JP2009078499A - Inkjet type image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet type image forming apparatus which prevents ink from drying without disturbing delivering of the ink from a recording head. <P>SOLUTION: Liquid droplets for moistening delivered from a moistening head 22H are vaporized during flying (or after reaching a recording medium P) to become water vapor and reach faces and their surroundings of respective recording heads 22K, 22C, 22M and 22Y to moisten them. In addition, air flow containing the water vapor flows in the conveying direction (an arrow mark A direction) along the faces of respective recording heads 22K, 22C, 22M, 22Y, 22 and 22 to hold the respective faces at a humidity of a specified value or higher without drying the respective faces. As a result, no delivery of the ink caused by drying of nozzles by exposure during printing is prevented from occurring, and the number of recovery during printing caused by exposure during printing is reduced to be able to effectively use the ink. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inkjet image forming apparatus that forms an image by ejecting ink onto a recording medium from a plurality of ink ejection openings formed in a recording head.

  2. Description of the Related Art Inkjet image forming apparatuses (inkjet printers) that form images by ejecting ink (ink droplets) onto a recording medium from a plurality of nozzles formed on a recording head (printing head) are widely used. As a technique for ejecting ink droplets from a nozzle, a technique is known in which thermal energy corresponding to a driving pulse is supplied to ink in the nozzle to form bubbles due to film boiling, and ink bubbles are ejected from the nozzles by the bubbles. . In this technique, an image is formed on a recording medium by selectively ejecting a large number of ink droplets corresponding to the image to be formed from a plurality of nozzles onto the recording medium.

  In order to improve the image recording speed (image forming speed), an ink jet printer employing the above technique uses a multi-nozzle head in which a plurality of nozzles including ink discharge ports and ink flow paths are integrated. This type has a line head in which a multi-nozzle head is arranged in many directions perpendicular to the recording medium conveyance direction, and ink is selectively ejected from each ink ejection port of a plurality of nozzles in accordance with the conveyance of the recording medium (line Printer).

  In general, an image forming apparatus that forms an image on a recording medium is required to form a high-resolution image with high image quality at a high speed. By using an inkjet printer such as the above-described line printer, These requirements can be satisfied. In addition, the ink jet printer has an advantage that a very stable image recording can be performed because the recording head and the recording medium are not in contact with each other during image formation (image recording).

  However, in the case of an ink jet printer, since ink that is a fluid is handled, various problems in hydrodynamics occur in the recording head. Further, since the ink is a liquid, its viscosity changes as needed depending on the environmental temperature, the standing time, and the like. Such a change in viscosity greatly affects image recording.

  By the way, when a full-line type ink jet head is used, a plurality of ink ejection openings formed in the recording head and its peripheral portion (face surface) are always exposed to air during recording. For this reason, in a low-humidity (low humidity) environment, the ink is easily dried at an ink discharge port from which ink is not discharged among a plurality of ink discharge ports. For this reason, when the recording time becomes longer, the viscosity of the ink adhering to the ink discharge port and its periphery increases. As a result, there is a risk of causing non-ejection of ink that does not eject ink. In other words, since the ink jet printer has a mechanism for ejecting ink from the ink ejection port, the ink ejection may become unstable when the composition of the ink changes (particularly, a thickening phenomenon).

  Also, in recording where the nozzles that eject ink change (recording data changes), the time that the ink ejection port is exposed to the air tends to increase, so it has not been used for recording until now (ink is ejected). When ink is suddenly ejected from the ink ejection port, the first ink ejection tends to be non-ejection.

  In order to eliminate ink instability as described above and stabilize ink ejection, inkjet printers recover by intentionally ejecting (preliminary ejection) or sucking ink mixed with dry ink or dust. Processing is performed.

By the way, an ink jet printer provided with a humidifier or a steam generator for preventing ink drying is also known (see, for example, Patent Documents 1 and 2). However, since the humidifier or the steam generator is a device that blows out the humidified air, there is a possibility that the ink flow from the recording head may be disturbed to disturb the ink landing on the recording medium.
JP 2000-255053 A JP-A-11-268256

  In view of the above circumstances, an object of the present invention is to provide an ink jet type image forming apparatus that prevents ink from drying without disturbing ink ejection from a recording head.

In order to achieve the above object, an inkjet image forming apparatus of the present invention is an inkjet image forming apparatus that forms an image by discharging ink to a recording medium from a plurality of ink discharge ports formed in a recording head.
(1) A humidifying head disposed in the vicinity of the recording head for humidifying the ink discharge port and its periphery by discharging a droplet for humidification is provided.

here,
(2) The humidifying head may have a plurality of ejection openings from which humidifying droplets are ejected, and may have the same structure as the recording head.

Also,
(3) The humidification head may be disposed upstream of the recording head in the recording medium conveyance direction.

further,
(4) The humidifying head may discharge the humidifying droplets so that the discharged humidifying droplets are vaporized before landing on the recording medium.

Furthermore,
(5) You may provide the humidity sensor which detects the humidity around the said ink ejection opening.

Furthermore,
(6) You may provide the controller which controls the said humidification head so that the humidity of the said ink discharge port and its periphery becomes a humidity in a predetermined range based on the humidity detected by the said humidity sensor.

Furthermore,
(7) The controller may eject a humidifying droplet from the humidifying head based on an ink ejection state of the recording head.

Furthermore,
(8) The controller may control the humidifying head to discharge humidifying droplets prior to forming an image by discharging ink from the recording head onto a recording medium.

