled, and it is not possible to effectively dissipate heat to the ejection elements in the head.

  In Patent Document 2, the radiator only cools the drive circuit, and cannot radiate heat to the ejection elements in the head.

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid discharge head and an image forming apparatus that are excellent in refilling properties and enable stable ink discharge.

  In order to achieve the above object, the invention according to claim 1 includes a plurality of discharge ports for discharging liquid, a plurality of pressure chambers communicating with each of the plurality of discharge ports, and the discharge ports of the plurality of pressure chambers. A piezoelectric element that deforms each of the plurality of pressure chambers, and is disposed on the opposite side of the pressure chamber from the side on which the discharge port is formed. A common liquid chamber for supplying a liquid and a direction substantially perpendicular to a surface on which the piezoelectric element is disposed, and at least a part of the common liquid chamber is disposed in a direction substantially perpendicular to the surface on which the piezoelectric element is disposed. There is provided a liquid discharge head comprising: a heat dissipating element that includes at least a member having electrical conductivity and heat conductivity and that radiates heat generated by the piezoelectric element.

  According to the present invention, the common liquid chamber and each pressure chamber have a simple configuration in which the common liquid chamber and the pressure chamber communicate with each other substantially straight, and the refilling property is improved. Further, since each piezoelectric element is radiated by the heat radiating element, stable ejection is possible without changing the ejection characteristics of the liquid ejection head, and deterioration of the piezoelectric element can be prevented.

  The invention according to claim 2 is the liquid discharge head according to claim 1, wherein the heat dissipating element also serves as a wiring member for driving the piezoelectric element.

  According to the second aspect of the present invention, the wiring member is not newly provided, and the configuration of the liquid discharge head is simplified.

  The invention according to claim 3 is the liquid discharge head according to claim 1 or 2, wherein the heat radiating element is in the atmosphere outside the liquid discharge head and in the liquid inside the liquid discharge head. The heat generated by the piezoelectric element is radiated to at least one of the above.

  The invention according to a fourth aspect is the liquid ejection head according to any one of the first to third aspects, wherein the thermal conductivity of the heat radiating element on the center side of the liquid ejection head is the liquid ejection head. It is configured to be larger than the thermal conductivity of the piezoelectric element on the end side of the discharge head.

  The aspect of claim 4 is effective when the driving frequency of the piezoelectric element closer to the center side than the end side of the liquid discharge head is high and the heat generation amount on the center side is large. In particular, this is a preferred embodiment for a line head.

  The invention according to claim 5 is the liquid discharge head according to claim 4, wherein the cross-sectional area of the heat radiating element on the center side of the liquid discharge head is the piezoelectric element on the end side of the liquid discharge head. It is characterized by being configured to be larger than the cross-sectional area.

  A sixth aspect of the present invention is the liquid ejection head according to any one of the first to fifth aspects, wherein the heat radiating element includes a core material having electrical conductivity and thermal conductivity, It is comprised from the coating | covering material which has insulation and heat conductivity.

  In order to achieve the above object, an image forming apparatus comprising the liquid ejection head according to any one of claims 1 to 6 is provided.

  According to the present invention, the common liquid chamber and each pressure chamber have a simple configuration in which the common liquid chamber and the pressure chamber communicate with each other substantially straight, and the refilling property is improved. Further, since each piezoelectric element is radiated by the heat radiating element, stable ejection is possible without changing the ejection characteristics of the liquid ejection head, and deterioration of the piezoelectric element 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 of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the ink jet recording apparatus 10 includes a plurality of ink jet heads (hereinafter referred to as “ink jet heads”) corresponding to black (K), cyan (C), magenta (M), and yellow (Y) inks. A printing unit 12 having 12K, 12C, 12M, and 12Y, an ink storage / loading unit 14 that stores ink to be supplied to each of the heads 12K, 12C, 12M, and 12Y (liquid ejection heads); A paper feeding unit 18 that supplies recording paper 16 as a medium to be ejected, a decurling unit 20 that removes curl of the recording paper 16, and a nozzle surface (ink ejection surface) of the printing unit 12 are arranged to face recording. Adsorption belt conveyance unit 22 (conveyance means) that conveys the recording paper 16 while maintaining the flatness of the paper 16, a print detection unit 24 that reads a printing result by the printing unit 12, and a recorded recording paper A paper output unit 26 for discharging the printed matter) to the outside, and a.

  The ink storage / loading unit 14 has an ink tank that stores ink of a color corresponding to each of the heads 12K, 12C, 12M, and 12Y, and each tank has a head 12K, 12C, 12M, and 12Y through a required pipe line. Communicated with. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  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.

  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. Thus, it is preferable to automatically determine the type of recording medium (media type) to be used and perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  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.

  In the case of an apparatus configuration that uses roll paper, a cutter (first 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 disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  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 portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is wider 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, a suction 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. The recording paper 16 is sucked and held on the belt 33 by sucking the suction chamber 34 with a fan 35 to a negative pressure.

  When the power of the motor (reference numeral 88 in FIG. 7) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 is driven in the clockwise direction in FIG. The held 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 blow method of blowing 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 conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print 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 blows heated air on the recording paper 16 before printing to heat the recording paper 16. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  Each of the heads 12K, 12C, 12M, and 12Y of the printing unit 12 has a length corresponding to the maximum paper width of the recording paper 16 targeted by the inkjet recording apparatus 10, and the nozzle surface has a recording medium of the maximum size. This is a full-line type head in which a plurality of nozzles for ink discharge are arranged over a length exceeding at least one side (full width of the drawable range) (see FIG. 2).

