JP7023615B2 - Inkjet recording method and inkjet recording device - Google Patents

Description

The present invention relates to an inkjet recording method and an inkjet recording device used thereof.

In recent years, inkjet recording devices have been increasingly used in offices and the like, taking advantage of their advantages of low power consumption, low cost, and space saving. As a scanning method of the recording head adopted in the inkjet recording apparatus, a serial method can be mentioned. In the serial method, an image is recorded by repeatedly moving the recording head in a direction (sub-scanning direction) orthogonal to the paper feed direction (main scanning direction). Since the serial type recording head is relatively small, the recording device main body can be miniaturized.

In recent years, in order to further improve the recording speed (throughput), a recording head that extends the arrangement width of the ejection port to the maximum width of the recording medium, that is, a recording device that employs a line head has been developed (Patent Document 1). .. Unlike the serial method, the line head method does not move the recording head, but only conveys the paper, which is advantageous for improving the recording speed.

However, with the improvement of the recording speed, there is a concern that stains (smear) may occur due to contact with the second recorded object before the recording unit of the first recorded object dries during continuous recording. .. In order to suppress the occurrence of such stains, for example, an ink capable of recording an image with improved fixability by controlling dynamic surface tension during a life time of 5,000 msec has been proposed (Patent Document 2). In addition, there is an increasing demand for the density (optical density) of recorded images in documents used in offices and the like. It can be said that being able to record images and characters with high optical density on plain paper is indispensable for inkjet recording devices for office use.

On the other hand, the line head has a big problem in the performance (recoverability) of recovering the ink ejection state to the normal state when non-ejection occurs as compared with the serial head. That is, in the line head, since the recording head is fixed, it is not possible to frequently perform a recovery operation such as preliminary ejection. As a recovery mechanism adopted for the line head, for example, a recovery mechanism has been proposed in which ink is forcibly discharged from a nozzle by pressurization or suction to recover the ink ejection state (Patent Document 3).

Japanese Unexamined Patent Publication No. 2010-143147 Japanese Unexamined Patent Publication No. 2008-001891 Japanese Unexamined Patent Publication No. 2007-152830

In order to record an image with excellent optical density, it is important to design an ink to efficiently leave the pigment on the recording medium. Specifically, there is a method of controlling the surface tension of the ink, slowing the penetration of the ink into the recording medium, and leaving a large amount of pigment in the vicinity of the surface of the recording medium. On the other hand, in order to improve the fixability of the image, it is important to control the surface tension of the ink and quickly permeate the liquid component of the ink applied to the recording medium into the recording medium. That is, when recording with an inkjet recording device using pigment ink, it can be said that there is a trade-off relationship between the optical density of the image and the fixability of the image.

Further, in the inkjet recording apparatus provided with the line head, it is necessary to accelerate the penetration of ink and further improve the fixing property of the image in order to realize higher speed recording. Therefore, when an inkjet recording device provided with a line head is used, the optical density of the recorded image is likely to be further reduced. It has been found that even with the ink proposed in Patent Document 2, it is difficult to realize the high fixing property required with the dramatic increase in recording speed in recent years.

In order to improve the optical density while maintaining the fixability when recording an image with an inkjet recording device equipped with a line head, it is necessary to design the ink with an emphasis on the color development of the image. However, if an ink designed with an emphasis on the color development of an image is used, the reliability of the inkjet recording system tends to decrease, such as a decrease in recoverability.

The recovery mechanism proposed in Patent Document 3 is a mechanism for filling a recording head with fresh ink while discharging bubbles from an ink flow path by pressurizing or sucking ink. However, when the excessively thickened ink sticks to the nozzle and remains, it is difficult to recover the ink efficiently. This is because simply increasing the flow rate of the ink by pressurization or the like only promotes the outflow of the ink from the nozzles in which the sticking has not occurred, and it is difficult to remove the ink from the nozzles in which the sticking has occurred. Further, in the recovery mechanism proposed in Patent Document 3, the structure of the device is complicated because it is necessary to provide two caps for each head, a sealing cap for suction operation and a cap serving as a tray for preliminary discharge. There is a problem such as becoming.

Therefore, an object of the present invention is that when a recording device provided with a line head is used, it is possible to record an image having excellent image fixing property and an excellent optical density, and the image is recoverable. Is to provide an excellent inkjet recording method. Another object of the present invention is to provide an inkjet recording apparatus used in the inkjet recording method.

The above object is achieved by the following invention. That is, according to the present invention, an inkjet recording device including a line head having a nozzle for ejecting water-based ink containing a pigment and a recovery mechanism for recovering the ejection state of the water-based ink from the nozzle is used. In an inkjet recording method in which the water-based ink is applied to a recording medium to record an image, the average particle size of the pigment is 80 nm or more, and the dynamic surface tension of the water-based ink in a life time of 10 msec is high. , 55 mN / m or less, the water-based ink further contains a surfactant, the surfactant is an acetylene glycol-based surfactant, and the recovery mechanism flows the water-based ink in the nozzle. The ink flow mechanism is included to heat the water-based ink in the nozzle to reduce the viscosity of the water-based ink, while operating the ink flow mechanism to flow the water-based ink in the nozzle from the nozzle. Provided is an inkjet recording method characterized by recovering the ejection state of the water-based ink.

According to the present invention, when a recording device provided with a line head is used, it is possible to record an image having excellent image fixing property, an image having excellent optical density, and excellent recovery property. It is possible to provide an inkjet recording method. Further, according to the present invention, it is possible to provide an inkjet recording apparatus used in the above-mentioned inkjet recording method.

It is an image diagram which records an image by a line head. It is a schematic diagram which shows an example of an inkjet recording apparatus. It is a figure which shows an example of a line head schematically, (a) is a perspective view, (b) is an exploded perspective view. It is a figure which shows an example of the wiping mechanism, (a) is a perspective view, (b) is a schematic view. It is a schematic diagram which shows an example of the supply mechanism which supplies ink to a line head. It is a block diagram which shows an example of the control structure of the inkjet recording apparatus shown in FIG. It is a schematic diagram which shows an example of a recording procedure. It is a schematic diagram which shows a part of an example of a recovery operation procedure. It is a schematic diagram which shows a part of an example of a recovery operation procedure.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions and exists in the ink, but for convenience, it is expressed as "containing a salt". Further, the water-based ink for inkjet may be simply referred to as "ink". The physical characteristic values are values at room temperature (25 ° C.) unless otherwise specified.

<Inkjet recording method>
In the inkjet recording method of the present invention, an ink jet recording device provided with a line head having a nozzle for ejecting ink containing a pigment and a nozzle recovery mechanism is used to apply ink to a recording medium and record an image. This is an inkjet recording method. The average particle size of the pigment is 80 nm or more, and the dynamic surface tension at the ink life time of 10 msec is 55 mN / m or less. Further, the recovery mechanism includes an ink flow mechanism for flowing ink, and is characterized in that the viscosity of the ink in the nozzle is reduced when the ink flow mechanism is operated.

As described above, in order to expand the use of inkjet recording devices in offices and the like, it is strongly required to improve the recording speed (throughput) that can compete with electrophotographic recording devices. In order to increase the recording speed when using the serial type recording head, it is necessary to increase the moving speed of the recording head in the sub-scanning direction and increase the number of ejections per nozzle (that is, increase the ejection frequency). There is. However, in order to increase the ejection frequency, there are various restrictions such as mechanical restrictions and the inability to supply ink (refill) from the ink accommodating portion to the ejection port in time. Therefore, there is a limit to improving the recording speed of an inkjet recording device equipped with a serial recording head.

In view of this situation, in recent years, a line-type recording head (hereinafter, also referred to as a "line head") in which an ejection port (nozzle) for ejecting ink is arranged over the entire width of the recording medium in the transport direction (maximum paper width). A recording device that employs (described) has been developed. Since the line head has a number of ejection ports corresponding to the maximum paper width of the recording medium, there is no need to move the recording head, and there is an advantage that high-speed recording is possible. That is, in the case of a recording device that employs a line head, it is not necessary to move the recording head in a direction (main scanning direction) orthogonal to the conveying direction (secondary scanning direction) of the recording medium. Therefore, the unit area of the recording medium passes directly under the recording head only once, that is, the image can be recorded in "1 pass", and the time required for recording can be shortened.