Furthermore,
(9) The humidifier head may discharge the humidifying liquid droplets from the humidifying liquid droplet discharge port corresponding to the ink discharge port that discharges ink from the recording head in accordance with an image to be formed. It may be one that controls.

Furthermore,
(10) The controller is not limited to the number of nozzles in which the humidifying liquid droplet discharge ports corresponding to the ink discharge ports that discharge ink from the print head according to the formed image coincide with the print head. There may be provided a humidifying head nozzle number selecting means for performing no control.

Furthermore,
(11) In the controller, a droplet discharge port conditioned for the humidification corresponding to the ink discharge port that discharges ink from the recording head according to an image to be formed corresponds to the recording head. There may be provided a humidifying intensity adjusting means for selectively discharging the droplet discharge ports conditioned for humidification of the humidifying head every other nozzle or every plural nozzles.

Furthermore,
(12) The controller is configured to discharge the humidifying liquid droplets only from the humidifying liquid droplet discharge ports corresponding to the ink discharge ports that discharge ink from the recording head according to an image to be formed. The head may be controlled.

Furthermore,
(13) The controller may discharge humidifying droplets from the humidifying head so that the humidity of the ink discharge port and its periphery is within a certain range.

Furthermore,
(14) The humidifying droplets may be clear ink droplets or water droplets that have the same components as the ink and do not contain a coloring material.

  According to the present invention, the humidifying liquid droplets are ejected from the humidifying head disposed in the vicinity of the recording head to increase the humidity at the ink ejection port and its surroundings, so that the ink ejection from the recording head is not disturbed. It is possible to prevent the ink adhering to the discharge port and its periphery from being dried. For this reason, even if the frequency of the recovery process is reduced, the ink can be prevented from drying, so that wasteful consumption of ink can be prevented.

  The present invention has been realized in an inkjet image forming apparatus that forms an image by ejecting ink onto a recording medium from a plurality of ink ejection openings formed in a recording head.

  With reference to FIG. 1, a printer as an example of an ink jet image forming apparatus of the present invention will be described.

  FIG. 1 is a front view schematically showing a printer which is an example of an ink jet image forming apparatus of the present invention.

  The printer 10 is connected to a host PC (personal computer) 12 that sends image information to the printer 10. In the printer 10, four (four) recording heads 22K, 22C, 22M, and 22Y are arranged side by side in the conveyance direction (arrow A direction) of the recording medium (roll paper in this case). The four recording heads 22K, 22C, 22M, and 22Y eject black, cyan, magenta, and yellow inks, respectively. These four recording heads 22K, 22C, 22M, and 22Y are so-called line heads, and extend in a direction orthogonal to the paper surface of FIG. 1 (a direction orthogonal to the arrow A direction). The lengths of these four recording heads 22K, 22C, 22M, and 22Y are slightly longer than the maximum width (the length in the direction perpendicular to the paper surface of FIG. 1) of the recording media that can be printed by the printer 10. Further, these four recording heads 22K, 22C, 22M, and 22Y are fixed and do not move during image formation. The printer 10 has a structure in which two recording heads 22 and 22 can be preliminarily mounted in addition to the four recording heads 22K, 22C, 22M, and 22Y. A humidifying head 22H is mounted on the upstream side of the recording head 22K in the direction of arrow A (recording medium conveyance direction) alongside the recording head 22K. The structure of the humidifying head 22H is the same as the structure of the four recording heads 22K, 22C, 22M, and 22Y, which will be described later.

  A recovery unit 40 is incorporated in the printer 10 so that ink can be stably ejected from the four recording heads 22K, 22C, 22M, and 22Y. By the recovery unit 40, the ink ejection state from the recording heads 22K, 22C, 22M, and 22Y is restored to the initial ink ejection state. The recovery unit 40 includes a capping mechanism 50 that removes ink from the ink discharge port formations (face surfaces) 22Ks, 22Cs, 22Ms, and 22Ys of the four recording heads 22K, 22C, 22M, and 22Y during the recovery operation. Yes. The capping mechanism 50 is provided independently for each of the recording heads 22K, 22C, 22M, and 22Y. In the example of FIG. 1, six colors (that is, six capping mechanisms 50) are shown. The color component is a preliminary mechanism when the recording head is added. The capping mechanism 50 includes a known blade, an ink removing member, a blade holding member, a cap, and the like.

  The roll paper P is supplied from the roll paper supply unit 24 and is conveyed in the direction of arrow A by the conveyance mechanism 26 incorporated in the printer 10. The transport mechanism 26 includes a transport belt 26a for loading and transporting the roll paper P, a transport motor 26b for rotating the transport belt 26a, and a roller 26c for applying tension to the transport belt 26a.

  When forming an image on the roll paper P, after the recording start position of the roll paper P being conveyed reaches below the black recording head 22K, the recording head is based on the recording data (image information). Black ink is selectively ejected from 22K. Similarly, each color ink is ejected in the order of the recording head 22C, the recording head 22M, and the recording head 22Y to form a color image on the roll paper P. The printer 10 includes main tanks 28K, 28C, 28M, and 28Y for storing ink supplied to the recording heads 22K, 22C, 22M, and 22Y, and the recording heads 22K, 22C, and 22M, in addition to the components and members described above. , 22Y are provided with various pumps (see FIG. 3 and the like) for supplying ink and performing a recovery operation. Further, the printer 10 includes a humidity sensor 30 that detects the humidity around the face surfaces 22Ks, 22Cs, 22Ms, and 22Ys. In FIG. 1, the humidity sensor 30 is located upstream of the humidification head 22H in the transport direction, but the humidity detection portion is arranged at a position where the humidity around the face surfaces 22Ks, 22Cs, 22Ms, and 22Ys can be detected. Yes. Further, a humidifying liquid tank 28H that stores a humidifying liquid supplied to the humidifying head 22H is disposed adjacent to the main tank 28K.