  As shown in FIG. 2, the heads 12K, 12C, 12M, and 12Y are black (K), cyan (C), magenta (M), and yellow (Y) colors from the upstream side along the feeding direction of the recording paper 16. The heads 12 </ b> K, 12 </ b> C, 12 </ b> M, and 12 </ b> Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the recording paper 16.

  A color image can be formed on the recording paper 16 by discharging different color inks from the heads 12K, 12C, 12M, and 12Y while transporting the recording paper 16 by the suction belt transporting section 22.

  As described above, according to the configuration in which the full-line heads 12K, 12C, 12M, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the recording paper 16 and the printing unit in the paper feeding direction (sub-scanning direction). The image can be recorded on the entire surface of the recording paper 16 by performing the operation of relatively moving the 12 only once (that is, by one sub-scanning). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the recording head reciprocates in a direction orthogonal to the paper transport direction, and productivity can be improved.

  Here, the main scanning direction and the sub-scanning direction are used in the following meaning. That is, when driving the nozzles with a full line head having a nozzle row corresponding to the full width of the recording paper, (1) whether all the nozzles are driven simultaneously or (2) whether the nozzles are driven sequentially from one side to the other (3) The nozzles are divided into blocks, and each nozzle is driven sequentially from one side to the other for each block, and the width direction of the paper (perpendicular to the conveyance direction of the recording paper) Nozzle driving that prints one line (a line made up of a single row of dots or a line made up of a plurality of rows of dots) in the direction of scanning is defined as main scanning. A direction indicated by one line (longitudinal direction of the belt-like region) recorded by the main scanning is called a main scanning direction.

  On the other hand, by relatively moving the above-described full line head and the recording paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. Is defined as sub-scanning. A direction in which sub-scanning is performed is referred to as a sub-scanning direction. After all, the conveyance direction of the recording paper is the sub-scanning direction, and the direction orthogonal to it is the main scanning direction.

  Further, 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, dark ink, and special color ink are used as necessary. May be added. For example, it is possible to add an ink jet head that discharges light ink such as light cyan and light magenta. Also, the arrangement order of the color heads is not particularly limited. Further, in the two-liquid system in which the ink and the processing liquid are reacted on the recording paper 16 to aggregate the ink coloring material, a processing liquid discharge head for discharging the processing liquid is added in addition to the head for discharging the ink. There is also.

  The print detection unit 24 shown in FIG. 1 includes an image sensor for imaging the droplet ejection result of the printing 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 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 is composed of 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.

  A test pattern or practical image printed by the heads 12K, 12C, 12M, and 12Y of each color is read by the print detection unit 24, and ejection determination of each head is performed. 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 pressurizing the paper holes with pressure. 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 surface uneven 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 a 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. Yes. 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 in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the head will be described. Since the structures of the respective heads 12K, 12C, 12M, and 12Y for each color are common, the heads are represented by the reference numeral 50 in the following.

  FIG. 3 is a plane perspective view showing the head 50 (liquid ejection head) in a simplified manner, and FIG. 4 is a plane perspective view showing another structural example of the head 50. FIG. 5 is an enlarged view of one ejection element (ink chamber unit corresponding to one nozzle 51) of the head 50 shown in FIG.

  In order to increase the dot pitch printed on the recording paper 16, it is necessary to increase the nozzle pitch in the head 50. As shown in FIG. 3, the head 50 of this example includes a plurality of ejection elements (ink chamber units) 53 including nozzles 51 serving as ink droplet ejection ports and pressure chambers 52 corresponding to the nozzles 51. In this way, a substantial nozzle interval (projection nozzle pitch) projected so as to be arranged along the longitudinal direction of the head (direction perpendicular to the paper feed direction) is arranged in a matrix (two-dimensional). ) Is achieved.

  Specifically, along a row direction along a direction (main scanning direction) substantially orthogonal to the conveyance direction of the recording paper 16 and an oblique row direction having a constant angle θ that is not orthogonal to the main scanning direction. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern with a fixed arrangement pattern. That is, the head 50 of this example has a structure in which a plurality of ejection element groups 53A having a plurality of ejection elements arranged along the column direction are arranged along the main scanning direction. In the aspect shown in FIG. 3, one ejection element group 53 </ b> A has six ejection elements 53.

  The configuration in which one or more nozzle rows are configured over a length corresponding to the entire width of the recording paper 16 in a direction substantially orthogonal to the feeding direction of the recording paper 16 is not limited to this example. For example, instead of the configuration of FIG. 3, as shown in FIG. 4, the entire width of the recording paper 16 is obtained by arranging short head blocks 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged in a staggered manner and joined together. You may comprise the line head which has a nozzle row of the length corresponding to.

  As shown in FIG. 5, the pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape. A nozzle 51 is provided at one corner of the pressure chamber 52, and an inlet (supply port) 54 of supply ink formed to extend outward is provided at the other corner facing the nozzle 51. .

  A piezoelectric element (actuator) 58 is provided so as to substantially overlap the pressure chamber 52. The nozzle 51 side corner of the piezoelectric element 58 is formed so as to protrude outward, and a heat radiating element 60 for radiating heat of the piezoelectric element 58 is provided at the end thereof.

  6 is a cross-sectional view taken along line 6-6 in FIG. As shown in the figure, the nozzle plate 62 on which the nozzle 51 is formed is joined to one surface (the lower surface in FIG. 6) of the cavity plate 61 in which a space corresponding to the pressure chamber 52 is formed, and the opposite surface is supplied. A diaphragm 56 having a hole corresponding to a part of the mouth 54 is joined. One end of the pressure chamber 52 communicates with the nozzle 51, and the other end communicates with the common liquid chamber 55 via the supply port 54.

