Image forming apparatus and image forming method

Abstract

To provide an image formation apparatus which can efficiently remove air bubbles in a liquid discharge head and a flow channel communicating with the liquid discharge head, stabilize the discharge performance and output a high-definition image.SOLUTION: An image formation apparatus comprises: ink which contains water, a pigment and a siloxane compound; a liquid discharge head 108 which discharges the ink; a main tank 101 which stores the ink; and a sub tank 120 which is connected with the main tank and the liquid discharge head. The sub tank comprises: a positive pressure sub tank 103 which supplies the ink to the liquid discharge head; and a negative pressure sub tank 102 which recovers the ink from the liquid discharge head. The difference between the pressure of gas in the positive pressure sub tank and the pressure of gas in the negative pressure sub tank is between 2 kPa and 30 kPa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and an image forming method. [Background technology]

[0002] For example, ink ejection type recording devices having a liquid ejection head are known as image forming devices such as printers, facsimiles, copiers, plotters, and combination machines thereof. A known liquid ejection head is a circulation type liquid ejection head that has a supply flow path to an individual liquid chamber that communicates with a nozzle, a discharge flow path that communicates with the individual liquid chamber, a liquid supply port that communicates with the supply flow path, and a liquid discharge port that communicates with the discharge flow path.

[0003] A known configuration of a circulation-type liquid ejection head is one that has liquid tanks on the supply side and discharge side (recovery side), and sends liquid from the positive pressure side to the negative pressure side using the pressure difference between the positive and negative air in the two liquid tanks, and also sends liquid from the negative pressure side to the positive pressure side using a pump, thereby circulating the liquid between the liquid tanks and the head that ejects the liquid (see, for example, Patent Document 1). This type of circulation mechanism can prevent the nozzles from drying out and the settling of high-density pigments, etc.

[0004] In conventional devices, when ink is circulated at high speed to increase productivity, the ink passing through the openings in the nozzles of the head entrains tiny air bubbles inside the head, which then travel down the flow path and accumulate in the ink tank and head. This causes the problem of unstable ink ejection. When ink ejection becomes unstable, the ink does not land in the intended position, resulting in a decrease in image quality.

[0005] In response to this, Patent Documents 2 and 3 disclose a technology for stabilizing the ejection properties by adding a silicone-based compound with excellent defoaming and foam-breaking properties to the inkjet ink in order to remove bubbles inside the head. Summary of the Invention [Problem to be solved by the invention]

[0006] However, due to the molecular structure of silicone-based compounds intended to defoam, static surface tension tends to decrease, destabilizing meniscus formation in the nozzle and making air bubbles more likely to be entrained. Furthermore, defoaming agents alone cannot remove air bubbles that have infiltrated the flow path from the liquid ejection head. Therefore, a technology that can achieve both air bubble removal and ink ejection stability is desired.

[0007] Therefore, the present invention aims to provide an image forming device that can efficiently remove air bubbles from a liquid ejection head and a flow path connected to the liquid ejection head, stabilize ejection performance, and output high-resolution images. [Means for solving the problem]

[0008] In order to solve the above problems, the image forming apparatus of the present invention is an image forming apparatus comprising an ink containing water, a pigment, and a siloxane compound, a liquid ejection head that ejects the ink, a main tank that stores the ink, and a sub-tank that is connected to the main tank and the liquid ejection head, wherein the sub-tank has a positive pressure sub-tank that supplies the ink to the liquid ejection head, and a negative pressure sub-tank that recovers the ink from the liquid ejection head, and wherein the difference between the pressure of the gas inside the positive pressure sub-tank and the pressure of the gas inside the negative pressure sub-tank is: 8.9 The pressure is characterized by being equal to or greater than 30 kPa and equal to or less than 30 kPa. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an image forming device that can efficiently remove air bubbles from a liquid ejection head or a flow path connected to the liquid ejection head, stabilize ejection performance, and output high-resolution images. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. [Figure 2]FIG. 10 is a schematic view showing another example of an image forming apparatus according to the present invention. [Figure 3] FIG. 1 is a perspective view of an external appearance of an example of a liquid ejection head. [Figure 4] 1 is a cross-sectional view of an example of a liquid ejection head taken in a direction perpendicular to the nozzle arrangement direction. [Figure 5] 1 is a cross-sectional view of an example of a liquid ejection head in a direction parallel to the nozzle arrangement direction. [Figure 6] FIG. 2 is a plan view showing a nozzle plate of an example of a liquid ejection head. [Figure 7] 5A to 5F are plan views showing the components that constitute the flow path member of an example of a liquid ejection head. [Figure 8] 1A and 1B are plan views showing the components that constitute a common liquid chamber member of an example of a liquid ejection head. DETAILED DESCRIPTION OF THE INVENTION

[0011] The image forming apparatus and image forming method according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and other modifications, additions, corrections, deletions, and other changes can be made within the scope of what can be conceived by those skilled in the art. Any embodiment is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0012] The image forming apparatus of the present invention is an image forming apparatus comprising an ink containing water, pigment, and a siloxane compound, a liquid ejection head that ejects the ink, a main tank that contains the ink, and a sub-tank that is connected to the main tank and the liquid ejection head, wherein the sub-tank has a positive pressure sub-tank that supplies the ink to the liquid ejection head, and a negative pressure sub-tank that recovers the ink from the liquid ejection head, and the difference between the gas pressure inside the positive pressure sub-tank and the gas pressure inside the negative pressure sub-tank is 2 kPa or more and 30 kPa or less.

[0013] The image forming device may be called a printing device, a recording device, an image forming device, a two-dimensional or three-dimensional image forming device, etc., and when an inkjet head is used as the liquid ejection head, the image forming device may be called an inkjet recording device, etc.

[0014] The image forming method of the present invention is an image forming method performed by an image forming apparatus comprising an ink containing water, pigment, and a siloxane compound, a liquid ejection head that ejects the ink, a main tank that contains the ink, and a sub-tank connected to the main tank and the liquid ejection head, wherein the sub-tank has a positive pressure sub-tank that supplies the ink to the liquid ejection head, and a negative pressure sub-tank that recovers the ink from the liquid ejection head, and the difference between the gas pressure inside the positive pressure sub-tank and the gas pressure inside the negative pressure sub-tank is 2 kPa or more and 30 kPa or less.

[0015] The image forming method may be called a printing method, a recording method, an image forming method, a two-dimensional or three-dimensional image forming method, etc., and when an inkjet head is used as the liquid ejection head, the image forming method may be called an inkjet recording method, etc.

[0016] (One embodiment of an image forming apparatus and an image forming method) FIG. 1 is a schematic diagram showing a main part of an embodiment of an image forming apparatus according to the present invention. The arrows in the figure schematically indicate the direction of flow of the liquid or substrate, with black arrows indicating the flow of the liquid and white arrows indicating the flow of the gas.

