JP2006044021A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer capable of stably preventing a nozzle from being dried without enlarging a whole structure of a recording head. <P>SOLUTION: This inkjet printer comprises a conveyance means 2 for conveying a recording sheet P supplied from a paper supply section 3, a head unit 1 that forms an image on the recording paper P conveyed by the conveyance means by ejecting ink droplets and is disposed at a portion in the vicinity of the recording sheet P with a predetermined gap region G, and a gas supply section 6 which is provided at the upstream side of the gap region G and supplies a gas to the gap region G for preventing an ink droplet at the head unit 1 from being dried. The gap region G is continuously formed between the head unit 1 and the conveyance means 2 in the conveyance direction of the recording sheet P so that a gas guide section 1b for guiding the gas supplied from the gas supply section 6 is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a recording medium fed from a paper feeding unit is transported to a head unit by a transporting unit, and an ink droplet is ejected from the head unit to the recording medium to form an image and then transported. The present invention relates to an ink jet printer.

In general, in order to perform high-speed printing with an ink jet printer, an ink jet printer in which a plurality of ink jet heads are arranged and a line type ink jet printer have been proposed.
For example, in a line type ink jet printer, in order to record on A3 size (420 × 297 mm) recording paper, if the recording resolution is 720 dpi (dot per inch), 297 ÷ 25.4 × 720 = 8 per color. 419 nozzles are required. Further, when there are four colors to be recorded, 8,419 × 4 = 33,676 nozzles are required. Ink jet heads sometimes cause ink solvents (water, solvent, etc.) to evaporate and dry from nozzles that do not frequently eject ink droplets, clog the nozzles, and ink droplets may not be ejected. Therefore, in a line type ink jet printer having a large number of nozzles, in order not to cause image defects due to non-ejection of ink droplets or flight bending, it is necessary to maintain that any one of all nozzles is not clogged. Is extremely important.

For this reason, conventionally, in order to keep all the nozzles of the inkjet head in a good state and prevent paper dust or dust from adhering to the nozzle surface, it is provided so as to surround a nozzle plate having a plurality of nozzles. An ink jet recording head has been proposed in which the air duct is movable with respect to the nozzle plate, and the air duct is projected from the nozzle forming surface of the nozzle plate during recording and recording standby to inject humid air. (For example, see Patent Document 1)
Further, in an ink jet recording apparatus that performs recording by ejecting ink from an image forming unit to a recording medium fed from a feeding unit that feeds the recording medium, a vapor is interposed between the feeding unit and the image forming unit. An ink jet recording apparatus in which a steam generating means for generating a gas is disposed has also been proposed (for example, see Patent Document 2).
JP2003-165230 (first page, FIG. 1) JP 2000-255053 (first page, FIG. 1)

  However, in the conventional example described in the above-mentioned Patent Document 1, at least the air duct is protruded to the lower side of the nozzle at the time of recording so as to inject the humidified air. There is a limit to narrowing the gap area between them, and it is unsolved that the line size inkjet printer cannot satisfy the gap size (for example, 0.5 to 2.0 mm) necessary for high-speed and high-precision recording There is a problem. Moreover, in the air ejection hole region of Patent Document 1, there is a possibility that the difference between the flow rate of the humidified air and the ejection speed of the ink droplets may disturb the flight of the ink droplets, and the configuration of the entire recording head is large. There is also an unresolved issue that will be solved.

  Further, in the conventional example described in Patent Document 2, since the steam generating means for generating steam is arranged between the feeding means for feeding the recording medium and the image forming means, the nozzle of the image forming means Although the gap region between the surface and the recording medium can be narrowed, a plurality of four recording heads constituting the image forming means are arranged independently, so that the steam generated by the steam generating means Since the moisture inside the case surrounding the forming means diffuses and the humidity in the case body becomes a humidity that suppresses drying of the ink discharge portion of the recording head, the humidity of the nozzle surface of the recording head can be set to an appropriate value. The steam generated by the steam generating means cannot be effectively supplied to the nozzle surface of the recording head, and the ink discharge section of the recording head is kept at an appropriate humidity after the steam generating means is in an activated state. A time consuming, more steam flow is required, there is an unsolved problem that water consumption is also increased.

  Accordingly, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, and efficiently supplies a gas that suppresses drying of the nozzle surface of the recording head, and the ink ejection unit of the recording head. An object of the present invention is to provide an ink jet printer that can be adjusted to an appropriate humidity in a short time, and that the amount of solution to be used can be reduced to the minimum necessary.

  According to a first aspect of the present invention, there is provided a conveying unit that conveys a recording medium fed from a paper feeding unit, and an ink droplet that is disposed in proximity to the recording medium conveyed by the conveying unit via a predetermined gap region. A head unit that forms an image on the recording medium; and a gas supply unit that supplies a gas that suppresses drying of ink droplets in the head unit disposed upstream of the gap region to the gap region. The head unit is formed with a gas guide portion that forms the gap region continuous in the conveyance direction of the recording medium with the conveyance means and guides the gas supplied from the gas supply portion. It is a feature.

  In the first aspect of the invention, the gas is guided by the gas guide portion formed in the head unit by supplying the gap region with a gas that suppresses drying of the ink droplets from the upstream side of the gap region. The ink can be efficiently supplied to the ink ejection unit in a short time, and the amount of solution used to form a gas that suppresses drying of the ink droplets can be reduced, so that the ink droplets can be dried in the head unit. Can be stably suppressed, and the gap size in the gap region can be ensured to a narrow gap size necessary for the line-type inkjet printer to record at high speed and with high accuracy.

According to a second aspect of the present invention, in the first aspect, the gas supply unit is configured such that the moving speed of the recording medium is U, the gap length of the gap region is G, and the kinematic viscosity coefficient of air is ν. The Reynolds number R represented by = UG / ν is set to a value within a range in which the gas can be sucked into the gap region.
In the second aspect of the invention, the Reynolds number R is set to a value within a range in which the gas can be sucked into the gap region, so that the gas is efficiently supplied to the ink discharge portion of the head unit without diffusing to other than the head unit. And drying of ink droplets in the head unit can be stably suppressed.