  The electrical system of the printer 10 will be described with reference to FIG.

  FIG. 2 is a block diagram showing an electrical system of the printer of FIG.

  Recording data and commands transmitted from the host PC 12 are received by the CPU 100 via the interface controller 102. The CPU 100 is an arithmetic processing unit that performs overall control such as reception of recording data of the printer 10, recording operation, handling of the roll paper P, and the like. After analyzing the received command, the CPU 100 renders the image data of each color component of the recording data by developing a bitmap on the image memory 106. As an operation process before recording, the capping motor 122 and the head up / down motor 118 are driven via the output port 114 and the motor drive unit 116, and the recording heads 22K, 22C, 22M, and 22Y are connected to the capping mechanism 50 (see FIG. 1). ) To move to the recording position (image forming position).

  Subsequently, the roll motor (not shown) that feeds the roll paper P through the output port 114, the motor drive unit 116, the transport motor 120 that transports the roll paper P at a low speed, and the like are driven to drive the roll paper P. -The paper P is conveyed to the recording position. The leading end position of the roll paper P is detected by a leading edge detection sensor (not shown) for determining the timing (recording timing) at which ink starts to be discharged onto the roll paper P conveyed at a constant speed. Thereafter, in synchronization with the conveyance of the roll paper P, the CPU 100 sequentially reads out the corresponding color recording data from the image memory 106, and controls the recording heads 22K, 22C, 22M, and 22Y to read the read data. Transfer via the circuit 112. The humidity detected by the humidifying head 22H is transmitted to the CPU 100, and the humidifying head 22H is controlled by the recording head control circuit 112 so that the humidity falls within a certain range.

  The operation of the CPU 100 is executed based on a processing program stored in the program ROM 104. The program ROM 104 stores a processing program (including a program for executing a flow to be described later) corresponding to the control flow, a table, and the like. A work RAM 108 is used as a working memory. During each operation such as cleaning of the recording heads 22K, 22C, 22M, and 22Y, the CPU 100 drives the pump motor 124 via the output port 114 and the motor driving unit 116 to control ink pressurization and suction, Viscosity detection is performed via the output port 114.

  The structure of the humidifying head 22H will be described with reference to FIG. The recording heads 22K, 22C, 22M, and 22Y have the same structure. FIG. 3 is a cross-sectional view showing the nozzle of the humidifying head and its peripheral portion. Although only one nozzle 22Hn is shown in FIG. 3, the humidifying head 22H has a large number of nozzles arranged side by side perpendicular to the recording medium conveyance direction.

  In the humidifying head 22H, a large number of nozzles 22Hn for discharging humidifying droplets are formed side by side in the direction perpendicular to the paper surface of FIG. The humidifying droplets ejected from the humidifying head 22H are very fine mist-like and have the same size as the ink droplets ejected from the recording heads 22K, 22C, 22M, and 22Y. The large number of nozzles 22Hn are connected (communicated) with a common liquid chamber 22Hr in which a humidifying liquid is stored. The common liquid chamber 22Hr is connected to a humidifying liquid tank 28H (see FIG. 1), and the humidifying liquid is supplied from the humidifying liquid tank 28H to the common liquid chamber 22Hr.

  The nozzle 22Hn is provided with a heating element 152 for foaming (forming bubbles) in the humidifying liquid in the nozzle 22Hn. By energizing the heating element 152 to generate heat, bubbles (bubbles) are generated in the humidifying liquid in the nozzle 22Hn, and the humidifying liquid droplets are pushed out from the outlet (humidifying liquid droplet discharge port 154) of the nozzle 22Hn. Discharged in the direction of arrow D.

  The heating element 152 is formed on the silicon element substrate 156 by a known technique. A silicon top plate 158 and a nozzle I160 are formed on the silicon element substrate 156 to make the wettability of the humidifying liquid uniform. The silicon top plate 158 and the nozzle I160 face the inner wall of the nozzle 22Hn. Yes. The nozzle I160 is formed on the inner wall in the vicinity of the discharge port 154 of the nozzle 22Hn, and narrows the humidification droplet discharge port 154.

  The common liquid chamber 22Hr is also formed in the silicon element substrate 156. There are also a valve 162 that efficiently directs energy in the humidifying droplet discharge direction (arrow D direction) during foaming by the heating element 152, and a flow path wall 164 that extends vertically from the silicon top plate 158 toward the inside of the nozzle 22Hn. It is formed on the silicon element substrate 156. The nozzle I160 is for preventing chipping (chipping) when the silicon top plate 158 is cut when a large number of nozzles 22Hn and the like are manufactured.

  The heating element 152 is formed by patterning an electric resistance layer and wiring. The heating element 152 generates heat by applying a voltage to the electric resistance layer through this wiring and passing a current. With this heat generation, the humidifying liquid on the surface portion of the heating element 152 is foamed, and the humidifying liquid droplets are pushed out from the humidifying liquid droplet discharge port 154 and discharged. The driving condition of the humidifying head 22H is determined based on the humidity detected by the humidity sensor 30 (see FIGS. 1 and 2).

  An example in which the humidifying head 22H is driven will be described with reference to FIGS.

