Image formation methods

Abstract

The image forming method of the present invention uses an inkjet recording device with an inkjet head, the inkjet head having a pressure chamber, a nozzle and a plurality of ink discharge paths, two or more of the plurality of ink discharge paths being provided for the discharge opening of the nozzle, and an ink circulation device for circulating the ink from the ink supply path to the ink discharge path. When the viscosity of the ink at 25°C at a shear rate of 1 [1 / s] is set as A1, the viscosity at a shear rate of 100 [1 / s] is set as A100, and the viscosity at a shear rate of 1000 [1 / s] is set as A1000, the following relationships (I) and (II) are satisfied, and the ink circulation device is controlled to make the average shear rate in the flow path communicating with the nozzle in the pressure chamber 100 [1 / s] or more, Equation (I): A1000 < A100 < A1 Equation (II): |A100 - A1000| < |A1 - A100|.

Description

Technical Field

[0001] This invention relates to an image forming method, and more particularly to an image forming method that, when using a highly thixotropic ink and circulating the ink near the nozzle to discharge the ink, suppresses changes in ink viscosity during discharge and enables uniform discharge speeds between nozzles to improve image quality. Background Technology

[0002] Previously, inkjet heads with circulation mechanisms were used to ensure stable discharge of water-based inks. With the pursuit of higher image quality, inks now require smaller droplets and higher pinning properties, necessitating increased solids concentration.

[0003] If the concentration of solid components in the ink is increased, the ink will exhibit thixotropy, and the ink viscosity will change according to the shear force, thus causing the discharge to become unstable.

[0004] In addition, inks that are actively made thixotropic to increase viscosity after discharge in order to obtain higher pinning properties have also been disclosed (for example, see Patent Document 1).

[0005] For inks with high thixotropy, the ink flow rate increases sharply upon discharge, while the ink viscosity decreases sharply (e.g., by...). Figure 13 The shear velocity range of region A is limited, so there are problems such as difficulty in achieving uniform flow velocity in multiple pressure chambers and uneven discharge velocity between nozzles when manufacturing deviations exist, leading to image quality degradation. Figure 13 In the text, ink A represents an ink with higher thixotropy than ink B and ink C.

[0006] Furthermore, when such a highly thixotropic ink is used in the inkjet head with a circulating flow path described in Patent Document 1, if the ink is circulated near the nozzle, the ink viscosity will be only... Figure 13 Variations in the shear rate range of region B can suppress changes in ink viscosity during ejection, resulting in uniform ejection speeds between nozzles. However, in inkjet heads with a structure where the ink circulation direction is perpendicular to the ejection direction, there is a problem where increasing the circulation velocity causes droplets to bend along the circulation direction, leading to image quality degradation.

[0007] On the other hand, in the structure disclosed in Patent Document 2, where there is a discharge flow path (circulation flow path) on one side of the ink channel (flow path connected to the nozzle), the circulation flow rate on the side without the discharge flow path is extremely slow, and the ink viscosity distribution is formed in the ink channel.

[0008] Patent Document 1: Japanese Patent Application Publication No. 2011-225859

[0009] Patent Document 2: Japanese Patent No. 5514579 Summary of the Invention

[0010] The present invention was made in view of the above-mentioned problems / situations, and its solution is to provide an image forming method that, when using ink with high thixotropic properties and circulating the ink near the nozzle to discharge the ink, can suppress changes in ink viscosity during discharge, can make the discharge speed between nozzles uniform, and can improve image quality.

[0011] In order to solve the above-mentioned problems, the inventors, in the process of studying the causes of the above problems, discovered that by using an ink with high thixotropic properties relative to the shear rate within a specific range, and by using an ink circulation device to control the average shear rate in the flow path connected to the nozzle to 100 [1 / s] or more, the discharge speed between the nozzles can be made uniform to improve image quality, and thus the present invention was formed.

[0012] That is, the above-mentioned problems of the present invention can be solved by the following methods.

[0013] 1. An image forming method using an inkjet recording device with an inkjet head, the inkjet head comprising:

[0014] The pressure chamber supplies ink from the ink supply path and can freely apply pressure to the ink stored inside;

[0015] The nozzle has a discharge opening for discharging the ink and is disposed in communication with the pressure chamber; and

[0016] Multiple ink discharge paths are connected close to the communication positions of the nozzles relative to the pressure chambers.

[0017] in,

[0018] For the discharge opening of the nozzle described above, two or more ink discharge paths are provided.

[0019] An ink circulation device is provided that circulates the ink from the ink supply path to the ink discharge path.

[0020] When the viscosity of the ink at 25°C at a shear speed of 1 [1 / s] is set to A1, the viscosity of the ink at 25°C at a shear speed of 100 [1 / s] is set to A100, and the viscosity of the ink at 25°C at a shear speed of 1000 [1 / s] is set to A1000, the following relationships (I) and (II) are satisfied.

[0021] The ink circulation device described above is controlled to ensure that the average shear velocity in the flow path connected to the nozzle in the pressure chamber is above 100 [1 / s].

[0022] Equation (I): A1000 < A100 < A1

[0023] Equation (II): |A100-A1000|<|A1-A100|.

[0024] 2. According to the image forming method described in the first item, wherein the ink satisfies the following relationship (III) to (V).

[0025] Equation (III): 1 mPa·s < |A1-A1000|

[0026] Equation (IV): |A100-A1000|<10mPa·s

[0027] Equation (V): 2 mPa·s < A1000 < 20 mPa·s

[0028] 3. The image forming method according to the first or second item, wherein the speed variation of the discharge speed of the ink discharged from the nozzle is less than 5%.

[0029] 4. The image forming method according to any one of items 1 to 3, wherein an actuator is provided for applying pressure to the ink in the pressure chamber.

[0030] An oscillating waveform is applied, which has a lower voltage than the drive waveform that causes the ink to be discharged from the nozzle, and causes the interface of the ink in the pressure chamber to vibrate.

[0031] 5. The image forming method according to any one of items 1 to 4, wherein the ink contains pigment, fixing resin, water-soluble solvent, and water.

[0032] Containing 3 to 10% by mass of the above-mentioned pigments,

[0033] Containing 8-20% by mass of the above-mentioned fixing resin,

[0034] Containing 10-30% by mass of the above-mentioned water-soluble solvent, and,

[0035] The water contains 40% to 79% by mass of the above-mentioned water.

[0036] 6. The image forming method according to any one of items 1 to 5, wherein the surface tension of the ink is in the range of 22 to 25 mN / m.

[0037] The method described above by the present invention provides an image forming method that, when using ink with high thixotropic properties and circulating the ink near the nozzle to discharge the ink, can suppress changes in ink viscosity during discharge, can achieve uniform discharge speed between nozzles, and can improve image quality.

[0038] Although the mechanism of expression or action of the effects of this invention is not clear, it is speculated as follows.

[0039] By setting the viscosity of the ink at 25°C at a shear speed of 1 [1 / s] as A1, the viscosity of the ink at 25°C at a shear speed of 100 [1 / s] as A100, and the viscosity of the ink at 25°C at a shear speed of 1000 [1 / s] as A1000, the relationships of equations (I) and (II) above are satisfied, thus the ink viscosity only... Figure 13 The viscosity varies in region B. As a result, when discharging such highly thixotropic ink, even when the ink is circulated near the nozzle, the viscosity change during discharge can be suppressed. This allows for uniform discharge speed between nozzles, resulting in improved image quality. Attached Figure Description

[0040] Figure 1 This is a schematic diagram representing an inkjet recording device.

[0041] Figure 2 This is a bottom view of the head unit.

[0042] Figure 3A This is a 3D view of the inkjet head.

[0043] Figure 3B This is a cross-sectional view of the inkjet head.

[0044] Figure 4 This is an exploded 3D view of the inkjet head.

[0045] Figure 5 This is an exploded 3D view of the chip.

[0046] Figure 6A This is a top view of the pressure chamber substrate.

[0047] Figure 6B This is a bottom view of the pressure chamber substrate.

[0048] Figure 7A This is a top view of the flow path isolation substrate.

[0049] Figure 7B This is a bottom view of the flow path isolation substrate.

[0050] Figure 8 This is a top view of the nozzle substrate.

[0051] Figure 9A This is a cross-sectional view of the head chip during the IXA-IXA cut.

[0052] Figure 9B This is a cross-sectional view of the head chip during the IXB-IXB cut.

[0053] Figure 10A This is a cross-sectional view of the chip head during the XA-XA cut.

[0054] Figure 10B This is a cross-sectional view of the head chip during the XB-XB cutting process.

[0055] Figure 11 This is a schematic diagram representing the ink circulation system.

[0056] Figure 12 This is a block diagram illustrating the main functional components of an inkjet recording device.

[0057] Figure 13 This is a graph representing the viscosity of the ink relative to the shear rate. Detailed Implementation

[0058] The image forming method of the present invention utilizes an inkjet recording apparatus having an inkjet head, which includes: a pressure chamber for supplying ink from an ink supply path and for freely applying pressure to the ink stored therein; a nozzle having a discharge opening for discharging the ink and disposed in communication with the pressure chamber; and a plurality of ink discharge paths connected close to the nozzle at a communication position relative to the pressure chamber, wherein two or more of the plurality of ink discharge paths are provided for the discharge opening of the nozzle, and the ink is directed upward from the ink supply path. The ink circulation device for circulating ink discharge flow path satisfies the relationship between the above-mentioned formulas (I) and (II) when the viscosity of the ink at 25°C is set to A1 at a shear speed of 1 [1 / s], A100 at a shear speed of 100 [1 / s], and A1000 at a shear speed of 1000 [1 / s]. The ink circulation device performs control so that the average shear speed in the flow path connected to the nozzle in the pressure chamber is 100 [1 / s] or higher.

[0059] This feature is a technical feature shared by or corresponding to the following embodiments.

[0060] As an embodiment of the present invention, the ink is preferably satisfied with the relationship of the above formulas (III) to (V) so that even thixotropic inks can be discharged from the inkjet head within an appropriate viscosity range, thus achieving both discharge and fixing properties.

[0061] Preferably, the speed variation of the ink ejected from the above-mentioned nozzle is less than 5%. That is, by controlling the speed to satisfy the relationship between equations (I) and (II) above, even for inks with high thixotropic properties, the speed variation in the same nozzle can be suppressed to less than 5%, thereby improving image quality.

[0062] Furthermore, it is preferable to have an actuator that applies pressure to the ink in the pressure chamber and applies an oscillating waveform that has a lower voltage than the drive waveform that discharges the ink from the nozzle, thereby causing the interface of the ink in the pressure chamber to vibrate. By applying the oscillating waveform, the ink is stirred (vibrated), which reduces the viscosity of the thixotropic ink, thereby suppressing nozzle clogging and poor discharge.

[0063] In terms of ink ejectibility, adhesion to substrate, and ink drying properties, the ink preferably contains pigment, fixing resin, water-soluble solvent, and water, with the pigment comprising 3 to 10% by mass, the fixing resin comprising 8 to 20% by mass, the water-soluble solvent comprising 10 to 30% by mass, and the water comprising 40 to 79% by mass.

[0064] Furthermore, in order to improve the stability of the ink ejected from the nozzle of the inkjet head and to make the resulting image more refined, it is preferable that the surface tension of the ink is in the range of 22 to 25 mN / m.

