JP2005104135A - Liquid discharge apparatus and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a stable liquid discharge and rapid refilling and also to maintain that discharge and refilling performances by controlling the liquid physical properties in the vicinity of the nozzles. <P>SOLUTION: The inkjet recording head has a laminate structure composed of a plurality of flow channel plates (61-64) to form ink flow channels. A nozzle heater 66 is installed in the first flow channel plate 61 having a built-in nozzle orifice 51. A supply channel heater 67 is installed in the third flow channel plate which forms a supply channel 56. By controlling the heating timing of the nozzle heater 66 and the supply channel heater 67 in accordance with the ink discharge drive timing from the nozzle 51, nozzle portions having relatively high flow channel resistance and supply channel portions are locally heated, thus enabling high-viscosity ink to be discharged with the minimum required amount of energy and discharge pressure to work effectively on the side of the nozzle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid ejection apparatus and an ink jet recording apparatus, and more particularly to a structure of an ejection head suitable for realizing stable liquid ejection and a drive control technique thereof.

  An ink jet recording apparatus ejects ink from a recording head in response to a print signal while moving the recording medium such as recording paper relative to a recording head having an ink ejection nozzle. An ink droplet is landed on the top, and an image is formed on the print medium by the ink dot. In such an ink jet recording apparatus, when the viscosity of the ink in the nozzle rises due to drying or the like, a discharge failure such as no ink discharge occurs. Further, when the ink viscosity increases, the ink resupply performance (refill performance) to the nozzles decreases.

  From such a viewpoint, Patent Document 1 discloses a so-called thermal jet type (particularly, side shooter type) ink jet printing apparatus provided with a heating and foaming heater that generates thermal energy necessary for ink ejection in an ink flow path. A first heater dedicated heater is disposed near the discharge port in the ink flow path, and a second heater dedicated heater is disposed farther from the discharge port than the heating and foaming heater. A technique for improving the discharge performance and the refill performance by controlling the viscosity of the ink with a dedicated heater is proposed.

Patent Document 2 discloses an ink jet printer including a head heater that heats the entire head and an ink chamber heater that individually heats each ink chamber.
JP-A-11-10878 Japanese Unexamined Patent Publication No. 6-91893

  The method proposed in Patent Document 2 pays attention to the ink temperature in the ejection direction and controls the viscosity and volume of the ink. In order to obtain sufficient liquid properties for ejection by this method, the entire head is used. It takes a lot of energy to warm up. In particular, initial heating is required from when the power is turned on until the first printing can be performed.

  In this regard, according to the method disclosed in Patent Document 1, it is not necessary to heat the entire head because of the structure in which the dedicated heater is provided in the individual flow path. However, the method proposed in Patent Document 1 has a structure in which dedicated heaters are arranged close to each other on the ejection side and the supply side with respect to the ink flow path on the same plane, and the number of ejections increases. As a result, there is a problem that the temperature difference between these two heaters becomes smaller and the effect of increasing the discharge force is diminished. Furthermore, the configuration disclosed in Patent Document 1 is a discharge method using foaming by a heating resistor, and has a heating foaming heater that performs higher-temperature heating stronger than a dedicated heating heater. Since the heaters for heating are arranged in a very close positional relationship, there is a problem that the temperature difference between the heaters is further reduced.

  The present invention has been made in view of such circumstances, and realizes stable liquid ejection by controlling the liquid physical properties in the vicinity of the nozzle, and also realizes quick refill even with high viscosity ink. An object of the present invention is to provide a liquid ejection apparatus capable of maintaining the ejection performance and refill performance, and an ink jet recording apparatus using the liquid ejection apparatus.

  In order to achieve the above object, according to the present invention, in a liquid ejection device that ejects liquid from a nozzle hole, according to a nozzle unit heating unit disposed in the nozzle unit, and ejection drive timing at which liquid is ejected from the nozzle hole Nozzle heating control means for controlling the heating timing by the nozzle part heating means.

  According to the present invention, since the temperature of the nozzle portion is adjusted in accordance with the timing of discharging the liquid from the nozzle hole, the viscosity of the liquid in the nozzle can be reduced with the minimum necessary heating energy. Thereby, it is possible to stabilize the ejection performance with less energy than in the past with respect to high viscosity ink.

  The liquid discharge apparatus according to one aspect of the present invention has a temperature increase time required for the liquid viscosity in the nozzle to become a predetermined value or less based on the temperature dependency characteristic of the viscosity of the liquid to be discharged and the liquid temperature increase characteristic in the nozzle. And a timing setting means for setting the drive timing of the nozzle unit heating means according to the temperature rise time calculated by the calculating means.

  According to this aspect, an appropriate heating timing is calculated so as to obtain a required viscosity at the time of ejection according to the type of liquid used. Thereby, it is possible to reliably raise the temperature so that the viscosity in the nozzle can be discharged.

  In this case, the calculation means includes a first calculation processing unit that obtains a relationship between a desired viscosity and a required heating temperature from the temperature dependence characteristic of the liquid viscosity, and the required heating temperature from the liquid temperature rise characteristic in the nozzle. And a second arithmetic processing unit for obtaining a temperature raising time required for raising the temperature.