  FIG. 4 is a schematic diagram illustrating a humidifying droplet discharge state by the humidifying head. FIG. 4A is an initial state in which the printer does not receive print data and the face surface of each head is covered with a cap. (B) shows a state in which the printer has received print data, each head has moved to the print position, and the humidifying liquid droplets have started to be ejected from the humidification head. FIG. 4D shows a state in which the air stream containing moisture is diffused out of the apparatus, and FIG. 4D shows a state in which the humidity control and printing are finished and the initial state is restored. FIG. 5 is a flowchart showing driving of the humidifying head.

  The flow in FIG. 5 is activated when the printer 10 receives a print command from the host PC 12 (see FIG. 1). Until this reception, the face surfaces of the recording heads 22K, 22C, 22M, 22Y, and 22 and the humidifying head 22H are covered with a cap 50 as shown in FIG. When the above reception is received, first, the recording heads 22K, 22C, 22M, 22Y, 22 and the humidifying head 22H are moved to the printing position as shown in FIG. Humidity of the face surface and its surroundings is detected (S501). Subsequently, it is determined whether or not the detected humidity is equal to or higher than a specified value (S502). The specified value here is predetermined for each printer in accordance with the type of ink to be used, and is stored in the CPU 100 (see FIG. 2). When it is determined that the detected humidity is equal to or higher than the specified value, the humidification head 22H is not driven (no droplets for humidification are discharged), and printing (image formation) is performed by the recording heads 22K, 22C, 22M, and 22Y. ) Is started (S503), and when predetermined printing is completed (S506), this flow ends.

  If it is determined in S502 that the detected humidity is less than the specified value, the process proceeds to S504 and humidity control is executed (S504). This humidity control is performed based on the detected humidity. When the detected humidity is less than the specified value but close to the specified value, the amount of humidifying droplets discharged from the humidifying head 22H is small, and when it is far below the specified value, it is discharged from the humidifying head 22H. The humidifying head 22H is controlled so that the amount of humidifying droplets increases. An appropriate relationship between the detected humidity and the amount of the humidifying droplet from the humidifying head 22H is obtained in advance through experiments or the like, and this relationship is stored in advance in the program ROM 104 (see FIG. 2) for each printer. Yes. Accordingly, appropriate humidifying droplets are ejected from the humidifying head 22H according to the humidity detected by the humidity sensor 30. After the humidifying liquid droplets are ejected from the humidifying head 22H, printing is started when the humidity detected by the humidity sensor 30 becomes equal to or higher than a specified value (S505). Even during printing, the humidity sensor 30 continues to detect the humidity, and based on the detected humidity, the humidifying liquid droplets are discharged from the humidifying head 22H in the same manner as described above, and the humidity is maintained at a predetermined value or more. When the printing is continued in this manner and the predetermined printing is finished (S506), this flow is finished.

  As shown in FIGS. 4B and 4C, the humidifying droplets discharged from the humidifying head 22H are vaporized during the flight (or after landing on the recording medium P) to become water vapor. The face surfaces of 22K, 22C, 22M, and 22Y and the periphery thereof are reached and humidified. Further, the air flow containing the water vapor flows in the transport direction (in the direction of arrow A) along the face surfaces of the recording heads 22K, 22C, 22M, 22Y, 22 and 22, so that each face surface is not dried. Keep humidity above the specified value. As a result, non-ejection of ink due to nozzle drying due to exposure during printing can be prevented, the number of times of recovery during printing due to exposure during printing can be reduced, and ink can be used effectively. Moreover, since the humidifying droplets are ejected from the humidifying head 22H in the same manner as the ink ejecting from the recording heads 22K, 22C, 22M, and 22Y, the ink ejected from the recording heads 22K, 22C, 22M, and 22Y is not disturbed. Land on the recording medium. This also applies to other examples described later.

  With reference to FIG. 6, the driving of the humidification head 22H for forming a higher quality image will be described.

  FIG. 6 is a flowchart showing a procedure for setting the humidity to exceed the minimum required humidity for printing.

  6 starts when the printer 10 receives a print command from the host PC 12 (see FIG. 1). Until this reception, the face surfaces of the recording heads 22K, 22C, 22M, 22Y, and 22 and the humidifying head 22H are covered with a cap 50 as shown in FIG. When the above reception is received, first, the recording heads 22K, 22C, 22M, 22Y, 22 and the humidifying head 22H are moved to the printing position as shown in FIG. Humidity of the face surface and its surroundings is detected (S601). Subsequently, it is determined whether or not the detected humidity is equal to or higher than a specified value (S602). The specified value here is predetermined for each printer in accordance with the type of ink to be used, and is stored in the CPU 100 (see FIG. 2). When it is determined that the detected humidity is equal to or higher than the specified value, the humidification head 22H is not driven (no droplets for humidification are discharged), and printing (image formation) is performed by the recording heads 22K, 22C, 22M, and 22Y. ) Is started (S603), and when predetermined printing is completed (S606), this flow ends.