  The common liquid chamber 55 is disposed on the opposite side of the pressure chamber 52 from the side where the nozzle 51 is formed, specifically, on the opposite side of the pressure chamber 52 with the diaphragm 56 interposed therebetween. Such an arrangement configuration of the common liquid chamber 55 is a simple configuration in which the common liquid chamber 55 communicates with the pressure chamber 52 almost straight. As a result, refilling properties are improved and high-viscosity ink can be discharged. The common liquid chamber 55 communicates with an ink tank (not shown in FIG. 6, described as reference numeral 64 in FIG. 8) as an ink supply source, and the ink supplied from the ink tank 64 passes through the common liquid chamber 55 in FIG. Then, it is distributed and supplied to each pressure chamber 52.

  A piezoelectric element (actuator) 58 including an individual electrode 57 is joined to a position corresponding to the pressure chamber 52 on the surface opposite to the pressure chamber 52 side of the diaphragm 56. The diaphragm 56 is made of a conductive member such as SUS, and also serves as a common electrode of the piezoelectric element 58. An insulating / protective film (not shown) such as a resin is formed on the surface of the piezoelectric element 58 and the diaphragm 56 that come into contact with the ink in the common liquid chamber 55. An electrode layer serving as a common electrode may be formed on the surface of the diaphragm 56 on the piezoelectric element 58 side.

  At the left end of the piezoelectric element 58 (individual electrode 57) in FIG. 6, a substantially cylindrical shape formed so as to rise up the common liquid chamber 55 in a direction substantially perpendicular to the diaphragm 56 (where the piezoelectric element 58 is disposed). The heat dissipating element 60 is provided. The heat dissipating element 60 also serves as a wiring member for driving the piezoelectric element 58, and includes an internal wiring member 60A that is a core material and a covering material 60B that covers the surface thereof. One end (lower end in FIG. 6) of the heat dissipating element 60 (internal wiring member 60A) is connected to the individual electrode 57 on the upper surface of the piezoelectric element 58, and the other end (upper end in FIG. 6) is passed through a top plate 59 above the common liquid chamber 55. To the external wiring 63. The external wiring 63 is connected to a driving circuit (head driver) (not shown in FIG. 6, described as reference numeral 84 in FIG. 9), and a driving signal (driving voltage) according to image data is transmitted to the heat dissipation element 60 (internal wiring member). 60A) to be supplied to the piezoelectric element 58 (individual electrode 57). Note that, from the viewpoint of ensuring the rigidity of the head 50, the heat dissipating element 60 is preferably disposed at a position corresponding to the pressure chamber partition wall 52A as shown in FIG.

The internal wiring member 60A used in this example is made of a material having electrical conductivity and thermal conductivity. The thermal conductivity is determined by a mechanism in which energy of thermal motion is transmitted by movement or collision of the constituent particles of the substance. Metals have a large thermal conductivity k due to free electrons. According to the Wiedeman-Franz law (Wiedeman-Franz law), k = LTσ (where L is the Lorentz coefficient and T is (Absolute temperature). That is, if the electrical conductivity σ is high (that is, if the resistivity is low), the thermal conductivity k becomes high. Therefore, the resistivity of the internal wiring member 60A is preferably a sufficiently low value, and in particular, the resistivity is preferably less than 100 [× 10 ⁻³ μΩm].

表１は、内部配線部材６０Ａの材料例であり、抵抗率が100［×10^-3μΩm］未満である材料には評価を○とし、それ以外の材料は評価を×としている。同表から分かるように、内部配線部材６０Ａには金、銅、Ａｌ（アルミニウム）が適している。

Table 1 shows an example of the material of the internal wiring member 60A. The evaluation is “good” for a material having a resistivity of less than 100 [× 10 ⁻³ μΩm], and the evaluation for other materials is “poor”. As can be seen from the table, gold, copper, and Al (aluminum) are suitable for the internal wiring member 60A.

On the other hand, the covering material 60B used in this example is made of a material having electrical insulation and thermal conductivity. The covering material 60B is preferably made of a material having high insulation (that is, having a high resistivity), and more preferably a material having a resistivity higher than 10 ⁶ [Ωm]. Further, it is desirable that the thermal conductivity of the covering material 60B is equal to or higher than that of the internal wiring member 60A in order to transfer heat from the internal wiring member 60A to the outside.

表２は、被覆材６０Ｂの材料例であり、表１の内部配線部材６０Ａとして適しているＡｌ（アルミニウム）相当である２００［W/(m・K)］以上の熱伝導率であり、且つ、絶縁性が保障される抵抗率が10⁶ [Ωm]より大きい材料には評価を○とし、それら以外の材料は評価を×としている。同表から分かるように、被覆材６０ＢにはＡＩＮ（窒化アルミニウム）、ＢｅＯ（酸化ベリウム）が適している。尚、環境的な観点から、電気絶縁性が高く誘電率が低い低熱膨張率の材料として、ＡＩＮ（窒化アルミニウム）を使用することが好ましい。

Table 2 is a material example of the covering material 60B, and has a thermal conductivity of 200 [W / (m · K)] or more equivalent to Al (aluminum) suitable as the internal wiring member 60A of Table 1, and In addition, a material having a resistivity greater than 10 ⁶ [Ωm] for which insulation is guaranteed is evaluated as “good”, and other materials are evaluated as “poor”. As can be seen from the table, AIN (aluminum nitride) and BeO (berium oxide) are suitable for the covering material 60B. From an environmental point of view, it is preferable to use AIN (aluminum nitride) as a low thermal expansion material with high electrical insulation and low dielectric constant.