  Further, the first arithmetic processing unit has a first table indicating the temperature dependence characteristic of the viscosity of the liquid, and the second arithmetic processing unit has a second table indicating the liquid temperature rise characteristic in the nozzle. There is a mode. In addition, it is possible to cope with a plurality of liquid types by having the first table corresponding to the plurality of liquid types.

  As another aspect of the present invention, the nozzle heating control means controls the liquid in the nozzle so as to raise a predetermined heating penetration depth from the nozzle wall surface to a predetermined temperature.

  Since at least the liquid near the nozzle wall surface is heated to lower the viscosity, the liquid can be discharged from the nozzle hole. Therefore, sufficient heating control may be performed to heat only the liquid near the nozzle wall surface.

As a specific aspect, when the nozzle diameter is D, the heating penetration depth δd is expressed by the following formula: 0.05 ≦ δd / D ≦ 0.15
It is preferable to satisfy.

  Thus, the mode of heating only the liquid in the vicinity of the nozzle wall surface can achieve energy saving as compared with the case of heating the entire ink in the nozzle portion.

  A liquid discharge apparatus according to still another aspect of the present invention includes a discharge head including a plurality of nozzles, individual pressure chambers corresponding to the nozzles, and a common flow path for supplying liquid to the plurality of pressure chambers. The nozzle section heating means is provided for each nozzle of the discharge head, and the supply path heating means is provided in a supply path that communicates the pressure chamber and the common flow path.

  The liquid supplied from the liquid supply source to the ejection head is sent to individual pressure chambers through a common flow path in the head. The pressure chamber is provided with means (discharge driving element) for generating a liquid discharge force, such as an actuator or a heater for foaming heating, and the liquid is discharged from the nozzle hole by driving the element. That is, the liquid flows into the individual pressure chambers from the common channel through the supply channel, and is discharged to the outside from the pressure chamber via the nozzle.

  Considering the entire flow path in the head, the common flow path and the pressure chamber have a relatively large cross-sectional area, and the supply path (supply hole) and the nozzle portion have a relatively small cross-sectional area. As described above, by heating the supply path and the nozzle portion having a relatively large fluid resistance to locally reduce the viscosity of the liquid, even a liquid having a relatively high viscosity can be discharged. Moreover, according to this aspect, since it is a local heating, it has high responsiveness, can improve a discharge frequency, and can reduce energy consumption compared with the method of heating the whole liquid.

  According to another aspect of the present invention, in the aspect in which the heating unit is provided in each of the supply path and the nozzle portion, the supply path heating for controlling the heating timing by the supply path heating unit in accordance with the ejection driving timing for ejecting ink from the nozzle hole. Control means is provided.

  By controlling the supply path heating means for heating the upstream supply path across the pressure chamber and the nozzle section heating means for heating the downstream nozzle section in association with the discharge drive timing, discharge characteristics and refill characteristics are controlled. Improvements can be made.

  For example, during ejection, only the nozzle portion is heated to lower the viscosity of the ink in the nozzle portion, while the supply passage is not heated, and the liquid in the vicinity of the supply passage is relatively increased in viscosity to thereby increase the pressure chamber. The discharge pressure can be effectively operated in the discharge direction. Further, at the time of refilling, by increasing the temperature around the supply path, the liquid can easily flow from the supply path, and the refill can be performed quickly. Further, after the refill is almost completed, heating of the nozzle portion is stopped to increase the liquid viscosity around the nozzle. Thus, the meniscus vibration caused by the refill can be rapidly converged.

  In a preferred aspect of the present invention, the nozzle, the pressure chamber, the common flow path, and the supply path are formed by a laminated structure, and the nozzle and the supply path are configured by members of different layers, and the nozzle section heating The means and the supply path heating means are arranged in different layers.

  According to this aspect, in the head in which the nozzle, the pressure chamber, the common flow path, and the supply path are formed by the laminated structure of the plate members (flow path plates), the nozzle unit heating means and the supply path heating means are respectively in different levels. Therefore, these heating means can be arranged in a relatively distant positional relationship, and the mutual temperature effect can be eliminated. Therefore, it is possible to increase the accuracy of each temperature adjustment and to maintain the discharge performance and the refill performance for a long time.

  In this aspect, an aspect in which a heat insulating layer is further formed between the flow path plate (nozzle layer) in which the nozzle is formed and the flow path plate (supply path layer) in which the supply path is formed is also preferable.

Another aspect of the present invention provides an ink jet recording apparatus using the above-described liquid ejection apparatus of the present invention as an ink droplet ejection apparatus. That is, the ink jet recording apparatus of the present invention forms an image on the recording medium by ejecting ink from the nozzle holes while moving the recording medium relative to the recording head having the nozzle holes. It is characterized by.

  In the implementation of the present invention, the form of the recording head is not particularly limited, and may be a shuttle type recording head that performs printing while the print head reciprocates in a direction substantially perpendicular to the feeding direction of the printing medium. A full-line type recording head having a plurality of nozzle rows in which a plurality of nozzles for ejecting ink are arranged over the entire width of the print medium in a direction substantially orthogonal to the feed direction of the print medium may be used.