  When it is determined in S602 that the detected humidity is less than the specified value, the process proceeds to S604 and humidity control is executed (S604). This humidity control is performed based on the detected humidity. Since the specified value is the minimum humidity required for printing, in order to obtain a higher-quality and stable image, the humidity within the range exceeding the specified value (referred to as “in a certain range” in the present invention). Humidity is controlled by discharging droplets for humidification from the humidification head 22H so as to be “humidity”. This makes it possible to obtain a higher quality and stable image. An appropriate relationship between the humidity and the amount of humidifying droplets from the humidifying head 22H that exceeds this specified value is determined in advance through experiments or the like, and this relationship is determined according to the program ROM 104 (for each type of printer. (See FIG. 2). Accordingly, appropriate humidifying droplets are ejected from the humidifying head 22H according to the humidity detected by the humidity sensor 30. After the humidifying droplets are ejected from the humidifying head 22H, printing starts when the humidity detected by the humidity sensor 30 exceeds a specified value (a value capable of obtaining a higher quality and stable image). (S605). Even during printing, the humidity sensor 30 continues to detect the humidity, and based on the detected humidity, the humidifying liquid droplets are discharged from the humidifying head 22H in the same manner as described above, and the humidity is maintained at a predetermined value or more. When the printing is continued in this manner and the predetermined printing is finished (S606), this flow is finished.

  With reference to FIG. 7, another example of driving the humidifying head 22H will be described.

  FIG. 7 is a flowchart showing a procedure of humidifying only before printing.

  7 starts when the printer 10 receives a print command from the host PC 12 (see FIG. 1). Until this reception, the face surfaces of the recording heads 22K, 22C, 22M, 22Y, and 22 and the humidifying head 22H are covered with a cap 50 as shown in FIG. When the above reception is received, first, the recording heads 22K, 22C, 22M, 22Y, 22 and the humidifying head 22H are moved to the printing position as shown in FIG. Humidity on the face surface and its surroundings is detected (S701). Subsequently, it is determined whether or not the detected humidity is equal to or higher than a specified value (S702). The specified value here is predetermined for each printer in accordance with the type of ink to be used, and is stored in the CPU 100 (see FIG. 2). When it is determined that the detected humidity is equal to or higher than the specified value, the humidification head 22H is not driven (no droplets for humidification are discharged), and printing (image formation) is performed by the recording heads 22K, 22C, 22M, and 22Y. ) Is started (S703), and when predetermined printing is completed (S707), this flow ends.

  When it is determined in S702 that the detected humidity is less than the specified value, the amount (Duty) of the humidifying droplets discharged from the humidifying head 22H is calculated to obtain the specified value (S704). This calculation is performed based on the detected humidity. When the detected humidity is less than the specified value but close to the specified value, the amount of humidifying droplets discharged from the humidifying head 22H is small, and when it is far below the specified value, it is discharged from the humidifying head 22H. The humidifying head 22H is controlled so that the amount of humidifying droplets increases. An appropriate relationship between the detected humidity and the duty of the humidifying head 22H is obtained in advance through experiments or the like, and this relationship is stored in advance in the program ROM 104 (see FIG. 2) for each type of printer.

  An appropriate amount of humidifying droplets is ejected from the humidifying head 22H based on the duty calculated in S704, and humidity control is executed (S705). After this humidity control is completed, printing is started (S706). When predetermined printing ends (S707), this flow ends. In this way, the optimum humidity environment for printing is prepared before printing is started, and a high-quality image can be reliably obtained.

  An example in which the humidification head 22H is driven according to an image formed on the recording medium (based on the ink ejection state of the recording head) will be described with reference to FIGS.

  FIG. 8 is a plan view schematically showing an example of an image formed on a recording medium and an airflow generated by humidifying droplets. FIG. 10 is a flowchart showing a procedure for driving the humidifying head based on the ink ejection state of the recording head.

  Here, each of the recording heads 22K, 22C, 22M, and 22Y forms an image only in a part of the width direction orthogonal to the arrow A direction (recording medium conveyance direction) (in the example of FIG. 8, the image is formed only at the center in the width direction). An example of forming an image is that no image is formed at both ends in the width direction.

  With reference to FIG. 9, the relationship between the nozzle positions of the recording head and the humidifying head at the boundary between the print nozzle area and the non-print nozzle area in FIG. 8 will be described. (A) shows the relationship of the nozzles when the nozzles of the recording head and the humidifying head are arranged without a gap at the boundary in the paper conveyance direction. This is called “in the case of complete matching” for convenience. (B) shows that after the droplets for humidification are ejected, they become vapor, which is a gas, and tend to disperse as the paper is transported. Yes. Here, one nozzle is opened, but this number may be determined appropriately depending on the temperature, humidity, and the like at that time. Thereby, it is possible to prevent the humidifying droplets from entering the print nozzle area, and this is referred to as “when adjustment by gas dispersion is performed” for convenience. Furthermore, (c), when adjusting the degree of humidification, thins out the nozzles of the humidification head 22H and discharges the droplets for humidification. For convenience, it is called “when adjustment by gas dispersion + adjustment of humidification intensity” is performed. It is out. Here, thinning of the humidifying nozzles is performed every other nozzle. (D) is similar to the above (c), but shows a case where “thickness adjustment by gas dispersion + humidification strength adjustment” is performed and thinning is performed every three nozzles. The thinning ratio may be determined appropriately according to the temperature, humidity, etc. at that time.

  9 starts when the printer 10 receives a print command from the host PC 12 (see FIG. 1). Until this reception, the face surfaces of the recording heads 22K, 22C, 22M, 22Y, and 22 and the humidifying head 22H are covered with a cap 50 as shown in FIG. When the above reception is received, first, the recording heads 22K, 22C, 22M, 22Y, 22 and the humidifying head 22H are moved to the printing position as shown in FIG. Humidity of the face surface and its surroundings is detected (S901). Subsequently, it is determined whether or not the detected humidity is equal to or higher than a specified value (S902). The specified value here is predetermined for each printer in accordance with the type of ink to be used, and is stored in the CPU 100 (see FIG. 2). When it is determined that the detected humidity is equal to or higher than the specified value, the humidification head 22H is not driven (no droplets for humidification are discharged), and printing (image formation) is performed by the recording heads 22K, 22C, 22M, and 22Y. ) Is started (S903), and when predetermined printing is completed (S907), this flow ends.