The present inventor has investigated further high-speed recording by combining an inkjet recording device that employs a line head with conventional ink for inkjet. As a result, it was found that the following new problems arise.

As described above, there is a trade-off relationship between the optical density and the fixability of an image recorded by using an inkjet recording device. And, with the further improvement of the recording speed, the above-mentioned trade-off relationship tends to become more remarkable. The fixability of an image has a correlation with the penetration behavior of the ink after being applied to the recording medium, and the image recorded with the ink that easily penetrates the recording medium tends to have improved fixability. When continuous recording is performed using ink having a slow penetration rate into the recording medium, stains called smears are likely to occur because the next recording material comes into contact with the ink applied to the first recording medium before it dries. .. Further, when recording an image on both sides of a recording medium (so-called double-sided printing), it is necessary to pass the recording medium immediately after recording through an inversion mechanism in the apparatus in order to reverse the front and back of the recording medium. For this reason, the recording unit may come into contact with a part of the reversing mechanism of the recording device before the ink dries, and the unfixed image may stain the back surface of the recording medium or another recording medium.

In order to achieve both the optical density and the fixability of the recorded image, it is necessary to design an ink having excellent color development while imparting permeability. In order to design a pigment ink having excellent color development property, there are methods such as imparting a function capable of improving color development property to the pigment (for example, increasing the average particle size of the pigment) and increasing the content of the pigment. .. However, if an ink whose color development property is improved by the above method or the like is used, the reliability of the inkjet recording apparatus tends to decrease. For example, when a pigment having a large average particle size is used, a problem due to sedimentation arises. When the ink locally thickened by the precipitation of the pigment particles is supplied to the nozzle of the recording head, the ejection property of the ink tends to be deteriorated. Further, even when the content of the pigment is increased, problems associated with the increase in the viscosity of the ink are likely to occur.

In particular, in the case of an inkjet recording device provided with a line head, since the recording head has a number of nozzles corresponding to the maximum width of the recording medium, the used nozzles and the unused nozzles may be biased depending on the recording pattern. For example, when the same pattern is continuously recorded in a state where ink in which pigment particles have settled or ink having a high pigment concentration is supplied into the nozzle, the nozzle corresponding to the unrecorded portion continues to be in a state of not ejecting ink. If the state in which the ink is not ejected continues, the liquid component of the ink evaporates from the ejection port of the nozzle, and the ink further thickens.

Inkjet recording devices are usually provided with a recovery mechanism for keeping the ink in the nozzles in a fresh state (a state in which sedimentation or evaporation has not occurred) and for restoring the ink ejection state from the nozzles to a normal state. For example, the recovery mechanism is activated to recover the ink ejection state from the nozzle when continuous recording is performed to some extent or when the ink is left in the ejection pause state for a long period of time. However, when the ink in the nozzle is extremely thickened or fixed, it is difficult to recover the ink ejection state by a normal recovery operation.

When continuously recording an image with the serial head, the thickened ink is discharged as a preliminary ejection at a position where the recording head does not face the recording medium while the recording head is repeatedly moved in the sub-scanning direction. Therefore, the ink in the nozzle does not become extremely thickened, and the recoverability does not decrease to a level that causes a problem in the line head. When an ink having a viscosity of 1 to 2 mPa · s without evaporation is applied to a general serial head, the viscosity is increased by about 10 mPa · s. At this level, preliminary ejection during the recording scan is sufficient to recover.

On the other hand, when the line head continuously records an image on a recording medium such as roll paper, the recording head is always in a position facing the recording medium. Therefore, when the thickening ink is ejected and ejected, unnecessary ink is applied to the recording medium, and the image quality is deteriorated. Therefore, it is difficult to perform such a recovery operation. When an ink having a viscosity of 1 to 2 mPa · s without evaporation is applied to a general line head, the viscosity far exceeds 10 mPa · s, and the viscosity is usually increased to about 20 mPa · s, which is localized. Can even have an extremely high viscosity of 100 mPa · s. At this level, it is difficult to recover by the conventional recovery operation.

The present inventor used an inkjet recording apparatus equipped with a line head to eject ink in which pigments had settled and inks having a large pigment content after being left for a long period of time, and continuously recorded the same pattern. Then, the nozzle check pattern was recorded in the middle of continuous recording. As a result, it was found that the unused nozzles did not eject ink or twisted. Further, although a recovery operation was carried out to eliminate the non-ejection and the ejection twist of the ink, it was not possible to recover all the nozzles in which the non-ejection and the ejection twist occurred. The present inventor speculates the mechanism by which this series of phenomena occurs as follows.

When the same pattern is continuously recorded, in a line head having a nozzle filled with ink, ink is regularly ejected from the nozzle used for recording, so that the ink in the nozzle is significantly thickened. There is no. On the other hand, in an unused nozzle that does not eject ink, the ink in the nozzle thickens as the liquid component evaporates. With ordinary ink, even if the ink is thickened in the nozzle, the thickened ink is discharged by operating the recovery mechanism provided in a general inkjet recording device, and the ink is discharged from the ink storage portion. By being supplied into the nozzle, the ejection state can be restored. However, in the case of an ink in which the pigment has settled after being left for a long period of time or an ink containing a high concentration of the pigment, the ink is significantly thickened in the nozzle and, in the worst case, sticks. If the recovery mechanism is activated many times when the ink is significantly thickened or stuck in the nozzle, the ink will flow preferentially in the nozzle that is easy to recover, and the ink will flow in the other nozzles. It becomes difficult to do. As a result, thickened or fixed ink remains in the unused nozzles, and it is considered that non-ejection and ejection wrinkles occur.

The present inventor relates to an inkjet recording method capable of suppressing a decrease in recoverability even when the same pattern is continuously recorded at high speed with a pigment ink capable of recording an image having excellent fixing property and high optical density. investigated. As a result, an inkjet recording device equipped with a recovery mechanism including an ink flow mechanism for flowing the ink in the nozzle is used, and excellent recovery is achieved by reducing the viscosity of the ink in the nozzle when the ink flow mechanism is operated. Was found to be exhibited.

As a means for reducing the viscosity of the ink in the nozzle, a means for mechanically causing a pressure change in the nozzle by driving and deforming the piezoelectric element when the ink flow mechanism is operated to stir the ink in the nozzle. Can be mentioned. Further, as another example of the means for reducing the viscosity of the ink in the nozzle, there is a means for applying thermal energy to the ink in the nozzle when the ink flow mechanism is operated to heat the ink in the nozzle.

As described above, the present inventor of the present invention can achieve both improvement of image fixability and optical density in the case of high-speed recording of an image by using an inkjet recording apparatus provided with a line head. I came to find a way. Further, regarding a new problem such as a decrease in recoverability caused when recording an image having a high optical density, the inkjet recording apparatus of the present invention provided with a means for reducing the viscosity of the ink in the nozzle when the ink flow mechanism is operated. I found that it could be solved by.

(Inkjet recording device)
The inkjet recording apparatus used in the inkjet recording method of the present invention includes a line head having a nozzle for ejecting ink containing a pigment and ink filled therein, and a recovery mechanism for recovering the ink ejection state from the nozzle. To prepare for. The average particle size of the pigment in the ink filled in the nozzle is 80 nm or more, and the dynamic surface tension at the ink life time of 10 msec is 55 mN / m or less. Further, the recovery mechanism includes an ink flow mechanism for flowing the ink in the nozzle. Further, a means for reducing the viscosity of the ink in the nozzle when the ink flow mechanism is operated is further provided. Hereinafter, the details of the inkjet recording apparatus of the present invention will be described with reference to the drawings.

FIG. 1 is an image diagram in which an image is recorded by a line head. Further, FIG. 2 is a schematic diagram showing an example of an inkjet recording device. In the recording device M4000 shown in FIG. 2, a line head (recording head H1000) is fixed to the recording device main body, and a method is adopted in which the recording medium 47 is conveyed in the direction of the arrow 45 for recording. The recording device M4000 includes, for example, a recording head H1000Y for yellow ink, a recording head H1000M for magenta ink, a recording head H1000C for cyan ink, and a recording head H1000Bk for black ink (FIG. 1).

The recording heads H1000Y to H1000R shown in FIG. 2 are fixed by a recording head holder 42 mounted on the recording device M4000. FIGS. 1 and 2 show configurations in which yellow, magenta, cyan, and black colors, as well as reaction solutions, are discharged from separate recording heads. Of course, an image may be recorded by ejecting a plurality of inks and reaction liquids from each of a plurality of ejection port rows provided on one recording element substrate.