  In the case of a long head such as a full-line type recording head, unused nozzles may exist during printing. However, the conventional method of heating the entire head dries and discharges ink from unused nozzles by heating. It tends to be defective. Therefore, prevention of nozzle drying is an important issue. According to the present invention, since the nozzle portion is locally heated by the nozzle portion heating means, it is not necessary to heat the entire head, and drying of unused nozzles can be prevented. Therefore, the present invention is particularly effective when applied to a full-line type recording head.

  In a “full-line type recording head”, the nozzle array is usually arranged along a direction perpendicular to the relative feeding direction (relative movement direction) of the recording medium, but with respect to the direction perpendicular to the relative movement direction. Thus, there may be a mode in which the recording head is arranged along an oblique direction having a certain predetermined angle. Further, the arrangement form of the nozzles in the recording head is not limited to a single line arrangement, and may be a matrix arrangement composed of a plurality of columns. Furthermore, by combining a plurality of short recording head units each having a nozzle row that is less than the length corresponding to the full width of the recording medium, a nozzle row corresponding to the full width of the recording medium is configured as the whole unit. possible.

  The “recording medium” is a medium that receives printing by a recording head, and can be called an image forming medium, a printing medium, an image receiving medium, or the like. Specific modes of the recording medium include various media regardless of materials and shapes, such as continuous paper, cut paper, sticker paper, resin sheets such as OHP sheets, film, cloth, and the like.

  The transport means for moving the recording medium relative to the recording head includes a mode for transporting the recording medium to the stopped (fixed) recording head, and a mode for moving the recording head relative to the stopped recording medium. Alternatively, both of the modes in which both the recording head and the recording medium are moved are included.

  In this specification, the term “printing” represents not only the formation of characters but also the concept of forming an image in a broad sense including characters.

  According to the present invention, the nozzle portion heating means is provided in the nozzle portion that defines the size of the discharged droplet, and the heating of the nozzle portion is controlled according to the discharge drive timing. The viscosity can be lowered to the required viscosity, and the liquid can be easily discharged from the nozzle hole.

  In addition, according to the present invention, since the temperature of the nozzle portion is locally controlled, the heat-up time is short as compared with the conventional mode in which the temperature of the entire head is controlled, and the first printing can be executed after the power is turned on. The initial startup time can be shortened. Furthermore, since the present invention can prevent drying of unused nozzles, it is very effective for a liquid discharge apparatus including a long discharge head with a large number of nozzles.

  In the present invention, nozzles, pressure chambers, common flow paths, supply paths and the like, which are elements necessary for liquid ejection, are formed by a laminated structure of plate members, and nozzle unit heating means and supply to plate members (flow path plates) at different levels By providing the path heating means, the distance between these heating means can be made relatively large, and the influence of temperature on each other can be avoided. Therefore, heat can be transmitted only to the periphery of the nozzle and the vicinity of the supply path (the periphery of the individual flow path), and the effect of adjusting the temperature of the liquid is maintained.

  Further, as an incidental effect, in the present invention, since the temperature adjustment timing of the nozzle portion is controlled in accordance with the liquid discharge timing, the nozzle portion heating means is turned on immediately before the discharge, and turned off immediately before and after the discharge. According to the aspect, it is possible to effectively tear off the ejected droplets in combination with the driving of the ejection driving element such as an actuator. Thereby, generation | occurrence | production of a satellite and a splash can be suppressed.

  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 inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper 16, a decurling unit 20 for removing curling of the recording paper 16, and a nozzle of the printing unit 12 A suction belt transport unit 22 that is disposed to face a surface (ink ejection surface) and transports the recording paper 16 while maintaining the flatness of the recording paper 16, and a print detection unit 24 that reads a printing result by the printing unit 12, A paper discharge unit 26 that discharges 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.

  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.

  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. 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.

  When the power of the motor (reference numeral 100 in FIG. 6) 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 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 feed direction (see FIG. 2). Although the detailed structure is not shown, each of the print heads 12K, 12C, 12M, and 12Y has a length that exceeds at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10, as shown in FIG. A line type head in which a plurality of ink discharge ports (nozzles) are arranged is formed.

  A print head 12K corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the paper transport direction). , 12C, 12M, 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.

  As described above, according to the printing unit 12 in which the full line head that covers the entire paper width is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is performed. The image can be recorded on the entire surface of the recording paper 16 only by performing it once (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning 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 includes tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y. The print heads 12K, 12C, 12M, and 12Y are communicated with each other via the drawing. 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.

  The print detection unit 24 includes an image sensor for imaging the droplet ejection result of the print unit 12, and functions as a means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the image sensor.

  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 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.

  The print detection unit 24 reads the test pattern 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 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 cut into a predetermined size by the cutter 28 and then discharged from the paper discharge 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) that switches the paper discharge path so as 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.