According to a third aspect of the present invention, in the first or second aspect, the gas supply unit evaporates a solution evaporation unit that evaporates a solution that suppresses drying of the ink droplets of the head unit, and the solution evaporation unit evaporates the solution. And a gas feeding means for mixing the solution and the carrier gas fed to the gap region.
In the third aspect of the invention, the solution that suppresses drying of the ink droplets is evaporated by the solution evaporation means, the solution evaporated by the solution evaporation means and the carrier gas are mixed, and the gap is supplied by the gas supply means. By supplying to the area, it is possible to stably supply gas that suppresses drying of ink droplets to the head unit.

According to a fourth aspect, in the third aspect, the solution is formed of any one of water, a solvent contained in ink droplets, and oil.
In the fourth aspect of the invention, by forming the solution with any one of water, a solvent contained in the ink droplets, and oil, drying of the ink droplets in the head unit can be reliably suppressed.
In addition, a fifth invention is characterized in that, in the third or fourth invention, the solution evaporation means includes any one of an ultrasonic vibrator, a heating element and an evaporation filter.

In the fifth aspect of the invention, the solution evaporation means includes any one of an ultrasonic vibrator, a heating element, and an evaporation filter, so that the solution can be evaporated quantitatively.
According to a sixth invention, in any one of the third to fifth inventions, the solution evaporation means includes a container for storing the solution, and a liquid level measurement for measuring a liquid level of the solution in the container. And a warning means for issuing a warning when the liquid level measurement value detected by the liquid level measurement means is equal to or lower than a set value.

In the sixth aspect of the invention, a warning is issued when the liquid level of the solution in the container containing the solution falls below the set value, so that replenishment of the solution is promoted to dry the ink droplets due to lack of the solution. It is possible to prevent a decrease in the suppressing function.
According to a seventh aspect of the present invention, in the first or second aspect of the invention, the gas supply unit generates water vapor for generating water vapor for preventing drying of ink droplets of the head unit, and is generated by the water vapor generation means. Gas supply means for mixing the water vapor and the carrier gas which have been mixed and feeding them to the gap region, relative humidity detection means for detecting the relative humidity of the mixed gas of the gas supply means, and detection by the relative humidity detection means And a water vapor control means for controlling the water vapor generation amount of the water vapor generation means so that the relative humidity is in a predetermined range that suppresses drying of the ink droplets.

  In the seventh aspect of the invention, the relative humidity of the mixed gas of water vapor and carrier gas generated by the water vapor generating means is detected by the relative humidity detecting means, and the relative humidity detected by the relative humidity detecting means is used to dry the ink droplets. By controlling the water vapor generation amount of the water vapor generation means in the previous period so as to be within a predetermined range, it is possible to manage the minimum humidity necessary for suppressing the drying of ink droplets. Can be prevented from being formed.

Further, according to an eighth invention, in any one of the third to seventh inventions, the gas supply unit is recovered by a gas recovery unit disposed on the downstream side of the gap region, and the gas recovery unit. And a circulation path for circulating the gas to the gas feeding means.
In the eighth aspect of the invention, a gas recovery unit is provided on the downstream side of the gap region, and the gas recovered by the gas recovery unit is circulated through the circulation path to the gas supply means, whereby the used gas is recovered and the head is recovered. It is possible to reliably prevent the surrounding environment from being deteriorated. Moreover, the usage-amount of a solution can also be reduced.

In addition, a ninth invention is characterized in that, in any one of the first to eighth inventions, the conveying means is composed of an endless conveying belt for conveying the recording medium.
In the ninth aspect of the invention, the conveying means is constituted by an endless conveying belt, so that the recording medium can be stably conveyed while maintaining a flat surface.
According to a tenth aspect of the present invention, in any one of the first to eighth aspects, the transport unit is configured by a transport drum that sucks and transports the recording medium.

In the tenth aspect of the invention, the length of the conveying means can be shortened by configuring the conveying means with a conveying drum.
Furthermore, an eleventh invention is characterized in that, in any one of the first to tenth inventions, the transport means includes an air suction mechanism for sucking and holding the recording medium.
In the eleventh aspect of the invention, the conveying means includes the air suction mechanism, so that the recording medium can be reliably adsorbed and held and stably conveyed.

Furthermore, a twelfth invention is characterized in that, in any one of the first to tenth inventions, the transport means includes an electrostatic adsorption mechanism for electrostatically adsorbing the recording medium.
In the twelfth aspect of the invention, the conveying means includes an electrostatic attraction mechanism, so that the recording medium can be reliably electrostatically held and stably conveyed.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a plan view showing a first embodiment of a line type ink jet printer to which the present invention can be applied, and FIG. 2 is a side view of FIG.
In the figure, reference numeral 3 denotes a paper feed unit, which stores a large number of recording papers P as recording media, a paper feed roller 31 for feeding the stored recording papers P one by one, and this paper feed roller. And a gate roller 32 that feeds the recording paper P fed by 31 after skew correction, and the skew-corrected recording paper P fed from the gate roller 32 is delivered to the paper transport unit 2.

  The paper conveying unit 2 includes a driving roller 22 and a driven roller 23 that are arranged in parallel with each other at a predetermined interval, and a wide belt-like endless conveying belt 21 stretched between the driving roller 22 and the driven roller 23. It consists of Here, the driving roller 22 is disposed on the discharge side of the recording paper P, and the driven roller 23 is disposed on the paper feeding side of the recording paper P, that is, the gate roller 32 side. The drive roller 22 is rotationally driven by a drive motor 22M. The tension of the endless transport belt 21 is adjusted by a tension roller 24.