The inkjet recording apparatus may be provided with means for applying a reaction liquid containing a component that agglomerates the coloring material in the ink to the recording medium. Examples of the means for applying the reaction solution to the recording medium include a means for applying the reaction solution to the recording medium by a coating method, a means for applying the reaction solution to the recording medium by a discharge method, and the like. In the means for applying the reaction solution to the recording medium by the coating method, for example, the reaction solution is applied to the recording medium using a coating member such as a conventionally known roller. Further, in the means for applying the reaction liquid to the recording medium by the discharge method, for example, the reaction liquid is applied to the recording medium by using a discharge device such as a line head for the reaction liquid (recording head H1000R) as shown in FIG. do. As shown in FIG. 1, when four recording heads are provided corresponding to four colors of ink, a means for applying the reaction solution to the recording medium can be separately provided. In the present invention, it is preferable to apply the reaction liquid to the recording medium by a method such as coating, and then eject the ink from the recording head to apply the ink to the recording medium.

The paper cassette 46 contains a recording medium 47 such as plain paper, and is detachably attached to the main body of the apparatus. The pickup roller 48 is a member that sends out one of the uppermost surfaces of the recording media 47 housed in the paper feed cassette 46. The transport roller 49 is a member that transports the recording medium 47 sent out from the pickup roller 48 to the transport path 50. Further, the transport roller 51 arranged on the outlet side of the transport path 50 is a member that transports the recording medium 47 toward the recording head H1000 while being mounted on the transport belt 44.

3A and 3B are views schematically showing an example of a line head, where FIG. 3A is a perspective view and FIG. 3B is an exploded perspective view. As shown in FIG. 3, the line head (recording head H1000) includes a recording element unit H1400 and an ink supply unit H1500 which is a liquid supply unit for supplying ink to the recording element unit H1400. The ink supply unit H1500 includes a connection portion H1700 formed with a connection port H1710 for connecting to the outside in order to supply ink from the outside such as a recording device to the ink chamber (not shown). Further, the recording element unit H1400 is composed of a recording element substrate H1100, a support substrate H1200, and a wiring member H1300.

The support substrate H1200 is a member that holds and fixes the recording element substrate H1100 and the wiring member H1300, and is formed with an ink supply hole H1210 that supplies ink supplied from the ink supply unit H1500 to the recording element substrate H1100. The plurality of recording element substrates H1100 are arranged and fixed on the main surface of the support substrate H1200 with predetermined position accuracy. Further, the plurality of recording element substrates H1100 are arranged in a staggered manner on the support substrate H1200 so that the ejection ports are continuously arranged between the adjacent recording element substrates H1100 along the direction of the ejection port row. .. In this way, by arranging the recording element board H1100 so as to overlap the discharge ports at the joints of the adjacent recording element boards H1100, it is possible to correct the influence on the image due to the misalignment of the recording element board, and the recording width is long. A full-line type recording head is realized.

The wiring member H1300 transmits an electric signal or electric power for driving a recording element provided on the recording element substrate H1100 from the outside (recording device) of the recording head H1000 to the recording element substrate H1100, so that the recording element substrate H1100 Is electrically connected to. As the wiring member H1300, a flexible printed wiring board such as a flexible wiring board is used. The flexible wiring member H1300 is bent so that the recording element substrate H1100 and the recording device can be easily electrically connected, and is fixed to the ink supply unit H1500.

Examples of the method of ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, any line head that ejects ink by any method can be suitably adopted.

The inkjet recording device may include means for controlling the temperature of the ink in the line head. The temperature of the ink in the line head can be controlled, for example, by means for controlling the temperature of the line head. Examples of the means for controlling the temperature of the line head include a heater for adjusting the ink temperature arranged so as to be in contact with the line head, a heater for ejecting ink, and the like. In order to control (heat or heat) the temperature of the ink by the heater for ejecting the ink, for example, a current that does not eject the ink may be repeatedly applied. The temperature of the ink can be read by, for example, a temperature sensor provided on the line head. The temperature of the line head and the ink is preferably adjusted to 40 to 70 ° C.

[Configuration of wiping mechanism]
The recovery mechanism of the inkjet recording device may include a wiping mechanism for recovering the sticking of ink at the ejection port of the line head and the wet state of the ejection port surface. 4A and 4B are views showing an example of a wiping mechanism, where FIG. 4A is a perspective view and FIG. 4B is a schematic view. As shown in FIG. 4, the wiper W1001 is held by the clip member W1002, and the clip member W1002 is held by the connecting member W1003. Further, the clip member W1002 is attached to the wipe base W1011 on which the slide rail W1006 can be moved. The wipe base W1011 can move on the slide rail W1006 by driving the timing belt W1007 through the connecting member W1003. The timing belt W1007 is supported by a driven pulley W1004 and a drive pulley W1005, and a shaft of a drive motor W1010 for driving the timing belt W1007 is connected to the drive pulley W1005. Further, in order to control the position of the wiper W1001 during the recovery operation, photosensors W1008 and W1009 are provided at both ends of the slide rail W1006. During the recovery operation by wiping, the wiper W1001 slides and moves by the slide rail W1006, so that the wiper W1001 bends and wipes the discharge port surface H1001 of the recording head H1000.

[Structure of ink flow mechanism]
Next, the ink flow mechanism for flowing the ink in the nozzle, which is included in the recovery mechanism of the inkjet recording apparatus of the present invention, will be described. FIG. 5 is a schematic diagram showing an example of a supply mechanism for supplying ink to the line head. As shown in FIG. 5, ink is supplied from the sub tank T2 to the line head H1000 by the pump P1. The ink overflowing from the line head H1000 is returned to the sub tank T2. The valve V1 is provided for switching the ink liquid chamber inside the line head to pressurize or release the pressure during the recovery operation. When the pressure is restored, the valve V1 is closed and the pump P1 pressurizes the ink to remove a part of the bubbles in the ink supply path and the ink flow path. The ink liquid level in the sub tank T2 is configured to maintain the head difference from the discharge port surface of the line head H1000 within a certain range, and maintains the negative pressure of the discharge port surface of the line head H1000 within an appropriate range. do. When the ink in the sub tank T2 is insufficient, the ink is sent from the main tank T1 to the sub tank T2 by the pump P2. The temperature of each tank and the ink contained in each tank depends on the environmental temperature at which the inkjet recording device is installed, but is preferably in the range of, for example, 15 to 45 ° C.

When the recovery mechanism for recovering the ink ejection state from the nozzle is composed only of the wiping mechanism as shown in FIG. 4, the ink in the nozzle of the line head cannot be flowed, so that excellent recovery is achieved. It is difficult to achieve. On the other hand, the recovery mechanism of the inkjet recording apparatus of the present invention includes an ink flow mechanism for flowing the ink in the nozzle. This ink flow mechanism is, for example, a mechanism capable of pressurizing or sucking ink in a nozzle to cause the ink in the nozzle to flow. Further, the inkjet recording apparatus of the present invention includes means for reducing the viscosity of the ink in the nozzle when the ink flow mechanism is operated. Therefore, if an inkjet recording device provided with a recovery mechanism including such an ink flow mechanism is used, excellent recovery is achieved even if an ink that is easily thickened or easily fixed and can record an image having excellent optical density is used. Can be achieved.

[Control configuration]
FIG. 6 is a block diagram showing an example of a control configuration of the inkjet recording apparatus shown in FIG. The controller 800 is a main control unit, and executes the procedure shown in FIGS. 7 to 9. The controller 800 has, for example, a CPU 801 in the form of a microcomputer, a ROM 803 that stores programs and other fixed data corresponding to the procedure, and a RAM 805 provided with an area for developing image data, a working area, and the like. Further, the controller 800 has a timer 807 and a counter 809 used to perform a recovery operation under predetermined conditions. The host device 810 is a source of image data, and may be a computer that generates or processes image data related to recording, or may be a reader unit for reading an image. Image data, other commands, status signals, etc. are transmitted to and received from the controller 800 via the interface (I / F) 812.