[Cross sectional structure around the nozzle]
FIG. 3 is a cross-sectional view showing a schematic configuration of an ink flow path formed in each of the print heads 12K, 12C, 12M, and 12Y (hereinafter, these are represented by reference numeral 50). In FIG. 3, reference numeral 51 denotes an ink ejection nozzle, 52 denotes a pressure chamber, 53 denotes a common flow path, 54 denotes a diaphragm, and 55 denotes an actuator.

  The pressure chamber 52 provided corresponding to the nozzle 51 communicates with the common flow path 53 via the supply path 56. The ink sent from the ink storage / loading unit 14 is supplied to the pressure chamber 52 through the common channel 53. An actuator 55 having individual electrodes (not shown) is joined to the diaphragm 54 constituting the bottom surface of the pressure chamber 52. By applying a driving voltage to the individual electrodes, the actuator 55 is deformed, and the pressure chamber When the ink in 52 is pressurized, the ink is ejected from the nozzle 51. That is, in this embodiment, a method (piezo jet method) in which ink droplets are ejected by deformation of an actuator 55 typified by a piezo element (piezoelectric element) is employed.

  As shown in the figure, the print head 50 of this embodiment has an ink flow path formed by laminating a plurality of plate members formed with holes and grooves by etching or the like on a thin plate material such as a SUS plate. FIG. 3 shows a structure in which four plate members are laminated on the vibration plate 54. That is, the first flow path plate (nozzle layer) 61 that includes the discharge port of the nozzle 51, the second flow path plate 62 that forms the side surface of the common flow path 53, and the third flow path that includes the supply path 56. A flow path plate (supply path layer) 63 and a fourth flow path plate 64 that forms the side surface of the pressure chamber 52 are stacked.

  As shown in the figure, a first flow path plate (nozzle layer) 61 that forms a flow path communicating with the discharge port of the nozzle 51 includes a first heater (hereinafter referred to as a nozzle heater) around the flow path of the nozzle 51. .) 66 is provided. Further, a third flow path plate (supply path layer) 63 forming a supply path 56 that connects the pressure chamber 52 and the common flow path 53 has a second heater (hereinafter referred to as a supply path) around the supply path 56. 67) is provided.

  FIG. 4 is a plan view showing a structural example of the nozzle heater 66. The nozzle heater 66 includes a plurality of heater blocks (three blocks in FIG. 4) 66A, 66B, and 66C, and these heater blocks 66A to 66C are arranged along the circumference so as to surround the periphery of the flow path of the nozzle 51. It has a structure. Each of the heater blocks 66A to 66C is connected to electrodes 68A, 68B, 68C corresponding to ground lines and electrodes 69A, 69B, 69C corresponding to signal lines, and applies a required voltage between the electrodes. As a result, the heater blocks 66A to 66C generate heat.

  FIG. 5 is an enlarged view of the vicinity of the nozzle tip (enlarged view of a portion indicated by reference numeral 5 in FIG. 3). As shown in the figure, the periphery of the flow path of the nozzle 51 is constituted by an insulating layer 70. In addition, an insulating layer 73 is provided on the uppermost layer of the ejection surface 72, and a signal line 74, a heater (heating element) 75, and a ground line 76 are sequentially stacked on the lower layer, and an insulating layer 77 is provided below the ground line 76. ing.

  For example, the wiring portions of the signal line 74 and the ground line 76 have an aluminum (Al) film thickness of 0.8 μm, a wiring width of 5 μm, and a wiring interval of 5 μm. Of course, the configuration of the wiring portion is not limited to this example, and a metal other than aluminum can be used.

The heater 75 is made of, for example, a Ta—Si—O ternary alloy. In addition, a Ta single layer, TaN, or the like may be used. The insulating layers 70, 73 and 77 are made of SiO ₂ and have a thickness of 0.5 μm. Instead of SiO ₂ , a fluorinated resin such as CYTOP (trade name: manufactured by Asahi Glass Co., Ltd.) may be used. Even in this case, the thickness is desirably about 0.5 μm or less.

  The structure of the nozzle heater 66 has been described with reference to FIGS. 4 and 5, but the structure of the supply path heater 67 indicated by reference numeral 67 in FIG.

〔System configuration〕
FIG. 6 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 80, a system controller 82, an image memory 84, a motor driver 86, a heater driver 88, a print control unit 90, an image buffer memory 92, a head driver 94, a head heater driver 96, and the like. .

  The communication interface 80 is an interface unit that receives image data sent from the host computer 98. As the communication interface 80, a serial interface such as USB, IEEE 1394, Ethernet, and wireless network, and a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. The image data sent from the host computer 98 is taken into the inkjet recording apparatus 10 via the communication interface 80 and temporarily stored in the image memory 84. The image memory 84 is a storage unit that temporarily stores an image input via the communication interface 80, and data is read and written through the system controller 82. The image memory 84 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.

  The system controller 82 is a control unit that controls each unit such as the communication interface 80, the image memory 84, the motor driver 86, the heater driver 88, and the like. The system controller 82 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 98, read / write control of the image memory 84, and the like, as well as a transport system motor 100 and heater 102. A control signal for controlling is generated.