[0065] [Summary of the image forming method of the present invention]

[0066] The image forming method of the present invention uses an inkjet recording apparatus equipped with an ink circulation device. When the viscosity of the ink at 25°C at a shear speed of 1 [1 / s] is set to A1, the viscosity of the ink at 25°C at a shear speed of 100 [1 / s] is set to A100, and the viscosity of the ink at 25°C at a shear speed of 1000 [1 / s] is set to A1000, the following relationships (I) and (II) are satisfied. Furthermore, the ink circulation device is controlled to ensure that the average shear speed in the flow path connected to the nozzle in the pressure chamber is 100 [1 / s] or higher.

[0067] Equation (I): A1000 < A100 < A1

[0068] Equation (II): |A100-A1000|<|A1-A100|

[0069] The inkjet recording apparatus of the present invention includes: a pressure chamber for supplying ink from an ink supply path and for freely applying pressure to the ink stored therein; a nozzle having a discharge opening for discharging the ink and disposed in communication with the pressure chamber; and a plurality of ink discharge paths connected close to the nozzle at a communication position relative to the pressure chamber, wherein two or more of the plurality of ink discharge paths are provided for the discharge opening of the nozzle. Furthermore, it includes an ink circulation device for circulating ink from the ink supply path to the ink discharge paths. Details of the inkjet recording apparatus will be described later.

[0070] <Ink viscosity>

[0071] The viscosity of the ink of the present invention at 25°C satisfies the relationship of formulas (I) and (II) above. Furthermore, it is preferable that the ink of the present invention satisfies the relationship of formulas (III) to (V) below.

[0072] Equation (III): 1 mPa·s < |A1-A1000|

[0073] Equation (IV): |A100-A1000|<10mPa·s

[0074] Equation (V): 2 mPa·s < A1000 < 20 mPa·s

[0075] The above viscosity was measured using a rheometer (viscoelasticity measuring device). Examples of rheometers include the MCR-102 (manufactured by Anton Paar). Furthermore, the viscosity at various shear rates was measured under the following conditions.

[0076] Measuring fixture: CP75-1-SN30423; d = 0.151 mm

[0077] Measurement conditions: The measurement was performed at 25℃.

[0078] <Average shear velocity in the flow path connected to the nozzle>

[0079] The ink circulation device of the present invention performs control such that the average shear rate in the flow path connected to the nozzle in the pressure chamber is above 100 [1 / s].

[0080] Here, "average shear rate" refers to the average shear rate during circulation, not at discharge. Additionally, "flow path connected to the nozzle" is as follows: Figure 9A As indicated by the reference numeral R in the attached diagram, it refers to the flow path near the nozzle in the pressure chamber 131. "Flow path near the nozzle" refers to the flow path formed by the flow path components closest to the nozzle, specifically the flow path R formed by the flow path isolation substrate 12.

[0081] The average shear rate in this invention is calculated using the following formula.

[0082] Average shear rate = Average flow velocity ÷ Radius of the circular pipe

[0083] The radius of a circular tube is the positive square root of (cross-sectional area ÷ π) in the case of a non-circular flow path.

[0084] The circulating flow rate of a single nozzle = the circulating flow rate of all nozzles (also known as "circulating flow rate Q") (measured value) ÷ the number of nozzles.

[0085] Average flow velocity = circulating flow rate of a single nozzle ÷ cross-sectional area of ​​the flow path connected to the nozzle

[0086] The ink circulation device of the present invention performs control such that the average shear rate in the flow path connected to the nozzle is 100 [1 / s] or more, preferably controlled in the range of 100 to 1000 [1 / s].

[0087] As a method for controlling the average shear rate within the aforementioned range, as can be seen from the formula for calculating the average shear rate described above, it is possible to, for example, control the circulating flow rate Q of all the aforementioned nozzles.

[0088] Furthermore, since the circulating flow rate Q can be calculated using the following formula, in order to control this circulating flow rate Q, adjustments can be made to the first ink port 53 and the fourth ink port 56 constituting the ink flow path of the inkjet head in the inkjet recording apparatus 200 described later (see [reference]). Figure 11 The circulating pressure difference (pressure difference) in the inkjet recording device 200 (the pressure difference between the INNET and OUTLET of the inkjet head). Specifically, the control unit 240 of the inkjet recording device 200 adjusts pressure P1 and pressure P2 by appropriately changing the pressure applied to the pump 88 of the ink circulation device 8, the ink filling amount in each sub-reservoir 81 and 82, and the vertical (gravity direction) position of each sub-reservoir 81 and 82, and controls the ink flow rate (circulating flow rate Q) connected to the nozzle by the pressure difference (circulating pressure difference ΔP) between pressure P1 and pressure P2.

[0089] Circulation flow rate Q = Circulation pressure difference ΔP / Head flow path resistance R

[0090] (The aforementioned circulating pressure difference ΔP represents the circulating pressure difference between the first ink port 53 and the fourth ink port 56. The aforementioned head flow path resistance represents the flow path resistance from the fourth ink port 56 to the first ink port 53.)

[0091] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the scope of the invention is not limited to the examples shown in the drawings. Furthermore, for ease of explanation, in this specification, the arrangement direction of the nozzles 111 of the inkjet head 100, i.e., the printing width direction, is defined as the left-right direction; the direction of conveying the recording medium below the nozzles 111 is defined as the front-back direction; and the direction orthogonal to the left-right and front-back directions is defined as the up-down direction. Additionally, the arrows in the flow paths of the accompanying drawings indicate the direction of ink flow.

[0092] Furthermore, in this application, “~” is used to mean the lower limit and the upper limit of the values ​​contained before and after it.

[0093] [Inkjet recording device]

[0094] like Figure 1As shown, the inkjet recording device 200 includes a paper feeding unit 210, an image recording unit 220, a paper output unit 230, and an ink circulation device 8 (see reference) that serves as an ink supply unit. Figure 11 ), and control unit (see Figure 12 The inkjet recording apparatus 200 delivers the recording medium M stored in the paper supply unit 210 to the image recording unit 220, forms an image on the recording medium M in the image recording unit 220, and delivers the recording medium M with the formed image to the paper output unit 230.

[0095] The paper supply unit 210 includes a paper supply tray 211 for storing the recording medium M and a media supply unit 212 for conveying the recording medium M from the paper supply tray 211 and supplying it to the image recording unit 220. The media supply unit 212 has a wheel-shaped belt supported on its inner side by two rollers. By rotating the rollers while the recording medium M is placed on the belt, the recording medium M is conveyed from the paper supply tray 211 to the image recording unit 220.

[0096] The image recording unit 220 includes a transport drum 221, a transfer unit 222, a heating unit 223, a head unit 224, a fixing unit 225, and a delivery unit 226.

[0097] The transport drum 221 is cylindrical, and its outer circumferential surface forms the transport surface for placing the recording medium M. The transport drum 221, while holding the recording medium M on its transport surface, transports... Figure 1 The recording medium M is rotated in the direction of the arrow in the figure, thereby conveying the recording medium M along the conveying surface. In addition, the conveying drum 221 has a claw and an air suction part (not shown). The claw presses the end of the recording medium M and the air suction part draws the recording medium M to the conveying surface, thereby holding the recording medium M on the conveying surface.

[0098] The transfer unit 222 is located between the media supply section 212 and the transport drum 221 of the paper supply section 210. It holds and picks up one end of the recording medium M transported from the media supply section 212 via the rocker arm 222a and delivers it to the transport drum 221 via the transfer drum 222b.

[0099] A heating unit 223 is disposed between the placement position of the transfer drum 222b and the placement position of the head unit 224, and heats the recording medium M conveyed by the transfer drum 221 to bring the recording medium M to a temperature within a specified temperature range. The heating unit 223 may include, for example, an infrared heater, which is energized based on a control signal supplied from a control unit (not shown) to generate heat.

[0100] The head unit 224 ejects ink from the recording medium M based on image data at an appropriate timing corresponding to the rotation of the transport drum 221 holding the recording medium M, thereby forming an image. The head unit 224 is configured such that the ink ejection surface faces the transport drum 221 and is spaced apart by a predetermined distance. In the inkjet recording apparatus 200 of this embodiment, for example, four head units 224 corresponding to four colors of ink—yellow (Y), magenta (M), cyan (C), and black (K)—are arranged at predetermined intervals starting from the upstream side of the transport direction of the recording medium M in the order of the colors Y, M, C, and K.

[0101] For example, such as Figure 2 As shown, in the head unit 224, a pair of inkjet heads 100 adjacent in the front-to-back direction are arranged in an alternating pattern at different positions in the front-to-back direction. Furthermore, the head unit 224 is used to maintain a fixed position relative to the rotation axis of the transport drum 221 during image recording. That is, the inkjet recording apparatus 200 is an inkjet recording apparatus 200 that uses a line head to record images in a one-pass drawing manner.

[0102] The fixing unit 225 has a light-emitting portion arranged across the width of the transport drum 221 in the X direction. Ultraviolet light or other energy rays are irradiated onto the recording medium M placed on the transport drum 221 from this light-emitting portion to cure and fix the ink ejected onto the recording medium M. The light-emitting portion of the fixing unit 225 is positioned downstream of the head unit 224 in the transport direction and upstream of the transfer drum 226a of the transport unit 226, facing the transport surface.

[0103] The conveyor section 226 includes a belt ring 226b with a wheel-shaped belt supported on the inner side by two rollers, and a cylindrical transfer drum 226a that transfers the recording medium M from the conveyor drum 221 to the belt ring 226b. The recording medium M is conveyed from the conveyor drum 221 to the belt ring 226b via the belt ring 226b and then sent out to the paper discharge section 230.

[0104] The paper discharge section 230 has a plate-shaped paper discharge tray 231 for holding the recording medium P sent from the image recording section 220 via the conveying section 226.

[0105] [Inkjet head]

[0106] like Figure 3A , Figure 3B as well as Figure 4As shown, the inkjet head 100 of this embodiment includes a head chip 1, a wiring board 2 on which the head chip 1 is disposed, a drive circuit board 4 connected to the wiring board 2 via a flexible board 3, a manifold 5 for storing ink supplied to the pressure chamber 131 inside the head chip 1, a housing 6 for housing the manifold 5 inside, a cap plate 7 installed to block the bottom opening of the housing 6, and a cover member 9 installed on the housing 6.

[0107] In addition, Figure 3A The diagram of manifold 5 is omitted in the text. Figure 3B as well as Figure 4 The illustration of the cover component 9 is omitted.

[0108] In addition, in this embodiment, an example with four columns of nozzles 111 on the head chip 1 is described, but the number of columns and configuration of nozzles 111 can be appropriately changed. For example, it can be any one to three columns, or more than five columns.

[0109] The head chip 1 is a roughly quadrangular prism-shaped component that runs long along the left-right direction. It is constructed by sequentially stacking a pressure chamber substrate 13, a flow path isolation substrate 12, and a nozzle substrate 11 (see reference). Figure 5-1 0. ).

[0110] The pressure chamber substrate 13 is provided with a pressure chamber 131, an air chamber 132, and a common ink discharge path 133, etc. (see reference) Figure 5 , Figure 6A as well as Figure 6B wait).

[0111] The pressure chambers 131 and air chambers 132 are arranged in a plurality of alternating configurations in the left-right direction and in four columns in the front-back direction.