  In addition, the paper transport unit 2 includes a charging mechanism 27 disposed in the vicinity of the driven roller 23 side of the endless transport belt 21 and in contact with the outer surface of the endless transport belt 21, and an endless charge charged by the charging mechanism 27. A neutralization mechanism 29 that neutralizes the conveyance belt 21 below the driving roller 22 is provided. The charging mechanism 27 has a high voltage power supply 28 that applies a high voltage to the endless transport belt 21, and applies the high voltage generated by the high voltage power supply 28 to the endless transport belt 21 to electrostatically charge the endless transport belt 21. Then, the recording paper P placed on the endless transport belt 21 is conveyed while being electrostatically held on the upper surface of the endless transport belt 21.

  On the other hand, the recording paper faces the recording paper P conveyed by being electrostatically attracted and held by the endless conveying belt 21 of the paper conveying unit 2 so as to form a gap region G having a narrow gap (for example, gap dimension L: around 1 mm). A head unit 1 for forming an image on P is disposed. As shown in FIG. 1, the head unit 1 includes four line-type head units that eject black, cyan, magenta, and yellow ink droplets onto a support member 1a disposed in parallel with the endless conveyance belt 21. 1K, 1C, 1M, and 1Y are sequentially held at a predetermined interval in the conveyance direction of the recording paper P. A gas guide portion 1b that is a flat surface parallel to the endless transport belt 21 that continuously forms the gap region G is formed on the surface of the support member 1a facing the endless transport belt 21.

  As shown in FIG. 3, each of the head units 1 </ b> K to 1 </ b> Y transports, for example, n = 6 divided heads having an ink droplet discharge surface on which a large number of nozzles for discharging ink droplets are formed. The head rows are arranged in a staggered manner in two rows in the direction, and the plurality of nozzles of each head row are connected in the width direction of the recording paper P so as to discharge a single row of ink droplets, which will be described later. It is controlled by the control unit 840.

  Further, the head unit 1 communicates with ink cartridges 13K to 13Y for supplying ink via ink supply tubes 12K to 12Y configured by flexible tubes corresponding to the respective ink colors of the head units 1K to 1Y. ing. Ink of each color is stored in the ink cartridges 13K to 13Y, and is supplied to the head unit 1 as necessary. The ink supply tubes 12K to 12Y are provided with an allowance in the length of the tubes so that the head unit 1 can move to the cleaning unit 5 described later.

  The recording paper P electrostatically held on the upper surface of the endless transport belt 21 passes through the gap region G between the endless transport belt 21 and the ink discharge surface of the head unit 1 from the paper feed side, that is, the gate roller 32 side. The ink is transported to the discharge side, that is, the drive roller 22 side by the drive roller 22 at a constant paper transport speed U, and ink droplets of each color necessary for image formation are sequentially ejected from the head unit 1 onto the recording paper P to form an image. . The recording paper P is separated from the endless transport belt 21 by the waist of the recording paper P at a position beyond the driving roller 22 and is stored in the paper discharge unit 4.

On the other hand, the endless conveyance belt 21 is neutralized by the neutralization mechanism 29 below the driving roller 22 and prevents dust and the like from being adsorbed to the charging mechanism 27.
In order to properly discharge ink droplets from the head unit 1, it is necessary to maintain that one of all the nozzles constituting the head unit 1 is not clogged. The unit 5 is provided on the rear side of the paper transport unit 2. The head unit 1 is configured to be movable from a gap region G where recording is performed on the recording paper P to a cleaning unit 5 shown in FIG. The cleaning unit 5 includes a suction pump for eliminating these defective states when paper dust or dust adheres to the vicinity of the nozzles of the head unit 1 or when bubbles are generated in the cavity of the head. . Further, a wiper for cleaning the nozzle surface of the head and adjusting the ink meniscus in the vicinity of the nozzle, a cap (receiving part) for receiving ink droplets that have been flushed (preliminary discharge) to eliminate nozzle clogging, and discharged A waste ink tank for storing ink is provided.

Further, as shown in FIG. 2, a gas that suppresses drying of ink droplets is supplied to the upstream side of the head unit 1 on the ink droplet ejection surfaces of the nozzles that eject ink droplets of the recording heads 1K to 1Y. A gas supply unit 6 is provided.
As shown in an enlarged view in FIG. 4, the gas supply unit 6 is fixedly disposed, for example, at a predetermined distance above the sheet feeding unit 3, and has a container 64 that stores the water W as a solution by opening the top surface. An ultrasonic transducer 641 serving as a water vapor generating means disposed at the bottom of the container 64 and the upper surface of the container 64 communicate with the recording paper in the gap region G between the gas guide portion 1b of the head unit 1 and the conveyor belt 21. A feeding duct 61 that feeds a mixed gas containing water vapor from the upstream side in the conveying direction of P, and a gas feeding means disposed on the opposite side of the gap region G from the container 64 of the feeding duct 61 A blower 66, a filter 67 provided outside the blower 66 to prevent intrusion of dust, and a relative humidity detection means for detecting a relative humidity h disposed in the vicinity of the gap region G of the feeding duct 61. At least a humidity sensor 601, a water level detector 63 as liquid level measuring means for measuring the liquid level of the container 64, and a gas supply control unit 69 for controlling the ultrasonic vibrator 641 to control the amount of water vapor generated. I have. An opening / closing lid 65 for replenishing the container 64 with water W is disposed on the upper surface of the supply duct 61 facing the container 64.

  Here, the water level detector 63 includes an annular float 63b in which a magnet is built in a guide shaft 63a supported by extending vertically along the inner wall of the container 64, and an upper end side and a lower end side of the guide shaft 63a. The upper limit water level detection unit 63c and the lower limit water level detection unit 63d are configured by magnetically sensitive reed switches that respond to the magnets of the floats 63b respectively disposed. The upper limit water level detection unit 63c and the lower limit water level detection unit 63d are provided. The upper limit water level detection signal and the lower limit water level detection signal detected in step (1) are output to the gas supply control unit 69.

  The gas supply control unit 69 receives the relative humidity h detected by the humidity sensor 601, the upper limit water level detection signal and the lower limit water level detection signal detected by the water level detector 63, and the input relative humidity h and a preset tolerance. Compared with the humidity range, when the relative humidity is within the allowable humidity range, the drive signal for the current ultrasonic transducer 641 is continuously output. When the relative humidity h falls below the allowable humidity range, the ultrasonic wave is output. The drive signal for the vibrator 641 is changed in the direction in which the water vapor generation amount increases, and conversely, when the relative humidity h exceeds the allowable humidity range, the drive signal for the ultrasonic vibrator 641 is changed in the direction in which the water vapor generation amount decreases. Perform humidity control processing.