  The motor driver 86 is a driver (drive circuit) that drives the motor 100 in accordance with an instruction from the system controller 82. The heater driver 88 is a driver that drives the heater 102 such as the post-drying unit 42 in accordance with an instruction from the system controller 82.

  The print control unit 90 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the image memory 84 according to the control of the system controller 82, and the generated print It is a control unit that supplies a control signal (print data) to the head driver 94 and controls the head heater driver 96. Necessary signal processing is performed in the print control unit 90, and the ejection amount and ejection timing of the ink droplets of the print head 50 are controlled via the head driver 94 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print controller 90 is provided with an image buffer memory 92, and image data, parameters, and other data are temporarily stored in the image buffer memory 92 when image data is processed in the print controller 90. In FIG. 6, the image buffer memory 92 is shown in a mode associated with the print control unit 90, but it can also be used as the image memory 84. Also possible is an aspect in which the print controller 90 and the system controller 82 are integrated and configured with a single processor.

  The head driver 94 drives the actuator 55 of the print head 50 for each color based on the print data given from the print control unit 90. The head driver 94 may include a feedback control system for keeping the head driving conditions constant.

  The head heater driver 96 generates a signal for driving the nozzle heater 66 and the supply path heater 67 in accordance with a command from the print control unit 90. Control of ink ejection drive timing and heating timing of the nozzle heater 66 and the supply path heater 67 will be described later.

  Image data to be printed is input from the outside via the communication interface 80 and stored in the image memory 84. At this stage, RGB image data is stored in the image memory 84.

  The image data stored in the image memory 84 is sent to the print control unit 90 via the system controller 82, and is converted into dot data for each ink color by a method such as a known error diffusion algorithm. The That is, the print control unit 90 performs processing for converting the input RGB image data into YCMK four-color dot data. The dot data generated by the print control unit 90 is stored in the image buffer memory 92.

  The head driver 94 generates a drive control signal for the print head 50 based on the dot data stored in the image buffer memory 92. When the drive control signal generated by the head driver 94 is applied to the print head 50, ink is ejected from the nozzles 51 of the print head 50. An image is formed on the recording paper 16 by controlling ink ejection from the print 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 90. The print control unit 90 performs various corrections for the print head 50 based on information obtained from the print detection unit 24 as necessary.

  Next, ink temperature adjustment timing in the inkjet recording apparatus 10 configured as described above will be described.

[Temperature control timing focusing on fluid phenomena]
FIG. 7 is a schematic diagram showing an example of an ink droplet ejection process by pull push pull meniscus control. The illustrated series of discharge processes is realized by driving control of the actuator 55. First, a gentle pulling operation is performed to reduce the pressure before ink discharge, and the state of the meniscus 120 (interface between the ink 122 in the nozzle 51 and the outside air) is changed to a predetermined shape (FIGS. 7A to 7B). . From this state, the ejecting operation is performed vigorously (FIGS. 7C to 7H), and after the ink ejection, the pulling operation is performed again to tear the ink droplet 126 to a predetermined size and to suppress the vibration of the meniscus 120. (FIGS. 7 (i) to (j)).

  In such a fluid phenomenon, the state shown by (d), that is, the time t = Tn when the ink 122 exits from the ejection surface (nozzle surface) 124 is set as a reference for the temperature control timing.

  FIG. 8 is an example of a timing chart showing the drive timing of the nozzle heater 66 and the supply path heater 67. In this section, the state of (d) is defined as “ejection”.

  The drive start timing T1 of the nozzle heater 66 is 1 μs to 100 μs before Tn. If ΔTn1 = T1−Tn, then −100 μs ≦ ΔTn1 ≦ −1 μs. Here, the condition of ΔTn1 ≦ −1 μs indicates that 1 μs or more is required to heat the ink around the nozzles and raise the temperature.

  The driving end timing T1 ′ of the nozzle heater 66 is 20 μs before and 50 μs after Tn. If ΔTn1 ′ = T1′−Tn, −20 μs ≦ ΔTn1 ′ ≦ 50 μs. The reason why the nozzle heater 66 is turned off immediately before or immediately after discharge (−20 μs to +20 μs) is to shorten the heat-up time and reduce the amount of heat. In order to reduce ink viscosity during refilling in order to perform refilling quickly after ejection, it is preferable to turn off the nozzle heater 66 after ejection (+20 μs to +50 μs).

  The drive start timing T2 of the supply path heater 67 is 1 μs to 100 μs after Tn. If ΔTn2 = T2−Tn, then 1 μs ≦ ΔTn1 ≦ 100 μs. Here, the condition of ΔTn1 ≧ 1 μs indicates that 1 μs or more is required to heat the ink in the supply path 56 and raise the temperature.

  Since refilling is started at 0 to 100 [mu] s, most of them at 0 to 50 [mu] s after the start of discharge, the supply path heater 67 starts to be driven at the above timing. The driving end timing T2 ′ of the supply path heater 67 is determined depending on the driving frequency of the actuator 55.

  That the heating time of at least 1 μs is required to raise the ink temperature by the nozzle heater 66 or the supply path heater 67 is derived from the following calculation of the temperature distribution in the nozzle.