  A part of the heat generated by the piezoelectric element 58 is maintained in the common liquid chamber 55 while maintaining electrical insulation with respect to the ink in the common liquid chamber 55 by the heat dissipating element 60 composed of the internal wiring member 60A and the covering material 60B. Heat is dissipated to the ink inside. Since the ink circulates moderately by ink discharge (or discharge) in the head, the heat dissipated from the heat radiating element 60 to the ink in the common liquid chamber 55 is not accumulated, and the ink temperature in the head rises excessively. In addition, the piezoelectric element 58 can be cooled. Further, another part of the heat generated by the piezoelectric element 58 is transmitted to the external wiring 63 via the heat dissipation element 60 (internal wiring member 60A), and is radiated to the atmosphere outside the head. Therefore, compared with the case where heat is radiated to either the inside or the outside of the head, the heat radiation effect on the piezoelectric element 58 is superior. Since the thermal conductivity of air (0.02 [W / (m · K)]) is extremely low compared to metals such as gold and copper, the surface area of the external wiring 63 is increased so as to increase the contact area with the atmosphere. Is preferably increased.

  FIG. 7 is a plan view showing a simplified arrangement of the heat dissipating elements 60 in the common liquid chamber 55. As shown in FIGS. 5 and 6, the heat dissipation element 60 is provided for each piezoelectric element 58 corresponding to the pressure chamber 52. That is, similarly to the arrangement pattern of the ejection elements 53 shown in FIG. 3, the row direction along the direction (main scanning direction) substantially orthogonal to the conveyance direction of the recording paper 16 and a constant not orthogonal to the main scanning direction. A large number of heat dissipating elements 60 are arranged in a lattice pattern in a fixed arrangement pattern along an oblique row direction having an angle θ.

  With this configuration, when a drive voltage (drive signal) is applied from the drive circuit 84 to the piezoelectric element 58 (individual electrode 57) via the external wiring 63 and the heat dissipation element 60 (internal wiring member 60B), the piezoelectric element 58 is deformed. As a result, the volume of the pressure chamber 52 changes, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. After ink discharge, new ink is supplied from the common liquid chamber 55 to the pressure chamber 52 through the supply port 54.

  Heat generated when the piezoelectric element 58 is driven is dissipated by the heat dissipating element 60 into the ink inside the head (in the common liquid chamber 55) and the atmospheric air outside the head. Thereby, excessive heat generation of the piezoelectric element 58 is suppressed, stable ejection can be performed without changing the ejection characteristics of the head 50, and deterioration of the piezoelectric element 58 can be suppressed.

  In the present embodiment, since the heat dissipating element 60 (internal wiring member 60A) formed so as to rise in the common liquid chamber 55 also serves as a wiring member for driving the piezoelectric element 58, the configuration of the head 50 is not complicated. As compared with the surface on which the piezoelectric element 58 is arranged, a sufficient wiring space can be secured above the common liquid chamber 55, and high-density wiring can be mounted.

  Further, the constituent members of the head 50, in particular, the diaphragm 56 on which the piezoelectric element 58 is disposed, the top plate 59 constituting the upper surface of the common liquid chamber 55, and the like are made of members having high thermal conductivity such as SUS. It is preferable that the heat dissipation of the piezoelectric element 58 can be performed more efficiently.

[Configuration of ink supply system]
FIG. 8 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10. The ink tank 64 is a base tank that supplies ink to the head 50 and is installed in the ink storage / loading unit 14 described with reference to FIG. There are two types of the ink tank 64: a system that replenishes ink from a replenishing port (not shown) and a cartridge system that replaces the entire tank when the ink remaining amount is low. 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 64 in FIG. 8 is equivalent to the ink storage / loading unit 14 in FIG. 1 described above.

  As shown in FIG. 8, a filter 65 is provided between the ink tank 64 and the 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. 8, a configuration in which a sub tank is provided in the vicinity of the head 50 or integrally with the 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 inkjet recording apparatus 10 is provided with a cap 69 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a means for cleaning the nozzle surface 50A. . The maintenance unit including the cap 69 and the cleaning blade 66 can be moved relative to the head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the head 50 as necessary.

  The cap 69 is displaced up and down relatively with respect to the head 50 by an elevator mechanism (not shown). The cap 69 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 head 50, thereby covering the nozzle surface 50 </ b> A with the cap 69.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (nozzle plate surface) of the head 50 by a blade moving mechanism (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface.

  During printing or standby, when a specific nozzle is used less frequently and the ink viscosity in the vicinity of the nozzle increases, preliminary discharge is performed toward the cap 69 to discharge the deteriorated ink.

  When air bubbles are mixed in the ink in the head 50 (in the pressure chamber 52), the cap 69 is applied to the head 50, and the ink in the pressure chamber 52 (ink in which the air bubbles are mixed) is removed by suction with the suction pump 67. Then, the sucked and removed ink is sent to the collection tank 68. In this suction operation, the deteriorated ink that has increased in viscosity (solidified) is sucked out when the ink is initially loaded into the head 50 or when the ink is used after being stopped for a long time.

