JP2009298014A - Inkjet recording device - Google Patents

Abstract

An object of the present invention is to obtain stable ejection when the nozzles are arranged vertically, and to improve the reliability of image quality and image quality particularly when a long head is used.
An ink jet recording apparatus using a recording head having a plurality of ejection openings for ejecting a liquid in a straight line, having a liquid flow path 704 communicating with each of the ejection openings, and communicating with the ejection opening. The channel length of the liquid channel changes stepwise from one end of the recording head toward the other end.
[Selection] Figure 7

Description

  The present invention relates to an ink jet recording apparatus that has a liquid discharge head that discharges droplets and forms an image on a recording medium.

  In recording devices that have functions such as printers, copiers, and facsimiles, or recording devices that are used as output devices such as composite electronic devices and workstations, including computers and word processors, paper, cloth, plastics are used based on the recorded information. 2. Description of the Related Art Inkjet recording apparatuses that perform image recording by ejecting ink toward a sheet, an OHP sheet, or the like (hereinafter collectively referred to as a medium) have become widespread.

  This inkjet recording apparatus is now widely applied to printers, copiers, facsimiles, etc. from the viewpoints of low noise, low running cost, easy size reduction, and easy colorization. Yes.

  As a distinction between printing methods that compare the relative movement of the recording head and the media, there are firstly a recording method called a serial method in which recording is performed by moving the recording head relative to the medium, and secondly a fixed recording head. On the other hand, it is classified into a recording method called a line method for moving media.

  Printers for industrial use require specifications such as continuous printing, high-speed printing, and mass printing. When optimal conditions are selected to meet these requirements, a long head exceeding 2 inches is adopted as the recording head, and a line method is used as the recording method. High-speed printing and continuous printing can be advantageously performed by fixing the long head and forming an image in one line pass (one line is formed by one nozzle).

  In order to achieve large-capacity printing, the ink jet recording apparatus described in which the ink tank is made directly into the recording head in which the ink is infiltrated into the absorber such as a conventional porous material is directly placed on the recording head. Since it cannot be filled, it is difficult to increase the ink capacity. Therefore, a container-type ink tank is used so that a large capacity can be accommodated.

  Incidentally, the absorber ink tank can apply a negative pressure to the recording head by a negative pressure generated in the absorber. That is, it is not necessary to generate a negative pressure using another mechanism. On the other hand, the container-type ink tank must use a negative pressure generation technique using other mechanisms.

  For example, Patent Document 1 discloses a method of forming a meniscus by creating a height difference between a print head and an ink supply tank and generating a negative pressure at a nozzle of the print head using a water head difference. Japanese Patent Application Laid-Open No. H10-260260 discloses a method of forming a meniscus in a nozzle of a recording head by providing a negative pressure generating means in a supply tank, and any one of several methods is selected and adopted.

JP2007-196519 JP 2007-253402 A

  In recent years, there has been a demand for an ink jet recording apparatus that directly prints on each plane of a three-dimensional medium having a three-dimensional surface such as cardboard or canned food.

  Conventionally, a nozzle array provided in a recording head is arranged in a direction perpendicular to the direction of gravity, and a medium passes thereunder to form an image. However, the recording head side must be tilted with respect to the three-dimensional media, such as when the posture of the three-dimensional media cannot be changed.

  That is, if the recording surface is a vertical surface, the image in a nozzle vertical array (hereinafter referred to as a nozzle vertical array) in which the recording head is arranged along the gravity direction with the discharge nozzles provided in the recording head. A technique for forming is required.

  A plurality of ejection nozzles for ejecting ink, which is liquid, are provided in the recording head, and each has a liquid flow path communicating with each other. Normally, a liquid meniscus 801 is generated at the same position in the discharge nozzle due to a uniform water head difference generated in the recording head.

  However, when the recording heads are arranged vertically in the nozzles, the difference in the width of the nozzle array of the recording heads, that is, the height becomes the water head difference in the recording heads, and a pressure difference is generated only in the recording heads. It will be in a changed state.

  FIG. 10 shows that the upper portion of the recording head is in a state where the height difference from the ink supply tank is large and the water head difference is large. The meniscus position is a position recessed from the nozzle (A in the figure). Since the lower part of the recording head is in a state where the height difference from the ink supply tank is small and the water head difference is small, the meniscus position is close to the nozzle (B in the figure). When ink is ejected in such a different meniscus state in the recording head, a difference in ink ejection amount and ink ejection speed occurs.