The operation unit 820 is composed of a switch that receives an instruction input by an operator, such as a power switch 822, a copy switch 824 for instructing the start of recording or copying, and a recovery switch 826 for instructing the activation of a recovery operation. To. The sensor group 830 is composed of a sensor group for detecting the state of the recording device, such as a pump position sensor 834 for detecting the position of the suction pump P3 (FIG. 5). The head driver 840 drives a heater 421 for ejecting ink in the recording head 1 and a heater (sub-heater 429) for adjusting the ink temperature. The transport motor 850 is a motor for transporting a recording medium, and the motor driver 852 drives the motor.

Next, a specific operation method of the ink flow mechanism will be described with reference to FIG. To pressurize and flow the ink in the nozzle, the valve V1 is closed, the valve V2 is opened, and the pump P1 pressurizes the ink. As a result, the thickened ink is discharged from the nozzle H100 of the line head H1000. On the other hand, in order to suck and flow the ink in the nozzle, the cap C10 is brought into contact with the discharge port surface H1001 with the valve V1 closed and the valve V2 open, and the ink is sucked by the pump P3. As a result, the thickened ink (waste ink 75) is discharged from the nozzle H100 of the line head H1000.

Further, both the valve V1 and the valve V2 are closed, and the cap C10 is brought into contact with the discharge port surface H1001. Then, when suction is performed by the pump P3, the inside of the nozzle H100 (inside the ink flow path of the line head) becomes a reduced pressure state. When the valve V2 is opened in this state, the ink in the sub tank T2 flows into the head flow path at once, and the thickened ink is discharged from the nozzle H100.

It is preferable that the ink flow mechanism is a mechanism for sucking and flowing the ink in the nozzle from the viewpoint of further improving the recoverability. A plurality of recording element substrates constituting the line head may be collectively capped and then sucked, or each recording element substrate may be capped and then sucked. Further, the tip of the tube connected to the pump P3 as shown in FIG. 5 may be swept by each nozzle for suction. The suction pressure, suction time, etc. are appropriately set according to the number of nozzles, the viscosity of the ink, and the like.

The inkjet recording device includes means for reducing the viscosity of the ink in the nozzle when the ink flow mechanism is activated. The means (method) for reducing the viscosity of the ink in the nozzle can be set according to the ejection mechanism of the line head. For example, a line head having a discharge mechanism using mechanical energy usually has a nozzle substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material arranged opposite to each other, and the pressure generating element. It has an ink that fills the surroundings. Then, by displacing the pressure generating element by the applied voltage, ink can be ejected from the nozzle. In order to reduce the viscosity of the ink in the nozzle of an inkjet recording device equipped with a line head having such a ejection mechanism, first, the pressure generating element is displaced to the extent that the ink is not ejected from the nozzle to increase the viscosity in the nozzle. Shake the ink. By this fluctuation, the thickened ink and the relatively low-viscosity ink existing upstream of the ink flow path are mixed and the ink is agitated, so that the viscosity of the ink in the nozzle can be lowered.

Next, the viscosity of the ink in the nozzle of an inkjet recording apparatus equipped with a thermal inkjet line head, which has an electric heat converter (recording element) for generating heat energy for causing film boiling in the ink, is reduced. The method will be described. In the case of an inkjet recording device equipped with a thermal inkjet type line head, first, heat energy is applied to such an extent that ink is not ejected from the nozzle, and the thickened ink in the nozzle is shaken. Then, by further applying heat energy to raise the temperature, the viscosity of the ink in the nozzle can be lowered. Usually, the amount of energy for rocking the ink is larger than the amount of energy for raising the temperature of the ink.

Of course, the line head having a discharge mechanism using mechanical energy may be provided with a means for heating the ink such as an external heater, and the viscosity of the ink may be lowered by heating. Further, the line head having a discharge mechanism using heat energy may be provided with a means for swinging the ink separately from the heater, and the viscosity of the ink may be lowered by utilizing the stirring by the swing. In the present invention, it is preferable to apply heat energy when the ink flow mechanism is operated to heat the ink in the nozzle to reduce the viscosity of the ink. As a means for generating heat energy and inputting it into ink, for example, an electric heat converter such as a heater for temperature adjustment arranged so as to be in contact with a recording head or a heater for ejecting ink can be mentioned. .. The timing of heating the ink in the nozzle will be described later.

(Recording method)
Next, a specific example of the recording procedure of the inkjet recording method of the present invention will be described. FIG. 7 is a schematic diagram showing an example of the recording procedure. When the recording command is detected in step S1, the recovery operation is executed in step S3 as necessary. If it is determined that the recovery operation is unnecessary, preliminary discharge is executed in step S5. This preliminary ejection is a step performed to eject thickened ink, foreign matter, etc. existing in the vicinity of the ejection port, and ink is ejected from each ejection port before the recording operation. The ink ejection as the preliminary ejection is performed based on the preliminary ejection data regardless of the recorded data. Immediately after the preliminary discharge is executed in step S5, the recording operation is executed in step S7. After the recording operation is completed, the recovery operation may be executed in step S9, if necessary.

Next, the recovery operation of the above-mentioned steps S3 and S9 will be described. FIG. 8 is a schematic diagram showing a part of an example of the recovery operation procedure. Here, a case where the ink in the nozzle is sucked and made to flow will be described as an example. First, in step S21 and step S27, it is determined whether or not suction or wiping of the discharge port surface is necessary. Then, the suction in step S21 is executed in the following cases. If the suction is not executed for a long time, the ink in the nozzle becomes thick and bubbles are generated in the ink. This may reduce the ink ejection property. In order to prevent such deterioration of ink ejection property, the ink in the nozzle is sucked under predetermined conditions. For example, a timer provided in the recording device is used to measure the elapsed time from the final suction operation, and control is performed so that suction is performed when the elapsed time exceeds the threshold value.

Further, when recording is performed for a long time without suction being executed, air bubbles may gradually adhere to the inside of the nozzle or the vicinity of the ejection port, and the ink ejection property may be deteriorated. In order to prevent such deterioration of ink ejection property, the ink in the nozzle is sucked under predetermined conditions. For example, a counter (suction counter) provided in the recording device is used to measure the cumulative number of discharges from the final suction operation, and control is performed so that suction is performed when the cumulative number of discharges exceeds the threshold value.

On the other hand, the wiping in step S27 is executed in the following cases. If recording is performed for a long time without wiping being executed, a large amount of ink droplets may adhere to the vicinity of the ejection port, and the ink ejection property may deteriorate. Wiping is performed under predetermined conditions in order to suppress such a decrease in ink ejection property. For example, a counter (wiping counter) provided in the recording device is used to measure the cumulative number of discharges from the final wiping operation, and when the cumulative number of discharges exceeds the threshold value, wiping is controlled. If it is determined in step S21 that suction is necessary, suction is executed in step S23. After the suction is completed, or when it is determined in step S27 that wiping is necessary, wiping is executed in step S25.

FIG. 9 is a schematic diagram showing a part of an example of the recovery operation procedure. First, prior to the recovery operation, the viscosity of the thickened ink in the nozzle is reduced in step S29. Here, a case where the ink in the nozzle is heated to reduce the viscosity of the ink will be described as an example. Even when the recovery operation (operation of the ink flow mechanism) is executed in a state where heating is continued, the effect (recoverability) of the present invention can be sufficiently obtained. However, if the temperature of the ink in the nozzle rises too much, the liquid component in the ink tends to evaporate from the ejection port, and the ink may stick to the vicinity of the ejection port, resulting in a decrease in recoverability. Therefore, it is preferable to finish the heating at an appropriate temperature in step S31 and to keep the ink in the nozzle at an appropriate temperature in step S33.

Examples of the means for keeping the ink in the nozzle warm include an electric heat converter such as a heater for temperature adjustment arranged so as to be in contact with the recording head and a heater for ejecting ink. When the electric heat converter is used to keep the ink in the nozzle warm, it is preferable to drive the electric heat converter to such an extent that the ink is not ejected from the ejection port. The heating temperature and the heat retaining temperature of the ink in the nozzle may be higher than the environmental temperature (25 ° C.), preferably 30 ° C. or higher and 70 ° C. or lower, and more preferably 40 ° C. or higher and 60 ° C. or lower. It is particularly preferable that the temperature is 45 ° C. or higher and 55 ° C. or lower.