  If the head 50 is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the viscosity of the ink near the nozzle increases. Ink will not be ejected. Therefore, before this state is reached (within the viscosity range in which ink can be ejected by the operation of the piezoelectric element 58), the piezoelectric element 58 is operated toward the ink receiver, and the ink in the vicinity of the nozzle whose viscosity has increased is removed. “Preliminary discharge” is performed. In addition, after the dirt on the surface of the nozzle plate is cleaned by a wiper such as a cleaning blade 66 provided as a cleaning means for the nozzle surface 50A, the foreign matter is prevented from entering the nozzle 51 by the wiper rubbing operation. Also, preliminary discharge is performed. Note that the preliminary discharge may be referred to as “empty discharge”, “purge”, “spitting”, or the like.

  In addition, if bubbles are mixed into the nozzle 51 or the pressure chamber 52 or if the viscosity increase of the ink in the nozzle 51 exceeds a certain level, ink cannot be ejected by the preliminary ejection, and the suction operation described below is performed.

  That is, when bubbles are mixed in the ink in the nozzle 51 or the pressure chamber 52, or when the ink viscosity in the nozzle 51 rises to a certain level or more, ink is ejected from the nozzle 51 even if the piezoelectric element 58 is operated. become unable. In such a case, a suction means for sucking ink in the pressure chamber 52 with a pump or the like is brought into contact with the nozzle surface 50A of the head 50, and an operation of sucking ink mixed with bubbles or thickened ink is performed.

  However, since the above suction operation is performed on the entire ink in the pressure chamber 52, the ink consumption is large. Therefore, when the increase in viscosity is small, it is preferable to perform preliminary discharge as much as possible.

[Explanation of control system]
FIG. 9 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a ROM 75, a motor driver 76, a heater driver 78, a print control unit 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74. The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls each part such as the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, etc., performs communication control with the host computer 86, read / write control of the image memory 74, etc. A control signal for controlling the motor 88 and the heater 89 of the transport system is generated.

  The ROM 75 stores programs executed by the CPU of the system controller 72, various data necessary for control, control parameters, and the like. The ROM 75 may be a non-rewritable storage element (storage means) or a rewritable storage element such as an EEPROM. The image memory 74 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 76 is a driver that drives the motor 88 in accordance with instructions from the system controller 72. The heater driver 78 is a driver for driving the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72. The motor 88 includes a plurality of motors such as motors for driving the rollers 31 and 32 of the belt suction conveyance unit 22, and the heater 89 includes a plurality of heaters such as a heater provided in the post-drying unit 42.

  The print control unit 80 has a signal processing function for performing various processing and correction processing for generating a print control signal from the image data in the image memory 74 according to the control of the system controller 72, and the generated print It is a control unit that supplies data (dot data) to the head driver 84. Necessary signal processing is performed in the print control unit 80, and the ejection amount and ejection timing of the ink droplets of the head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 9, the image buffer memory 82 is shown as being attached to the print control unit 80, but can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 drives the piezoelectric elements 58 of the heads 12K, 12C, 12M, and 12Y of the respective colors based on the dot data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, RGB image data is stored in the image memory 74.

  The image data stored in the image memory 74 is sent to the print control unit 80 via the system controller 72, and the print control unit 80 converts it into dot data for each ink color by a known method such as dithering or error diffusion. Converted. That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors of KCMY. The dot data generated by the print controller 80 is stored in the image buffer memory 82.

  The head driver 84 applies a drive signal output from the head driver 84 that outputs a signal for driving each piezoelectric element 58 of the head 50 to the head 50 based on the dot data stored in the image buffer memory 82. Thus, ink is ejected from the head 50. An image is formed on the recording paper 16 by controlling the ink ejection from the head 50 in synchronization with the conveyance speed of the recording paper 16.

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor, reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a print status (whether ejection is performed, droplet ejection And the detection result is provided to the print control unit 80.

  The print controller 80 performs various corrections on the head 50 based on information obtained from the print detector 24 as necessary. Further, the system controller 72 performs control to perform a predetermined recovery operation such as preliminary ejection, suction, or the like based on information obtained from the print detection unit 24.

[Description of head drive method]
Next, a method for driving the head 50 in the inkjet recording apparatus 10 of this example will be described. FIG. 10 is a main part configuration diagram of main circuits related to head driving of the ink jet recording apparatus 10.

  A communication interface IC 102, a CPU 104, a ROM 75, a RAM 108, a line buffer 110, and a print controller (head controller) 80 are mounted on the circuit board 100 mounted on the inkjet recording apparatus 10.

  The communication interface IC 102 corresponds to the communication interface indicated by reference numeral 70 in FIG. The CPU 104 in FIG. 10 functions as the system controller 72 described in FIG. 10 functions as the image memory 74 described in FIG. 9, and the line buffer 110 in FIG. 10 functions as the image buffer memory 82 in FIG. Note that the memory 114 may be provided in place of or in combination with the line buffer 110. The memory 114 can share a part of the RAM 108.

  The print control unit 80 shown in FIG. 10 includes an ejection driving unit 116 corresponding to the head driver 84 of FIG. The print control unit 80 is electrically connected to the head 50 (the heat radiating element 60 and the piezoelectric element 58) via the switch IC 120 (ejection drive selection unit). The switch IC 120 includes a serial / parallel (S / P) conversion circuit and a switch array (indicated by reference numeral 134 in FIG. 13). A power circuit 124 is connected to the circuit board 100, and power is supplied from the power circuit 124 to each circuit block.

  FIG. 11 shows a basic configuration of the drive circuit 130 included in the print control unit 80. As shown in FIG. 11, the drive circuit 130 includes a D / A converter 126, an amplifier circuit 127 including a feedback circuit (feedback loop) 127A, a charge / discharge circuit 128, a push-pull circuit 129 including a transistor, and the like. The heat radiating element 60 and the piezoelectric element 58 are connected in series to the output unit 130A of the drive circuit 130 via the switch element 120A included in the switch IC 120 of FIG. A drive signal (drive voltage) output from the output unit 130A is supplied to the heat dissipation element 60 and the piezoelectric element 58 by switching control of each switch element 120A.