[0017] In FIG. 1, a liquid ejection head 108, a main tank 101, and a sub-tank 120 are shown. The liquid ejection head 108 ejects ink. The main tank 101 stores ink. The sub-tank 120 has a positive pressure sub-tank 103 and a negative pressure sub-tank 102. The positive pressure sub-tank 103 supplies ink to the liquid ejection head 108. The negative pressure sub-tank 102 collects ink from the liquid ejection head 108.

[0018] The positive pressure sub-tank 103 and the negative pressure sub-tank 102 contain gas and liquid. The positive pressure sub-tank 103 is connected to the negative pressure sub-tank 102 and the liquid ejection head 108. The negative pressure sub-tank 102 is connected to the main tank 101 and the liquid ejection head 108.

[0019] The positive pressure sub-tank 103 and the negative pressure sub-tank 102 are each equipped with a pressure gauge 106 and a pressure gauge 107 that measure the pressure of the gas inside, and are equipped with a mechanism for controlling the pressure of the gas inside each sub-tank. This allows the gas inside each sub-tank to move (arrows e and f). The mechanism for controlling the pressure of the gas inside each sub-tank is not particularly limited and can be selected as appropriate.

[0020] The image forming apparatus of this embodiment is provided with an ink supply flow path 109 that connects the main tank 101 and the negative pressure sub-tank 102. It is also provided with a liquid feed pump 104, which causes ink to flow through the ink supply flow path 109. In this embodiment, ink flows from the main tank 101 to the negative pressure sub-tank 102 (arrow a).

[0021] The image forming apparatus of this embodiment also includes a bypass flow path 110 that connects the negative pressure sub-tank 102 and the positive pressure sub-tank 103. It also includes a liquid feed pump 105, which causes ink to flow through the bypass flow path 110. In this embodiment, ink flows from the negative pressure sub-tank 102 to the positive pressure sub-tank 103 (arrow b).

[0022] In this embodiment, the difference in gas pressure between the positive pressure sub-tank 103 and the negative pressure sub-tank 102 must be 2 kPa or more and 30 kPa or less. The difference between the gas pressure inside the positive pressure sub-tank 103 and the gas pressure inside the negative pressure sub-tank 102 may also be simply referred to as the pressure difference.

[0023] When the pressure difference is 2 kPa or more, the ink circulates sufficiently, and the pressure difference within the subtank causes bubbles to break in the flow path and the negative-pressure subtank, facilitating bubble removal. When the pressure difference is 30 kPa or less, the ink circulates properly, reducing the entrainment of bubbles from the nozzles of the liquid ejection head due to ink circulation. Furthermore, when the ink described below is used in addition to maintaining the pressure difference within the above range, siloxane compounds and inorganic silica penetrate the surfaces of bubbles at the ink-air interface, disrupting the uniformity of the film that forms the bubbles and hindering their maintenance. This promotes bubble breakage within the subtank, resulting in a synergistic effect in bubble removal. According to this embodiment, excellent bubble removal is achieved, ejection stability is improved, and high-resolution images can be output.

[0024] The pressure difference is in the range of 2 kPa to 30 kPa, preferably 4 kPa to 24 kPa, and more preferably 6 kPa to 20 kPa, in which case the ability to remove bubbles can be further improved.

[0025] It is preferable that the pressure of the gas inside the positive pressure sub-tank 103 is greater than the atmospheric pressure outside the liquid ejection head 108, and that the pressure of the gas inside the negative pressure sub-tank 102 is less than the atmospheric pressure outside the liquid ejection head 108. In this case, the amount of air bubbles entrained from the nozzles during ink circulation is reduced, which is preferable because it improves ejection stability.

[0026] The pressure of the gas inside the positive pressure subtank 103 can be selected as appropriate, but is preferably between 0.1 kPa and 15 kPa, based on the atmospheric pressure outside the subtank. When it is in this range, ink leakage from the nozzles can be suppressed, and ejection defects and image distortion can be further suppressed. The gas pressure inside the negative pressure subtank 102 can be selected as appropriate, but is preferably between -20 kPa and -0.1 kPa, and more preferably between -15 kPa and -2 kPa, based on the atmospheric pressure outside the subtank. Within this range, air can be further prevented from being drawn in from the nozzles, and ink drying inside the liquid ejection head 108 due to contact with air can be prevented.

[0027] Ink is supplied to the interior of the liquid ejection head 108 through the ink supply port of the liquid ejection head 108 and is recovered from the ink recovery port of the liquid ejection head 108 (arrows c and d). Due to the pressure inside the subtank, the ink supplied from the positive pressure subtank 103 circulates through the interior of the liquid ejection head 108 to the negative pressure subtank 102.

[0028] At this time, a flow meter may be used to monitor the amount of ink supplied to the liquid ejection head 108 and the amount of ink recovered from the liquid ejection head 108. The image forming apparatus of this embodiment is equipped with flow meter 112 and flow meter 111, and flow meter 112 monitors the amount of ink supplied to the liquid ejection head 108, and flow meter 111 monitors the amount of ink recovered from the liquid ejection head 108.

[0029] The liquid ejection head 108 has, for example, a supply port through which ink is supplied from the subtank 120, and a recovery port through which ink is recovered into the subtank 120. The amount of ink supplied to the supply port and the amount of ink recovered from the recovery port can be selected as appropriate. It is preferable that the amount of ink supplied to the supply port is equal to or greater than the amount of ink recovered from the recovery port, and that the amount of ink recovered is 1.0 mL / min or more and 30.0 mL / min or less.

[0030] If the ink supply rate is equal to or greater than the ink recovery rate, air is less likely to be drawn in from the nozzles when ink inside the liquid ejection head 108 is consumed by ejection. This reduces the generation of air bubbles. Furthermore, if the ink recovery rate is 1.0 mL / min or more, a sufficient amount of ink can be supplied to the liquid ejection head 108, making it easier to remove air bubbles from the flow paths. If the ink recovery rate is 30.0 mL / min or less, it is possible to reduce the entrainment of air bubbles from the nozzles during ink circulation, thereby improving ejection stability.

[0031] Next, another example of the image forming apparatus of this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of the main parts of the image forming apparatus of this example. Explanation of matters similar to those in the above example will be omitted.

[0032] In this embodiment, the positive pressure subtank 103 and the negative pressure subtank 102 may each be provided with a spare air tank. As shown in the example in Fig. 2, in this embodiment, the positive pressure subtank 103 preferably has a positive pressure air tank 114, and the negative pressure subtank 102 preferably has a negative pressure air tank 113. Furthermore, it is more preferable that the positive pressure air tank 114 has a larger capacity than the positive pressure subtank 103, and it is more preferable that the negative pressure air tank 113 has a larger capacity than the negative pressure subtank 102.

[0033] As in this example, by providing an air tank for each of the positive pressure sub-tank and the negative pressure sub-tank, it is possible to reduce the change in air pressure inside the sub-tank caused by the supply of ink and the ejection of ink, thereby further improving ejection stability. In addition, gas moves between the positive pressure air tank 114 and the negative pressure air tank 113 and the outside of the air tank as indicated by arrows g and h. As the gas, for example, air or any other gas can be used.