  The allowable humidity range is that any one of all nozzles constituting the head unit 1 is stably ejected from the ink droplet ejection surface without drying and clogging the ink droplet. In order to do so, it is preferable that the relative humidity of the mixed gas in the vicinity of the air outlet 62 in the supply duct 61 is set in a range of at least 70% to 99%. That is, when the relative humidity of the mixed gas is less than 70%, there is a problem that drying of ink droplets cannot be completely prevented. When the relative humidity of the mixed gas exceeds 99%, fine water droplets in the mixed gas condense and dew and adhere to the feeding duct 61 and the ink droplet discharge surface, and the water droplets drip on the recording paper P. As a result, there is a problem that the ink droplets ejected onto the recording paper P blur or the flight of the ink droplets is disturbed and the ink droplets cannot be ejected stably.

  Further, the gas supply control unit 69 outputs a water shortage alarm signal indicating that the water W in the container 64 is insufficient to the alarm circuit 69a when the lower limit water level detection signal detected by the water level detector 63 is turned on. By notifying water shortage by sound and / or display and replenishing water W into the container 64, the water W in the container 64 is full when the upper limit water level detection signal is turned on. A water management process is performed to output a water full tank warning signal representing the above to the alarm circuit 69a and notify the full state by sound and / or display.

Then, when the ultrasonic vibrator 641 resonates and ultrasonically vibrates in response to a drive signal having a predetermined frequency sent from the gas supply control unit 69, the water W stored in the container 64 is ultrasonically vibrated to form fine water droplets. The water vapor is scattered in the feed duct 61 and a mixed gas composed of fine water droplets and the carrier gas fed from the blower 66 is generated in the feed duct 61.
At this time, since the relative humidity h of the mixed gas is detected by the humidity sensor 601, and this is input to the gas supply control unit 69, the gas supply control unit 69 causes the ultrasonic vibrator 641 and the blower 66 to be connected based on the relative humidity h. By controlling, the relative humidity of the mixed gas is maintained in an appropriate range for suppressing and preventing drying of ink droplets.

Next, an appropriate air volume of the mixed gas in the vicinity of the air outlet 62, which is necessary for the mixed gas to be efficiently sucked into the gap region G without diffusing, is obtained by hydrodynamic consideration. First, the Reynolds number R is calculated for the air flowing in the gap between the head unit 1 and the recording paper P.
Preconditions 1) The head unit 1 is a fixed type, and the head unit 1 and the recording paper P face each other in parallel while maintaining a gap dimension L.

2) Size and transport direction of recording paper P: A3 (horizontal 297 × 420 mm) size recording paper P is transported in the vertical direction.
3) Conveying speed U of recording paper P: 200 to 500 mm / s
4) Gap dimension L between the head unit 1 and the recording paper P: 0.5 to 2.0 mm
5) Kinematic viscosity coefficient of mixed gas ν: Kinematic viscosity coefficient of air at 25 ° C. ν = 15.4 × 10 ⁻⁶ (m ² / s) is used as a representative.
The Reynolds number R is R = UL / ν, where U is the transport speed, L is the gap size of the gap region G, and ν is the kinematic viscosity coefficient of air.

R = UL / ν (1)
Next, the Reynolds number R is calculated by the above equation (1). For reference, a calculation example in which the Reynolds number R is 100 is added using the gap dimension L and the conveyance speed U that are within the range of the preconditions. Calculation example E shows a case where the gap size is 3.1 mm, and calculation example F shows a case where the speed U is 0.77 m / s.

  As apparent from Table 1, the number R of lay nozzles when the recording paper P moves in a narrow gap region G where the head unit 1 and the recording paper P are opposed to each other is approximately R ≦ 100. Generally, it is said that when the Reynolds number R becomes 100 or less, the viscosity of air increases. In other words, in the calculation example of Table 1, the Reynolds number R is less dependent on the denominator viscosity term consisting of the kinematic viscosity coefficient ν of air than the inertial term of the numerator consisting of the product of the conveyance speed U and the gap dimension L. Means big.

  That is, when the mixed gas is fed from the paper feeding side of the recording paper P to the narrow gap region G where the gas guiding portion 1b of the head unit 1 and the recording paper P face each other, the viscosity of the mixed gas is positively increased. The mixed gas can be fed by utilizing. That is, when the mixed gas is fed to the upstream side closest to the gap region G by the feeding duct 61, the mixed gas is dragged to the recording paper P that moves at the paper transport speed U from the paper feeding side to the paper discharging side. As described above, the gas is fed to the gap region G formed by the gas guide portion 1b and the recording paper P, and can be efficiently supplied to the gap region G without diffusing outside the head unit 1. The wind pressure by the blower 66 may be small. Thus, since the wind pressure by the blower 66 can be kept small, the mixed gas can be stably supplied to the gap region G without disturbing the flight of ink droplets.

On the other hand, in order to stably eject ink droplets from all the nozzles constituting the head unit 1, the gas mixture necessary and sufficient to suppress / prevent drying of the ink droplets is supplied to the gap region G. It is necessary to supply. Next, the air volume when the mixed gas is fed to the gap region G between the head unit 1 and the recording paper P at the same speed as the conveyance speed U of the recording paper P is calculated. The width of the recording paper P is about 300 mm (A3 size), the gap dimension L = 0.5 to 2.0 mm, the conveyance speed U of the recording paper P = 200 to 500 mm / s, and the air speed on the head unit surface is the recording paper P However, the maximum required air amount is calculated here, assuming that the speed is the same.
Necessary gas amount = conveying speed U × gap size L × width W of recording paper P (2)

  From the calculation results of Table 2, the amount of gas that does not interfere with the flight of ink droplets ejected from each nozzle of the head unit 1 supplied from the outlet 62 to the gap region G is suppressed and prevented from drying. The necessary gas amount required for the above-described operation may be calculated based on the above equation (2), and the gas supply control unit 69 may control the air volume of the blower 66 in accordance with the calculated required gas amount.