  In FIG. 12, a drive signal is sent from the drive circuit 130 to a plurality of (m) radiating elements 60-1 to 60-m and the piezoelectric elements 58-1 to 58-m connected in series via the switch IC. The basic structure for selectively supplying the is shown.

  The drive circuit 130 in FIG. 12 includes a waveform generation circuit 132 including a D / A converter 126 (shown in FIG. 11) that converts digital waveform data output from the print control unit 80 in FIG. 10 into an analog signal, and waveform generation An amplifier circuit 127 and a push-pull circuit 129 ′ that amplify the drive waveform in accordance with the output level of the circuit 132 are configured. In other words, the digital waveform data of the drive waveform output from the print control unit 80 is input to the waveform generation circuit 132 and converted into an analog waveform signal corresponding to the input waveform data by the waveform generation circuit 132. The analog waveform signal is amplified to a predetermined level by the amplifier circuit 127, and after power amplification using the push-pull circuit 129 ', the analog waveform signal is output as a drive signal.

  Note that the push-pull circuit 129 shown in FIG. 11 uses a bipolar transistor, but a configuration using a FET instead of the bipolar transistor as in the push-pull circuit 129 ′ shown in FIG. 12 is also possible. In the drive circuit 130 of FIG. 12, the waveform generation circuit 132 includes the D / A converter 126 of FIG. 11, and the charge / discharge circuit 128 of FIG. 11 is omitted.

  The drive signal output from the output unit 130A of the drive circuit 130 is input to the COM port of each switch IC 120, and the switch elements 120A-1 to 120A-m are selectively switched, so that the switch elements 120A-1 to 120A are switched. -m is selectively supplied to the heat dissipating elements 60-1 to 60-m connected to -m and the piezoelectric elements 58-1 to 58-m connected in series therewith.

  Here, the configuration of the switch IC 120 will be described in detail with reference to FIG. As shown in FIG. 13, the print control unit 80 generates print data developed in a dot pattern based on image information given from the host computer 86 (see FIG. 9), and also transmits a serial transmission clock signal ( CLK) and a latch signal (LAT) for controlling the latch timing. The print data generated by the print control unit 80 in FIG. 13 is transmitted (serial transmission) to the shift register 140 as print serial data SD together with the clock signal CLK in synchronization with the clock signal CLK. The print data stored in the shift register 140 is latched by the latch circuit 142 based on the latch signal LAT output from the print control unit 80.

  The signal latched by the latch circuit 142 is converted into a predetermined voltage value capable of driving the switch elements 120A-1 to 120A-m in the level conversion circuit 144. The ON / OFF of the switch elements 120A-1 to 120A-m is controlled by the output signal of the level conversion circuit 144.

  FIG. 14 shows a configuration example when a plurality of drive circuits 130 are mounted on the inkjet recording apparatus 10. As shown in FIG. 14, each drive circuit 130 includes a waveform generation circuit 132, an amplifier circuit 127, and a push-pull circuit 129 '. The drive signal output from each drive circuit 130 is selectively supplied to each heat dissipating element 60 and the piezoelectric element 58 connected in series via the switch IC 120 connected to the output part 130A of each drive circuit 130. Is done. The drive circuit 130 and the switch IC 120 in FIG. 14 have the same configuration as the drive circuit 130 and the switch IC 120 shown in FIG.

  FIG. 15A is a waveform diagram showing an example of a common drive waveform for ejection. As shown in FIG. 15A, the discharge common drive waveform 160 includes a first waveform element 161 for discharging a small dot droplet (for example, 3 pl) and a medium dot droplet (for example, 6 pl). The second waveform element 162 for discharging the gas is continuously connected, and the waveform obtained by combining the first waveform element 161 and the second waveform element 162 is repeated at the period T1.

  By applying the first waveform element 161 of the ejection common drive waveform 160 to the piezoelectric element 58, a small dot droplet is ejected, and by applying only the second waveform element 162, a medium dot droplet is ejected. Is done. Further, by continuously applying the first waveform element 161 and the second waveform element 162 to the piezoelectric element 58, a large dot droplet (for example, 9pl) is ejected.

  Note that the drive waveform application timing (ejection timing) varies within the ejection cycle T1 depending on the volume of the ejected droplet. The difference in the landing positions of small dots and medium dots due to this time difference is substantially the same on the recording medium. Within a range that can be regarded as one pixel.

  By controlling the switch IC 120 described with reference to FIGS. 12 to 14, the first waveform element 161 or the second waveform element 162 shown in FIG. 15A is applied to the piezoelectric element 58 corresponding to each ejection element 53. It is possible to selectively apply.

  FIG. 15B shows a waveform applied to the piezoelectric element 58 during small dot ejection, FIG. 15C shows a waveform applied during medium dot ejection, and FIG. 15D applies during large dot ejection. Waveform is shown.

  In each of the waveform diagrams of FIGS. 15 (b) to 15 (d), “n” (n = n = representing the letters “A” to “C”) for the portions indicated by A1 to A4, B1 to B4, and C1 to C4. A, B, and C), “n1” is the meniscus stabilization, “n2” is the meniscus pull, “n3” is the meniscus pull (ie, discharge), and “n4” is the next discharge ready state. Each corresponds.