  Therefore, the present invention is for solving the problems obtained by the above research, and for obtaining stable ejection when the nozzles are arranged vertically, and particularly when a long head is used. -It is intended to solve the problem of improving the reliability of image quality.

    In order to solve the above problems, in an ink jet recording apparatus equipped with a recording head having a plurality of discharge ports for discharging liquid in a straight line, each having a liquid flow path communicating with each of the discharge ports, The channel length of the liquid channel communicating with the ejection port is achieved by changing from one end of the recording head toward the other liquid channel.

  With the above configuration, it is possible to stably discharge when the recording head is arranged in a nozzle vertical arrangement, and it is possible to improve the reliability of image quality and image quality particularly when a long head is used.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic perspective view showing an ink jet recording apparatus including a recording head 101 for discharging a liquid according to an embodiment of the present invention.

  In this configuration, the size of the recording head 101 in the recording head width direction is not limited. However, a long head exceeding 2 inches can achieve a high effect, and a 4-inch head is used as an example of this embodiment. Further, four recording heads are mounted, and are indicated as recording head 101a to recording head 101d. If at least one recording head 101 is mounted, the present invention can be achieved, and the number of mounted recording heads 101 can be determined according to the purpose.

  In addition, each recording head 101 can be arranged using a single ink for the purpose of speeding up, or can be arranged for performing full color printing using a plurality of types of ink. It is.

  The transport unit 103 is for passing various media in the vicinity of the recording head 101. The media used in this embodiment is an assembled cardboard box, and shows a state in which the side surface of the cardboard box 106 is printed.

  The recording head 101 has a nozzle vertical arrangement in which nozzles provided on the recording head 101 are arranged along the direction of gravity in order to print the side surface of the cardboard box 106. Further, the recording head 101 is arranged in a state of being fixed by the head holder 102.

  In addition to the present embodiment, the recording head 101 may be mounted on a rail or the like that can move in the horizontal direction to change the arrangement of the recording head 101, and the method for fixing the head is not limited.

  The ink tanks 104a to 104d are filled with ink, and are connected to the recording heads 101a to 101b, respectively. As described above, since the recording head 101 can be used properly according to the purpose, the ink filled in the ink tank 104 can also be selected according to the purpose. Further, due to the difference in the height direction between the recording head 101 and the ink tank 104, the recording head 101 is arranged so that pressure due to the water head difference is applied.

  The pump 105, which is a pump mechanism, causes ink to flow from the ink tank 104 to the recording head 101 other than during the printing operation, and performs ink filling operation in the recording head 101 and recovery operation in the recording head 101 (removal of bubbles, removal of foreign matter). Removal, removal of deteriorated ink, etc.).

  2 and 3 show an outline of the ink flow path, and an outline of the ink flow path from the ink tank to the recording head 101 will be described.

  The ink in the ink tank 104 flows by driving the pump 105. First, it passes through the tubes 204 to 205, passes through the joint 200, and arrives at the recording head 101. After passing through the head common channel 201 which is a channel in the recording head 101, the ink circulates to the ink tank 104 through the tubes 206 and 207.

  Reference numeral 208 denotes an on-off valve 208 that can connect and disconnect the recording head 101 and the pump 105. When the pump 105 is not operating, the recording head 101 stands by while maintaining a negative pressure due to a water head difference from the ink tank 104.

  4 to 6 illustrate the ink flow path inside the head in detail, FIG. 4 is a perspective view seen from the ejection port of the recording head 101, and FIG. 5 is a YY ′ cross-sectional view in FIG. FIG. 6 is a plan view of the recording head.

  A plurality of heaters 403, which are electrothermal conversion elements for heating and foaming the liquid, are arranged on the heater substrate 402 serving as the bottom of the liquid flow path. The heater 403 is made of a resistor such as tantalum nitride, and has a thickness of 0.01 to 0.5 μm and a sheet resistance of 10 to 300 Ω per unit area.

  In this embodiment, a thermal jet discharge type inkjet head using a heater which is an electrothermal transducer is used. However, the same effect can be obtained in a piezo discharge type using a piezoelectric element. The method is not limited.