  Here, a control signal for operating the gas supply control unit 69 is output from a control unit 840 that performs overall control of the ink jet printer as shown in FIG. The controller 840 outputs to the gas supply controller 69 a command signal that instructs at least the start and stop of the operation of the gas supply controller 69. The control unit 840 outputs a command signal to the gas supply control unit 69, and controls the head driver 850 that controls the ejection of ink droplets from the nozzles in the head unit 1, and the drive of the paper feed roller 31 of the paper feed unit 3. A paper feed driver 860 that controls the drive motor 22M of the paper transport unit 2, a pump driver 880 that controls the suction pump motor 881 of the cleaning unit 5, and a wiper motor 891 of the cleaning unit 5 A control signal is output to the wiper driver 890 to be controlled.

Next, the operation of the first embodiment will be described.
When the power is turned on, the head unit 1 is first sent to the cleaning unit 5, and the cleaning unit 5 performs predetermined cleaning such as flushing, pumping, and wiping. Thereafter, the head unit 1 is returned onto the paper transport unit 2, and the transport belt 21 is transported and driven at the same time or before and after that, and the gas supply unit 6 is started to operate. Is supplied to the gap region G between the gas guiding portion 1b of the head unit 1 and the paper conveying belt 21 from the nearest upstream side through the feeding duct 61.

  At this time, the mixed gas is sent to the upstream side nearest to the gap region G by the feeding duct 61, and the Reynolds number R mixed gas is set to a value within a range in which the mixed gas can be sucked into the gap region G as described above. The mixed gas is introduced into the gap region G between the gas guiding portion 1b and the paper transport belt 21 so as to be wound without being diffused from the outlet 62 of the feeding duct 61 to the outside of the head unit 1. The mixed gas introduced into the gap region G is guided to a gas guide 1b formed on a flat surface parallel to the endless transport belt 21 including the ink discharge surfaces of the recording heads 1Y to 1K of the head unit 1. The fluid flows from the upstream side to the downstream side in a laminar flow state without diffusing outside, and the humidity of the ink ejection surfaces of the recording heads 1Y to 1K is maintained at an appropriate humidity.

  On the other hand, when the recording paper P is fed one by one from the paper feeding unit 3 by the paper feeding roller 31 and subsequently skew-corrected by the gate roller 32 and delivered to the paper transport unit 2, the recording paper P is fed by the charging mechanism 27. The electrostatically charged and held upper surface of the endless transport belt 21 is electrostatically charged, and the endless transport belt 21 and the head unit 1 that forms an image on the recording paper P are transported to a gap region G facing each other.

  The recording paper P is separated from the upper surface of the endless transport belt 21, which is formed by discharging ink droplets from the nozzles while being transported through the gap region G at a constant paper transport speed U, and is neutralized by the neutralization mechanism 29. The paper is discharged to the paper discharge unit 4. Then, the printing operation is repeated until there is no image information. The line type ink jet printer of the present invention continues to supply the mixed gas from the outlet 62 to the gap region G and continue to drive the transport belt 21 at least during the operation of the printing process.

  In this way, by constantly supplying the mixed gas from the gas supply unit 6 to the gap region G, it is possible to reliably suppress drying of ink droplets at the ink droplet discharge unit of the nozzle of the head unit 1. In addition, the frequency of cleaning in the cleaning unit 5 can be lowered, thereby increasing the printing throughput. At this time, since the gas guide portion 1b that forms a continuous gap region is formed in the head unit 1, the gas guide portion 1b allows the mixed gas to flow stably without diffusing to the outside. It is possible to maintain the ink droplet discharge portion of the nozzle at an appropriate humidity in a short time.

  And by continuing supply of mixed gas from the gas supply part 6, when the water level in the container 64 will decrease and the float 63b will be in the state which adjoins the minimum water level detection part 63d, a minimum water level will be carried out by the magnet in the float 63b. The magnetically sensitive reed switch of the detection unit 63d is turned on, and the lower limit water level detection signal is supplied to the gas supply control unit 69. For this reason, the gas supply control unit 69 outputs an alarm signal for prompting water supply to the alarm circuit 69a, and an alarm for sound and / or display for prompting water supply is generated from the alarm circuit 69a.

When the user recognizes this alarm, opens the open / close lid 65 of the gas supply unit 6 and replenishes water W into the container 64, the float 63b rises, and the reed switch of the lower limit water level detection unit 63d is turned off. As a result, the output of the alarm signal from the gas supply control unit 69 to the alarm circuit 69a is stopped, and the alarm by the alarm circuit 69a is stopped.
When water is supplied to the container 64, if the water level approaches the upper limit water level detection unit 63c, the reed switch constituting the upper limit water level detection unit 63c is turned on by the magnet in the float 63b as described above, and the upper limit water level is set. By supplying the detection signal to the gas supply control unit 69, a warning signal indicating fullness is output to the warning circuit 69a, and a warning and / or display warning indicating fullness is issued from the warning circuit 69a.

For this reason, when the user stops the replenishment of the water W to the container 64 and closes the opening / closing lid 65, the normal gas generation state is restored.
In the first embodiment, the case where the paper transport unit 2 is configured by the endless transport belt 21, the high-voltage power supply 28, and the charging mechanism 27 has been described. However, the present invention is not limited to this, and FIG. As shown, air that draws air to the inner position of the endless transport belt A between the driving roller 22 and the driven roller using an endless transport belt A having a wide belt shape and a large number of through holes and another air suction mechanism B. The suction mechanism B is disposed so that its air suction surface is in contact with the inner surface of the endless transport belt A, and the air suction mechanism B sucks air through the through hole of the endless transport belt A on the upper side, thereby The recording paper P placed on the transport belt A may be transported while being sucked and held on the upper surface of the endless transport belt A.