  When it is determined in S902 that the detected humidity is less than the specified value, the amount (Duty) of the humidifying droplets discharged from the humidifying head 22H is calculated to obtain the specified value (S904). This calculation is performed based on the detected humidity. When the detected humidity is less than the specified value but close to the specified value, the amount of humidifying droplets discharged from the humidifying head 22H is small, and when it is far below the specified value, it is discharged from the humidifying head 22H. The humidifying head 22H is controlled so that the amount of humidifying droplets increases. An appropriate relationship between the detected humidity and the duty of the humidifying head 22H is obtained in advance through experiments or the like, and this relationship is stored in advance in the program ROM 104 (see FIG. 2) for each type of printer.

  As described above, the amount of the humidifying droplet discharged from the humidifying head 22H is determined. Here, the humidifying droplet is uniformly distributed from all of the plurality of humidifying droplet discharge ports of the humidifying head 22H. Instead of discharging, it is determined from which humidifying liquid droplet discharge port of the humidifying head 22H the humidifying liquid droplets are discharged based on the ink discharge state of the recording heads 22K, 22C, 22M, and 22Y. Specifically, humidification is performed only from an ejection port corresponding to an ink ejection port (a nozzle that does not require ink ejection) that does not eject ink when forming an image among the respective ink ejection ports of the recording heads 22K, 22C, 22M, and 22Y. Liquid droplets are discharged. That is, as shown in FIG. 8, among the plurality of ink discharge ports of the humidification head 22H, the humidifying liquid only from the humidifying liquid droplet discharge ports located above both ends (non-printing areas) in the width direction of the recording medium P. Let the drops be ejected. The humidifying droplet discharge port located above the non-printing area is determined by the print data from the host PC 12 (see FIG. 1) in S905.

  The humidity detected by the humidity sensor 30 after the appropriate amount of humidifying droplets is ejected from the humidifying head 22H based on the duty calculated in S904 from the humidifying droplet ejection port determined in S905 is equal to or higher than the specified value. When it becomes, printing is started (S906). Even during printing, the humidity sensor 30 continues to detect the humidity, and based on the detected humidity, the humidifying liquid droplets are discharged from the humidifying head 22H in the same manner as described above, and the humidity is maintained at a predetermined value or more. When the printing is continued in this manner and the predetermined printing is finished (S907), this flow is finished.

  Ink in non-print nozzles (nozzles that do not eject ink during image formation) by humidifying droplets only from the humidification droplet discharge ports located above the non-print area as described above. Thus, even when the image to be formed is changed (when the pattern is changed), printing can be reliably performed. Further, it is not necessary to discharge unnecessary humidifying droplets in the printing area (area where the image is formed), and humidity control can be performed without impairing the ink fixing property.

  With reference to FIG. 11 to FIG. 13, an example in which the humidifying droplets discharged from the humidifying head evaporate before landing on the recording medium will be described.

  FIG. 11 is a schematic view showing the process from when the humidifying droplet is discharged from the humidifying droplet discharge port of the humidifying head to evaporate. FIG. 11A shows the humidifying droplet discharged from the humidifying droplet discharging port. (B) shows a state in which the ejected humidifying droplets are evaporated during flight, and (c) shows that the ejected humidifying droplets do not land on the recording medium and increase the surrounding humidity. It shows how it is. FIG. 11 is a flowchart showing a procedure for contributing to humidification of the surroundings without causing the droplets for humidification discharged from the humidification head to land on the recording medium. FIG. 13A is an explanatory diagram showing an example of a pulse for driving a heating element to eject ink from the ink ejection port of the recording head 22K onto the recording medium, and FIG. It is explanatory drawing which shows an example of the pulse which drives a heat generating body in order to vaporize, before making the droplet for humidification discharged from the exit land on a recording medium.

  The flow in FIG. 12 is activated when the printer 10 receives a print command from the host PC 12 (see FIG. 1). Until this reception, the face surfaces of the recording heads 22K, 22C, 22M, 22Y, and 22 and the humidifying head 22H are covered with a cap 50 as shown in FIG. When the above reception is received, first, the recording heads 22K, 22C, 22M, 22Y, 22 and the humidifying head 22H are moved to the printing position as shown in FIG. Humidity of the face surface and its surroundings is detected (S1101). Subsequently, it is determined whether or not the detected humidity is a specified value or more (S1102). The specified value here is predetermined for each printer in accordance with the type of ink to be used, and is stored in the CPU 100 (see FIG. 2). When it is determined that the detected humidity is equal to or higher than the specified value, the humidification head 22H is not driven (no droplets for humidification are discharged), and printing (image formation) is performed by the recording heads 22K, 22C, 22M, and 22Y. ) Is started (S1103), and when predetermined printing is completed (S1106), this flow ends.

  If it is determined in S1102 that the detected humidity is less than the specified value, the amount (Duty) of the humidifying droplets discharged from the humidifying head 22H is calculated to obtain the specified value (S1104). This calculation is performed based on the detected humidity. When the detected humidity is less than the specified value but close to the specified value, the amount of humidifying droplets discharged from the humidifying head 22H is small, and when it is far below the specified value, it is discharged from the humidifying head 22H. The humidifying head 22H is controlled so that the amount of humidifying droplets increases. An appropriate relationship between the detected humidity and the duty of the humidifying head 22H is obtained in advance through experiments or the like, and this relationship is stored in advance in the program ROM 104 (see FIG. 2) for each type of printer.