Both the heating in step S29 and the heat retention in step S33 shown in FIG. 9 are included in the operation of heating the ink in the nozzle. While the heat retention of the ink in the nozzle is continued, the recovery operation of sucking and flowing the ink in the nozzle is executed in step S35. After the recovery operation in step S35 is completed, the heat insulation is finished in step S39, and the preliminary discharge is executed in step S41. The preliminary ejection in step S41 is executed to eject a mixture of inks existing in the vicinity of the ejection port in order to suppress color mixing when adjacent inks of different colors are mixed during the recovery operation of step S35. ..

As shown in FIG. 7, even when the operator determines that the recovery switch is necessary in step S11 due to an unexpected situation such as ink not being ejected normally, the recovery operation is executed in step S13. .. Further, when the recording operation or the recovery operation is not performed for a long period of time, it is preferable to cap the discharge port surface with a cap provided in the recording device in step S15. As a result, it is possible to prevent ink from sticking to the inside of the nozzle or the vicinity of the ejection port and foreign matter from adhering to the nozzle. When capping the ejection port surface by capping, it is preferable to perform wiping in step S17 prior to closing the cap in step S19 to remove ink droplets and the like adhering to the vicinity of the ejection port.

In the present invention, it is important that the viscosity of the ink in the nozzle is lowered when the ink flow mechanism is operated. That is, to explain the case where the viscosity of the ink is lowered by heating as an example, it is necessary to operate the ink flow mechanism in a state where heating or heat retention is continued. On the contrary, even if the ink is heated or kept warm, the recoverability is not improved when the ink flow mechanism is operated after the heating or heat keeping is stopped. This is because, for example, when the viscosity of the ink is extremely high due to the aggregation of the pigment, the viscosity rises sharply when the heating or heat retention is stopped, so that it cannot be recovered even if the ink flow mechanism is operated. Because.

Any recording medium may be used as a recording medium for recording an image by the inkjet recording method of the present invention. Among them, it is preferable to use a recording medium having no coated layer such as plain paper or uncoated paper, and a paper having permeability such as a recording medium having a coated layer such as glossy paper or art paper.

(ink)
Hereinafter, each component constituting the ink used in the inkjet recording method of the present invention, the physical characteristics of the ink, and the like will be described in detail. The ink used in the present invention does not have to be a so-called "curable ink". Therefore, the ink used in the present invention does not have to contain a compound such as a polymerizable monomer that can be polymerized by the addition of external energy.

The dynamic surface tension of the ink used in the inkjet recording method of the present invention at a life time of 10 msec is 55 mN / m or less, preferably 47 mN / m or less. As long as the dynamic surface tension of the ink in the life time of 10 msec is within the above range, the image fixability can be improved even when high-speed recording is performed by an inkjet recording device equipped with a line head. .. The dynamic surface tension of the ink at a life time of 10 msec is preferably 30 mN / m or more. When the dynamic surface tension of the ink at the life time of 10 msec is less than 30 mN / m, the fixability of the image is good, but it may not be possible to record an image having excellent optical density. The dynamic surface tension of the ink can be adjusted, for example, by appropriately setting the content of the surfactant described later.

The dynamic surface tension of the ink can be measured by the maximum foam pressure method. The maximum bubble pressure method is a method in which the maximum pressure required to release bubbles formed at the tip of a probe (thin tube) immersed in the liquid to be measured is measured, and the surface tension of the liquid is obtained from the measured maximum pressure. be. The lifetime is the maximum foam pressure (radius of curvature of the bubble and the probe) from the time when the bubble is formed at the tip of the probe and the surface of the new bubble is formed away from the tip in the maximum bubble pressure method. It is the time until the radius of the tip part becomes equal). The dynamic surface tension of the ink in the present specification is a value measured at 25 ° C.

[Pigment]
The ink used in the inkjet recording method of the present invention contains a pigment. Examples of the pigment include an inorganic pigment and an organic pigment. As the pigment, a resin dispersion type pigment using a resin as a dispersant, a self-dispersion type pigment having a hydrophilic group introduced on the particle surface of the pigment (self-dispersion pigment), and the like can be used. Pigments with different dispersion methods can also be used in combination. In the inkjet recording method of the present invention, it is preferable to use a dispersion method that does not use a resin dispersant, and it is more preferable to use a self-dispersing pigment.

As the resin dispersion type pigment, a resin dispersion type pigment using a polymer dispersant, a microcapsule type pigment in which the surface of the pigment particles is coated with a resin, and an organic group containing a polymer on the surface of the pigment particles are chemically used. There are resin-bound pigments that are specifically bonded. Pigments with different dispersion methods can also be used in combination. As the resin, it is preferable to use an acrylic resin having at least a unit having an anionic group such as (meth) acrylic acid and a unit having no anionic group such as a monomer having an aromatic ring or an aliphatic group.

Examples of the self-dispersion type pigment include those in which an anionic group is directly bonded to the particle surface of the pigment or via another atomic group. Examples of the anionic group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group. Examples of the counter ion of the anionic group include cations such as hydrogen atom, alkali metal, ammonium, and organic ammonium. Further, the other atomic group has a function of a spacer between the particle surface of the pigment and the ionic group, and the molecular weight is preferably 1,000 or less. Examples of other atomic groups include an alkylene group having about 1 to 6 carbon atoms; an arylene group such as a phenylene group and a naphthylene group; an ester group; an imino group; an amide group; a sulfonyl group; an ether group. Further, it may be a group in which these groups are combined.

The average particle size of the pigment is 80 nm or more. If the average particle size of the pigment is less than 80 nm, the optical density of the recorded image will be insufficient. The average particle size of the pigment is preferably 100 nm or more. When the average particle size of the pigment is 100 nm or more, an image having a higher optical density can be recorded. The average particle size of the pigment is preferably 1000 nm or less. When the average particle size of the pigment is more than 1000 nm, the precipitation of the pigment becomes remarkable, so that even if the treatment for reducing the viscosity of the ink in the nozzle is performed, the recoverability may be low. The average particle size of the pigment is preferably 200 nm or less, more preferably 150 nm or less.

As used herein, the term "average particle size" means a value measured using a dynamic light scattering type particle size distribution measuring device. In the examples described later, D ₅₀ was measured using the trade name "Nanotrack UPA150EX" (manufactured by Nikkiso Co., Ltd.) as a dynamic light scattering type particle size distribution measuring device. The 50% cumulative value D ₅₀ (nm) of the particle size distribution of the pigment is an average value (volume average particle size) of the particle size based on the volume.

The content (% by mass) of the pigment in the ink is preferably 0.10% by mass or more and 15.00% by mass or less, and 1.00% by mass or more and 10.00% by mass or less, based on the total mass of the ink. Is more preferable. Above all, it is particularly preferable that it is 2.00% by mass or more and 10.00% by mass or less. If the pigment content is less than 2.00% by mass, the optical density of the recorded image may decrease. On the other hand, if the pigment content is more than 10.00% by mass, the recoverability may decrease.

[Water-soluble organic solvent]
The ink contains water as an aqueous medium. As the water, it is preferable to use deionized water (ion-exchanged water). The content (% by mass) of water in the ink is preferably 50.00% by mass or more and 95.00% by mass or less, and 60.00% by mass or more and 95.00% by mass or less, based on the total mass of the ink. Is more preferable.

The ink can further contain a water-soluble organic solvent as an aqueous medium. As the water-soluble organic solvent, any of those generally used for inks applied to inkjet recording methods can be used. Specific examples of the water-soluble organic solvent include alkyl alcohols having 1 to 4 carbon atoms, amides, ketones or keto alcohols, ethers, polyalkylene glycols, glycols, and alkylene groups having 2 to 6 carbon atoms. Alkylene glycols, alkyl ether acetates, alkyl ethers of polyhydric alcohols, nitrogen-containing compounds and the like can be mentioned. These water-soluble organic solvents can be used alone or in combination of two or more. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.00% by mass or more and 50.00% by mass or less, and 5.00% by mass or more and 30.00% by mass, based on the total mass of the ink. It is more preferably mass% or less.

As the water-soluble organic solvent, it is preferable to use a solvent having a surface tension of 40 mN / m or less at 25 ° C. By using a water-soluble organic solvent having a surface tension of 40 mN / m or less at 25 ° C., the permeability of the ink into the recording medium is enhanced and the fixability of the image is improved. The content of the water-soluble organic solvent having a surface tension of 40 mN / m or less is preferably adjusted appropriately so that the dynamic surface tension of the ink with a life time of 10 msec is 55 mN / m or less. Specifically, the content (mass%) of the water-soluble organic solvent having a surface tension of 40 mN / m or less in the ink is 0.10% by mass or more and 10.00% by mass or less based on the total mass of the ink. Is preferable.