Next, a second embodiment of the present invention will be described with reference to FIG.
In the second embodiment, a drum-type paper conveyance unit is applied in place of the belt-type paper conveyance unit 2 in the first embodiment described above.
That is, in the second embodiment, the configuration similar to that of FIG. 2 except that the paper transport unit 2 is changed from the transport belt configuration to the drum configuration in the configuration of FIG. 2 in the first embodiment described above. 2 corresponding to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown in FIG. 7, the paper transport unit 2 has a cylindrical transport drum 26 that transports the recording paper P while electrostatically holding it, and at least the outer surface of the transport drum 26 can be charged with static electricity. Consists of materials.
The transport drum 26 is electrostatically charged on the outer surface by a charging mechanism 27 having the same configuration as that of the first embodiment, which is in contact with the lower portion of the transport drum 26. After the recording paper P fed from the paper roller 31 is turned in the vertical direction by the guide roller 34, the recording paper P is sent to the gate roller 32 through the transport roller 33, and the skew is corrected by the gate roller 32 and the transport drum 26. Is supplied from the tangential direction at the left side position, and this recording paper P is electrostatically attracted and held on the outer surface of the transport drum 26. The transport drum 26 is rotationally driven by the drive motor 26a in the clockwise direction in FIG. 7 at a peripheral speed u equal to the transport speed U of the transport belt 21 in the first embodiment described above.

  A head unit 1 having recording heads 1 </ b> Y to 1 </ b> K is arranged on the upper surface side of the transport drum 26 via a gap region G and concentrically with the transport drum 26. The head unit 1 has a cylindrical inner surface and a cylindrical outer surface that are concentric with the conveying drum 26 disposed above the conveying drum 26 and face the cylindrical surface of the conveying drum 26 with a gap region G having a predetermined length. A semi-cylindrical support member 1a is provided, and recording heads 1Y to 1K having a multi-head configuration are ejected onto the support member 1a at predetermined intervals in the circumferential direction and ink droplets, as in the first embodiment. The ink droplets are ejected from the nozzles in such a manner that the ink droplet ejection direction is normal to the cylindrical surface of the transport drum 26. And the gas guide part 1b which forms the gap area | region G continuously in the opposing surface with the conveyance drum 26 of this support member 1a is formed.

  Further, a gas supply unit 6 having the same configuration as that of the first embodiment described above is disposed upstream of the gap region G between the support member 1a and the transport drum 26, that is, below the recording head 1Y. A recording sheet in which the leading end of the feeding duct 61 of the gas supply unit 6 is opened in the vicinity of the gas guide unit 1b and the mixed gas that suppresses drying of the recording heads 1Y to 1K is conveyed by the gas guide unit 1b and the conveyance drum 26. Introduced into the gap region G between P.

The transport drum 26 is neutralized by a static elimination mechanism 29 disposed in the vicinity of the paper discharge unit 4 side of the transport drum 26 and in contact with the outer surface of the transport drum 26, and the recording paper P is transferred to the transport drum 26. A series of printing processes are completed after being separated from the outer surface and discharged to the paper discharge unit 4.
Next, the operation of the second embodiment will be described.
Now, the recording paper P is fed one by one from the paper feed unit 3 by the paper feed roller 31, is changed in the direction perpendicular to the direction of the transport roller 33 by the guide roller 34, and then continues to the gate roller 32 through the transport roller 33. The skew is corrected and delivered to the transport drum 26 from the tangential direction on the left side. The recording paper P is electrostatically attracted and held on the cylindrical surface of the conveyance drum 26 electrostatically charged by the charging mechanism 27, and the conveyance drum 26 and the support member 1 a of the head unit 1 that forms an image on the recording paper P are arcuate. Is transferred to the gap region G facing the surface.

  An image is formed on the recording paper P by discharging ink droplets from the nozzles of the recording heads 1Y to 1K while being rotated and conveyed clockwise in the gap region G at a peripheral speed u equivalent to a constant paper conveying speed U. The recording sheet P is separated from the upper surface of the transport drum 26, which has been neutralized by the neutralization mechanism 29, at the right position where the rotary drum 26 has made a half turn. This series of printing operations is repeated until there is no image information.

  In this printing operation, when the transport drum 2 is rotated in the clockwise direction, the mixed gas containing water vapor discharged from the supply duct 61 of the gas supply unit 6 disposed on the upstream side of the gas guide unit 1b is generated. By being supplied, the mixed gas is applied to the semi-cylindrical belt-shaped gap region G formed by the conveyance drum 26 and the semi-cylindrical surface-shaped gas guide portion 1b facing the same as in the first embodiment. Since the gas mixture is efficiently introduced without diffusing to the outside and supplied to the nozzles for ejecting ink droplets of the recording heads 1Y to 1K, the ink droplets on the ink droplet ejection surface of these nozzles are dried. It can be surely prevented.

In addition, in the second embodiment, the total length of the paper conveying means can be shortened by applying the drum type paper conveying unit.
In the second embodiment, the case where the recording paper P is electrostatically held by charging the rotating drum 26 has been described. However, the present invention is not limited to this, and as shown in FIG. The transport drum 26 is formed as a hollow drum, and a large number of through holes are formed in the cylindrical surface holding the recording paper P. The transport drum 26 is driven by a drum drive roller 26b driven by a drive motor 26a. The air suction mechanism is rotated in the clockwise direction at a peripheral speed u equal to the transport speed U of the transport belt 21 in the first embodiment described above, and is opposed to the upper half periphery of the inner peripheral surface of the transport drum 26. By fixing 71, the air suction mechanism 71 sucks air through the through hole of the transport drum 26, so that the recording paper P is sucked and held. There.