[0034] Next, a detailed example of a liquid ejection head will be described. A liquid ejection head may be called an ink ejection head or simply a head.

[0035] The liquid ejection head 108 in this embodiment has, for example, a common liquid chamber and multiple individual liquid chambers. In the liquid ejection head 108, liquid is supplied to the individual liquid chambers via the common liquid chamber, and the liquid is ejected from nozzle holes (nozzles) that communicate with the individual liquid chambers. In the liquid ejection head 108 of this embodiment, the liquid is circulated to the common liquid chamber via circulation channels that communicate with the individual liquid chambers.

[0036] As the liquid ejection head in the present invention, for example, the following can be used, examples of which will be described with reference to FIGS. Fig. 3 is an external perspective view showing an example of an ink ejection head. Fig. 4 is a cross-sectional explanatory diagram in a direction perpendicular to the nozzle arrangement direction of the ink ejection head of Fig. 3. Fig. 5 is a partial cross-sectional explanatory diagram in a direction parallel to the nozzle arrangement direction of the ink ejection head of Fig. 3. Fig. 6 is a plan view of a nozzle plate of the ink ejection head of Fig. 3. Fig. 7 is a plan view of each member constituting a flow path member of the ink ejection head of Fig. 3. Fig. 8 is a plan view of each member constituting a common liquid chamber member of the ink ejection head of Fig. 3.

[0037] As shown in Figures 3 to 5, the ink ejection head of this example is formed by laminating and bonding a nozzle plate 1, a flow path plate 2, and a vibration plate member 3 as a wall member, and is equipped with a piezoelectric actuator 11 that displaces the vibration plate member 3, a common liquid chamber member 20, and a cover 29.

[0038] The nozzle plate 1 has a plurality of nozzles 4 that eject the ink. The flow path plate 2 is formed with an individual liquid chamber 6 communicating with the nozzle 4, a fluid resistance section 7 communicating with the individual liquid chamber 6 as the inflow flow path, and a liquid introduction section 8 communicating with the fluid resistance section 7. The flow path plate 2 is formed by stacking and bonding a plurality of plate-like members 41 to 45 from the nozzle plate 1 side, and the flow path member 40 is formed by stacking and bonding these plate-like members 41 to 45 and the vibration plate member 3.

[0039] The diaphragm member 3 has a filter portion 9 as an opening that communicates with the liquid introduction portion 8 and the common liquid chamber 10 formed by the common liquid chamber member 20. The diaphragm member 3 is a wall member that forms the wall surfaces of the individual liquid chambers 6 of the flow path plate 2. This diaphragm member 3 has a two-layer structure (not limited to this) and is formed from a first layer that forms a thin portion from the flow path plate 2 side and a second layer that forms a thick portion, and a deformable vibration region 30 is formed in the first layer in a portion that corresponds to the individual liquid chamber 6.

[0040] Here, the nozzle plate 1 has a plurality of nozzles 4 arranged in a staggered pattern, as shown in FIG.

[0041] As shown in Figure 7(a), the plate-like member 41 constituting the flow path plate 2 is formed with a through groove portion (meaning a groove-shaped through hole) 6a constituting an individual liquid chamber 6, a fluid resistance portion 51, and through groove portions 51a and 52a constituting the circulation flow path 52 as the outflow flow path.

[0042] Similarly, the plate-like member 42 is formed with a through groove 6b that constitutes the individual liquid chamber 6 and a through groove 52b that constitutes the circulation flow path 52, as shown in FIG. 7(b).

[0043] Similarly, as shown in Figure 7(c), the plate-shaped member 43 is formed with a through groove portion 6c that forms an individual liquid chamber 6 and a through groove portion 53a that forms the circulation flow path 53 and has its longitudinal direction aligned with the nozzle arrangement direction.

[0044] Similarly, as shown in Figure 7(d), the plate-shaped member 44 is formed with a through groove portion 6d that forms an individual liquid chamber 6, a through groove portion 7a that is a fluid resistance portion 7, a through groove portion 8a that forms a liquid introduction portion 8, and a through groove portion 53b that forms a circulation flow path 53 and has its longitudinal direction in the nozzle arrangement direction.

[0045] Similarly, as shown in Figure 7(e), the plate-shaped member 45 is formed with a through groove portion 6e that forms an individual liquid chamber 6, a through groove portion 8b (which becomes the liquid chamber downstream of the filter) that forms the liquid introduction portion 8 and whose longitudinal direction is the nozzle arrangement direction, and a through groove portion 53c that forms the circulation flow path 53 and whose longitudinal direction is the nozzle arrangement direction.

[0046] As shown in FIG. 7(f), the diaphragm member 3 is formed with a vibration region 30, a filter portion 9, and a through groove portion 53d that defines the circulation flow path 53 and whose longitudinal direction is the nozzle arrangement direction.

[0047] In this way, by forming the flow path member by stacking and joining a plurality of plate-like members, it is possible to form a complex flow path with a simple structure.

[0048] With the above configuration, the flow path member 40, which is made up of the flow path plate 2 and the vibration plate member 3, is formed with fluid resistance portions 51 extending along the surface direction of the flow path plate 2 and communicating with each individual liquid chamber 6, a circulation flow path 52, and a circulation flow path 53 extending in the thickness direction of the flow path member 40 and communicating with the circulation flow path 52. The circulation flow path 53 communicates with the common circulation liquid chamber 50, which will be described later.

[0049] On the other hand, the common liquid chamber member 20 is formed with a common liquid chamber 10 to which the ink is supplied from the positive pressure sub-tank, and a circulation common liquid chamber 50 which serves as a flow path on the side where the ink is collected in the negative pressure sub-tank.

[0050] As shown in Figure 8(a), the first common liquid chamber member 21 is formed with a through hole 25a for a piezoelectric actuator, a through groove portion 10a which becomes the downstream portion 10A of the common liquid chamber, and a groove portion 50a with a bottom which becomes the circulating common liquid chamber 50.

[0051] 8(b), a through-hole 25b for the piezoelectric actuator and a groove 10b that becomes the upstream portion 10B of the common liquid chamber are formed in the second common liquid chamber member 22. Also, a through-hole 71a that becomes a supply port portion that communicates with one end of the common liquid chamber 10 in the nozzle arrangement direction and the supply port 71 is formed in the second common liquid chamber member 22, as shown in FIG.

[0052] The first common liquid chamber member 21 and the second common liquid chamber member 22 are formed with through holes 81a and 81b that communicate with the other end of the circulation common liquid chamber 50 in the nozzle arrangement direction (the end opposite to the through hole 71a) and the circulation port 81.

[0053] In addition, in FIGS. 8(a) and (b), through holes are shown as white holes, and grooves with bottoms are shown as painted surfaces.