Specific examples of the water-soluble organic solvent having a surface tension of 40 mN / m or less at 25 ° C. (the value of the surface tension in parentheses (unit: mN / m)) include ethanol (21.3) and isopropanol (21.0). ) And other primary alcohols; 1,2-propanediol (35.9), 2-methyl-1,3-propanediol (39.1), 3-methyl-1,5-pentanediol (38.1). , 1,2-Hexanediol (27.6) and other glycols; ethylene glycol-mono-ethyl ether (28.2), diethylene glycol-mono-n-butyl ether (29.4), triethylene glycol-mono-n -Glycol ethers such as butyl ether (31.1) can be mentioned. Of these, glycol ethers and 1,2-alkanediol are preferable. These water-soluble organic solvents can be used alone or in combination of two or more.

[Surfactant]
The ink can contain a surfactant. The content (% by mass) of the surfactant in the ink is preferably 0.01% by mass or more and 5.00% by mass or less, and 0.25% by mass or more and 3.00% by mass, based on the total mass of the ink. It is more preferably% or less. The type of surfactant is not particularly limited, but the dynamic surface tension of the ink with a life time of 10 msec can be reduced to 55 mN / m or less by using it in combination with other components such as a water-soluble organic solvent as needed. It is preferable to use what is possible. Specific examples of surfactants include hydrocarbon-based surfactants such as ethylene oxide adducts of acetylene glycol, polyethylene glycol alkyl ethers, and polyoxyethylene polyoxypropylene block polymers; and fluorine-based surfactants such as perfluoroalkyl ethylene oxide adducts. Surfactant; A silicone-based surfactant such as a polyether-modified siloxane compound can be mentioned. Above all, it is preferable to use a hydrocarbon-based surfactant. These surfactants can be used alone or in combination of two or more. Of these, acetylene glycol-based surfactants are preferable. By containing an appropriate amount of the acetylene glycol-based surfactant in the ink, the dynamic surface tension of the ink with a life time of 10 msec can be easily adjusted within a desired range.

[Other ingredients]
In addition to the above components, the ink may contain a water-soluble organic compound that is solid at room temperature, such as urea, a urea derivative, trimethylolpropane, and trimethylolethane. In addition, various additives such as resins, pH adjusters, rust inhibitors, preservatives, fungicides, antioxidants, and antioxidants are used to obtain inks with desired physical properties as needed. It may be contained. When the resin is contained in the ink for various purposes such as a dispersant, it is preferable to use one whose acid value is not too high. Specifically, it is preferably 190 mgKOH / g or less, and more preferably 150 mgKOH / g or less.

[Physical characteristics of ink]
The viscosity of the ink at 25 ° C. is preferably 1.0 mPa · s or more and 5.0 mPa · s or less, and more preferably 1.0 mPa · s or more and 3.0 mPa · s or less. Further, the surface tension of the ink at 25 ° C. is preferably 28 mN / m or more and 45 mN / m or less. The pH of the ink at 25 ° C. is preferably 5 or more and 9 or less.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. Unless otherwise specified, those described as "parts" and "%" regarding the amount of components are based on mass.

<Preparation of pigment dispersion>
(Pigment dispersion liquid 1)
The solution obtained by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water was cooled to 5 ° C., and 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added. An aqueous sodium nitrite solution obtained by dissolving 1.8 g of sodium nitrite in 9 g of water at 5 ° C. was added while keeping the temperature of the solution at 10 ° C. or lower. After stirring for 15 minutes, 6 g of carbon black (average particle size 100 nm) having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added under stirring. The slurry obtained by further stirring for 15 minutes was filtered through a filter paper (trade name “Standard Filter Paper No. 2”, manufactured by Advantech). After thoroughly washing the filtrate with water, it was dried in an oven at 110 ° C. to obtain self-dispersed carbon black. Water was added to the obtained self-dispersed carbon black so that the content of the self-dispersed carbon black (pigment) was 10.0%. As a result, a pigment dispersion liquid in which self-dispersed carbon black in which _two -C ₆ H _3- (COONa) groups were introduced on the particle surface of carbon black was dispersed in water was obtained. Next, the sodium ion is replaced with potassium ion by an ion exchange method, and the self-dispersed carbon black in which _two -C ₆ H _3- (COOK) groups are bonded to the particle surface of the carbon black is dispersed in water. Dispersion liquid 1 was obtained. The average particle size of the pigment (carbon black) in the obtained pigment dispersion 1 was 100 nm.

(Pigment dispersion liquid 2)
500.0 g of ion-exchanged water and 15.0 g of carbon black were mixed and stirred at 15,000 rpm for 30 minutes to pre-wet the carbon black (pigment). After adding 4,485 g of ion-exchanged water, the mixture was dispersed with a high-pressure homogenizer to obtain a dispersion liquid. The average particle size of the pigment in the obtained dispersion was 100 nm. The obtained dispersion was transferred to a high-pressure container, pressurized at a pressure of 3.0 MPa, and then ozone water having an ozone concentration of 100 ppm was introduced to ozone-oxidize the pigment. After adjusting the pH to 10.0 using potassium hydroxide, the pigment content was adjusted so that the self-dispersed carbon black in which the -COOK group was bonded to the particle surface of the carbon black was dispersed in water. Pigment dispersion 2 was obtained. The content of the pigment in the obtained pigment dispersion 2 was 30.0%, and the average particle size of the pigment was 100 nm.

(Pigment dispersion liquid 3)
A water-soluble resin (resin dispersant) was dissolved in ion-exchanged water using sodium hydroxide having a neutralization equivalent of 1, to prepare an aqueous solution of the resin dispersant having a water-soluble resin content of 20.0%. As the water-soluble resin, a styrene / acrylic acid copolymer (styrene: acrylic acid (molar ratio) = 33:67, weight average molecular weight 10,000, acid value 200 mgKOH / g) was used. 15.0 parts of a pigment (carbon black), 30.0 parts of an aqueous solution of a resin dispersant, and 55.0 parts of water were placed in a sand grinder and dispersed for 1 hour. After centrifuging to remove coarse particles, the mixture was pressure-filtered with a microfilter (manufactured by Fujifilm) having a pore size of 3.0 μm, and an appropriate amount of ion-exchanged water was added to obtain a pigment dispersion liquid 3. The content of the pigment in the obtained pigment dispersion 3 was 15.0%, the content of the water-soluble resin (resin dispersant) was 6.0%, and the average particle size of the pigment was 100 nm. ..

(Pigment dispersion liquid 4)
500 g of carbon black, 45 g of aminophenyl (2-sulfoethyl) sulfone, and 900 g of distilled water were placed in a reactor and stirred at a temperature of 55 ° C. and a rotation speed of 300 rpm for 20 minutes. The specific surface area of carbon black was 220 m ² / g, and the DBP oil absorption was 112 mL / 100 g. After dropping 40 g of a 25% sodium nitrite aqueous solution for 15 minutes, 50 g of distilled water was added and reacted at 60 ° C. for 2 hours to obtain a reaction product. The obtained reaction product was taken out while diluting with distilled water, and the solid content was adjusted to 15.0%. Impurities were removed by centrifugation and purification to obtain a dispersion liquid (1). The carbon black in the dispersion liquid (1) had a functional group of aminophenyl (2-sulfoethyl) sulfone bonded to the surface of the particles. The number of moles of the functional group bonded to the surface of the carbon black particles in the dispersion liquid (1) was determined as follows. First, the sodium ion concentration of the dispersion liquid (1) was measured using a probe-type sodium electrode. Then, it was converted into the sodium ion concentration per unit mass of carbon black, and the number of moles of the functional group bonded to carbon black was determined.

Then, the pentaethylenehexamine solution was kept at room temperature with vigorous stirring, and the dispersion liquid (1) was added dropwise over 1 hour to obtain a mixture. At this time, the amount of pentaethylenehexamine was 1 to 10 mol times the amount of sodium ions calculated from the previously measured sodium ion concentration, and the amount of the solution was the same as that of the dispersion liquid (1). The obtained mixture was stirred for 18 to 48 hours and then purified to obtain a dispersion liquid (2) having a solid content of 10.0%. The carbon black in the dispersion liquid (2) had pentaethylenehexamine bonded to the particle surface.