  In the calculation, the approximation by the heat conduction of semi-infinite fluid (model without convection) is applied. As shown in FIG. 9, the coordinate axis of the position x is set with respect to the boundary surface 144 for the low temperature fluid (semi-infinite fluid 142) in contact with the temperature source 140. As an initial condition, the semi-infinite fluid 142 is initially uniform at the temperature T0, and the temperature of the surface at x = 0 at time τ = 0 is Ts. Ts is then kept constant.

  The following equation holds for the temperature T (τ, x) at the time τ and the position x under the above conditions.

erf (β) is an error function and is expressed by the following equation.

  Here, β is expressed by the following equation.

[Mathematical formula-see original document] a in the equation is temperature conductivity (m < ² > / s) and is represented by the following equation.

Where λ: thermal conductivity (W / (m · K)), ρ: density (kg / m ³ ), Cp: specific heat (J / (kg · K)). In the case of water, since λ = 0.61, ρ = 1000, and Cp = 4180, a = 1.46 × 10 ⁻⁷ .

  From the above, the temperature T at the time τ at a position separated by x from the temperature source can be obtained using the formula [Equation 1].

The amount of heat Q (J / m ² ) entered from the surface unit area between time τ = 0 and τ is expressed by the following equation.

  The required heat quantity can be calculated from the equation [5].

  Since the composition of a general water-based ink is 80% or more of water, the temperature distribution is calculated on the assumption that the liquid is water. FIG. 10 shows the calculation results when the initial temperature T0 = 300K and the boundary temperature Ts = 350K. FIG. 11 shows the calculation results when the initial temperature T0 = 300K and the boundary temperature Ts = 400K.

  According to these graphs, it can be seen that the temperature of ink (water in calculation) of 1 μm thickness can be raised from the heater boundary with a heating time of 1 μs. Further, the temperature rise in the range of several tens of μs is in the range of several μm from the heater boundary. Assuming that the nozzle diameter is about 30 μm, the temperature of the outer periphery increases by about 10% with respect to the nozzle diameter.

[Temperature control timing focusing on actuator drive waveform]
FIG. 12 is a timing chart showing the drive timing of the nozzle heater 66 and the supply path heater 67 with attention paid to the actuator drive waveform, and a diagram showing the correspondence between the ink movements during ejection. In the figure, the horizontal axis indicates time, and the vertical axis indicates voltage.

  As shown in FIG. 12, the actuator drive timing when ink 122 is ejected from the nozzle surface 124 is Ta, and this Ta is used as a reference for heater control. The operation of discharging the ink 122 from the nozzle surface 124 is realized by driving an actuator that reduces the volume of the pressure chamber 52. That is, the timing at which the ink 122 goes out of the nozzle surface 124 is within the drive period in which the actuator 55 is displaced in the pressure chamber volume decreasing direction. Or it is in the period when inclination becomes the maximum.

  In this way, paying attention to the place where the voltage change is the largest in a series of voltage drives or the place where the time differentiation of the voltage change is the largest, the actuator drive timing for realizing the discharge operation is set as the reference Ta. Then, the drive timing of the nozzle heater and the supply path heater is set before and after the reference Ta.

  Specifically, similarly to the example described with reference to FIG. 8, the drive timing of each heater is determined by replacing Tn with Ta.

  The actuator drive waveform is not limited to the example of FIG. FIG. 13 shows another waveform example of the actuator drive pulse. Various types of actuator drive waveforms are possible. In any case, an appropriate time is determined as the control reference time Ta from the period in which the potential difference is maximum and the gradient is maximum. It is not limited to Ta shown in FIG.12 and FIG.13, For example, the aspect which sets the time which becomes the voltage 0 as the reference time Ta is also possible.

[Evaluation of heat control]
The necessary amount of heat is calculated using the above-described equation (5). Assuming that the liquid is water, the initial temperature T0 is 300K. The nozzle is assumed to have a cylindrical shape with a nozzle radius of 15 μm, a nozzle height of 50 μm, and a nozzle inner surface area of 4.7 × 10 ⁻⁹ m ² . The calculation results in the case of heating temperatures of 350K and 400K are shown in FIG.

  As shown in FIG. 14, the amount of heat required in the range of several tens of μs is several μJ. Even if the head is heated to the same extent as the ink is heated, the amount of heat of the heater is about 10 μJ, which is 20 μJ or less at most. From such a viewpoint, the temperature adjustment time by the nozzle heater 66 and the supply path heater 67 is set to 100 μs or less.

[Temperature dependence of ink properties]
The change in ink physical property value due to temperature varies depending on the type of ink. FIG. 15 is a graph showing the relationship between surface tension and temperature for a certain ink. FIG. 16 is a graph showing the temperature dependence of the ink viscosity for each of the four types of ink. As shown in these drawings, as the ink temperature rises, the surface tension tends to decrease and the viscosity tends to decrease.