[0054] The common liquid chamber member 20 is composed of a first common liquid chamber member 21 and a second common liquid chamber member 22, and the first common liquid chamber member 21 is joined to the vibration plate member 3 side of the flow path member 40, and the second common liquid chamber member 22 is stacked and joined to the first common liquid chamber member 21.

[0055] Here, the first common liquid chamber member 21 forms a common liquid chamber downstream section 10A, which is a part of the common liquid chamber 10 that communicates with the liquid introduction section 8, and a circulation common liquid chamber 50 that communicates with the circulation flow path 53. In addition, the second common liquid chamber member 22 forms a common liquid chamber upstream section 10B, which is the remaining part of the common liquid chamber 10. In this case, the common liquid chamber downstream section 10A, which is a part of the common liquid chamber 10, and the circulation common liquid chamber 50 are arranged side by side in a direction perpendicular to the nozzle arrangement direction, and the circulation common liquid chamber 50 is arranged at a position projected into the common liquid chamber 10.

[0056] As a result, the dimensions (size) of the common circulating liquid chamber 50 are not restricted by the dimensions required for the flow path including the individual liquid chambers 6, fluid resistance section 7, and liquid introduction section 8 formed by the flow path member 40. Furthermore, by arranging the common circulating liquid chamber 50 and a portion of the common liquid chamber 10 side by side and arranging the common circulating liquid chamber 50 at a position projected into the common liquid chamber 10, it is possible to reduce the width of the head in the direction perpendicular to the nozzle arrangement direction, and to prevent the head from becoming larger.

[0057] As described above, the common liquid chamber member 20 is formed with the common liquid chamber 10 and the circulating common liquid chamber 50. The ink is supplied from the positive pressure sub-tank to the common liquid chamber 10. The circulating common liquid chamber 50 is the flow path through which the ink is collected in the negative pressure sub-tank.

[0058] Meanwhile, a piezoelectric actuator 11 including an electromechanical conversion element is disposed on the opposite side of the vibration plate member 3 from the individual liquid chamber 6, as a driving means (actuator means, pressure generating means) for deforming the vibration region 30 of the vibration plate member 3. As shown in Fig. 5, this piezoelectric actuator 11 has a piezoelectric member 12 bonded onto a base member 13. Grooves are formed in the piezoelectric member 12 by half-cut dicing, and a required number of columnar piezoelectric elements 12A, 12B are formed in a comb-like shape at predetermined intervals for each piezoelectric member 12.

[0059] Here, piezoelectric element 12A of piezoelectric member 12 is a piezoelectric element that is driven by applying a driving waveform, and piezoelectric element 12B is used simply as a support without applying a driving waveform, but it is also possible to use all piezoelectric elements 12A and 12B as a piezoelectric element that drives them.

[0060] The piezoelectric element 12A is bonded to a protrusion 30a, which is an island-shaped thick portion formed in the vibration region 30 of the vibration plate member 3. The piezoelectric element 12B is bonded to a protrusion 30b, which is a thick portion of the vibration plate member 3.

[0061] This piezoelectric member 12 is formed by alternately laminating piezoelectric layers and internal electrodes, and the internal electrodes are each drawn out to an end surface to provide an external electrode, to which a flexible wiring member 15 is connected.

[0062] In the ink ejection head configured in this manner, for example, by lowering the voltage applied to the piezoelectric element 12A from the reference potential, the piezoelectric element 12A contracts, the vibration area 30 of the vibration plate member 3 descends, and the volume of the individual liquid chamber 6 expands. As a result, the ink flows into the individual liquid chamber 6.

[0063] Thereafter, the voltage applied to the piezoelectric element 12A is increased to expand the piezoelectric element 12A in the stacking direction, and the vibration region 30 of the vibration plate member 3 is deformed in the direction toward the nozzle 4, thereby contracting the volume of the individual liquid chamber 6. As a result, the ink in the individual liquid chamber 6 is pressurized, and the ink is ejected from the nozzle 4.

[0064] Then, by returning the voltage applied to the piezoelectric element 12A to the reference potential, the vibration area 30 of the vibration plate member 3 is restored to its initial position, and a negative pressure is generated inside the individual liquid chamber 6, so that the ink is filled from the common liquid chamber 10 into the individual liquid chamber 6. After the vibration of the meniscus surface of the nozzle 4 has attenuated and stabilized, the operation proceeds to the next ejection.

[0065] The method of driving this head is not limited to the above example (pull-push hitting), and pull hitting or push hitting can also be performed depending on the driving waveform applied.

[0066] In the above-described embodiment, a laminated piezoelectric element was used as a means for applying pressure fluctuations to the individual liquid chambers 6. However, the driving method is not limited to this, and thin-film piezoelectric elements can also be used. Furthermore, a heating resistor can be disposed in the individual liquid chambers 6, and pressure fluctuations can be applied by generating bubbles using heat from the heating resistor, or by using electrostatic force to generate pressure fluctuations. From the viewpoints of protecting the liquid supply device and circulation path and ensuring ejection stability, a piezoelectric system is preferable.

[0067] As inkjet printing methods, line type and serial type inkjet heads are known. A line-type inkjet head has nozzles arranged in a line perpendicular to the transport direction of the substrate, and ejects droplets from the inkjet head, which is held in a fixed position, onto the substrate while the substrate is continuously moved in the transport direction. The serial inkjet head is a type in which droplets are ejected onto a substrate from an inkjet head that is movable in a direction perpendicular to the transport direction of the substrate while the substrate is intermittently moved in the transport direction.

[0068] In the present invention, either method can be used, but it is preferable to use a liquid ejection head of the line head type, which improves ejection stability in that the head is fixed and is less susceptible to environmental influences such as vibration.

[0069] (ink) Next, the ink used in the present invention will be described. The ink used in the present invention contains water, a pigment, and a siloxane compound, and may also contain an organic solvent, a surfactant, and other additives, as required.

[0070] <Siloxane compounds> The siloxane compound in the present invention can be appropriately selected, and examples thereof include compounds having a hydrophilic group or a hydrophilic polymer chain on the side chain of a compound having a polysiloxane repeating structure such as polydimethylsiloxane, or compounds having a hydrophilic group or a hydrophilic polymer chain at the end.

[0071] The siloxane compound in the present invention may also be an unmodified siloxane compound, such as unmodified polydimethylsiloxane, including octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane.

[0072] The siloxane compound may have a polysiloxane structure within its structure. Siloxane compounds have low surface tension and good miscibility with water due to the introduction of hydrophilic groups, which allows them to diffuse easily and penetrate into foam films. Therefore, even a small amount of addition will provide a defoaming effect. In the present invention, however, the use of a circulation mechanism using pressure operation promotes the diffusion of the siloxane compound, and the pressure is reduced inside the sub-tank, causing bubbles to break down, resulting in an even more excellent defoaming effect.