Next, a third embodiment of the present invention will be described with reference to FIG.
The third embodiment is the same as the first embodiment described above except that a gas circulation unit 68 is provided to return the mixed gas to the gas supply unit 6 from the downstream side of the gas guide unit 1b. 1 has the same configuration as that of the first embodiment, and the same parts as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

  As shown in FIG. 9, this gas circulation part 68 is comprised by the cylindrical duct, and forms one end part in the flat cylindrical gas introduction part 68a, and this gas introduction part 68a of the gas guide part 1b is formed. Located on the downstream side and disposed close to the upper surface of the recording paper P conveyed by the endless conveyance belt 21, the other end communicates with the conveyance gas intake port of the blower 66 in the gas supply unit 6. . The used mixed gas, which is guided by the gas guiding portion 1b and flows in the gap region G from the upstream side to the downstream side, circulates in the gas circulation portion 68 by the suction of the blower 66 and is reused as the carrier gas. Note that the gas circulation unit 68 has an outside air intake 681 for taking in outside air as necessary in the vicinity of the blower 66.

Next, the operation of the third embodiment will be described.
In the third embodiment, similarly to the first embodiment described above, the mixed gas containing water vapor generated in the gas supply unit 6 is supplied to the gas guide unit 1b of the head unit 1 and the transport belt 21 by the supply duct 61. The mixed gas sequentially travels around the recording heads 1K to 1Y as the conveying belt 21 is conveyed, thereby ejecting ink droplets of the recording heads 1K to 1Y. Although drying of the ink droplet discharge surface of the nozzle can be reliably prevented, the mixed gas after the last recording head 1Y is led out from the downstream side of the gap region G. A gas introduction part 68 a of the gas circulation part 68 is disposed downstream of the gap region G, and the other end of the gas circulation part 68 communicates with the blower 66 of the gas supply part 6. The inside of the circulation part 68 becomes a negative pressure, and the used mixed gas can be recovered from the gas introduction part 68a and returned to the gas supply part 6.

  As described above, according to the third embodiment, the used mixed gas discharged from the downstream side of the gap region G 1 around the recording heads 1K to 1Y is sucked by the gas introduction part 68a, and the gas circulation part 68 is set. Since it is returned to the gas supply unit 6 through, it is possible to extremely reduce the amount of leakage of the gas mixture with high humidity to the outside, and to reliably prevent the generation of water droplets due to the gas mixture leaked to the outside, The waterproof structure of the peripheral device can be simplified. Further, by returning the recovered mixed gas to the gas supply unit 6 and reusing it, the amount of water W used to generate water vapor can be further suppressed, and the replenishment frequency of the water W can be reduced. .

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This 4th Embodiment provides the gas circulation part 68 which returns the said mixed gas to the gas supply part 6 from the downstream of the gas guide part 1b in 2nd Embodiment mentioned above.
That is, in the fourth embodiment, in the configuration of FIG. 7 in the second embodiment described above, the downstream side of the gap region G formed by the gas guide portion 1b of the head unit 1 and the rotary drum 26, that is, the paper discharge portion. 4 has the same configuration as that of the second embodiment described above except for the configuration in which the gas circulation unit 68 for returning the mixed gas to the gas supply unit 6 from the vicinity of 4 is provided. The same reference numerals are given, and detailed description thereof is omitted.

  As shown in FIG. 10, the gas circulation portion 68 is formed of a cylindrical duct, and one end portion is formed in a flat cylindrical gas introduction portion 68 a, and the gas introduction portion 68 a is a gas in the head unit 1. Located on the downstream side of the guide portion 1 b and disposed close to the upper surface of the recording paper P conveyed by the conveyance drum 26, the other end communicates with the conveyance gas intake port of the blower 66 in the gas supply unit 6. I am letting. The used mixed gas that has flowed through the gap region G from the upstream side to the downstream side by the gas guide portion 1b of the head unit 1 circulates in the gas circulation portion 68 by the suction of the blower 66 and is reused as the carrier gas. Note that the gas circulation unit 68 has an outside air intake 681 for taking in outside air as necessary in the vicinity of the blower 66.

  According to the fourth embodiment, the mixed gas formed by the support member 1 a and the transport drum 26 and supplied from the upstream side of the gap region G by the feed duct 61 of the gas supply unit 6 is mixed with the gas guide unit 1 b and the transport drum 26. Is introduced into the gap region G between the nozzle and the ink droplet discharge surface of the nozzle that discharges the ink droplets of the recording heads 1Y to 1K, and the drying of the ink droplet discharge surface of the nozzle is suppressed. When the mixed gas is discharged from the downstream side of the gap region G, the mixed gas is sucked by the gas introduction part 68 a disposed on the downstream side and returned to the gas supply part 6 through the gas circulation part 68.

  Therefore, also in the fourth embodiment, similar to the third embodiment described above, the used mixed gas is recovered and returned to the gas supply unit 6, so that the amount of leakage that the high-humidity mixed gas leaks to the outside The generation of water droplets due to the gas mixture leaking to the outside can be reliably prevented, and the waterproof structure of the peripheral device can be simplified. Further, by returning the recovered mixed gas to the gas supply unit 6 and reusing it, the amount of water W used to generate water vapor can be suppressed, and the replenishment frequency of the water W can be reduced.

In the first to fourth embodiments, the case where the head unit 1 is configured by four color recording heads of yellow, magenta, cyan, and black has been described. However, the present invention is not limited to this. The color and arrangement order, and the number of head units arranged can be arbitrarily set.
In the first to fourth embodiments, the case where the ultrasonic vibrator 641 is applied as the water vapor generating means has been described. However, the present invention is not limited to this. The heating element is formed by a heating element such as an induction heater to be generated or a coil around which a litz wire is wound and a conductive heating element, and a heating element driving signal sent from a gas supply unit 69. May be generated and the water W may be converted into water vapor to be scattered in the supply duct 61.

  Furthermore, as shown in FIG. 11, the ultrasonic transducer 641 is omitted, and instead of this, an evaporation filter 642 that sucks and evaporates the water W in the container 64 by capillary action is applied. It may be arranged so as to be opposed to the blower 66 in the upper feeding duct 61 of 64. In this case, the humidity in the vicinity of the outlet of the feeding duct 61 may be controlled within an allowable range by adjusting the air volume of the blower 66. Thus, by using the evaporation filter 642, an inexpensive water vapor generating means can be configured.