  Experiments have found that ink can be ejected if the viscosity of the ink in the nozzle 51 near the contact surface with the nozzle inner wall can be reduced. That is, as shown in FIG. 17, assuming that the diameter of the nozzle 51 is D and the heat penetration depth from the inner wall of the nozzle is δd, if the penetration depth of 0.05 ≦ δd / D is ensured to a minimum, no problem is discharged. The heating energy can be halved by setting δd / D ≦ 0.15.

  [Table 1] below summarizes the evaluation of the discharge state, the relative ratio of the heating energy, and the evaluation of the energy saving effect when the discharge experiment is performed under the condition of δd / D.

  According to the experimental results in [Table 1], when the condition of 0.05 ≦ δd / D ≦ 0.15 is satisfied, good results can be obtained for the discharge state and the energy saving effect.

[Example of temperature control considering ink properties]
The temperature control in this embodiment will be described using a more specific example. From the simulation by numerical calculation, it was found that even if the ink is high viscosity, it can be ejected if 1 μm ink is low viscosity liquid ink of 5 cP or less from the nozzle wall.

  As already explained, it is known as a characteristic of ink that the viscosity decreases with increasing temperature. Here, it is assumed that ink having a temperature characteristic of viscosity as shown in FIG. 18 is used. It is 40 ° C. or more that the ink shown in this graph is 5 cP or less.

  The rise in the ink temperature at the nozzle portion by the nozzle heater 66 is obtained by calculation of heat conduction. FIG. 19 is a graph showing the relationship between the ink depth (distance) from the nozzle wall (heater boundary) and the temperature when the nozzle wall is 350K, using the elapsed time (μs) as a parameter. According to the figure, it can be seen that 3 μs or more is necessary to bring the ink of 1 μm from the nozzle wall to 40 ° C. or more (5 cP or less). Therefore, in this ink, the drive start timing T1 of the nozzle heater 66 needs to be set 3 μs or more before Tn or Ta.

  In this way, the necessary heating temperature and temperature rise time are calculated from the physical properties of the ink used, the nozzle conditions, and the like, and the drive timing of the nozzle heater 66 is set according to the calculation results. The drive timing of the supply path heater 67 is set according to the same calculation.

  FIG. 20 is a process block diagram relating to the heater drive timing setting process. The ink jet recording apparatus 10 according to the present embodiment includes an ink information acquisition unit 160 that acquires information on ink to be used, a first calculation processing unit 162 that calculates temperature-dependent characteristics of ink viscosity, and at least one type (preferably Is a first table storage unit 164 that stores table data indicating the temperature dependence of the viscosity of the ink (a plurality of types), a second calculation processing unit 166 that calculates ink temperature rise characteristics in the nozzle, and ink A second table storage unit 168 in which table data indicating the time dependence of the temperature distribution of the nozzle heater 66 is supplied based on the calculation results of the first calculation processing unit 162 and the second calculation processing unit 166. Timing setting units 170 and 172 for setting the driving timing of the road heater 67 are provided.

  The processing functions shown in FIG. 20 are realized by the system controller 82, the print control unit 90, or a combination thereof described with reference to FIG.

  As shown in FIG. 20, information on the ink to be used is obtained from the ink information acquisition unit 160, and the temperature dependency characteristic of the viscosity of the used ink is calculated in the first arithmetic processing unit 162. At this time, the first arithmetic processing unit 162 refers to the table data stored in the first table storage unit 164, and as shown in FIG. 21, heating necessary to obtain the dischargeable viscosity for the corresponding ink. Find the temperature (required heating temperature).

  The calculation result of the first calculation processing unit 162 shown in FIG. 20 is sent to the second calculation processing unit 166. The second arithmetic processing unit 166 refers to the table data stored in the second table storage unit 168, and as shown in FIG. 22, information on the required heating temperature and information on the required heating penetration depth δd. Based on this, a heating time required to raise the required heating penetration depth δd to the required heating temperature is obtained.

  The information on the temperature rise time thus obtained is sent to the timing setting units 170 and 172 in FIG. 20, and the drive timings of the nozzle heater 66 and the supply path heater 67 are set according to the temperature rise time.

  According to this embodiment, since the nozzle temperature is adjusted in accordance with the ink discharge timing, it is possible to discharge high-viscosity ink with minimum heating energy. By storing information relating to a plurality of types of ink in the first table storage unit 164, it is possible to handle a plurality of types of ink, and an appropriate ink viscosity that can be ejected according to the type of ink used. The temperature can be adjusted as follows.

  In addition, as described with reference to FIG. 3, since the ink viscosity is locally decreased by heating only a place where the fluid resistance of the ink is relatively large, the responsiveness of the heating control is high and the ejection frequency is improved. Reduction of energy consumption can be realized.

  Furthermore, since the nozzle heater 66 and the supply path heater 67 are separately provided on the flow path plates of different levels, the temperature influence on each other is reduced, and heat is effectively applied only around the nozzle and the individual flow path (supply path). It can communicate and maintain its temperature control effect. For example, if 62 in FIG.

  In the above embodiment, the inkjet recording apparatus 10 has been described. However, the scope of application of the present invention is not limited to this, and the present invention is applied to various liquid ejecting apparatuses such as a coating apparatus that applies treatment liquid and other liquids to a medium. be able to.