[0073] The siloxane compound can be appropriately selected depending on the purpose, and examples thereof include side-chain-modified polydimethylsiloxane, both-terminal-modified polydimethylsiloxane, one-terminal-modified polydimethylsiloxane, and both-terminal-modified side-chain polydimethylsiloxane. The modifying group can be appropriately selected, and examples thereof include a polyoxyethylene group, a polyoxyethylene polyoxypropylene group, etc. Polyether-modified siloxane compounds having a polyoxyethylene group or a polyoxyethylene polyoxypropylene group are preferred because they exhibit good properties.

[0074] Such siloxane compounds may be synthesized appropriately or commercially available products, such as those available from BYK Corporation, Shin-Etsu Chemical Co., Ltd., Dow Corning Toray Silicone Co., Ltd., Nippon Emulsion Co., Ltd., and Kyoeisha Chemical Co., Ltd.

[0075] As the polyether-modified siloxane compound, commercially available products can be used, such as KF-618, KF-642, KF-643, KF-6004 (Shin-Etsu Chemical Co., Ltd.), EMALEX-SS-5602, SS-1906EX (Nihon Emulsion Co., Ltd.), FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, FZ-2164, DOWSIL DK Q1-1247, DOWSIL FS 1277, DOWSIL FS 013A, DOWSIL 1313 (Dow Corning Toray Silicone Co., Ltd.), BYK-019, BYK-025, BYK-033, BYK-387 (BYK-Chemie Co., Ltd.), TSF4440, TSF4452, TSF4453 (Toshiba Silicon Co., Ltd.), etc. These may be used alone or in combination of two or more.

[0076] The form of the siloxane compound is not particularly limited, and may be an oil type, a compound type, an emulsion type, an aqueous solution, etc. From the viewpoint of dispersibility in the ink, the siloxane compound is preferably in the form of an emulsion or an aqueous solution.

[0077] The siloxane compound is preferably contained in the ink in an amount of 0.01% by mass to 1.0% by mass, which is preferable because this range provides excellent effects in wetting the nozzle and defoaming inside the subtank, improving ejection stability.

[0078] The siloxane compound is preferably a compound represented by the following general formula (1): In this case, it has excellent dispersibility in water and can improve ejection stability.

[0079] [ka]

[0080] (In general formula (1), m represents an integer of 1 or more, n represents an integer, R1 and R2 represent a methyl group or a cyclic structure connected via O, and X represents the following general formula (2).)

[0081] [ka]

[0082] (In general formula (2), a and b represent integers, R3 represents an alkylene group, and R4 represents an alkyl group.)

[0083] By using the polyether-modified siloxane compound in which such a polyalkylene oxide structure is introduced into the Si part side chain of dimethylpolysiloxane, it is possible to obtain an ink with excellent dispersibility in water and improve ejection stability.

[0084] In the structure of general formula (1), it is preferable that the structure has an integer m of modified siloxane repeating structural units, and while m may be 0, it is preferable that m is 1 or greater because this improves affinity with aqueous ink and promotes bubble removal. Furthermore, an integer n of dimethylsiloxane repeating structural units has the effect of reducing the surface tension of the ink and improving jetting properties, and to enhance this effect, it is preferable that n be greater than m.

[0085] In the structure of general formula (1), R1 and R2 are methyl groups or cyclic structures with an O atom interposed therebetween. A cyclic structure with an O atom refers to a cyclic siloxane in which the main chain ends are bonded in the form of —R1—O—R2—. Examples include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexanesiloxane. Siloxane compounds in which modified siloxanes have been introduced into some of these to improve hydrophilicity may also be used.

[0086] In the structure of the general formula (2), R3 is preferably a short-chain alkylene group, and more preferably a methylene group, an ethylene group, or a propylene group. R4 is preferably an alkyl group, and more preferably a methyl group or an ethyl group.

[0087] <Inorganic silica particles> The ink used in the present invention preferably contains inorganic silica particles as a component, which can improve the bubble removal properties.

[0088] The type of inorganic silica particles is not particularly limited, but for example, fumed silica or colloidal silica can be used. Those which have been subjected to a hydrophilic surface treatment, or dispersions obtained by mill-dispersing the particles while adding a dispersant or the like can also be suitably used.

[0089] The volume average primary particle diameter of the inorganic silica particles is preferably 1 nm or more and 50 nm or less. When it is in this range, dispersibility is improved. The volume average primary particle diameter of the inorganic silica particles refers to the volume average particle diameter of the primary particles of inorganic silica.

[0090] The inorganic silica particles are preferably contained in the ink in an amount of 0.01% by mass to 0.1% by mass, which improves the ability to break down bubbles inside the sub-tank of the image forming apparatus.

[0091] The inorganic silica particles used in the present invention may be commercially available products, such as ST-XS, ST-S, ST-30, ST-50-T, ST-30L, ST-CM, ST-YL, ST-PS-M, and ST-NS (Nissan Chemical Industries, Ltd.), AEROSIL 50, AEROSIL OX50, AEROSIL 130, AEROSIL 200, AEROSIL 200CF, AEROSIL 300, AERODISP W7520, AERODISP W7622, and AERODISP W1813 (Nippon Aerosil Co., Ltd.), and QSG-10, QSG-30, QSG-100, and X-24-9600A (Shin-Etsu Chemical Co., Ltd.). These may be used alone or in combination of two or more.

[0092] <Organic solvents> The organic solvent used in the present invention is not particularly limited, and any water-soluble organic solvent can be used, including, for example, polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.

[0093] Specific examples of the water-soluble organic solvent include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, and the like. Polyhydric alcohols such as pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, and petriol, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether. polyhydric alcohol alkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether; nitrogen-containing heterocyclic compounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, and γ-butyrolactone; amides such as formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N-dimethylpropionamide, and 3-butoxy-N,N-dimethylpropionamide; amines such as monoethanolamine, diethanolamine, and triethylamine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol; propylene carbonate; and ethylene carbonate.

[0094] It is preferable to use an organic solvent having a boiling point of 250° C. or less, since it not only functions as a wetting agent but also provides good drying properties.

[0095] Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used. Specific examples of polyol compounds having 8 or more carbon atoms include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol. Specific examples of glycol ether compounds include polyhydric alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether; and polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether.

[0096] Polyol compounds having 8 or more carbon atoms and glycol ether compounds can improve the permeability of ink when paper is used as the recording medium.

[0097] The content of the organic solvent in the ink is not particularly limited and can be selected appropriately depending on the purpose. From the viewpoint of the drying property and ejection reliability of the ink, however, the content is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 60% by mass or less.

[0098] <Water> The water content in the ink is not particularly limited and can be selected appropriately depending on the purpose, but from the viewpoint of the drying property and ejection reliability of the ink, it is preferably 10% by mass or more and 90% by mass or less, and more preferably 20% by mass to 60% by mass.

[0099] <Pigments> The pigment may be an inorganic pigment or an organic pigment. These may be used alone or in combination of two or more. Mixed crystals may also be used. Examples of pigments that can be used include black pigments, yellow pigments, magenta pigments, cyan pigments, white pigments, green pigments, orange pigments, glossy pigments such as gold and silver pigments, and metallic pigments.