After mixing 190 g of styrene-acrylic acid resin and 1,800 g of distilled water, potassium hydroxide necessary for neutralizing the resin was added and stirred to dissolve the resin to obtain a styrene-acrylic acid resin aqueous solution. The styrene-acrylic acid resin had a weight average molecular weight of 8,000, an acid value of 140 mgKOH / g, and a polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of 1.5. 500 g of the dispersion liquid (2) was added dropwise to the obtained styrene-acrylic acid resin aqueous solution with stirring to obtain a mixture. The obtained mixture was transferred to an evaporating dish, heated at 150 ° C. for 15 hours to dry, and then cooled to room temperature to obtain a dried product.

The obtained dried product was added to distilled water whose pH was adjusted to 9.0 using potassium hydroxide, dispersed using a disperser, and then a 1.0 mol / L potassium hydroxide aqueous solution was added under stirring. The pH was adjusted to 10-11. Impurities and coarse particles were removed by desalting and refining treatment to obtain a pigment dispersion liquid 4 in which the resin-bonded self-dispersed carbon black was dispersed in water. The content of the pigment in the obtained pigment dispersion 4 was 10.0%, the pH was 10.1, and the average particle size of the pigment was 100 nm.

(Pigment dispersion liquid 5)
A commercially available cyan pigment dispersion containing a self-dispersing pigment (trade name "CAB-O-JET450C", manufactured by Cabot, pigment content 15.0%, average particle diameter of pigment 115 nm) was used as the pigment dispersion 5.

(Pigment dispersion liquid 6)
A commercially available magenta pigment dispersion containing a self-dispersing pigment (trade name "CAB-O-JET465M", manufactured by Cabot, pigment content 15.0%, average particle diameter of pigment 100 nm) was used as the pigment dispersion 6.

(Pigment dispersion liquid 7)
A commercially available yellow pigment dispersion containing a self-dispersing pigment (trade name "CAB-O-JET470Y", manufactured by Cabot, pigment content 15.0%, average particle diameter of pigment 170 nm) was used as the pigment dispersion 7.

(Pigment dispersion liquid 8)
A pigment dispersion 8 was obtained in the same manner as in the case of the pigment dispersion 1 described above, except that carbon black having an average particle diameter of 80 nm was used. The average particle size of the pigment in the obtained pigment dispersion 8 was 80 nm.

(Pigment dispersion liquid 9)
A pigment dispersion 9 was obtained in the same manner as in the case of the pigment dispersion 1 described above, except that carbon black having an average particle diameter of 99 nm was used. The average particle size of the pigment in the obtained pigment dispersion 9 was 99 nm.

(Pigment dispersion liquid 10)
A pigment dispersion 10 was obtained in the same manner as in the case of the pigment dispersion 1 described above, except that carbon black having an average particle diameter of 130 nm was used. The average particle size of the pigment in the obtained pigment dispersion 10 was 130 nm.

(Pigment dispersion liquid 11)
A pigment dispersion 11 was obtained in the same manner as in the case of the pigment dispersion 1 described above, except that carbon black having an average particle diameter of 70 nm was used. The average particle size of the pigment in the obtained pigment dispersion 11 was 70 nm.

<Measuring method of average particle size of pigment>
The value of D ₅₀ measured using a dynamic light scattering type particle size distribution measuring device (trade name "Nanotrack UPA150EX", manufactured by Nikkiso Co., Ltd.) was taken as the average particle size of the pigment. The 50% cumulative value D ₅₀ (nm) of the particle size distribution of the pigment corresponds to the average value of the volume-based particle size (that is, the volume average particle size).

<Ink preparation>
Each component (unit:%) shown in the upper part of Tables 1-1 to 1-3 is mixed and sufficiently stirred, and then pressure-filtered with a microfilter (manufactured by FUJIFILM) having a pore size of 3.0 μm, and ink 1 ~ 27 was prepared. In Tables 1-1 to 1-3, the numerical values attached to the water-soluble organic solvent are the surface tension (unit: mN / m) of the water-soluble organic solvent in an environment of a temperature of 25 ° C. and a humidity of 50%. The surface tension of the water-soluble organic solvent was measured using an automatic surface tension meter (trade name "CBVP-Z type", manufactured by Kyowa Interface Science).

The details of each component in Tables 1-1 to 1-3 are shown below.
-Acetyleneol E100: Acetylene glycol-based surfactant (manufactured by Kawaken Fine Chemicals)
-Acetyleneol E60: Acetylene glycol-based surfactant (manufactured by Kawaken Fine Chemicals)
-NIKKOL BL-9EX: Polyoxyethylene alkyl ether (manufactured by Nikko Chemicals)

The average particle size of the pigment in each of the prepared inks was measured by the method described above. In addition, the dynamic surface tension (γ10 m) at the life time of 10 msec of each of the prepared inks was measured. The dynamic surface tension of the ink was measured using a device (trade name "Bubble Pressure Tensiometer BP2", manufactured by KRUSS) for measuring the dynamic surface tension by the maximum foam pressure method. The average particle size of the pigment of each ink and the dynamic surface tension (γ10 m) at 10 msec are shown in the lower part of Tables 1-1 to 1-3.

<Evaluation>
An inkjet recording apparatus having the configuration shown in FIG. 2 and having the wiping mechanism shown in FIG. 4 and the supply mechanism shown in FIG. 5 was prepared. In this embodiment, 1/600 inch × 1/600 inch is defined as 1 pixel, and the recording duty of an image in which the amount of ink applied per pixel is 18 ng is defined as 100%. Table 2 shows the evaluation results of each item. In the evaluation criteria shown below, (“AA”,) “A” and “B” were defined as acceptable levels, and “C” was defined as an unacceptable level.

(Optical density)
Using the above-mentioned inkjet recording device, a solid image (recording duty 100%) of 2 cm × 2 cm was recorded on the following three recording media (plain paper) with each of the prepared inks to prepare a recorded material.
・ Product name "PB PAPER" (manufactured by Canon)
-Product name "BUSINESS MULTIPURPOSE4200 PAPER (made by Xerox)
-Product name "Bright White Inkjet Paper" (manufactured by Hewlett-Packard)

At the time of recording, the recovery operation was carried out by the method shown below. That is, prior to recording the image, the valve V1 shown in FIG. 5 was closed, the valve V2 was opened, and the discharge port surface H1001 was capped and sucked by the pump P3. At the time of suction, the ink in the nozzle was heated by the ink ejection heater to the extent that the ink was not ejected immediately before the recovery operation was executed according to the procedure shown in FIG. After that, the recovery operation was executed with the ink in the nozzle kept warm by the sub-heater provided in the recording head. Then, immediately after the end of the recovery operation, the heat retention of the ink in the nozzle was completed. After performing this series of operations, an image (nozzle check pattern) was recorded, and after confirming that there were no non-ejection nozzles, the above-mentioned solid image was recorded to obtain a recorded object.

After leaving the obtained recorded material for one day, the optical density of the solid image was measured. The optical density of the solid image recorded using the ink whose pigment type is carbon black was measured using a reflection densitometer (trade name "Macbeth RD-918", manufactured by Macbeth). For the optical density of solid images recorded using ink whose pigment type is an organic pigment, a spectrophotometer (trade name "Spectrolino", manufactured by Gretag Macbeth) was used, and the light source: D50, the field of view: 2 °. It was measured under the condition of. From the measured optical density values, the optical concentrations were evaluated according to the evaluation criteria shown below. When recording with an ink whose pigment type is an organic pigment, the evaluation was made based on the values in parentheses.
A: The average of the three papers was 1.1 or more (0.8 or more).
B: The average of the three papers was 0.9 or more and less than 1.1 (0.7 or more and less than 0.8).
C: The average of 3 papers was less than 0.9 (less than 0.7).