[0112] The pressure chamber 131 has a generally rectangular cross-section and is formed along the vertical direction. It has an inlet on the upper surface of the pressure chamber substrate 13 and an outlet on the lower surface. Furthermore, the pressure chamber 131 communicates with an ink storage section 51 at its upper end, from which ink is supplied to the pressure chamber 131. Ink for ejection from the nozzle 111 is stored inside the pressure chamber 131. Additionally, the pressure chamber 131 spans the pressure chamber substrate 13 and the flow path isolation substrate 12, and is formed with a generally rectangular cross-section having the same area along the vertical direction. Its lower end communicates with the nozzle 111 (see reference). Figure 9A , Figure 9B wait.).

[0113] Air chamber 132 has a generally rectangular cross-section slightly larger than pressure chamber 131 and is formed parallel to pressure chamber 131 in the vertical direction. Unlike pressure chamber 131, air chamber 132 is not connected to ink storage section 51, and ink does not flow into air chamber 132. Furthermore, air chamber 132 is not connected to nozzle 111 (see reference). Figure 9A , Figure 9B wait.).

[0114] A pressure chamber 131 and an air chamber 132 are formed by a partition 136 made of piezoelectric material, which serves as a pressure generating unit (see reference). Figure 10A A drive electrode (not shown) is provided in the partition 136, and the partition 136 and the drive electrode constitute an actuator. Furthermore, when a voltage is applied to the drive electrode, portions of the partition 136 between adjacent pressure chambers 131 repeatedly share a pattern displacement, thereby applying pressure to the ink within the pressure chamber 131. Additionally, in Figures 5-1 In the pressure chamber 131 shown in 0, the pressure chamber 131 located at the end in the left-right direction that has a partition wall 136 on only one side is not used, but a pressure chamber 131 with partition walls 136 on both sides is used instead.

[0115] Furthermore, in the inkjet head 100 of the present invention, so-called meniscus oscillation is preferably performed. The meniscus oscillation is based on the oscillation waveform that causes the volume of the pressure chamber 131 to continuously reciprocate within a constant range, without discharging ink, and causes the meniscus (curved interface) formed by the ink in the nozzle 111, the ink in the nozzle 111, and the ink in the pressure chamber 131 to vibrate.

[0116] Here, the "oscillating waveform" is a driving pulse weaker than the contraction pulse that causes droplet discharge. It is a contraction or expansion pulse that causes the volume of the pressure chamber to contract or expand within the range that only generates pressure waves. It is a waveform used to oscillate the interface of the liquid in the nozzle in order to suppress the blockage (decap) caused by the increased viscosity of the liquid (ink) near the nozzle due to drying.

[0117] Therefore, when ink is not being discharged (not during printing), the ink in the nozzle 111 can be agitated by circulating the nozzle and oscillating the meniscus. So when discharging (printing) is performed next, the nozzle blockage caused by sedimentation and the poor discharge caused by the thickening of ink in the nozzle 111 can be suppressed, and the decrease in discharge speed can be suppressed.

[0118] Specifically, by applying pressure to the ink in the pressure chamber 131, the aforementioned actuator (partition wall 136 and drive electrode, etc.) applies an oscillating waveform with a smaller voltage than the drive waveform that causes the ink to be discharged from the nozzle 111, which causes the interface of the ink in the pressure chamber 131 to vibrate.

[0119] Alternatively, the air chamber 132 may be omitted and only the pressure chamber 131 may be formed. However, as described above, it is preferable to alternately arrange the pressure chamber 131 and the air chamber 132. This ensures that the pressure chambers 131 are not adjacent to each other, so that when the partition wall 136 adjacent to one pressure chamber 131 deforms, it will not affect the other pressure chambers 131.

[0120] The first common ink discharge path 134 and the second common ink discharge path 135 are connected to form a common ink discharge path 133. Figure 5 as well as Figure 6B (See reference).

[0121] The first common ink discharge path 134 is located on the lower surface of the pressure chamber substrate 13, arranged in three rows on the front, rear, and central sides of the head chip 1, and positioned along the left-right direction to avoid the portions where the pressure chamber 131 and air chamber 132 are located. Furthermore, multiple individual ink discharge paths 121 located on the flow path isolation substrate 12 are connected to the lower surface of the first common ink discharge path 134. Ink flowing from these individual ink discharge paths 121 (second individual ink discharge paths 123) can merge into the first common ink discharge path 134. Figure 6B , Figure 7A as well as Figure 9A Additionally, near the right end, the first common ink discharge path 134 is connected to the second common ink discharge path 135, which is capable of discharging ink to the outside of the head chip 1. Therefore, the first common ink discharge path 134 becomes a flow path for ink flowing from the individual ink discharge path 121 (the second individual ink discharge path 123) to flow toward the second common ink discharge path 135.

[0122] The second common ink discharge path 135 is the same as the pressure chamber 131, and is formed along the vertical direction. Furthermore, for the second common ink discharge path 135, the lower surface of the pressure chamber substrate 13 communicates with the first common ink discharge path 134, and the upper surface communicates with the discharge liquid chamber 57, forming a flow path for discharging ink flowing from the first common ink discharge path 134 upwards (opposite to the nozzle substrate 11 side) to the outside of the head chip 1. Additionally, the second common ink discharge path 135 is located near the right end of the head chip 1 and communicates with the first common ink discharge path 134. Furthermore, by having a larger volume than each pressure chamber 131, the second common ink discharge path 135 can improve ink discharge efficiency.

[0123] A pressure chamber 131 and a separate ink discharge path 121 branching from the pressure chamber 131 are formed on the flow path isolation substrate 12 (see reference). Figure 9A as well as Figure 9B wait).

[0124] The pressure chamber 131 spans the flow path isolation substrate 12 and the pressure chamber substrate 13, and is formed in a generally rectangular cross-section with the same area along the vertical direction.

[0125] For the individual ink discharge path 121, one end is connected to the pressure chamber 131 and the other end is connected to the first common ink discharge path 134, thus forming a flow path for discharging ink from the pressure chamber 131 to the first common ink discharge path 134.

[0126] From the viewpoint of easily expelling air bubbles, foreign matter, etc., along with the ink, two or more separate ink discharge paths 121 are provided at the discharge opening of the nozzle 111. That is, at least two or more separate ink discharge paths 121 are provided for each pressure chamber 131. Furthermore, for example, Figure 9A as well as Figure 9B As shown, two separate ink discharge paths 121 are provided in the front and rear directions of the pressure chamber 131, respectively. This arrangement facilitates the discharge of air bubbles, foreign matter, etc., along with the ink, and also improves manufacturing efficiency, making it a preferred option.

[0127] From the perspective that the flow path isolation substrate 12 is easy to process from the individual ink discharge path 121 (high precision) and that its high thermal conductivity allows for easy and uniform maintenance of ink temperature, a substrate made of silicone, stainless steel (SUS), or alloy 42 is preferred. Furthermore, substrates made of materials whose coefficient of thermal expansion is close to that of the material forming the pressure chamber substrate 13 are preferred.

[0128] A through hole, i.e., nozzle 111, is provided on the nozzle substrate 11 in the thickness direction (vertical direction) (see reference). Figure 8 The nozzle 111 is connected to the pressure chamber 131, serving as an ejection port (discharge opening) for ejecting ink stored in the pressure chamber 131 when pressure is applied to the ink within the pressure chamber 131. Furthermore, in this embodiment, the nozzles 111 are arranged in four rows in the left-right direction and in the front-back direction.

[0129] In addition, such as Figure 9A as well as Figure 9B As shown, the nozzle substrate 11 preferably forms one of the flow path walls of the first individual ink discharge path 122. Furthermore, since the nozzle substrate 11 is relatively thin, it can function as a damper capable of slightly elastically deforming under pressure to change the volume of the flow path.

[0130] Preferably, the nozzle substrate 11 is made of a substrate composed of polyimide resin, polyethylene terephthalate resin, polyamide resin, polysulfone resin, etc. This allows for high-precision manufacturing of the nozzle substrate 11 via laser processing, and also provides excellent ink resistance, making it preferable. Furthermore, due to the high elasticity of these resin substrates, they can be suitable for use as the flow path wall of the first individual ink supply path.

[0131] Alternatively, the nozzle substrate 11 can also be manufactured by etching a silicone substrate.

[0132] Furthermore, from the viewpoint of flow path protection, it is preferable to provide an ink-resistant protective film on the flow path surface of the pressure chamber 131, the individual ink discharge path 121, and the common ink discharge path 133 within the head chip 1, which serve as the ink flow path.

[0133] The protective film is not particularly limited as long as it is ink-resistant, but for example, it is preferred to use a film containing parylene or its derivatives (hereinafter also referred to as parylene film).

[0134] Parylene films are resin coatings made of parylene resin or its derivatives, and can be formed, for example, by chemical vapor deposition (CVD) using solid parylene dimers or their derivatives as the deposition source. Specifically, the parylene dimer is vaporized and thermally decomposed, producing parylene free radicals that adsorb onto the surface of flow path components or metal layers, where they undergo a polymerization reaction to form the coating.

[0135] Parylene films are available with various properties, and multilayer parylene films, including those composed of multiple parylene films stacked together, can be used to achieve desired properties. From the viewpoint of obtaining excellent insulation and ink resistance, a parylene film thickness in the range of 5–20 μm is preferred.

[0136] Parylene is a crystalline polymer with a molecular weight of up to 500,000. The process involves sublimating and thermally decomposing the parylene dimer in the raw material to generate parylene free radicals. These free radicals attach to the insulating substrate 40 and simultaneously polymerize to form parylene, creating a protective film.

[0137] As parylene, parylene N (a trade name manufactured by Parylene Corporation of Japan) can be listed.

[0138] Examples of parylene derivatives include parylene C (trade name manufactured by Parylene Co., Ltd. of Japan), which has a chlorine atom substituted on the benzene ring; parylene D (trade name manufactured by Parylene Co., Ltd. of Japan), which has chlorine atoms substituted at positions 2 and 5 on the benzene ring; and parylene HT (trade name manufactured by Parylene Co., Ltd. of Japan), which has a hydrogen atom substituted for a fluorine atom in the methylene group attached to the benzene ring.

[0139] From the viewpoint that the above-mentioned layer thickness achieves excellent insulation and ink resistance, in these products, parylene N or parylene C are preferred as parylene and its derivatives in this embodiment.

[0140] Furthermore, although the first separate ink discharge path 122 of this embodiment is provided on the lower surface side of the flow path isolation substrate 12, it is not limited thereto. For example, the first separate ink discharge path 122 may be provided across both the nozzle substrate 11 and the flow path isolation substrate 12, may be provided only on the nozzle substrate 11, or may be provided slightly above the bottom surface of the flow path isolation substrate 12 without being adjacent to the nozzle substrate 11.

[0141] like Figure 4 As shown, a wiring substrate 2 is disposed on the upper surface of the head chip 1, and two flexible substrates 3 connected to the driving circuit substrate 4 are disposed on the two edges along the front-back direction of the wiring substrate 2.

[0142] The wiring substrate 2 is formed as a generally rectangular plate that is elongated in the left-right direction, and has an opening 22 in its approximately central part. The width of the wiring substrate 2 in the left-right direction and the front-back direction is larger than that of the head chip 1.

[0143] The opening 22 is formed into a roughly rectangular shape that is elongated in the left-right direction. With the head chip 1 installed on the wiring substrate 2, the inlets of each pressure chamber 131 in the head chip 1 and the outlet of the second common ink discharge path 135 are exposed on the upper side.