  The switching transistor is driven by an IC comprising a circuit such as a control gate element, and is driven in a predetermined pattern by a signal from the outside of the recording head.

  The discharge nozzle 404 is formed corresponding to each of the plurality of heaters 403, and the discharge nozzle 404 forms a tubular liquid flow path surrounded by the heater substrate 402, the nozzle wall 405, and the top plate 406. One end of the discharge nozzle 404 is open to the outside, and ink is discharged from the open end surface. Further, the portion opposite to the open end face is separated from the adjacent nozzle by the nozzle wall 405, and the flow path is divided.

  Except for the portion separated by the nozzle wall 405, a common liquid chamber 501 is formed in which the ink communicates, and the ink is supplied to each ejection nozzle 404. A throttle channel member 701 is provided at the boundary portion between the nozzle wall 405 and the common liquid chamber 501, and the throttle channel member 701 has a different length for each liquid channel, thereby reducing the channel resistance in the liquid channel. Is changing. The liquid flow path refers to a portion obtained by removing the throttle flow path member 701 existing between the discharge nozzle 404 and the common liquid chamber 501.

  The liquid channel has a length excluding the throttle channel member 701. The longer the throttle channel, the shorter the liquid channel and the greater the channel resistance. Conversely, the shorter the throttle channel, the longer the liquid channel and the lower the channel resistance.

The top plate 406 is a single crystal member made of Si or the like, and includes an ink supply opening 505 formed by cutting out the shape by etching or the like, so that liquid from the outside can be introduced into the common liquid chamber. The liquid supplied from the common liquid chamber 501 to the discharge nozzle 404 is heated and foamed by the heater 403 disposed at a predetermined position in the discharge nozzle 404, and ink is discharged from the nozzle.
Furthermore, even if a 4 inch long head continuously prints at a high frequency of 5 to 20 kHz, it has a capacity that can sufficiently supply ink to the nozzles.

A throttle channel member 701 is provided at a boundary portion between the nozzle wall 405 and the common liquid chamber, and the throttle channel member 701 makes a part of the nozzle cross section a narrow channel. The pressure applied to the discharge nozzle 404 can be expressed by the water head difference between the height direction position of the discharge nozzle 404 and the height direction position of the ink water surface in the ink tank 104 (P = ρ · g · h1, ρ: ink density). [G / cm ³ ], g: gravitational acceleration [m / sec ² ]). Since the ink tank 104 is below the position of the recording head 101, a negative pressure is applied to the ejection nozzle 404 of the recording head 101.

  Similarly, when the recording head 101 is installed vertically, the water head difference in the recording head is 4 inches (101.6 mm), and the pressure difference is about 100 mmAq. The nozzle 404a is a nozzle provided in the upper part of the recording head 101, and is a nozzle located at the highest place in this embodiment. The discharge nozzle 404b is a nozzle provided in the lower part of the discharge nozzle 404b, and is a nozzle located in the lowest place in this embodiment.

The throttle channel provided in the discharge nozzle 404a is the shortest in the throttle channel and the liquid channel is long, so the channel resistance is low. Since the throttle channel provided in the discharge nozzle 404b is the longest in the throttle channel, the liquid channel is shortened and the channel resistance is high. The length of the throttle channel changes from the discharge nozzle 404a toward the discharge nozzle 404b.
Next, the flow of ink during the image formation by the recording head 101 and the fluctuation of the pressure in the recording head will be described. FIG. 7 shows a part of the recording head plane in detail. The throttle channel member 701 is a nozzle wall of the ink channel in the nozzle.

  The nozzles configured in the recording head 101 have a height difference in the width direction of the recording head, and the nozzles located in the high portion have a large water head difference because the height difference from the ink tank 104 is large. At this time, the length of the liquid channel is increased by configuring the narrowed channel member 701, which is a resistance portion in the channel, to be short (X). A large number of liquid channel portions having a large channel cross section are formed, and the number of throttle channel portions is reduced, so that the resistance of the entire liquid channel is reduced.

  On the contrary, since the nozzle at the lower end has a low elevation head pressure, the length of the liquid channel is shortened by increasing the length of the throttle channel member 701 to increase the resistance of the liquid channel (Y).