(Fixability)
Using the above-mentioned inkjet recording device, a solid image (recording duty 100%) of 15 cm × 15 cm is continuously recorded on three recording media (PPC paper) shown below with each ink prepared, and a recorded matter is recorded. Made. At the time of recording, a paper ejection form was adopted in which the second recorded material was loaded on the first recorded material.
・ Product name "Hammermill Tidal MP" (manufactured by International Paper)
-Product name "STEINBEIS Classic White" (manufactured by Steinbeis)
-Product name "Bright White Inkjet Paper" (manufactured by Hewlett-Packard)

At the time of recording, a recovery operation was carried out under the same conditions as the above-mentioned evaluation of "optical density". The prepared recorded material was visually confirmed, and the fixability of the image was evaluated according to the evaluation criteria shown below.
AA: The back of the second recording was not contaminated.
A: The back side of the second recorded material was contaminated with one paper.
B: The back side of the second recorded material was contaminated with two papers.
C: The back side of the second recorded material was contaminated with three papers.

(Recoverability)
The prepared ink was left at room temperature and evaporated by 20% by mass, and the evaluation ink obtained was filled in the nozzle of the line head. Using this inkjet recording device, a pattern drawn with a ruled line having a width of 1 dot and a length of 20 cm was continuously recorded on 600 recording media in parallel with the transport direction of the recording medium. No recovery action (pressurization, suction, wiping) was performed during continuous recording. After continuous recording, a solid image with a recording duty of 10% was recorded to confirm the presence or absence of non-ejection nozzles. When a non-ejection nozzle was generated, the recovery operation and the viscosity reducing step shown below were executed. Table 2 shows the combination of the recovery operation and the low viscosity step. Then, after the recovery operation was completed, a solid image was recorded again to confirm the presence or absence of a non-ejection nozzle.

[Recovery operation]
i) The valve V1 shown in FIG. 5 is closed, the valve V2 is opened, and the discharge port surface H1001 is capped and sucked by the pump P3.
ii) Without the cap C10 shown in FIG. 5, the tip of the tube connected to the pump P3 is brought into contact with the discharge port surface H1001, and all the nozzles are swept and sucked.
iii) Both the valve V1 and the valve V2 shown in FIG. 5 are closed, and the discharge port surface H1001 is capped and sucked by the pump P3. The valve V2 is opened by setting the inside of the nozzle H100 to a reduced pressure state.
iv) The valve V1 shown in FIG. 5 is closed, the valve V2 is opened, and the pump P1 pressurizes.
v) The discharge port surface H1001 is wiped by the wiper W1001 shown in FIG. However, the recovery operation of flowing the ink in the nozzle is not executed.
vi) Neither wiping nor the recovery operation of flowing the ink in the nozzle is executed, and 16 drops are pre-discharged for each recording.

[Ink low viscosity process]
a) According to the procedure shown in FIG. 9, immediately before the recovery operation is executed, the ink in the nozzle is heated to the extent that the ink is not ejected by the ink ejection heater. After that, the recovery operation was executed with the ink in the nozzle kept warm by the sub-heater provided in the recording head. Then, immediately after the end of the recovery operation, the heat retention of the ink in the nozzle was completed.
b) According to the procedure shown in FIG. 9, immediately before the recovery operation was executed, the ink in the nozzle was shaken by generating a pressure to the extent that the ink did not eject. The pressure was generated by using a line head equipped with a piezoelectric material and displacement the piezoelectric material by an applied voltage. After shaking the ink in the nozzle, a recovery operation was performed. Then, by stopping the application of the voltage to the piezoelectric material immediately after the end of the recovery operation, the swing was stopped.
c) In the procedure shown in FIG. 9, the recovery operation was executed without executing the heat retention of S33.
d) In the procedure shown in FIG. 9, the recovery operation was executed without executing the heating of S29 and the heat retention of S33.

For the evaluation of the recoverability of Reference Examples 1 to 3, the same inkjet recording device is used except that the line head is replaced with a serial head (inkjet recording device, the same as the product name "PIXUS iP3100"). And evaluation ink was used. Then, under the condition that a ruled line having a width of 1 dot and a length of 20 cm is ejected from one nozzle in a direction orthogonal to the transport direction of the recording medium, 600 lines are continuously recorded by reciprocating scanning of the recording head. did. At the time of this recording, a preliminary discharge of 16 drops was performed every time one ruled line was recorded on both sides of the recording medium and at a position not facing the recording medium. Other than that, the recoverability was evaluated in the same manner as in the case of the line head.

The above operation was repeated until all nozzles recovered, and the recoverability was evaluated according to the evaluation criteria shown below.
A: All nozzles recovered within 5 recovery operations.
B: All nozzles recovered within 6 to 10 recovery operations.
C: After 10 recovery operations, there was a non-ejection nozzle.

Claims (15)

An inkjet recording apparatus provided with a line head having a nozzle for ejecting water-based ink containing a pigment and a recovery mechanism for recovering the ejection state of the water-based ink from the nozzle is used to record the water-based ink. It is an inkjet recording method that attaches to and records an image.
The average particle size of the pigment is 80 nm or more, and the pigment has an average particle size of 80 nm or more.
The dynamic surface tension of the water-based ink at a life time of 10 msec is 55 mN / m or less.
The water-based ink further contains a surfactant,
The surfactant is an acetylene glycol-based surfactant, and the surfactant is
The recovery mechanism includes an ink flow mechanism for flowing the water-based ink in the nozzle.
While heating the water-based ink in the nozzle to reduce the viscosity of the water-based ink, the ink flow mechanism is operated to flow the water-based ink in the nozzle, and the water-based ink is ejected from the nozzle. An inkjet recording method characterized by recovering. The inkjet recording method according to claim 1, wherein the method of ejecting the water-based ink from the nozzle is a method of applying heat energy to the water-based ink. The inkjet recording method according to claim 1 or 2, wherein the ink flow mechanism is a mechanism for pressurizing and flowing the water-based ink in the nozzle. The inkjet recording method according to claim 1 or 2, wherein the ink flow mechanism is a mechanism for sucking and flowing the water-based ink in the nozzle. The fourth aspect of claim 4 is that after depressurizing the inside of the nozzle with the ink supply path communicating with the nozzle of the line head blocked, the ink supply path is opened to suck the water-based ink in the nozzle. The inkjet recording method described. The inkjet recording method according to any one of claims 1 to 5, wherein the recovery mechanism further includes a wiping mechanism for wiping the discharge port surface of the line head. The inkjet recording method according to any one of claims 1 to 6, further comprising a step of performing preliminary ejection to eject the water-based ink from the nozzle based on preliminary ejection data. The inkjet recording method according to any one of claims 1 to 7, wherein the average particle size of the pigment is 200 nm or less. The inkjet recording method according to any one of claims 1 to 8, wherein the dynamic surface tension of the water-based ink at a life time of 10 msec is 47 mN / m or less. The inkjet recording method according to any one of claims 1 to 9, wherein the dynamic surface tension of the water-based ink at a life time of 10 msec is 30 mN / m or more. The invention according to any one of claims 1 to 10, wherein the content (% by mass) of the pigment in the water-based ink is 2.00% by mass or more and 10.00% by mass or less based on the total mass of the ink. Inkjet recording method. The item according to any one of claims 1 to 11, wherein the content (mass%) of the surfactant in the water-based ink is 0.25% by mass or more and 3.00% by mass or less based on the total mass of the ink. The inkjet recording method described. The inkjet recording method according to any one of claims 1 to 12 , wherein the water-based ink further contains a water-soluble organic solvent having a surface tension of 40 mN / m or less. The inkjet recording method according to claim 13 , wherein the water-soluble organic solvent is at least one selected from the group consisting of glycol ethers and 1,2-alkanediols. A claim comprising a water-based ink containing a pigment, a line head having a nozzle for ejecting the water-based ink filled therein, and a recovery mechanism for recovering the ejection state of the water-based ink from the nozzle. An inkjet recording apparatus used in the inkjet recording method according to any one of 1 to 14 .
The average particle size of the pigment is 80 nm or more, and the pigment has an average particle size of 80 nm or more.
The dynamic surface tension of the water-based ink at a life time of 10 msec is 55 mN / m or less.
The water-based ink further contains a surfactant,
The surfactant is an acetylene glycol-based surfactant, and the surfactant is
The recovery mechanism includes an ink flow mechanism for flowing the water-based ink in the nozzle.
While heating the water-based ink in the nozzle to reduce the viscosity of the water-based ink, the ink flow mechanism is operated to flow the water-based ink in the nozzle, and the water-based ink is ejected from the nozzle. An inkjet recording apparatus comprising further means for recovering the ink jet.

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