[0100] Examples of inorganic pigments that can be used include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, as well as carbon black produced by known methods such as the contact method, furnace method, and thermal method.

[0101] In addition, examples of organic pigments that can be used include azo pigments, polycyclic pigments (e.g., phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments), dye chelates (e.g., basic dye chelates and acid dye chelates), nitro pigments, nitroso pigments, and aniline black. Of these pigments, those with good affinity for the solvent are preferably used. In addition, resin hollow particles and inorganic hollow particles can also be used.

[0102] Specific examples of pigments for black include carbon blacks (CI Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, metals such as copper, iron (CI Pigment Black 11), and titanium oxide, and organic pigments such as aniline black (CI Pigment Black 1).

[0103] In addition, for color, CI Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, 213, CI Pigment Yellow Ranges 5, 13, 16, 17, 36, 43, 51, CI Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88 , 101 (Red Iron), 104, 105, 106, 108 (Cadmium Red), 112, 114, 122 (Quinacridone Magenta), 123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224, 254, 264, CI Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38; CI Pigment Blue 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3, 15:4 (Phthalocyanine Blue), 16, 17:1, 56, 60, 63; CI Pigment Green 1, 4, 7, 8, 10, 17, 18, 36, etc.

[0104] The content of the pigment in the ink is preferably from 0.1% to 25% by mass, and more preferably from 1.0% to 20.0% by mass, from the viewpoint of good fixability and ejection stability.

[0105] <Resin> The type of resin contained in the ink is not particularly limited and can be selected appropriately depending on the purpose. Examples include urethane resin, polyester resin, acrylic resin, vinyl acetate resin, styrene resin, butadiene resin, styrene-butadiene resin, vinyl chloride resin, acrylic styrene resin, and acrylic silicone resin. Resin particles made of these resins may also be used. The resin particles are dispersed in water as a dispersion medium to form a resin emulsion, which can be mixed with materials such as coloring materials and organic solvents to obtain an ink. The resin particles may be appropriately synthesized or commercially available. These may be used alone or in combination of two or more types of resin particles.

[0106] The volume average particle size of the resin particles is not particularly limited and can be appropriately selected depending on the purpose. However, from the viewpoint of obtaining good fixing properties and high image hardness, the volume average particle size is preferably 10 nm or more and 1,000 nm or less, more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less. The volume average particle size can be measured using, for example, a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

[0107] The resin content is not particularly limited and can be selected appropriately depending on the purpose. From the viewpoint of fixability and ink storage stability, however, it is preferably from 1% by mass to 30% by mass, and more preferably from 5% by mass to 20% by mass, of the total amount of ink.

[0108] <Additives> If necessary, surfactants, antifoaming agents, antiseptic and antifungal agents, antirust agents, pH adjusters, etc. may be added to the ink.

[0109] <Surfactant> As the surfactant, any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants and anionic surfactants can be used. The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. If the siloxane compound has a surfactant function, it may be used in place of or in combination with the siloxane compound. Furthermore, it is preferable that the silicone surfactant does not decompose even at high pH.

[0110] As fluorosurfactants, for example, perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in the side chain are particularly preferred due to their low foaming properties. Examples of perfluoroalkyl sulfonic acid compounds include perfluoroalkyl sulfonic acid and perfluoroalkyl sulfonate salts. Examples of perfluoroalkyl carboxylic acid compounds include perfluoroalkyl carboxylic acids and perfluoroalkyl carboxylate salts. Examples of polyoxyalkylene ether polymer compounds having perfluoroalkyl ether groups in the side chain include sulfate ester salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in the side chain, and salts of polyoxyalkylene ether polymers having perfluoroalkyl ether groups in the side chain. Examples of counter ions of the salts in these fluorosurfactants include Li, Na, K, NH, NHCHCHOH, NH(CHCHOH), NH(CHCHOH), and the like.

[0111] Examples of amphoteric surfactants include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, and lauryl dihydroxyethyl betaine. Examples of nonionic surfactants include polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyoxyethylene propylene block polymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adducts of acetylene alcohol. Examples of anionic surfactants include polyoxyethylene alkyl ether acetates, dodecylbenzenesulfonates, laurates, and salts of polyoxyethylene alkyl ether sulfates. These may be used alone or in combination of two or more.

[0112] The content of the surfactant in the ink is not particularly limited and can be appropriately selected according to the purpose. However, from the viewpoints of excellent wettability and ejection stability and improved image quality, it is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less.

[0113] <Antiseptic and mildew preventive agent> The antiseptic and mildew preventive agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

[0114] <Rust preventive agent> The rust preventive agent is not particularly limited, and examples thereof include acid sulfite and sodium thiosulfate.

[0115] <pH adjuster> The pH adjuster is not particularly limited as long as it can adjust the pH to 7 or more, and examples thereof include amines such as diethanolamine and triethanolamine.

[0116] <Physical properties of ink> The physical properties of the ink can be appropriately selected according to the purpose. For example, it is preferable that the viscosity, surface tension, pH, etc. are in the following ranges. The viscosity of the ink at 25°C is preferably 4 mPa·s or more and 10 mPa·s or less from the viewpoints of improved printing density and character quality and good ejection properties. Here, for example, a rotational viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used to measure the viscosity. The measurement conditions are: at 25°C, a standard cone rotor (1°34’×R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and it can be measured in 3 minutes.

[0117] The surface tension of the ink is preferably 35 mN / m or less, and more preferably 32 mN / m or less at 25°C from the viewpoints of stabilizing the meniscus of the nozzle, preferably leveling the ink on the recording medium, and shortening the drying time of the ink.

[0118] The pH of the ink is preferably 7 to 12, and more preferably 8 to 11, from the viewpoint of preventing corrosion of metal members that come into contact with the ink.

[0119] (Recording medium) The recording medium is not particularly limited, and although plain paper, glossy paper, special paper, cloth, etc. can be used, good image formation is also possible using an impermeable substrate. Furthermore, the recording medium is not limited to those commonly used as recording media, and building materials such as wallpaper and flooring, cloth for clothing, textiles, leather, etc. can also be used as appropriate. Furthermore, by adjusting the configuration of the path for transporting the printed material, ceramics, glass, and metal can also be used, but the present invention is not limited to these. [Example]

[0120] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples. It should be noted that Examples 7 and 8 refer to Reference Examples 7 and 8, which are not included in the present invention.

[0121] (Example of manufacturing cyan pigment dispersion) A 1 L flask equipped with a mechanical stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel was thoroughly purged with nitrogen gas, and then 11.2 parts by mass of styrene, 2.8 parts by mass of acrylic acid, 12.0 parts by mass of lauryl methacrylate, 4.0 parts by mass of polyethylene glycol methacrylate, 4.0 parts by mass of styrene macromer, and 0.4 parts by mass of mercaptoethanol were mixed and heated to 65°C.