  As described above, the amount of the humidifying droplet discharged from the humidifying head 22H is determined. Here, the humidifying droplet discharged from the humidifying droplet discharge port 154 of the humidifying head 22H is the recording medium P. Vaporized before landing (arriving). That is, as shown in FIG. 10A, the humidifying droplet H discharged from the humidifying droplet discharge port 154 flies slightly, and immediately after that, is vaporized as shown in FIG. 10B. As a result, (c As shown in (2), before landing on the recording medium P, it completely evaporates to increase the ambient humidity. When the humidifying droplets discharged from the humidifying droplet discharge port 154 of the humidifying head 22H are vaporized before reaching (arriving) on the recording medium P, the heating element 152 (see FIG. 3) is used. ) In advance, and the humidifying head 22H is driven in accordance with the heat generation conditions.

  Based on the duty calculated in S1104 and the heat generation condition determined as described above, the humidity detected by the humidity sensor 30 after the appropriate amount of the humidifying droplets is ejected from the humidifying head 22H is the specified value. When this is the case, printing is started (S1105). Even during printing, the humidity sensor 30 continues to detect the humidity, and based on the detected humidity, the humidifying liquid droplets are discharged from the humidifying head 22H in the same manner as described above, and the humidity is maintained at a predetermined value or more. When the printing is continued in this manner and the predetermined printing is finished (S1106), this flow is finished.

  As shown in FIG. 11, an example of a pulse for driving the heating element 152 in order to vaporize the humidifying droplets discharged from the humidifying droplet discharge port 154 of the humidifying head 22H on the recording medium P will be described. To do.

  In FIG. 13, the high part of the horizontal line (straight line indicated by ON) represents that the heating element 152 (see FIG. 3) is energized (giving an electric pulse), and the low part of the horizontal line (in the OFF state). The straight line shown represents that the heating element 152 is not energized (no electrical pulse is applied).

  As shown in FIG. 13A, when an image is formed on a recording medium (when ink is ejected from the recording heads 22K, 22C, 22M, and 22Y), the heating element 152 (see FIG. 3) is caused to generate heat (see FIG. 13). Ink droplets are ejected from a nozzle (not shown) by applying thermal energy. In this case, as shown in FIG. 13A, three stages including a pre-pulse time (preliminary heating time) T1, an off time (resting diffusion time) T2, and a main heat pulse time (foaming heating time) T3 are passed. At the pre-pulse time T1, a current is passed through the heating element 152 (see FIG. 3) for T1 time (about 1.0 μsec to 0.5 μsec) (the heating element 152 is energized). By this energization, thermal energy is given to the ink in the nozzle, and the viscosity of the ink is lowered to increase the ink ejection efficiency. After the pre-pulse time T1 has elapsed, the heating element 152 is turned off (the heating element 152 is not energized) for an off time T2 (about 1.5 μsec to 2.5 μsec). After the off time T2 has elapsed, the heating element 152 is turned on (energized to the heating element 152) for the main heat pulse time T3 (1.5 μsec to 2.5 μsec). Within the main heat pulse time T3, film boiling occurs on the surface of the heating element 152 to eject ink. The longer T3, the larger the amount of ink ejected, that is, the larger the ink droplets.

  The reason that the off-time T2 exists between the pre-pulse time T1 and the main heat pulse time T3 is that the efficiency of ink ejection is enhanced by diffusing heat due to the pre-pulse time T1 to the ink in the nozzle. Therefore, as T2 is longer, the heat is more widely diffused into the ink, so the region where the viscosity of the ink is lowered becomes wider, and the ejected ink droplets become larger. However, if the length is too long, the temperature of the ink decreases, and the ink droplets become smaller. In the present invention, by adjusting the off time T2 or (and) the main heat pulse time T3, the heat energy applied to the humidifying liquid in the nozzle of the humidifying head 22H is changed, and the humidifying liquid droplets discharged from the nozzle. Evaporates before landing on the recording medium.

  In order to evaporate the humidifying droplets early in this way, as shown in FIG. 13B, the off time T2 is shortened to, for example, about 1.0 μsec to 0.5 μsec. This narrows the region where the heat due to T1 diffuses, so the droplet becomes smaller. Further, the main heat pulse time T3 is shortened to, for example, about 1.0 μsec to 0.5 μsec. This also reduces the droplet size.

  As described above, the humidifying droplets discharged from the humidifying head 22H are completely vaporized before landing on the recording medium P to increase the ambient humidity. Printing can be performed without impairing image quality by the humidifying droplets.

  The ink-jet ink components are generally about 5% color material, about 75% water, and the rest are glycerin, ethylene glycol, triethylene glycol, and the like. If necessary, an antifungal agent for preventing mold generated in the piping may be included. The ink from which the color material is removed is referred to as a clear ink, and the humidifying liquid discharged from the humidifying head 22H is preferably a clear ink that has the same components as the ink but does not contain the color material. The reason is that the humidifying droplets are ejected in the same process as the ink using the ink head. Therefore, if the components are the same as the ink, it is easy to control the ejection characteristics, and the droplets do not vaporize downstream. Even if it adheres to the head of the side or each part in the apparatus, there is no problem because it is equivalent to the ink that is usually slightly adhered. In addition, when water is used as the humidifying liquid, a certain effect can be obtained. In the case of water, since the component does not contain glycerin, ethylene glycol, triethylene glycol or the like, the discharge characteristics are slightly different, but this can be dealt with by changing T2 and T3 of the drive pulse waveform shown in FIG. it can. Even an intermediate concentration composition of clear ink and water can be used.