[0144] The flexible substrate 3 electrically connects the drive circuit substrate 4 and the electrode portion of the wiring substrate 2, enabling the signal from the drive circuit substrate 4 to be applied to the drive electrode disposed in the partition 136 within the head chip 1 via the flexible substrate 3.

[0145] In addition, the lower end of the manifold 5 is fixed to the outer edge of the wiring substrate 2 by adhesive bonding. That is, the manifold 5 is disposed on the inlet side (upper side) of the pressure chamber 131 of the head chip 1 and is connected to the head chip 1 via the wiring substrate 2.

[0146] The manifold 5 is a resin-molded component located above the pressure chamber 131 of the head chip 1, storing the ink introduced into the pressure chamber 131. Specifically, as... Figure 3B As shown, the manifold 5 is formed as a long strip in the left-right direction, and has a hollow main body 52 that constitutes the ink storage section 51, and a first ink port 53 to a fourth ink port 56 that constitute the ink flow path. In addition, the ink storage section 51 is divided into two parts, a first liquid chamber 51a on the upper side and a second liquid chamber 51b on the lower side, by a filter F for removing impurities from the ink.

[0147] The first ink port 53 is connected to the upper right end of the first liquid chamber 51a and is used to introduce ink into the ink storage section 51. In addition, a first connector 81a is inserted into the front end of the first ink port 53.

[0148] The second ink port 54 is connected to the upper left end of the first liquid chamber 51a and is used to remove air bubbles from the first liquid chamber 51a. In addition, a second connector 81b is inserted into the front end of the second ink port 54.

[0149] The third ink port 55 is connected to the upper left end of the second liquid chamber 51b and is used to remove air bubbles from the second liquid chamber 51b. In addition, a third connector 82a is inserted into the front end of the third ink port 55.

[0150] The fourth ink port 56 is connected to the discharge chamber 57, which is connected to the second common ink discharge path 135 of the printhead chip 1. The ink discharged from the printhead chip 1 is discharged to the outside of the printhead 100 through the fourth ink port 56.

[0151] The housing 6 is, for example, a component formed by die casting using aluminum as the material, and is shaped as an elongated strip in the left-right direction. Furthermore, the housing 6 is configured to house the manifold 5, which houses the head chip 1, wiring substrate 2, and flexible substrate 3, and the bottom surface of the housing 6 is open. Additionally, mounting holes 68 are formed at both ends of the housing 6 in the left-right direction for mounting the housing 6 to the side of the printer body.

[0152] The cap plate 7 has a nozzle opening 71 that is elongated in the left-right direction at its approximately central part, and is installed such that the nozzle base plate 11 is exposed through the nozzle opening 71 in a manner that blocks the bottom opening of the housing 6.

[0153] [Ink circulation device]

[0154] The ink circulation device 8 is an ink supply unit used to circulate ink from the pressure chamber 131 inside the inkjet head 100 to the individual ink discharge path 121. The ink circulation device 8 consists of a supply sub-reservoir 81, a circulation sub-reservoir 82, and a main reservoir 83, etc. (see reference). Figure 11 。).

[0155] The supply sub-reservoir 81 is filled with ink for supplying to the ink storage section 51 of the manifold 5, and is connected to the first ink port 53 via the ink flow path 84.

[0156] The circulating sub-reservoir 82 is filled with ink discharged from the discharge chamber 57 of the manifold 5 and connected to the fourth ink port 56 via the ink flow path 85.

[0157] Furthermore, the supply sub-reservoir 81 and the circulation sub-reservoir 82 are positioned at different locations in the vertical direction (gravity direction) relative to the nozzle surface of the head chip 1 (hereinafter also referred to as the "position reference surface"). As a result, pressure P1 is generated due to the water level difference between the position reference surface and the supply sub-reservoir 81, and pressure P2 is generated due to the water level difference between the position reference surface and the circulation sub-reservoir 82.

[0158] Furthermore, the supply sub-reservoir 81 and the circulation sub-reservoir 82 are connected via the ink flow path 86. Moreover, the ink can be returned from the circulation sub-reservoir 82 to the supply sub-reservoir 81 by the pressure applied by the pump 88.

[0159] The main reservoir 83 is filled with ink for supplying to the supply sub-reservoir 81 and is connected to the supply sub-reservoir 81 via the ink flow path 87. Furthermore, ink can be supplied from the main reservoir 83 to the supply sub-reservoir 81 by pressure applied by the pump 89.

[0160] Furthermore, by appropriately changing the ink filling amount in each sub-reservoir and the vertical (gravity direction) position of each sub-reservoir, pressures P1 and P2 can be adjusted. Moreover, the pressure difference between P1 and P2 allows the ink within the inkjet head 100 to circulate at an appropriate flow rate. This removes air bubbles and foreign matter generated within the printhead chip 1, suppressing nozzle clogging and poor ejection.

[0161] Furthermore, although the method of controlling ink circulation by water level difference has been described as an example of ink circulation device 8, the configuration that can generate ink circulation flow can of course be appropriately modified.

[0162] Figure 12 This is a block diagram illustrating the main functional components of an inkjet recording device.

[0163] As described above, the inkjet recording apparatus 200 includes a paper supply unit 210, an image recording unit 220 (including a transport drum 221, a transfer unit 222, a heating unit 223, a head unit 224, a fixing unit 225, and a conveying unit 226), a paper discharge unit 230, an ink circulation device 8 which serves as an ink supply unit, and a control unit 240.

[0164] The control unit 240 is connected to each component constituting the inkjet recording apparatus 200 and controls each component. The control unit 240 includes a CPU 241, RAM 242, and ROM 243. The CPU 241 reads various programs and data corresponding to the processing content from storage devices such as the ROM 243 and executes them, controlling the operation of each component of the inkjet recording apparatus 200 according to the executed processing content. The RAM 242 temporarily stores various programs and data processed by the CPU 241. The ROM 243 stores various programs and data read from the CPU 241, etc.

[0165] Specifically, the control unit 240 performs the following processing on the ink circulation device 8 of the inkjet recording device 200.

[0166] That is, the control unit 240 can control the ink flow rate (circulation flow rate Q) flowing in the flow path R connected to the nozzle 111, i.e. the circulation pressure difference ΔP, to be such that the average shear rate of the flow path R connected to the nozzle 111 is 100 [1 / s] or more.

[0167] Specifically, pressures P1 and P2 are adjusted by appropriately changing the pressure applied to the pump 88 of the ink circulation device 8, the ink filling amount in each sub-reservoir 81 and 82, and the vertical (gravity direction) position of each sub-reservoir 81 and 82. The circulation flow rate Q is controlled by the pressure difference (circulation pressure difference ΔP) between pressures P1 and P2. Preferably, the circulation pressure difference ΔP is in the range of 5 kPa to 30 kPa.

[0168] [other]

[0169] It should be understood that the embodiments of the present invention described above are illustrative in all respects and are not restrictive embodiments. That is, the scope of the present invention is defined not by the foregoing description but by the claims, and includes all modifications within the same meaning and scope as the claims.

[0170] As the head chip 1 in this embodiment, an example is shown in which a nozzle substrate 11, a flow path isolation substrate 12, and a pressure chamber substrate 13 are stacked in sequence. However, it is not limited to this, and it may also be a double-layer structure of the nozzle substrate 11 and the pressure chamber substrate 13. In this case, a separate ink discharge path 121 may be provided on at least one of the nozzle substrate 11 and the pressure chamber substrate 13.

[0171] Furthermore, although an example of a shared mode is shown as the inkjet head 100 in this embodiment, it is not limited to this as long as a unit that applies pressure to the ink in the pressure chamber 131 is provided.

[0172] Furthermore, although the example shown for the inkjet recording apparatus 200 of this embodiment is a single-pass paper-fed drawing method using a line head, it is not limited to this, and for example, it may also be a scanning method.

[0173] Furthermore, although the head chip 1 of this embodiment is shown as a straight example with the pressure chamber 131 and the second common ink discharge path 135 opening on the upper and lower surfaces of the head chip 1, it is not limited to this. For example, it may be configured to have openings on any side in the front-back, left-right, or right-side directions of the head chip 1, or it may be configured to have a curved portion in the middle of the flow path to change the flow direction of the ink.

[0174] [Ink]

[0175] Next, the physical properties and composition of the inkjet ink (hereinafter, also referred to simply as "ink") used in this invention will be described.

[0176] <Physical Properties of Inkjet Inks>

[0177] The ink of the present invention preferably has a surface tension in the range of 20 to 50 mN / m in order to improve the discharge stability from the nozzle of the inkjet head, and more preferably in the range of 22 to 25 mN / m from the viewpoint of improving the wettability of the substrate and making the formed image more refined.

[0178] As for the above-mentioned methods for measuring surface tension, for example, one can refer to the New Experimental Chemistry Lectures, Volume 18 (Interfaces and Alternations), edited by the Chemical Society of Japan, published by Maruzen Co., Ltd.: pp. 68-117. Specifically, it can be determined using the ring method (DuNouy method) or the vertical plate method (Wilhelmy method), or by using a multi-functional automatic surface tension meter K100 (manufactured by KRUSS Co., Ltd.).

[0179] In addition, the surface tension of the ink can be adjusted to the above range by changing the type or amount of surfactant and water-soluble solvent described later.

[0180] Furthermore, when the viscosity of the ink of the present invention at 25°C with a shear speed of 1 [1 / s] is set to A1, the viscosity at 25°C with a shear speed of 100 [1 / s] is set to A100, and the viscosity at 25°C with a shear speed of 1000 [1 / s] is set to A1000, the ink satisfies the relationships of equations (I) and (II) above. Moreover, it is preferable that the ink of the present invention satisfies the relationships of equations (III) to (V) above.

[0181] Furthermore, in order to satisfy the relationship between formulas (I) and (II) above, the ink of the present invention preferably contains a water-soluble solvent, water, pigment, fixing resin, and thixotropic agent, as described below. Moreover, regarding viscosity characteristics, it is preferable to satisfy the conditions (1-1) and (1-2) below.

[0182] (1-1) The viscosity (at 25°C) at a shear rate of 1000 [1 / s] is below 15 mPa·s.

[0183] (1-2) When the ink drying rate is 20%, the viscosity (25°C) at a shear speed of 1 [1 / s] is above 150 mPa·s.

[0184] For the viscosity determination in (1-1) and (1-2) above, it can be measured by a rotational viscometer in the same way as the viscosity in formula (I) and formula (II) above. An example of a rotational viscometer is the Antonpah MCR-102. In this specification, unless otherwise stated, viscosity refers to the viscosity measured at 25°C.

[0185] In this specification, "aqueous solvent" means water, or a solvent containing water and a water-soluble solvent. A water-soluble solvent is a solvent that is miscible with water at room temperature.

[0186] "Ink drying rate of 20%" means the ink has been dried to 80% of its initial mass after removing the aqueous solvent. The ink drying rate can be calculated using the following formula (A) based on the ink's mass before and after drying at a temperature of 60°C.

[0187] Formula (A) Ink drying rate [%) = (W BEFORE -W AFTER ) / W BEFORE ×100

[0188] In equation (A), W BEFORE Indicates the quality of the ink before it dries (initial quality). W AFTER This indicates the mass of the ink after drying. Specifically, approximately 100 mL of ink is dropped onto a glass substrate, weighed to determine the ink's mass before drying, and then dried by heating the ink to 60°C on a heating plate capable of mass measurement.