1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Sectional drawing which shows schematic structure of the ink flow path currently formed in the print head Plan view showing a structure example of a nozzle heater Enlarged cross section near the nozzle Main block diagram showing the system configuration of the inkjet recording apparatus of this example Schematic diagram showing the process of ejecting ink droplets from a nozzle Timing chart showing drive timing of nozzle heater and supply path heater Diagram used to explain heat conduction calculation conditions Graph showing the calculation result of nozzle temperature distribution Graph showing the calculation result of nozzle temperature distribution Timing chart showing actuator drive waveform, drive timing of nose heater and supply path heater, and diagram showing correspondence of ink movement during ejection The figure which shows the other waveform example of an actuator drive pulse Graph showing calculation result of required heat Graph showing the relationship between surface tension and temperature for an ink Graph showing temperature dependence of ink viscosity for each of a plurality of (four types) inks Enlarged cross-sectional view of the main part of the nozzle used to explain the heat penetration depth Graph showing an example of temperature dependence of ink viscosity A graph showing the relationship between the ink depth (distance) from the nozzle wall (heater boundary) and temperature using elapsed time as a parameter Process block diagram related to heater drive timing setting process The figure used to explain the method of obtaining the heating temperature necessary to obtain the required dischargeable viscosity from the table showing the temperature dependence of the ink viscosity The figure used in order to explain the method of obtaining the temperature rise time required to raise the required heating penetration depth δd to the required heating temperature from the table showing the temperature distribution

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Print head, 14 ... Ink storage / loading part, 16 ... Recording paper, 50 ... Print head, 51 ... Nozzle, 52 ... Pressure chamber, 53 ... Common channel, 54 ... Vibration plate, 55 ... Actuator, 56 ... Supply channel, 61 ... First channel plate (nozzle layer), 62 ... Second channel plate, 63 ... Third channel plate ( (Supply path layer), 64 ... fourth flow path plate, 66 ... nozzle heater, 67 ... supply path heater, 82 ... system controller, 90 ... print controller, 120 ... meniscus, 122 ... ink

Claims (11)

In a liquid ejection device that ejects liquid from a nozzle hole,
A nozzle part heating means disposed in the nozzle part;
Nozzle heating control means for controlling the heating timing by the nozzle section heating means in accordance with the discharge drive timing for discharging liquid from the nozzle hole;
A liquid ejection apparatus comprising: Calculating means for calculating a temperature rise time for the liquid viscosity in the nozzle to become a predetermined value or less based on the temperature dependence characteristic of the viscosity of the liquid to be discharged and the liquid temperature rise characteristic in the nozzle;
Timing setting means for setting the drive timing of the nozzle section heating means according to the temperature rise time calculated by the calculating means;
The liquid ejection apparatus according to claim 1, further comprising: The calculation means includes a first calculation processing unit for obtaining a relationship between a desired viscosity and a necessary heating temperature from a temperature-dependent characteristic of the viscosity of the liquid;
A second arithmetic processing unit for obtaining a temperature raising time required for raising the temperature to the required heating temperature from the liquid temperature rise characteristic in the nozzle;
The liquid ejecting apparatus according to claim 2, further comprising: The first arithmetic processing unit has a first table showing temperature dependent characteristics of the viscosity of the liquid,
The liquid ejection apparatus according to claim 3, wherein the second arithmetic processing unit includes a second table showing a liquid temperature rise characteristic in the nozzle.   4. The liquid ejection apparatus according to claim 2, wherein the nozzle heating control means controls the liquid in the nozzle to raise a predetermined heating penetration depth from the nozzle wall surface to a predetermined temperature. The heating penetration depth δd is expressed by the following formula 0.05 ≦ δd / D ≦ 0.15, where D is the nozzle diameter.
The liquid ejecting apparatus according to claim 5, wherein: A discharge head comprising a plurality of nozzles, individual pressure chambers corresponding to each nozzle, and a common flow path for supplying liquid to the plurality of pressure chambers;
The nozzle part heating means is provided for each nozzle of the discharge head, and a supply path heating means is provided in a supply path communicating with the pressure chamber and the common flow path. The liquid discharge apparatus according to any one of the above.   8. The liquid discharge apparatus according to claim 7, further comprising a supply path heating control unit that controls a heating timing by the supply path heating unit in accordance with a discharge drive timing for discharging ink from the nozzle hole. The nozzle, the pressure chamber, the common flow path, and the supply path are formed by a laminated structure,
9. The liquid ejection according to claim 7, wherein the nozzle and the supply path are composed of members of different layers, and the nozzle part heating means and the supply path heating means are arranged in different layers. apparatus.   The liquid ejecting apparatus according to claim 9, wherein a heat insulating layer is provided between a nozzle layer in which the nozzle is formed and a supply path layer in which the supply path is formed. 11. The liquid ejection device according to claim 1, wherein the liquid ejection device ejects ink from the nozzle holes while moving the recording medium relative to the recording head having the nozzle holes. Thus, an ink jet recording apparatus is characterized in that an image is formed on the recording medium.

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