  Based on the print data, a nozzle that performs ejection (driven ejection element 53) and a nozzle that does not perform ejection (undriven ejection element 53) are determined, and the piezoelectric element 58 corresponding to the driven ejection element 53 is determined. As a result, any one of the drive waveforms in FIGS. 15B to 15D is applied.

  On the other hand, the meniscus slight vibration drive waveform 163 shown in FIG. 15E is applied to the piezoelectric elements 58 corresponding to a part or all of the ejection elements 53 that are not driven. This meniscus slight vibration driving waveform 163 is a waveform that vibrates the meniscus while suppressing the energy to the extent that ink is not ejected from the nozzles 51, and has an amplitude compared to the ejection common driving waveform 160 shown in FIG. A small vibration waveform element having a small length is repeated at a predetermined period T2. As an example of the predetermined period, there is an aspect in which the period T2 of the meniscus micro-vibration driving waveform 163 is set to 1/3 of the period T1 of the ejection common driving waveform 160. Of course, the relationship between the period T2 of the meniscus micro-vibration driving waveform 163 and the period T1 of the ejection common driving waveform 160 is not limited to this example. By controlling the period T2 of the meniscus micro-vibration driving waveform 163 to 1 / N (where N is a positive integer) of the period T1 of the ejection common driving waveform 160, the application timing of the meniscus micro-vibration driving waveform 163 can be easily controlled. This is preferable in terms of control.

  By applying the meniscus micro-vibration driving waveform 163 as described above to the piezoelectric elements 58 corresponding to a part or all of the ejection elements 53 that are not driven in this way, the viscosity of the ink in the meniscus that causes ejection failure is increased. Can be prevented in advance.

  In addition, although the piezoelectric element 58 generates heat by applying a drive waveform to the piezoelectric element 58, as described above, the heat radiating element 60 radiates heat to the air atmosphere outside the head or to the ink inside the head (in the common liquid chamber 55). Therefore, stable ink discharge is possible.

  In the present embodiment, an example in which the meniscus micro-vibration driving waveform 163 is applied to the piezoelectric elements 58 corresponding to a part or all of the ejection elements 53 that are not driven is shown as a preferable aspect. It is not limited to this.

  Next, a modified example of the heat dissipation element 60 will be described.

  FIG. 16 is a modified example in which the shape and arrangement of the heat dissipating elements 60 are changed, and the heat dissipating elements 60 shown in FIG. 7 are simply illustrated by being arranged in a direction substantially parallel to the paper feed direction (sub-scanning direction). It is. Here, description will be made assuming that the heat dissipation element 60 is equivalent to the internal wiring member 62.

  In FIG. 16A, the heat radiating elements 60 are two-dimensionally arranged in the main scanning direction corresponding to the longitudinal direction of the head 50 (common liquid chamber 55) and the sub-scanning direction (paper feeding direction) corresponding to the short direction. The size (cross-sectional area) of each heat dissipating element 60 is substantially uniform.

  On the other hand, in FIG. 16B, the size (cross-sectional area) of some of the heat dissipating elements 60 is changed. Specifically, the heat dissipating at the center of the head compared to the head end. The size (cross-sectional area) of the element 60 is increased. The resistance value of the heat dissipation element 60 is proportional to the length (wiring length) and inversely proportional to the cross-sectional area. Therefore, the heat radiating element 60 in the central portion of the head has a smaller resistance value (that is, higher thermal conductivity) than the head end portion.

  In a general image, the piezoelectric element 58 at the center of the head, which is the center of the image, is driven more frequently than the head end and tends to generate more heat. For this reason, the ejection characteristics of the head 50 may change, and image unevenness in which the density gradually changes from the head end to the center of the head may occur. Therefore, as in the example shown in FIG. 16B, the thermal conductivity of the heat radiating element 60 at the center of the head is larger than that at the end of the head. The heat generation distribution of the element 58 can be made uniform, and the image unevenness can be eliminated.

  In this example, the thermal conductivity is changed by changing the size (cross-sectional area) of the heat dissipating element 60. However, the present invention is not limited to this. For example, the material constituting the heat dissipating element 60 is changed. Alternatively, the length (wiring length) of the heat dissipation element 60 may be changed. When the shape and material of the heat dissipation element 60 are changed, it is desirable to adjust the overall resistance value by changing the wiring length and wiring width of the external wiring 63.

  Further, the arrangement configuration of the heat dissipating element 60 in the head 50 (common liquid chamber 55) is not limited to the above-described example, and the heat dissipating element 60 is disposed with the phase shifted in the main scanning direction as shown in FIG. Alternatively, the phase may be shifted in the sub-scanning direction as shown in FIG.

  In general, when high viscosity ink or the like is used, the ink heated outside is supplied to the head 50 (the common liquid chamber 55). The ink temperature on the ink discharge side is lower than that on the ink supply side of the common liquid chamber 55, and when the common liquid chamber 55 is composed of a main flow and a tributary, the ink temperature on the tributary side is lower than the main flow side. Therefore, the thermal conductivity of the heat radiating element 60 on the ink discharge side is higher than that on the ink supply side of the common liquid chamber 55 so that the ink temperature distribution in the common liquid chamber 55 is uniform, and the main flow side of the common liquid chamber 55 It is preferable to increase the thermal conductivity of the heat dissipation element 60 on the tributary side.

  As described above, the head 50 of this embodiment has a configuration in which the common liquid chamber 55 is disposed on the opposite side of the pressure chamber 52 from the nozzle 51 side, and the wiring member (internal wiring) for driving the piezoelectric element 58 is provided. The heat dissipating element 60 also serving as the common liquid chamber 55 is disposed. Accordingly, the refilling property is improved with a simple configuration in which the common liquid chamber 55 communicates with the pressure chamber 52 substantially straight, and it is suitable for discharging high-viscosity ink. Alternatively, heat can be radiated to the ink inside the head (in the common liquid chamber 55), and the ink can be stably ejected without changing the ejection characteristics of the head 50.