  Although there is a difference between the channel resistance of the long channel Y and the channel resistance of the short channel X, the length of the throttle channel 701 or the liquid channel may be changed intermittently for each nozzle. It is also possible to change the length for each of a plurality of nozzles.

  At that time, the bundle of a plurality of nozzles is a number that is 30 mmAq or less during normal use. For example, if the difference in water head differential pressure between the upper and lower ends of a 4-inch head is 100 mmAq (970 · 8 Pa), if the length of the lowermost nozzle Y is 60 μm and the length of the uppermost nozzle X is 15 μm, the flow resistance difference The pressure generated is 1/4 and 20 mmAq, which is 1/4, enabling stable ejection when the recording head is arranged vertically in the nozzle, especially when a long head is used, and the reliability of image quality and image quality It became possible to improve.

[Second Embodiment]
A second embodiment to which the present invention is applied will be described.
9 and 10 show an example to which the ink jet recording apparatus of the present invention is applied, and the recording head unit 1101 is mounted with the recording heads 101a to 101d used in the first embodiment.

  The recording head unit 1101 can be moved by a drive arm 1105, and the movement of the recording head unit 1101 is controlled by the movement of the angle arm joint 1104 and the height arm joint 1106.

  The cardboard box 1000 is transferred to the recording position by the conveyance belt 1103. In this embodiment, the conveyance belt 1103 does not move during recording of the cardboard 1000, and only feeds and discharges to the recording position. stay.

  The recording head unit 1101 performs a recording operation on the cardboard 1000 carried by the conveyor belt 1103. FIG. 8 shows a state where the lower part of the side of the cardboard 1000 is being recorded. The recording head unit 1101 is fixed by an angle arm joint 1104 and a height arm joint 1106, and the position of the recording unit in the height direction is fixed. In this state, the slide arm 1110 slides on the slide shaft 1115 to record “X” and “Y”.

FIG. 9 shows a state where the upper part of the cardboard 1000 is being recorded. The recording head unit 1101 is moved upward by the angle arm joint 1104 and the height arm joint 1106, and the height is determined and fixed. In this state, the slide arm 1110 slides on the slide shaft 1115 to record “2” and “6”.

Schematic diagram of products representing examples The figure which shows the flow-path outline of an Example Cross-sectional schematic diagram showing an outline of the flow path and configuration of the head portion of the embodiment The perspective view which shows the head nozzle part detail of an Example Sectional drawing which shows the detail of the head nozzle part of an Example The top view which shows the detail of the head nozzle part of an Example The top view which shows the liquid flow path of the head nozzle part of an Example Schematic showing the second embodiment Schematic showing the second embodiment Plan view showing the details of a conventional head nozzle

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Recording head 102 ... Head holder 103 ... Conveying part 104 ... Ink tank 105 ... Pump part 106 ... Cardboard box 402 ... Heater board 403 ... Heater 404 ... -Discharge nozzle 405 ... Nozzle wall 406 ... Top plate 701 ... Restriction channel member

Claims (8)

Inkjet recording apparatus comprising: a recording head having a plurality of ejection openings for ejecting liquid in a straight line and having a liquid flow path communicating with each of the ejection openings; and a liquid tank for supplying liquid to the recording head In
An ink jet recording apparatus, wherein a flow path length of the liquid flow path communicating with the ejection port changes from one end of the recording head toward the liquid flow path at the other end.   The inkjet recording apparatus according to claim 1, wherein the flow path length continuously changes.   The inkjet recording apparatus according to claim 1, wherein the recording head does not arrange the arrangement direction of the ejection ports perpendicular to the direction of gravity.   4. The ink jet recording apparatus according to claim 1, wherein a portion having a long flow path in the flow path length is mounted on an upper portion in a vertical direction.   The inkjet recording apparatus according to claim 1, wherein the liquid tank and the recording head are installed at different heights.   The inkjet recording apparatus according to claim 1, wherein the recording head is a long head.   The ink jet recording apparatus according to claim 1, wherein the recording head discharges a liquid by an electrothermal conversion element. In a recording head having a plurality of discharge ports for discharging liquid in a straight line and having a liquid flow path communicating with each of the discharge ports,
A recording head characterized in that the flow path length of the liquid flow path communicating with the ejection port changes from one end of the recording head toward the liquid flow path at the other end.

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