[0122] Next, a mixed solution containing 100.8 parts by weight of styrene, 25.2 parts by weight of acrylic acid, 108.0 parts by weight of lauryl methacrylate, 36.0 parts by weight of polyethylene glycol methacrylate, 60.0 parts by weight of hydroxylethyl methacrylate, 36.0 parts by weight of styrene macromer, 3.6 parts by weight of mercaptoethanol, 2.4 parts by weight of azobismethylvaleronitrile, and 18 parts by weight of methyl ethyl ketone was added dropwise to the flask over 2.5 hours. After the dropwise addition, a mixed solution containing 0.8 parts by weight of azobismethylvaleronitrile and 18 parts by weight of methyl ethyl ketone was added dropwise to the flask over 0.5 hours. After aging at 65°C for 1 hour, 0.8 parts by weight of azobismethylvaleronitrile was added, and the mixture was further aged for 1 hour. After the reaction was completed, 364 parts by weight of methyl ethyl ketone was added to the flask, yielding 800 parts by weight of polymer solution A with a concentration of 50% by weight.

[0123] Next, 28 parts by weight of the resulting polymer solution A, 26 parts by weight of phthalocyanine pigment (Dainichiseika Color & Chemicals Mfg. Co., Ltd., Chromofine Blue A-220JC), 13.6 parts by weight of 1 mol / L potassium hydroxide aqueous solution, 20 parts by weight of methyl ethyl ketone, and 13.6 parts by weight of ion-exchanged water were thoroughly stirred and then kneaded using a roll mill to obtain a paste. The resulting paste was added to 200 parts by weight of pure water and thoroughly stirred. After that, the methyl ethyl ketone and water were distilled off using an evaporator. Furthermore, to remove coarse particles, the dispersion was pressure-filtered through a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to obtain a pigment-containing polymer microparticle dispersion with a pigment content of 15% by weight and a solids content of 20% by weight. The average particle size (D50) of the polymer microparticles in the resulting pigment dispersion was measured. The average particle diameter (D50) measured with a particle size distribution analyzer (Nanotrac UPA-EX150, manufactured by Nikkiso Co., Ltd.) was 56.0 nm.

[0124] (Example of making ink 1) A mixture of 40.0 parts ion-exchanged water, 1.0 part by mass of Safinol 420 (Nissin Chemical Industry Co., Ltd.), 0.1 part by mass of 1,2,3-benzotriazole, and 0.1 part by mass of 1,2-benzisothiazol-3(2H)-one was mixed with 0.05 part by mass of AEROSIL 200 (Nippon Aerosil Co., Ltd.) and stirred using a homomixer to obtain a dispersion of inorganic silica. 20.0 parts by mass of propane-1,2-diol, 2.0 parts by mass of 2-ethyl-1,3-hexanediol, and 0.2 parts by mass of BYK-019 (BYK-Chemie Co., Ltd.) as a siloxane compound were added to the dispersion and stirred. Next, 20.0 parts by mass of the cyan pigment dispersion, 15.0 parts by mass of Superflex 130 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a binder, and the remaining amount of ion-exchanged water were added to make a total of 100 parts by mass, and the mixture was stirred for 1 hour. This liquid was pressure-filtered using a polyvinylidene fluoride membrane filter with an average pore size of 5.0 μm to remove coarse particles and dust, producing [Ink 1].

[0125] (Examples of inks 2 to 14) Inks 2 to 14 were prepared in the same manner as in the preparation example of Ink 1 above, except that the materials in Table 1 were substituted.

[0126] The materials used in preparing the ink are as follows: Primary particle size refers to the volume average primary particle size. BYK-019 (BYK Corporation): Side chain polyether modified siloxane compound KF-642 (Shin-Etsu Chemical Co., Ltd.): Side-chain polyether-modified siloxane compound Octamethylcyclotetrasiloxane (Fujifilm Wako Pure Chemical Industries, Ltd.): Cyclic polymethylsiloxane KF-6004 (Shin-Etsu Chemical Co., Ltd.): Polyether-modified siloxane compound at both ends AEROSIL 200 (Nippon Aerosil Co., Ltd.): inorganic silica (primary particle size 7 to 20 nm) X-24-9600A (Shin-Etsu Chemical Co., Ltd.): Inorganic silica (primary particle diameter 80 nm)

[0127] The siloxane compounds BYK-019 and KF-642 correspond to the compounds represented by the general formula (1).

[0128] In addition, in Table 1, PG and EHD are as follows: PG: Propane-1,2-diol EHD: 2-ethyl-1,3-hexanediol

[0129] In Table 1, the amount of ion-exchanged water is added so that the total amount of ink becomes 100 parts by mass, and the values are shown to one decimal place.

[0130] Example 1 An apparatus having a circulation means as shown in Figure 1 was prepared, equipped with an inkjet head (RICOH MH5421MF, manufactured by Ricoh Co., Ltd.), and filled with the above-mentioned [Ink 1]. The gas pressure in the positive pressure sub-tank was set to +9.0 kPa relative to the outside air pressure, and the gas pressure in the negative pressure sub-tank was set to -9.0 kPa. Ink circulation was carried out using this apparatus.

[0131] (Examples 2 to 6, Examples 12 to 18) In the same manner as in Example 1, except that the ink was replaced with the inks under the conditions in Table 2, ink circulation was carried out in the apparatuses under the conditions of Examples 2 to 6 and Examples 12 to 18.

[0132] Examples 7 to 9 In the apparatus of Example 1, ink circulation was carried out in the apparatus under the conditions of Examples 7 to 9 in the same manner as in Example 1, except that the conditions of the internal pressure of each sub-tank were replaced with the conditions in Table 2. In Example 8, the amount of ink supplied from the sub-tank to the head was less than the amount of ink recovered from the head to the sub-tank.

[0133] (Examples 10 and 11) In the device of Example 1, ink circulation was performed in the devices under the conditions of Examples 10 and 11 in the same manner, except that the internal pressure conditions of each sub-tank were replaced with the conditions in Table 2 and the ink flow rate was adjusted by changing the inner diameter of the silicone tube that serves as the ink flow path of the device.

[0134] (Comparative Example 1) Ink circulation was carried out in the apparatus of Comparative Example 1 in the same manner as in Example 1, except that the ink was replaced with the inks listed in Table 2.

[0135] (Comparative Example 2) Ink circulation was carried out in the apparatus under the conditions of Comparative Example 2 in the same manner as in Example 1, except that the negative pressure sub-tank and positive pressure sub-tank were opened to the atmosphere and ink collection and circulation downstream of the head was stopped.

[0136] (Comparative Examples 3 and 4) Ink circulation was carried out in the apparatus of Comparative Examples 3 and 4 in the same manner as in Example 1, except that the conditions of the internal pressure of the sub-tank were replaced with the conditions in Table 2.

[0137] (evaluation) The ejection stability and bubble removal properties were evaluated under each condition as follows, and the results are shown in Table 2 below.