[0189] To obtain the viscosity of the ink at a drying rate of 20%, the drying process is stopped when the ink reaches 80% of its initial mass (mass before drying), and the viscosity is measured using the dried ink.

[0190] Regarding the above (1-1), it is preferable that the viscosity of the ink of the present invention is less than 10 mPa·s at a shear speed of 1000 [1 / s]. Furthermore, the lower limit of the viscosity at a shear speed of 1000 [1 / s] is not particularly limited, but from the viewpoint of inkjet ejection performance, it is preferably around 5 mPa·s.

[0191] Regarding the above (1-2), it is preferred that the viscosity of the ink of the present invention is 300 mPa·s or higher at a shear rate of 1 [1 / s] with an ink drying rate of 20%.

[0192] Here, if the viscosity at a shear rate of 1 [1 / s] is at least 150 mPa·s, then the occurrence of color mixing and the like can be suppressed when the ink falls onto the substrate. The higher the ink drying rate, the higher the ink viscosity. If the ink of the present invention is used, even if the ink drying rate is relatively high, only 20%, the viscosity at a shear rate of 1 [1 / s] can reach 150 mPa·s. Therefore, when the ink falls onto the substrate, the ink can be heated without excessive heating, thus suppressing the occurrence of color mixing and the like.

[0193] Furthermore, the ink of the present invention preferably satisfies the following conditions (1-3) regarding the above (1-2).

[0194] (1-3) The viscosity (at 25°C) at a shear rate of 1 [1 / s] is above 25 mPa·s.

[0195] As described above, the higher the ink drying rate, the higher the ink viscosity. Therefore, considering a shear speed of 1 [1 / s], there is a certain degree of correlation between the ink viscosity in a completely undried state and an ink drying rate of 20%. Regarding the above (1-3), the ink of the present invention is more preferably 45 mPa·s or higher at a shear speed of 1 [1 / s], and even more preferably 100 mPa·s or higher.

[0196] Preferably, the ink of the present invention also satisfies at least one of the following conditions (1-4), (1-5) and (1-6), more preferably satisfies two or more, and even more preferably satisfies all of them.

[0197] (1-4) When the ink drying rate is 20%, under the conditions of temperature 25℃, angular frequency ω10rad / s, and swing angle γ1~1000%, the loss tangent (tanδ) when the distortion is 1% is less than 1.

[0198] (1-5) When the ink drying rate is 20%, under the conditions of temperature 25℃, angular frequency ω10rad / s and swing angle γ1~1000%, the cross distortion of the storage elastic modulus and the loss elastic modulus during distortion change is greater than 20%.

[0199] (1-6) The thixotropic index represented by n in the viscosity equation expressed by the following equation (2) is less than 0.85.

[0200] Equation (2) ηa=μD n-1

[0201] (In equation (2), ηa represents the apparent viscosity. D represents the shear rate. M represents the non-Newtonian viscosity coefficient.)

[0202] The loss tangent (tanδ) in (1-4) and the storage modulus and loss modulus in (1-5) can be measured using a rheometer (viscoelastic measuring device). For example, the Anton Paar MCR-102 can be cited as an example of a rheometer. In this specification, there are also cases where only the loss tangent is expressed as "tanδ".

[0203] In this specification, a rheometer, specifically the Anton Paar MCR-102, can be used to measure tanδ, storage modulus, and loss modulus under vibration mode conditions: temperature 25°C, angular frequency ω 10 rad / s, and swing angle γ 1–1000%. Furthermore, during measurement, the swing angle γ of the rheometer's cone plate is varied to distort the measurement sample. Here, the measurement sample is distorted with the swing angle γ, so the swing angle γ of the cone plate and the distortion of the measurement sample are the same value.

[0204] In the above (1-4), the tanδ value at 1% distortion is used as an indicator in the above measurements. Under these measurement conditions, if the tanδ value at 1% distortion is less than 1, the ink has more elastic properties, and when compared with the same viscosity, the pinning properties are better, and the image quality is further improved. In the above (1-4), it is more preferable that the tanδ value at 1% distortion is 0.8 or less, and even more preferably 0.6 or less.

[0205] In the above (1-5), the cross-distortion of the storage elastic modulus and the loss elastic modulus during the above measurements is used as an indicator. Specifically, "cross-distortion" refers to the distortion value (%) at the intersection of a graph where the storage elastic modulus (Pa) is logarithmically expressed on the vertical axis and the distortion (%) is logarithmically expressed on the horizontal axis, and a graph where the loss elastic modulus (Pa) is logarithmically expressed on the vertical axis and the distortion (%) is logarithmically expressed on the horizontal axis. If the cross-distortion (%) is 20% or more under the above measurement conditions, the ink has more elastic properties, and the image quality is improved as described above. More preferably, the cross-distortion is 30% or more, and even more preferably, it is 40% or more.

[0206] In the above (1-6), the viscosity equation is expressed by equation (2); ηa=μD n-1This is an expression representing the relationship between apparent viscosity ηa (mPa·s) and shear rate D [1 / s]. The relationship between apparent viscosity ηa (mPa·s) and shear rate D [1 / s] in the viscosity equation can be determined using a rheometer, such as the Anton Pareto MCR-102.

[0207] Specifically, in the rotation mode of the MCR102, the apparent viscosity ηa (mPa·s) was measured with a temperature of 25°C, a time setting of 150 measurement points, a measurement interval of 2 seconds, and a shear rate ranging from 1000 [1 / s] to 1 [1 / s]. A graph was created with the apparent viscosity ηa (mPa·s) logarithmically plotted on the vertical axis (Y-axis) and the shear rate [1 / s] logarithmically plotted on the horizontal axis (X-axis), and the thixotropic index n was calculated based on the slope (n-1) of the graph. Furthermore, the intercept of the graph was the non-Newtonian viscosity coefficient μ.

[0208] Here, according to the viscosity equation; ηa=μD n-1 n can be calculated as follows.

[0209] logηa=log(μD (n-1) )

[0210] =logμ+log(D) (n-1) )

[0211] =logμ+(n-1)×logD

[0212] If we plot logηa on the Y-axis and logD on the X-axis, then Y = (n-1)X + log, and we can calculate n based on the slope (n-1).

[0213] In the above (1-6), if the thixotropic index is below 0.85, the viscosity during head circulation can be reduced, and the viscosity increase rate during landing is accelerated, thus improving image quality. At higher printing speeds, it can further prevent color mixing.

[0214] <Composition of Inkjet Ink>

[0215] The ink of the present invention is an ink that satisfies the relationship of formula (I) and formula (II) above, preferably containing an aqueous solvent (water-soluble solvent, water), pigment and fixing resin, and particularly preferably containing a thixotropic agent.

[0216] In addition, the ink of the present invention preferably contains 3 to 10% by mass of pigment, 8 to 20% by mass of fixing resin, 10 to 30% by mass of water-soluble solvent, and 40 to 79% by mass of water.

[0217] Furthermore, it is preferable that the solid content of the ink of the present invention is 6 to 30% by mass. "Solid content of ink" refers to solid components that cannot be removed from the ink by drying at 100°C. Solid components of ink may be, for example, components other than solvents containing aqueous solvents.

[0218] In addition to the aqueous solvent, pigment, fixing resin, and thixotropic agent described above, the ink of the present invention may also contain any components that do not impair the effects of the present invention. Examples of such arbitrary components include pigment dispersants and surfactants. The components of the ink of the present invention will be described below.

[0219] (Thixotropic agent)

[0220] The thixotropic agent is not particularly limited as long as it is a material that can impart thixotropy to the ink in accordance with the conditions of formulas (I) and (II) above.

[0221] The thixotropic agent is preferably in particle shape (wherein, particle shape includes fiber shape), and more preferably has an aspect ratio of 20 or higher.

[0222] When the thixotropic agent is in particle form, its shape is preferably elliptical, flake-like, plate-like, needle-like, or fibrous. It is preferable that the aspect ratio (the ratio of the major axis to the minor axis) of the thixotropic agent is 20 or higher. An aspect ratio of 20 or higher facilitates the imparting of thixotropy to the ink. Furthermore, it is preferable that the major axis of the thixotropic agent is 2 μm or less. If the major axis of the thixotropic agent exceeds 2 μm, it may negatively impact ink ejection performance.

[0223] Furthermore, in this specification, the cross section used to measure the aspect ratio of the thixotropic agent is a section parallel to the length direction of the particles and cut in the thickness direction. The aspect ratio is calculated based on the average major and minor diameters of fifty particles obtained from this cross section. Here, in the case of scaly or plate-like particle shapes, the minor diameter is the particle thickness, and the major diameter is the length of the long side or the maximum diameter of the cross section orthogonal to the thickness direction of the particles, i.e., when the particle shape is viewed from above. In the case of needle-like or fibrous particle shapes, the major diameter is the particle length, and the minor diameter is the major diameter or the maximum width of the cross section orthogonal to the length direction of the particles, i.e., when the particle shape is viewed from above.

[0224] Materials that can be used as thixotropic agents include polysaccharides and inorganic particles. Specifically, polysaccharides include cellulose, chitosan, chitosan, xanthan gum, vestigman gum, succinosaccharide, guar gum, locust bean gum and its derivatives, glucomannan, agar, and carrageenan. Derivatives of the above can include methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose, among others.

[0225] As for polysaccharides, natural polysaccharides with a weight-average molecular weight of around several million are preferred. Specifically, xanthan gum, guar gum, and carrageenan are preferred.

[0226] Furthermore, in the ink of the present invention, nanofibers of polysaccharides, which are aggregates of polysaccharides such as the shells of crustaceans like trees, crabs, and shrimp, are finely broken down into fibers and micronized using conventionally known methods such as oxidation treatment with a catalyst or mechanical treatment with a grinding mill, are preferably used as thixotropic agents. The polysaccharide in the nanofibers is preferably at least one of cellulose, chitosan, and chitosan, and more preferably cellulose.

[0227] Furthermore, in this specification, nanofibers refer to fibers with a width of approximately 1–100 nm and an aspect ratio of 100 or greater. For example, the length and width of nanofibers can be measured using an electron microscope. Regarding the width of a nanofiber, it can be measured either from a top-view perspective or from the diameter of a cross-section perpendicular to its length direction. In either case, the average of the maximum widths of all fifty nanofibers is taken as the "width" of the nanofiber. The "length" of the nanofiber is the average length of the fifty nanofibers. The aspect ratio of the nanofiber is calculated by dividing this length by the width.

[0228] In the ink of the present invention, when polysaccharide-based nanofibers are used as thixotropic agents, smaller nanofibers are preferred. The width of the nanofibers is preferably 1 to 50 nm, more preferably 1 to 5 nm. Furthermore, the length of the nanofibers is preferably 0.5 to 2 μm, more preferably 0.5 to 1 μm, but not limited thereto. More preferably, the aspect ratio of the nanofibers is in the range of 20 to 400, and even more preferably in the range of 100 to 300.

[0229] In polysaccharide aggregates, polysaccharides such as cellulose, chitosan, and chitin exist in a state where they are bundled together as structural units called microfibrils. These microfibrils are 3–4 nm wide and a few μm long (e.g., 2–5 μm), but are difficult to untangle individually. In the case of mechanically pulverizing polysaccharide aggregates, many conventional methods result in nanofibers with a width of approximately 20–50 nm. Such nanofibers can also be used as polysaccharide nanofibers in this invention, but TEMPO-oxidized nanofibers, which are further finely untangled into microfibril units through TEMPO oxidation, are more preferred.