  In the first to fourth embodiments, the case where the mixed gas containing water vapor is applied as the gas for suppressing the drying of the ink droplet discharge surface of the nozzle of the recording head has been described. However, the present invention is not limited to this. Instead, a solvent or oil contained in the ink droplet that has affinity for the ink droplet and can suppress drying of the ink droplet is applied as a solution for drying suppression, and this solution is used as the ultrasonic vibrator 641. In this case, the liquid may be ultrasonically vibrated into fine droplets and scattered in the carrier gas to generate a mixed gas composed of the droplets and the carrier gas.

  In the first to fourth embodiments, the gas that suppresses the drying of the ink discharge surface in the gap region G using the transport airflow formed by the transport speed of the transport belt 21 or the peripheral speed of the transport drum 26. In the case where the conveyance belt 21 or the conveyance drum 26 is stopped in order to suppress the generation of power and noise when recording information is not input, the mixing into the gap region G is described. Since the gas introduction amount decreases, the gas supply control unit 69 increases the air volume of the blower 66 to positively feed the mixed gas to the gap region G, thereby ejecting ink droplets in the recording heads 1Y to 1K. It is preferable to suppress drying of the ink droplet discharge surface of the nozzle.

1 is a schematic plan view showing a first embodiment of the present invention. It is a side view of FIG. FIG. 2 is an enlarged bottom view showing the head unit in FIG. 1. It is sectional drawing which shows schematic structure of a gas supply part. It is a block diagram which shows an example of the control part of the 1st Embodiment of this invention. It is a side view which shows the modification of the paper conveyance unit in the 1st Embodiment of this invention. It is a schematic side view which shows the 2nd Embodiment of this invention. It is a side view which shows the modification of the paper conveyance unit in the 2nd Embodiment of this invention. It is a schematic side view which shows the 3rd Embodiment of this invention. It is a schematic side view which shows the 4th Embodiment of this invention. It is sectional drawing which shows the modification of a gas supply part.

Explanation of symbols

1: head unit, 1K: black head unit, 1M: magenta head unit, 1C: cyan head unit, 1Y: yellow head unit, 12: ink supply tube, 13: ink cartridge, 13K: black ink cartridge, 13M: magenta ink Cartridge, 13C: cyan ink cartridge, 13Y: yellow ink cartridge, 2: paper transport unit, 21: endless transport belt, 22: drive roller, 23: driven roller, 24: tension roller, 25: backup roller, 26: transport drum 27: electrostatic adsorption mechanism, 28: high-voltage power supply, 29: static elimination mechanism, 3: paper feeding unit, 31: paper feeding roller, 32: gate roller, 33: transport roller, 34: guide roller, 4: paper ejection unit , 6: gas supply unit, 601: humidity sensor, 61: feeding duct 62: outlet, 63: water level detector, 63a: guide shaft, 63b: float, 63c: upper limit water level detector, 63d: lower limit water level detector, 64: container, 641: ultrasonic transducer, 642: evaporation filter , 65: open / close lid, 66: blower, 67: filter, 68: gas circulation unit, 69: gas supply control unit, P: recording paper, W: water, G: gap region

Claims (12)

  An image is formed on the recording medium by ejecting ink droplets that are disposed in close proximity to the recording medium transported by the transporting means via a predetermined gap region. A head unit to be formed; and a gas supply unit that supplies a gas that suppresses drying of ink droplets in the head unit disposed on the upstream side of the gap region to the gap region. An ink jet printer comprising: a gas guide portion that forms a gap region continuous in a conveyance direction of the recording medium with a conveyance unit and guides a gas supplied from the gas supply unit.   The gas supply unit has a Reynolds number R represented by R = UG / ν, where U is a conveyance speed of the recording medium, G is a gap length of the gap region, and ν is a dynamic viscosity coefficient of air. 2. The ink jet printer according to claim 1, wherein the gas is set to a value within a range in which the gas can be sucked into the gap region.   The gas supply unit mixes a solution evaporation unit that evaporates a solution that suppresses drying of ink droplets of the head unit, the solution evaporated by the solution evaporation unit, and a carrier gas, and sends the mixture to the gap region. The inkjet printer according to claim 1, further comprising a gas feeding unit that feeds the gas.   4. The ink jet printer according to claim 3, wherein the solution is formed of any one of water, a solvent contained in ink droplets, and oil.   The inkjet printer according to claim 3 or 4, wherein the solution evaporation means includes any one of an ultrasonic vibrator, a heating element, and an evaporation filter.   The solution evaporation means includes a container for storing the solution, a liquid level measurement means for measuring the liquid level of the solution in the container, and a liquid level measurement value detected by the liquid level measurement means is equal to or less than a set value. An ink jet printer according to any one of claims 3 to 5, further comprising a warning means for issuing a warning when the alarm is detected.   The gas supply unit mixes water vapor generating means for generating water vapor to prevent drying of ink droplets of the head unit, water vapor generated by the water vapor generating means, and a carrier gas, and supplies the mixed gas to the gap region. A gas feeding means, a relative humidity detecting means for detecting the relative humidity of the mixed gas of the gas supplying means, and a relative humidity detected by the relative humidity detecting means so as to be within a predetermined range for suppressing drying of the ink droplets. The inkjet printer according to claim 1, further comprising a water vapor control unit that controls a water vapor generation amount of the water vapor generation unit.   The gas supply unit includes a gas recovery unit disposed on the downstream side of the gap region, and a circulation path for circulating the gas recovered by the gas recovery unit to the gas supply unit. An ink jet printer according to any one of claims 3 to 7.   The ink jet printer according to claim 1, wherein the transport unit is configured by an endless transport belt that transports the recording medium.   The ink jet printer according to claim 1, wherein the transport unit includes a transport drum that sucks and transports the recording medium.   The ink jet printer according to claim 1, wherein the transport unit includes an air suction mechanism that sucks and holds the recording medium. The inkjet printer according to claim 1, wherein the transport unit includes an electrostatic adsorption mechanism that electrostatically attracts the recording medium.

Images