1 is a front view schematically showing a printer which is an example of an inkjet image forming apparatus of the present invention. FIG. 2 is a block diagram illustrating an electrical system of the printer of FIG. 1. It is sectional drawing which shows the nozzle and its peripheral part of a humidification head. It is a schematic diagram showing the discharge state of the droplet for humidification by the humidification head, (a) shows the initial state where the printer has not received the print data, the face surface of each head is covered with a cap, (B) shows a state in which the printer has received print data, each head has moved to the print position, and the humidifying liquid droplets have started to be ejected from the humidification head. FIG. 4D shows a state in which the air flow containing the working liquid is diffused out of the apparatus, and FIG. 4D shows a state in which the humidity control and printing are completed and the initial state is restored. It is a flowchart which shows the drive of a humidification head. It is a flowchart which shows the procedure which sets it as the humidity exceeding minimum humidity required for printing. It is a flowchart which shows the procedure which humidifies only before printing. It is a top view which shows typically an example of the airflow by the image formed on a recording medium, and the droplet for humidification. It is nozzle position explanatory drawing of a recording head and a humidification head. FIG. 5 is a flowchart showing a procedure for driving a humidification head based on an ink discharge state of the recording head. It is a schematic diagram which shows until a droplet for humidification is discharged from the discharge port of a humidification head and evaporates, (a) shows immediately after the droplet for humidification was discharged from the discharge port, (b) was discharged FIG. 2C shows a state in which the humidifying droplets are evaporated during the flight, and FIG. 3C shows a state in which the surrounding humidifying droplets are increased without landing on the recording medium. It is a flowchart which shows the procedure which contributes to surrounding humidification, without making the droplet for humidification discharged from the humidification head land on a recording medium. (A) is explanatory drawing which shows an example of the pulse which drives a heat generating body in order to discharge an ink to a recording medium from the ink discharge port of 22 K of recording heads, (b) is discharged from the discharge port of a humidification head. FIG. 6 is an explanatory diagram showing an example of a pulse for driving a heating element to vaporize a humidifying droplet before landing on a recording medium.

Explanation of symbols

10 Printer 22H Humidification head 30 Humidity sensors 22K, 22C, 22M, 22Y Recording head 100 CPU

Claims (14)

In an inkjet image forming apparatus that forms an image by discharging ink to a recording medium from a plurality of ink discharge ports formed in a recording head.
An inkjet image forming apparatus comprising a humidifying head disposed in the vicinity of the recording head for discharging humidifying droplets to humidify the ink discharge port and its periphery. The inkjet type image forming apparatus according to claim 1, wherein the humidifying head has a plurality of ejection openings from which humidifying droplets are ejected and has the same structure as the recording head. The inkjet type image forming apparatus according to claim 1, wherein the humidifying head is disposed upstream of the recording head in a recording medium conveyance direction. The inkjet according to claim 1, 2 or 3, wherein the humidifying head discharges the humidifying droplets so that the discharged humidifying droplets are vaporized before landing on the recording medium. Method image forming apparatus. The inkjet image forming apparatus according to claim 1, further comprising a humidity sensor that detects humidity around the ink discharge port. 5. The apparatus according to claim 4, further comprising: a controller that controls the humidification head so that the humidity around the ink discharge port and the surrounding area is within a predetermined range based on the humidity detected by the humidity sensor. 2. An inkjet image forming apparatus according to 1. The ink jet type image forming apparatus according to claim 6, wherein the controller discharges a humidifying droplet from the humidifying head based on an ink discharging state of the recording head. The controller is configured to control the humidifying head to discharge a droplet for humidification before forming an image by discharging ink from the recording head to a recording medium. The inkjet image forming apparatus according to 6 or 7. The controller controls the humidification head to eject the humidifying droplet from the humidifying droplet ejection port corresponding to the ink ejection port from which the ink is ejected from the recording head according to an image to be formed. The inkjet image forming apparatus according to claim 6, wherein the image forming apparatus is an inkjet image forming apparatus. The controller performs control such that the humidifying liquid droplet ejection port corresponding to the ink ejection port that ejects ink from the recording head according to an image to be formed is not necessarily the number of nozzles coincident with the recording head. The inkjet image forming apparatus according to claim 9, further comprising a humidifying head nozzle number selecting unit that performs the operation. The controller is configured such that a droplet discharge port conditioned for the humidification corresponding to the ink discharge port that discharges ink from the recording head according to an image to be formed has a humidification head corresponding to the recording head. The inkjet image forming apparatus according to claim 9 or 10, further comprising a humidifying strength adjusting unit that selectively discharges the droplet discharge ports conditioned for humidification every other nozzle or every plurality of nozzles. The controller controls the humidification head to eject humidifying droplets only from the humidifying droplet ejection ports corresponding to the ink ejection ports that eject ink from the recording head in accordance with an image to be formed. The ink jet type image forming apparatus according to claim 6, wherein the image forming apparatus is an ink jet type image forming apparatus. 13. The controller according to claim 6, wherein the controller discharges the humidifying liquid droplets from the humidifying head so that the humidity around the ink discharge port and the periphery thereof is within a certain range. The inkjet image forming apparatus according to any one of the above. The inkjet type image formation according to any one of claims 1 to 13, wherein the humidifying droplet is a clear ink droplet or a water droplet having a component equivalent to an ink and not including a coloring material. apparatus.

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