[0230] "TEMPO oxidation" refers to an oxidation reaction using 2,2,6,6-tetramethyl-1-piperidine-oxygen radical (TEMPO) as a catalyst. By oxidizing polysaccharide aggregates in the presence of TEMPO, extremely fine nanofibers, equivalent to microfibrils, are obtained, for example, with a width of 3-4 nm and a length of several μm (e.g., 2-5 μm).

[0231] Cellulose nanofibers used as thixotropic agents are fibers that nanofiberize cellulose. Examples of nanofiberized cellulose include powdered cellulose and microcrystalline cellulose.

[0232] As cellulose nanofibers, appropriate materials can be used, such as RHEOCRYSTA (registered trademark) manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., TEMPO oxidized cellulose nanofibers manufactured by Nippon Paper Co., Ltd., Cellenpia TC-01A, Cellenpia TC-02X (“Cellenpia” is a registered trademark), IMa-10002, BMa-10002, WMa-10002, AMa-10002, FMa-10002 manufactured by Sugino Machine Co., Ltd., ELEX-☆, ELEX-S manufactured by Daio Paper Co., Ltd., and AUROVISCO manufactured by Oji Paper Co., Ltd.

[0233] As inorganic particles, there are no limitations on the material and shape of the particles, as long as they have thixotropic properties that can impart the ink to meet the conditions (1-1) and (1-2) above, but particles of various natural or synthetic clay minerals are preferred.

[0234] As a clay mineral, montmorillonite clay mineral is preferred. Montmorillonite clay minerals are classified as layered silicate minerals or phyllosilicates of the bentonite group. Based on their layered structure, montmorillonite clay minerals are further divided into the montmorillonite subgroup and the saponite subgroup. The montmorillonite subgroup includes montmorillonite, chlorite, or bedesite. The saponite subgroup includes lithium montmorillonite, saponite, or zinc montmorillonite.

[0235] Montmorillonite clay minerals can be natural or synthetic. Montmorillonite clay minerals are layered substances composed of stacked platy bodies. When used as thixotropic agents, they are typically used in the form of platy particles after interlayer exfoliation. Synthetic montmorillonite clay minerals have a smaller aspect ratio and fewer impurities compared to natural products.

[0236] The thickness of the platy particles of montmorillonite clay mineral is preferably in the range of 0.2 to 3.0 nm, and the length is in the range of 10 to 150 nm. More preferably, the thickness of the platy particles is in the range of 0.2 to 2.0 nm, and the length is in the range of 10 to 125 nm. The aspect ratio, which is the value of dividing the length of the platy particles by the thickness, is preferably 20 or more. More preferably, the aspect ratio is in the range of 20 to 200.

[0237] For example, the length and thickness of a plate-like particle can be measured using an electron microscope. The thickness of the plate-like particle is, for example, the average of fifty thicknesses measured in a specified cross-section. The "length" of the plate-like particle is the average of fifty lengths measured as its maximum diameter when viewed from above. The aspect ratio of the plate-like particle is then calculated by dividing this length by the thickness.

[0238] As a montmorillonite clay mineral, for example, LAPONITE (manufactured by BYK Corporation) can be used as a synthetic layered silicate. LAPONITE is a synthetic low-charge clay with a structure and chemical composition close to that of lithium montmorillonite, a natural montmorillonite clay mineral. The main particles of LAPONITE are disk-shaped with a maximum diameter of 30 nm and a thickness of 1 nm.

[0239] Commercially available products can be used as montmorillonite clay minerals. Examples of commercially available products include LAPONITERD (manufactured by BYK Corporation) and Kunipia F and Kunipia G, refined bentonite manufactured by KUNIMINE Industries, Ltd.

[0240] Alternatively, alumina nanofibers (with a short diameter of 4 nm and a long diameter of 1400 nm) manufactured by Kawaken Fine Chemicals can be used as inorganic particles.

[0241] Preferably, the content of the thixotropic agent in the ink of the present invention is in the range of 0.01 to 1% by mass relative to the total amount of ink, and more preferably in the range of 0.08 to 0.5% by mass.

[0242] In the ink of the present invention, either a single thixotropic agent or two or more thixotropic agents can be used. Furthermore, in the ink of the present invention, it is preferable that the thixotropic agent is composed of two or more materials. Moreover, it is preferable that one of these two or more materials is montmorillonite clay mineral. Preferred combinations of thixotropic agents include combinations of cellulose nanofibers and montmorillonite clay minerals, and combinations of xanthan gum and montmorillonite clay minerals. In particular, a combination of cellulose nanofibers and montmorillonite clay minerals is preferred.

[0243] Considering that even when cellulose nanofibers and montmorillonite clay minerals are used separately, for example, it is possible to impart elastic properties to the ink by forming a specific gel structure at an ink drying rate of 20%. Therefore, inks containing cellulose nanofibers or montmorillonite clay minerals can easily achieve the above-mentioned (1-4) and (1-5). Furthermore, by using a combination of cellulose nanofibers and montmorillonite clay minerals, the aforementioned elastic properties can be further improved, which is preferable.

[0244] Although the ratio of montmorillonite clay minerals to other thixotropic agents can be selected based on ink viscosity and thixotropy, the mass ratio of montmorillonite clay minerals to other thixotropic agents can be adjusted within the range of 10:1 to 1:10. Compared to adding them individually, combining them significantly improves the thixotropy of the ink and thus improves image quality. While the reason for the improved thixotropy is estimated, it is considered that montmorillonite clay minerals possess an electrical charge, and that montmorillonite clay minerals electroassociate with other thixotropic agents to form a structure.

[0245] (pigment)

[0246] As pigments contained in the inks of the present invention, conventionally known organic and inorganic pigments can be used. Examples include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, and chelated azo pigments; phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, diazine pigments, thioindole pigments, isoindolinone pigments, and quinophthalone pigments; dye lakes such as basic dye lakes and acid dye lakes; organic pigments such as nitro pigments, nitroso pigments, aniline black, and solar fluorescent pigments; and inorganic pigments such as carbon black.

[0247] The following pigments are examples of specific organic pigments that can be preferred for use.

[0248] Examples of pigments used as magenta or red include CI Pigment Red 2, CI Pigment Red 3, CI Pigment Red 5, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, CI Pigment Red 202, CI Pigment Red 222, and CI Pigment Violet 19.

[0249] Examples of pigments used for orange or yellow include CI Pigment Orange 31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 15, CI Pigment Yellow 15:3, CI Pigment Yellow 17, CI Pigment Yellow 74, CI Pigment Yellow 93, CI Pigment Yellow 128, CI Pigment Yellow 94, CI Pigment Yellow 138, and CI Pigment Yellow 155. CI Pigment Yellow 155 is particularly preferred in terms of its balance between hue and lightfastness.

[0250] Examples of pigments used for green or cyan include CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, CI Pigment Blue 60, and CI Pigment Green 7.

[0251] In addition, examples of brown pigments include CI Pigment Brown 1, CI Pigment Brown 6, and CI Pigment Brown 7.

[0252] There is no particular limitation on the pigment content in the ink, but for inorganic pigments it is preferred to be in the range of 7 to 18% by mass, and for organic pigments it is preferred to be in the range of 0.5 to 7% by mass.

[0253] (Pigment dispersant)

[0254] The ink of the present invention may contain any pigment dispersant for dispersing pigments. There are no particular limitations on the pigment dispersant, but a polymeric dispersant having anionic groups is preferred. Pigment dispersants with a number average molecular weight in the range of 5000 to 200000 may be appropriately used.

[0255] Examples of pigment dispersants include, for instance, block copolymers, random copolymers and their salts, polyoxyethylene, polyoxyethylene alkyl ethers, etc., having structures derived from two or more monomers selected from styrene, styrene derivatives, vinylnaphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives.

[0256] The pigment dispersant preferably has an acryloyl group and is preferably added by neutralization with a neutralizing base. Here, the neutralizing base is not particularly limited, but is preferably an organic base such as ammonia, monoethanolamine, diethanolamine, triethanolamine, or morpholine.

[0257] In addition, the amount of pigment dispersant added is preferably in the range of 10 to 100% by mass relative to the pigment, and more preferably in the range of 10 to 40% by mass.

[0258] The pigment is particularly preferred to have the form of a so-called encapsulated pigment obtained by coating the pigment with the aforementioned pigment dispersant. As a method of coating the pigment with the pigment dispersant, various known methods can be used. For example, examples include phase inversion emulsification, acid precipitation, or a method in which the pigment is dispersed by a polymerizable surfactant and a monomer is supplied thereto, and the pigment is coated while polymerizing.

[0259] As a particularly preferred method, the following method can be cited: dissolve the pigment dispersant in an organic solvent such as methyl ethyl ketone, then partially or completely neutralize the acidic groups in the resin with an alkali, add pigment and deionized water, disperse, remove the organic solvent, and add water as needed to prepare the product.

[0260] The preferred ink has an average particle size of pigment dispersion greater than 50 nm and less than 200 nm. This improves the dispersion stability of the pigment and the storage stability of the ink. The pigment particle size can be determined using commercially available particle size analyzers such as dynamic light scattering (DLS) or electrophoresis. DLS is a simple method that allows for high-precision measurement of this particle size range.

[0261] Pigments can be dispersed using a disperser together with pigment dispersants and other additives required for the desired purpose.

[0262] As a disperser, conventionally known ball mills, grinding mills, wire mills, high-pressure homogenizers, etc., can be used. Among these, grinding mills are preferred because they produce a sharper particle size distribution when dispersing pigments. Furthermore, the material of the beads used in grinding mill dispersion is not particularly limited, but from the viewpoint of preventing the formation of bead fragments and contamination by ionic components, zirconium oxide or zircon is preferred. In addition, the bead size is preferably in the range of 0.3 to 3 mm.

[0263] (Aqueous solvent)

[0264] The ink of the present invention contains an aqueous solvent. The aqueous solvent contains water as an essential solvent, and preferably includes any known water-soluble solvent for purposes such as viscosity adjustment.

[0265] The water contained in the ink of the present invention is not particularly limited and can be ion-exchanged water, distilled water or pure water.

[0266] Water-soluble solvents contained in inks include, for example, alcohols, polyols, amines, amides, diol ethers, and 1,2-alkanediols with 4 or more carbon atoms.

[0267] Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, tert-butanol, 3-methoxy-1-butanol, 3-methoxy-3-methylbutanol, 1-octanol, 2-octanol, n-nonanol, tridecanool, n-undecanool, stearyl alcohol, oleyl alcohol, benzyl alcohol, etc.

[0268] Examples of polyols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol with 5 or more ethylene oxide groups, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol with 4 or more propylene oxide groups, butanediol, hexanediol, pentanediol, glycerol, hexanetriol, and thiodiethylene glycol.

[0269] Examples of amines include ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, and tetramethylpropylenediamine.

[0270] Examples of amides include formamide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0271] Examples of diol ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether.

[0272] Examples of 1,2-alkanediols with 4 or more carbon atoms include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, and 1,2-heptanediol.

[0273] The preferred water-soluble solvent is a polyol, which can effectively suppress bleed-out during high-speed printing. Specifically, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol are preferred.

[0274] Inks can be combined to contain one or more of these water-soluble solvents.