[0138] <Discharge stability> A nozzle check pattern was printed on a PVC film to confirm the number of ejecting nozzles (A). Next, the ink was circulated for one hour while the nozzle surface was open to the atmosphere, and a nozzle check pattern was printed again on the PVC film to confirm the number of ejecting nozzles (B) that were printed correctly. The percentage of the number of ejecting nozzles (B) when the number of ejecting nozzles (A) was taken as 100% was calculated, and ejection stability was evaluated according to the following criteria. A rating indicates the best result, and a rating of C or higher is preferable.

[0139] -Evaluation criteria for discharge stability- A: Number of discharge nozzles is 98% or more B: Number of discharge nozzles is 90% or more but less than 98% C: Number of discharge nozzles is between 50% and 90% D: Number of discharge nozzles is less than 50%

[0140] <Air bubble removal> A nozzle check pattern is printed on PVC film to confirm the number of ejecting nozzles (A). Next, 1 mL of air is injected into the flow path using a plastic syringe from the three-way stopcock connected to the flow path between the positive pressure sub-tank and the head, circulating the ink. The head is cleaned, and a nozzle check pattern is printed to confirm the number of ejecting nozzles (C). Thereafter, cleaning and checking the number of ejecting nozzles are carried out as a set every 5 minutes. The ratio of the number of ejecting nozzles (C) when the number of ejecting nozzles (A) is taken as 100%, is calculated, and the time until the number of ejecting nozzles has recovered to 98% or more is used as the evaluation standard to evaluate the bubble removal ability within the device. A rating indicates the best result, and a rating of C or higher is preferable.

[0141] -Evaluation criteria for air bubble removal- A: Recovery time is less than 10 minutes B: Recovery time is less than 20 minutes C: Recovery time is less than 50 minutes D: Not recovered in 60 minutes

[0142] In Table 2, "amount of ink recovered downstream of the head" indicates the amount of ink recovered from the recovery port of the liquid ejection head.

[0143] [Table 1]

[0144] [Table 2] [Explanation of symbols]

[0145] 1 nozzle plate 2 Flow path plate 3 Diaphragm material 4 nozzles 6 individual liquid chambers 6a, 6b, 6c, 6d, 6e Through groove portions forming individual liquid chambers 7 Fluid resistance section 7a: Through groove portion which is a fluid resistance portion 8 Liquid introduction section 8a, 8b: through grooves constituting the liquid introduction section 9 Filter section 10 Common liquid chamber 10A Downstream of common liquid chamber 10a Through groove 10B Common liquid chamber upstream part 10b Groove 11 Piezoelectric Actuator 12 Piezoelectric member 12A, 12B Piezoelectric element 13 Base material 15 Flexible wiring materials 20 Common liquid chamber member 21 first common liquid chamber member 22 second common liquid chamber member 25a, 25b Piezoelectric actuator through holes 29 Cover 30 vibration area 30a, 30b convex parts 40 Flow path member 41~45 Plate-shaped members 50 Circulation common liquid chamber 50a Groove 51 Fluid resistance section 51a: Through groove portion constituting the fluid resistance portion 52, 53 Circulation flow path 52a, 52b: through grooves forming the circulation flow path 53a, 53b, 53c, 53d: through-groove portions forming the circulation flow path 71 Supply Port 71a Through hole 81 Circulation Port 81a, 81b through holes 101 Main Tank 102 Negative pressure sub-tank 103 Positive pressure sub-tank 104, 105 Liquid transfer pump 106, 107 Pressure gauge 108 Liquid ejection head 109 Ink supply channel 110 Bypass flow path 111, 112 Flowmeter 113 Negative pressure air tank 114 Positive pressure air tank 115, 116 Air pump 120 Subtank [Prior art documents] [Patent documents]

[0146] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-284824 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-105159 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-141053

Claims

1. an ink containing water, a pigment, and a siloxane compound; a liquid ejection head that ejects the ink; a main tank that contains the ink; an image forming apparatus including the main tank and a sub-tank connected to the liquid ejection head, the sub-tank includes a positive pressure sub-tank that supplies the ink to the liquid ejection head, and a negative pressure sub-tank that recovers the ink from the liquid ejection head; an image forming apparatus, wherein the difference between the gas pressure inside the positive pressure sub-tank and the gas pressure inside the negative pressure sub-tank is 8.9 kPa or more and 30 kPa or less;

2. An image forming apparatus as described in Claim 1, characterized in that the ink contains a urethane resin.

3. 3. The image forming apparatus according to claim 1, wherein the siloxane compound is a compound represented by the following general formula (1): 【Chemical 1】 (In general formula (1), m represents an integer of 1 or more, n represents an integer, and R １ and R ２ represents a methyl group or a cyclic structure connected via O, and X represents the following general formula (2): 【Chemistry 2】 (In the general formula (2), a and b represent integers, and R ３ represents an alkylene group, and R ４ represents an alkyl group.)

4. 4. The image forming apparatus according to claim 1, wherein the siloxane compound is contained in the ink in an amount of 0.01% by mass to 1.0% by mass.

5. the pressure of the gas inside the positive pressure sub-tank is greater than the atmospheric pressure outside the liquid ejection head; 5. The image forming apparatus according to claim 1, wherein the pressure of the gas inside the negative pressure sub-tank is lower than the atmospheric pressure outside the liquid ejection head.

6. the liquid ejection head has a supply port through which the ink is supplied from the sub-tank and a recovery port through which the ink is recovered into the sub-tank, an amount of ink supplied to the supply port is equal to or greater than an amount of ink recovered from the recovery port; 6. The image forming apparatus according to claim 1, wherein the amount of ink recovered is 1.0 mL / min or more and 30.0 mL / min or less.

7. 7. The image forming apparatus according to claim 1, wherein the ink contains inorganic silica particles.

8. 8. The image forming apparatus according to claim 7, wherein the inorganic silica particles have a volume average primary particle diameter of 1 nm or more and 50 nm or less.

9. 9. The image forming apparatus according to claim 7, wherein the content of the inorganic silica particles in the ink is 0.01% by mass or more and 0.1% by mass or less.

10. 10. The image forming apparatus according to claim 1, wherein the ink has a viscosity at 25° C. of 4 mPa·s or more and 10 mPa·s or less.

11. 11. The image forming apparatus according to claim 1, wherein the ink has a surface tension of 35 mN / m or less at 25°C.

12. 12. The image forming apparatus according to claim 1, wherein the liquid ejection head is a line head type.

13. an ink containing water, a pigment, and a siloxane compound; a liquid ejection head that ejects the ink; a main tank that contains the ink; an image forming method performed by an image forming apparatus including the main tank and a sub-tank connected to the liquid ejection head, the sub-tank includes a positive pressure sub-tank that supplies the ink to the liquid ejection head, and a negative pressure sub-tank that recovers the ink from the liquid ejection head; an image forming method, characterized in that the difference between the gas pressure inside the positive pressure sub-tank and the gas pressure inside the negative pressure sub-tank is set to 8.9 kPa or more and 30 kPa or less;

Images