  In the above-described embodiment, the heat dissipating element 60 configured in a substantially cylindrical shape is illustrated, but the present invention is not limited to this. For example, it may be a substantially prismatic shape, or may be a tapered shape whose diameter increases toward the piezoelectric element 58 side or the opposite side. Moreover, you may comprise the thermal radiation element 60 in the shape of a wall like the other modification of the thermal radiation element 60 shown in FIG. In this case, since the cross-sectional area of the heat dissipating element 60 is increased and the resistivity is decreased, the thermal conductivity is increased, and the heat dissipating property of the piezoelectric element 58 is further improved.

  Further, in order to grasp the temperature (distribution) change of the ink caused by heat generation or heat dissipation, a thermistor (not shown) having the same structure as the heat dissipation element 60 is mounted inside the head 50 (in the common liquid chamber 55). It may be. By enabling the ink temperature to be detected, when the ink temperature rises, in order to lower the ink temperature, the drive voltage applied to the piezoelectric element 58 is lowered to suppress the heat generation of the piezoelectric element 58, or the corresponding nozzle By reducing the number of micro-vibration drives 51, the number of ejection drives 51, etc., it is possible to more effectively use heat dissipation and to stabilize the ejection. In addition, when the thermistor has the same structure as the heat dissipation element 60, it can be processed in the same manner as the heat dissipation element 60, and the assemblability is improved. The number of mounted thermistors may be one as a representative, but in order to accurately detect the local temperature dependence of the head, the head central portion and the head end (peripheral portion), the ink supply side and the discharge side, or The main stream side and the tributary side may be provided.

  In the present embodiment, the configuration in the case where the head 50 is a full line head having a nozzle row corresponding to the entire width of the recording paper 16 is exemplified. However, the present invention is not limited to this. It may be a mold head.

  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 of an ink jet recording apparatus according to an embodiment of the present invention. It is a principal part top view of a printing part periphery. It is a plane perspective view which shows the structural example of a head. It is a plane perspective view which shows the other structural example of a head. It is a partial enlarged view of a head. It is sectional drawing which follows the 6-6 line in FIG. It is the top view which simplified and displayed the arrangement structure of the thermal radiation element in a common liquid chamber. It is the schematic which showed the structure of the ink supply system. It is a principal part block diagram which shows a system structure. It is a principal part block diagram of the main circuits relevant to head drive. FIG. 11 is a basic configuration diagram of a drive circuit included in the print control unit of FIG. 10. FIG. 4 is a basic configuration diagram for selectively supplying drive signals to a plurality of heat dissipation elements and piezoelectric elements. It is a figure explaining switch IC. It is a structural example in case a some drive circuit is mounted. It is a wave form diagram showing an example of a common drive waveform. It is the modification which changed the shape and arrangement | positioning of the thermal radiation element. It is another modification of a thermal radiation element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device 50 ... Head, 51 ... Nozzle, 52 ... Pressure chamber, 53 ... Discharge element, 54 ... Supply port, 55 ... Common liquid chamber, 56 ... Diaphragm, 57 ... Individual electrode, 58 ... Piezoelectric element, 60 ... Heat dissipation element, 60A ... Internal wiring member, 60B ... Coating material, 72 ... System controller, 75 ... ROM, 80 ... Print control unit, 104 ... CPU, 108 ... RAM, 116 ... Discharge drive unit, 120 ... Switch IC, 120A ... Switch element, 130 ... Drive circuit

Claims (7)

A plurality of outlets for discharging liquid;
A plurality of pressure chambers communicating with each of the plurality of discharge ports;
A piezoelectric element provided on the opposite side of the plurality of pressure chambers from the side on which the discharge ports are formed, and deforming each of the plurality of pressure chambers;
A common liquid chamber for supplying liquid to the plurality of pressure chambers on the opposite side of the pressure chamber from the side on which the discharge port is formed;
At least a part of the piezoelectric element is formed so as to rise in a direction substantially perpendicular to the surface on which the piezoelectric element is disposed, and at least part of the common liquid chamber rises in a direction substantially perpendicular to the surface on which the piezoelectric element is disposed. A liquid discharge head comprising: a member having heat conductivity and heat conductivity, and a heat dissipating element that dissipates heat generated by the piezoelectric element.   The liquid discharge head according to claim 1, wherein the heat dissipating element also serves as a wiring member for driving the piezoelectric element.   The heat radiating element radiates heat generated by the piezoelectric element in at least one of the atmosphere outside the liquid ejection head and the liquid inside the liquid ejection head. The liquid discharge head according to 2.   2. The thermal conductivity of the heat dissipating element on the center side of the liquid ejection head is configured to be greater than the thermal conductivity of the piezoelectric element on the end side of the liquid ejection head. Item 4. The liquid ejection head according to any one of Items 3 to 4.   5. The liquid according to claim 4, wherein a cross-sectional area of the heat dissipating element on the center side of the liquid discharge head is configured to be larger than a cross-sectional area of the piezoelectric element on the end side of the liquid discharge head. Discharge head.   6. The heat dissipation element includes a core material having electrical conductivity and thermal conductivity, and a covering material having electrical insulation properties and thermal conductivity. The liquid discharge head according to item.   An image forming apparatus comprising the liquid ejection head according to claim 1.

Images