[0275] (Fixing resin)

[0276] The ink of the present invention optionally contains a fixing resin. The fixing resin acts as a colorant, i.e., a binder for the pigment, improving the adhesion of the coating to a substrate, especially a non-absorbent substrate, and improving the abrasion resistance of the coating obtained using the ink. Preferably, the fixing resin is a water-insoluble resin. It is preferable to use a water-insoluble resin as the fixing resin in the form of microparticles dispersed in an aqueous solvent.

[0277] Water-insoluble resin microparticles are naturally present as tiny microparticles of water-insoluble resin dispersed in an aqueous solvent. These microparticles can be formed by forcibly emulsifying the water-insoluble resin using an emulsifier or similar agent, thus dispersing them as microparticles in the aqueous solvent. Alternatively, hydrophilic functional groups can be introduced into the molecules of the water-insoluble resin, allowing it to form stable microparticles in the aqueous solvent without the use of emulsifiers or dispersion stabilizers; these are called self-emulsifying microparticles. The aqueous solvents used to disperse the water-insoluble resin microparticles can be the same as those described above; typically, water or a water / ethanol mixture can be used. Hereinafter, the water-insoluble resin microparticles dispersed in an aqueous solvent will also be referred to as an aqueous dispersion.

[0278] Furthermore, in this invention, "water insoluble" refers to a resin that, after being dried at 105°C for two hours, dissolves in 100g of water at 25°C, with a solubility of 10g or less, preferably 5g or less, and more preferably 1g or less. However, in the case where the resin has salt-forming groups, the solubility, depending on its type, is the solubility achieved when the salt-forming groups of the resin are neutralized in 100% acetic acid or sodium hydroxide.

[0279] As the fixing resin of the present invention, polyester resin, polyurethane resin, and polyacrylic acid resin, etc., which are water-insoluble resins, are preferred. In the present invention, these resins can be used alone or in combination of two or more.

[0280] Preferably, the fixing resin is contained in the range of 3 to 10% by mass relative to the total mass (100% by mass) of the ink, without impairing the effect of the present invention, and from the viewpoint of improving the fixing properties of the coating to the substrate, it is preferable to contain the fixing resin in the range of 4 to 7% by mass.

[0281] (Polyester resin)

[0282] Polyester resins that can be used as fixing resins can be obtained by using polyol components and polycarboxylic acid components such as polycarboxylic acid, polycarboxylic anhydride, and polycarboxylic acid ester.

[0283] As polyol components mentioned above, diols (diols) can be listed, specifically alkylene glycols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, etc.) with 2 to 36 carbon atoms, alkylene ether glycols (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutanediol, etc.) with 4 to 36 carbon atoms, and alicyclic glycols (1,4-cyclohexanediol, etc.) with 6 to 36 carbon atoms. Alkyldiethanol, hydrogenated bisphenol A, etc.), and olefinic oxygen adducts (ethylene oxide (hereinafter referred to as EO), propylene oxide (hereinafter referred to as PO), butane oxide (hereinafter referred to as BO)) of the above-mentioned alicyclic diols with 2 to 4 carbon atoms (in the range of 1 to 30 moles of addition) or olefinic oxygen adducts (EO, PO, BO, etc.) of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.) with 2 to 4 carbon atoms (in the range of 2 to 30 moles of addition), etc. They can be used alone or in combination of two or more.

[0284] As components of the aforementioned polycarboxylic acids, dicarboxylic acids (dicarboxylic acids) can be listed. Specifically, they can include alkane dicarboxylic acids (succinic acid, adipic acid, sebacic acid, etc.) with 4 to 36 carbon atoms, alkenyl succinic acids (dodecenyl succinic acid, etc.), alicyclic dicarboxylic acids (dimeric acids (dimeric linoleic acid, etc.) with 4 to 36 carbon atoms, olefin dicarboxylic acids (maleic acid, fumaric acid, citrate, mesoconic acid, etc.) with 4 to 36 carbon atoms, or aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid or their derivatives, naphthalene dicarboxylic acid, etc.) with 8 to 36 carbon atoms. They can be used alone or in combination with two or more.

[0285] The number average molecular weight of the aforementioned polyester resin is preferably in the range of 1,000 to 50,000, and more preferably in the range of 2,000 to 20,000.

[0286] Commercially available polyester resins can also be used as the aforementioned polyester resins. For example, the aforementioned polyester resins can also be used as dispersions of aqueous components in aqueous solvents. Examples of commercially available dispersions include the following products. In the examples, the number-average molecular weight of the polyester resins contained in the product (dispersion) is shown in parentheses. These can be used alone or in combination of two or more.

[0287] The following are trade names, including Elitel KA-5034 (manufactured by UNITIKA, number average molecular weight: 8500), Elitel KA-5071S (manufactured by UNITIKA, number average molecular weight: 8500), Elitel KA-1449 (manufactured by UNITIKA, number average molecular weight: 7000), Elitel KA-0134 (manufactured by UNITIKA, number average molecular weight: 8500), Elitel KA-3556 (manufactured by UNITIKA, number average molecular weight: 8000), Elitel KA-6137 (manufactured by UNITIKA, number average molecular weight: 5000), Elitel KZA-6034 (manufactured by UNITIKA, number average molecular weight: 6500), Elitel KT-8803 (manufactured by UNITIKA, number average molecular weight: 15000), and Elitel... Elitel KT-8701 (manufactured by UNITIKA, number average molecular weight: 13000), Elitel KT-9204 (manufactured by UNITIKA, number average molecular weight: 17000), Elitel KT-8904 (manufactured by UNITIKA, number average molecular weight: 17000), Elitel KT-0507 (manufactured by UNITIKA, number average molecular weight: 17000), Elitel KT-9511 (manufactured by UNITIKA, number average molecular weight: 17000), Vylonal MD-2000 (manufactured by Toyobo, number average molecular weight: 18000), etc.

[0288] (Polyurethane resin)

[0289] As a fixing resin, a polyurethane resin having hydrophilic groups can be used. Examples of such hydrophilic groups include carboxyl groups (-COOH) and their salts, sulfonic acid groups (-SO3H) and their salts, etc. As such salts, alkali metal salts such as sodium salts and potassium salts, and amine salts, etc., are included. Among the aforementioned hydrophilic groups, carboxyl groups or their salts are preferred.

[0290] The aforementioned polyurethane resin is preferably an aqueous dispersion of a self-emulsifying polyurethane having water-soluble functional groups within its molecule, dispersed in an aqueous solvent, or an aqueous dispersion of a forced-emulsifying polyurethane obtained by emulsification with a surfactant under strong mechanical shear force, dispersed in an aqueous solvent. The polyurethane resin in the above-mentioned aqueous dispersion can be obtained by reacting a polyol with an organic polyisocyanate and a compound containing hydrophilic groups.

[0291] Examples of polyols that can be used in the preparation of the above-mentioned polyurethane resin aqueous dispersions include polyester polyols, polyether polyols, polycarbonate polyols, and polyolefin polyols.

[0292] Examples of polyester polyols include low molecular weight polyols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propanediol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylenediol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, and cyclohexanediol; and condensates of polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrofuranic acid, methyl methacrylate, and hexahydrophthalic acid.

[0293] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene polytetramethylene glycol, polypropylene polytetramethylene glycol, and polytetramethylene glycol.

[0294] Examples of polycarbonate polyols that can be obtained by reacting carbonic acid derivatives such as diphenyl carbonate, dimethyl carbonate, or phosgene with diols. Examples of the aforementioned diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2- and 1,3-propanediol, neopentyl glycol, 1,3- and 1,4-butanediol, 3-methylpentanediol, hexamethylenediol, 1,8-octanediol, 2-methyl-1,3-propanediol, bisphenol A, hydrogenated bisphenol A, trimethylolpropane, and cyclohexanediol.

[0295] In addition, examples of organic polyisocyanates that can be used in the preparation of aqueous dispersions of polyurethane resins include aromatic isocyanates such as toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, isophthalene diisocyanate (XDI), and tetramethyl isophthalene diisocyanate (TMXDI); aliphatic isocyanates such as hexamethylene diisocyanate (HMDI); and alicyclic isocyanates such as isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI, H12MDI). They can be used alone or in combination of two or more.

[0296] In addition, examples of compounds containing hydrophilic groups that can be used in the preparation of aqueous dispersions of polyurethane resins include carboxylic acid compounds such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylol-n-butyric acid, 2,2-dimethylolvalerate, and glycine, as well as their sodium salts, potassium salts, amine salts, and other derivatives; and sulfonic acid compounds such as taurine (i.e., aminoethylsulfonic acid) and ethoxylated polyethylene glycol sulfonic acid, as well as their sodium salts, potassium salts, amine salts, and other derivatives.

[0297] Polyurethane resin can be obtained by known methods. For example, polyurethane resin can be obtained by mixing the above-mentioned polyol, organic polyisocyanate and compound containing hydrophilic group and reacting at 30 to 130°C for 30 minutes to 50 hours.

[0298] The aforementioned polyurethane resin is polymerized using a chain extender to obtain a polyurethane resin with hydrophilic groups. Water and / or amine compounds are preferred as chain extenders. By using water or amine compounds as chain extenders, the reaction with free isocyanate can occur rapidly, enabling efficient chain extension of the isocyanate-terminated prepolymer.

[0299] Examples of amine compounds used as chain extenders include aliphatic polyamines such as ethylenediamine and triethylenediamine; aromatic polyamines such as m-phenylenediamine and toluenediamine; and polyhydrazine compounds such as hydrazine and adipic dihydrazide. These amine compounds may also contain monovalent amines such as dibutylamine and methyl ethyl ketoxime as reaction terminators, to a degree that does not significantly hinder polymerization.

[0300] It should be noted that in the synthesis of polyurethane resins, solvents that are inactive relative to isocyanates and can dissolve polyurethane prepolymers can also be used. Examples of such solvents include dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, and propylene glycol monomethyl ether acetate. Preferably, these hydrophilic organic solvents used in the reaction stage are ultimately removed.

[0301] In addition, in the synthesis of polyurethane resins, amine catalysts (e.g., triethylamine, N-ethylmorpholine, triethyldiamine, etc.), tin-based catalysts (e.g., dibutyltin dilaurate, dioctyltin dilaurate, tin octoate, etc.), and titanium-based catalysts (e.g., tetrabutyl titanate, etc.) can be added to promote the reaction.

[0302] Preferably, the number-average molecular weight of the polyurethane resin is increased as much as possible by introducing branched structures and internal cross-linking structures, with a preferred number-average molecular weight of 50,000 to 10,000,000. This is because by keeping the molecular weight within the above range, the polyurethane resin is less soluble in solvents, thus obtaining a coating film with excellent weather resistance and water resistance. It should be noted that in this specification, the number-average molecular weight (Mn) is a value determined by gel permeation chromatography (GPC). The number-average molecular weight (Mn) can be, for example, determined using a standard curve prepared from polystyrene standard samples using a "RID-6A" manufactured by Shimadzu Corporation (chromatographic column: "TSK-GEL" manufactured by Tosoh Corporation, solvent: tetrahydrofuran (THF) , column temperature: 40°C).

[0303] Alternatively, commercially available polyurethane resins can also be used. For example, these polyurethane resins can be used as dispersions of aqueous materials in aqueous solvents.

[0304] Examples of commercially available polyurethane resin dispersions include WBR-016U (manufactured by Taisei Fine Chemicals Co., Ltd.), SuperFlex620, SuperFlex 650, SuperFlex500M, SuperFlexE-2000 (all manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., "SuperFlex" is a registered trademark of the company), PERMARIN UC-20 (manufactured by Sanyo Chemical Industry Co., Ltd., "PERMARIN" is a registered trademark of the company), PARASURF UP-22 (manufactured by OHARA PARAGIUM Chemical Co., Ltd.), and Evafanol HA-560 (manufactured by Nichika Chemical Co., Ltd.), etc.

[0305] (Polyacrylic resin)

[0306] Polyacrylic resins used as fixing resins can include (co)polymers of (meth)acrylate components, or copolymers of (meth)acrylate components with polymeric components other than (meth)acrylate components such as styrene components. It should be noted that in this specification, (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

[0307] Examples of (meth)acrylate ingredients include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, benzyl (meth)acrylate, glyceryl (meth)acrylate, acrylic acid, di(di)ethylene glycol (meth)acrylate, di(1,4-butanediol) acrylate, di(1,6-hexanediol) acrylate, tri(meth)acrylate, trimethylolpropane, glyceryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and acrylamide, etc.

[0308] Examples of styrene components include styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetoxystyrene, 4-acetylstyrene, and styrenesulfonic acid. These components can be used alone or in combination with two or more.

[0309] The number average molecular weight (Mn) of the aforementioned polyacrylic acid resin is preferably 1,000 to 50,000, more preferably 2,000 to 20,000. This is because when the number average molecular weight (Mn) of the aforementioned polyacrylic acid resin is 1,000 or higher, the cohesiveness of the coating film becomes stronger and the adhesion is improved; when it is 50,000 or lower, it has good solubility in organic solvents, promoting the miniaturization of the particle size of the emulsion dispersion.

[0310] Alternatively, commercially available products can also be used as the aforementioned polyacrylic acid resin. For example, the aforementioned polyacrylic acid resin can also be used as a dispersion in an aqueous solvent.

[0311] Examples of commercially available polyacrylic acid resin dispersions include DELPET 60N, 80N (manufactured by Asahi Kasei Corporation, "DELPET" is a registered trademark of the company), DIANAAL BR52, BR80, BR83, BR85, BR88 (manufactured by Mitsubishi Chemical Corporation, "DIANAL" is a registered trademark of the company), KT75 (manufactured by Denka Corporation), or VINYBLAN 2680, 2682, 2684, 2685 (manufactured by Nissin Chemical Industries, Ltd., "VINYBLAN" is a registered trademark of the company), MOWINYL6800D (manufactured by Japan Coating Resin Co., Ltd.), etc.

[0312] The fixing resin preferably contains an acid structure. If it contains an acid structure, it can be dispersed in aqueous solvents even without the addition of surfactants, i.e., it can self-emulsify, thus improving the water resistance of the coating film. Such a self-emulsifying resin can be dispersed and stabilized in aqueous solvents solely due to the ionic nature of its molecules. Examples of acid structures include carboxyl groups (-COOH), sulfonic acid groups (-SO3H), and other acid groups. The acid structure can exist in the resin either on the side chains or at the ends.

[0313] It is preferable to neutralize part or all of the above-mentioned acid structure. Neutralizing the acid structure can improve the water dispersibility of the resin. Examples of neutralizing agents for neutralizing acid structures are preferably organic amines, and more preferably trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyldiethanolamine, triethanolamine, etc.

[0314] (surfactant)

[0315] Inks can contain surfactants at will. This improves the ejection stability of the ink and controls the diffusion (dot diameter) of droplets landing on the substrate.

[0316] Surfactants can be used without particular restriction as long as they do not impair the effects of the present invention. Where other components of the ink contain anionic compounds, the surfactant is preferably anionic, nonionic, or betaine-type.

[0317] In this invention, fluorinated or organosilicon surfactants with high static surface tension reduction capabilities, anionic surfactants such as dioctyl sulfosuccinate with high dynamic surface tension reduction capabilities, and relatively low molecular weight nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, ethynyl glycols, Pluronic (registered trademark) type surfactants, and dehydrated sorbitol derivatives are preferred. It is also preferable to use them in combination with fluorinated or organosilicon surfactants, using surfactants with high dynamic surface tension reduction capabilities.

[0318] By adding silicone-based or fluorine-based surfactants, ink mixing on substrates with slow absorption, such as substrates made of various hydrophobic resins, such as polyvinyl chloride and printing paper, can be further suppressed, resulting in high-quality printed images.

[0319] As surfactants for the aforementioned organosilicon systems, polyether-modified polysiloxane compounds are preferred, such as KF-351A and KF-642 manufactured by Shin-Etsu Chemical Industry Co., Ltd., and BYK345, BYK347, and BYK348 manufactured by BYK Corporation.

[0320] The aforementioned fluorinated surfactants refer to surfactants in which some or all of the hydrogen atoms bonded to the carbon atoms of the hydrophobic groups of conventional surfactants are replaced by fluorine. Preferably, the surfactant has a perfluoroalkyl group within the molecule.

[0321] Among the aforementioned fluorinated surfactants, some are commercially available under the trade names Megafac F (Dainippon Ink Chemical Industry Co., Ltd.), Surflon (Asahi Glass Co., Ltd.), Fluorad FC (Minnesota Mining & Manufacturing Co., Ltd.), Monflor (Imperial Chemical Industries Co., Ltd.), Zonyls (EIduPont deNemours and Company Co., Ltd.), and Licowet VPF (farbuwerkehoechst Co., Ltd.).

[0322] The content of surfactant in ink is not particularly limited, but is preferably in the range of 0.1 to 5.0% by mass.

[0323] (Other additives)

[0324] In addition to the components described above, the ink of the present invention may also use various known additives, such as viscosity modifiers, resistivity modifiers, film-forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, mildew inhibitors, rust inhibitors, etc., as needed, without impairing the effects of the present invention, to improve injection stability, printhead or cartridge suitability, storage stability, image preservation, and other various properties.

[0325] Specifically, examples include oil droplets such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, and silicone oil; ultraviolet absorbers described in Japanese Patent Application Publication Nos. 57-74193, 57-87988, and 62-261476; and Japanese Patent Application Publication Nos. 57-74192, 57-87989, and 60-72785. The fading prevention agents described in Japanese Patent Application Publication Nos. 61-146591, 1-95091, and 3-13376, and the fluorescent whitening agents described in Japanese Patent Application Publication Nos. 59-42993, 59-52689, 62-280069, 61-242871, and 4-219266, etc.

[0326] The ink is prepared by mixing the above-mentioned components in the manner described above to achieve the aforementioned amounts. Preferably, the pigment is mixed with the other components as a dispersion in a water-based solvent, dispersed by a pigment dispersant. In the case of a fixing resin, it is preferable that the fixing resin, using a surfactant added as needed, is mixed with the other components as a dispersion in a water-based solvent.

[0327] [Substrate]

[0328] The substrate that can be used in the image forming method of the present invention is not particularly limited, but a non-absorbent substrate is preferred. The image forming method of the present invention is more effective by using a non-absorbent substrate. In the present invention, "non-absorbent" refers to non-absorbency of water.

[0329] Examples of non-absorbent substrates include known plastic films. Specific examples include polyester films such as polyethylene terephthalate, polyethylene films, polypropylene films, polyamide films such as nylon, polystyrene films, polyvinyl chloride films, polycarbonate films, polyacrylonitrile films, and biodegradable films such as polylactic acid films. Furthermore, to impart gas barrier, moisture barrier, and aroma retention properties, films coated with polyvinylidene chloride on one or both sides, or films deposited with metal oxides, are preferred. Whether unstretched or stretched, non-absorbent films are preferred.

[0330] In addition, as a non-absorbent substrate, substrates composed of inorganic compounds such as metals and glass can be listed.

[0331] Alternatively, it can also be appropriately used for packaging materials for retortable foods, where a thermosetting resin is applied as a coating layer on a metal substrate. In order to seal the internal food by blocking air, moisture, and light, the aforementioned packaging material for retortable foods is, for example, made of polypropylene on the food side and a film made of a thermoplastic resin layer and an aluminum foil layer laminated together on the outside.

[0332] In this invention, the thickness of the substrate is preferably 10 to 120 μm, and more preferably in the range of 12 to 60 μm.

[0333] Example

[0334] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. It should be noted that, unless otherwise specified, the operation in the following examples is carried out at room temperature (25°C). In addition, unless otherwise specified, "%" and "parts" refer to "mass %" and "parts by mass", respectively.

[0335] Inkjet inks 1 to 7 with the compositions shown in Table I below are prepared using the following materials.

[0336] Magenta pigment; JM2120 (trade name, manufactured by DIC, compound name: PR202 / PV19)

[0337] Pigment dispersant; Joncryl 819 (trade name; manufactured by BASF, an acrylic dispersant with carboxyl groups neutralized by sodium hydroxide, acid value 75 mg KOH / g, solids content 20% by mass)

[0338] (Fixing resin)

[0339] • Vylonal MD-2000 (trade name; an aqueous dispersion of polyester resin with a number average molecular weight of 18,000, manufactured by Toyobo Co., Ltd.; solids content 40% by mass)

[0340] • MOWINYL6800D (trade name; manufactured by Japan Coating Resin Co., Ltd., aqueous dispersion of polyacrylic acid resin; solid content 45% by mass)

[0341] (Thixotropic agent)

[0342] • CellenpiaTC-01A (trade name, manufactured by Nippon Paper Corporation, cellulose nanofiber, average width 3-4 nm, average length 0.8 μm, aspect ratio 200)

[0343] ·LAPONITERD (trade name, manufactured by BYK, montmorillonite clay mineral, average thickness 0.92nm, average major diameter 25nm, aspect ratio 27)

[0344] (surfactant)

[0345] • KF-351A (trade name, manufactured by Shin-Etsu Chemical Industry, polyether-modified polysiloxane compound) • Olfine E1010 (trade name, manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol)

[0346] (Aqueous solvent)

[0347] • Water; Ion-exchanged water

[0348] ·Propylene glycol

[0349] ·1,2-Hexanediol

[0350] (Preparation of pigment dispersion)

[0351] A pigment dispersion was prepared by premixing 5.0 parts by weight of magenta pigment (JM2120), 2.0 parts by weight of pigment dispersant (Joncryl 819) (solids only), 30.0 parts by weight of propylene glycol, and 53.8 parts by weight of deionized water. The mixture was then dispersed in a sand mill filled with 0.5 mm zirconium oxide beads at a volume fraction of 50%. The average particle size of the pigment particles in this dispersion was 110 nm. It should be noted that the average particle size was determined using a Malvern Zetasizer 1000HS.

[0352] (Preparation of inkjet inks 1-7)

[0353] The pigment dispersion obtained above and the above-mentioned components are mixed in such a manner as shown in Table I below. The resulting mixture is then filtered through a 1 μm filter to obtain inkjet inks 1 to 7. It should be noted that the content (mass %) of each component in Table I indicates the content of solid components contained in that component when used as a dispersion or solution. For example, in inkjet ink 2, for Vylonal MD-2000, the content of the polyester resin itself, excluding the amount of water used as the dispersion medium, is 8.0% by mass.

[0354] (Preparation of primer inks Pr1 and Pr2)

[0355] In addition to the inkjet inks 1 to 7 mentioned above, primer inks Pr1 and Pr2 are obtained by filtering a mixture obtained by mixing in a manner that results in the composition shown in Table II below through a 1 μm filter.

[0356] (Evaluation of ink properties)

[0357] For the obtained ink, the physical properties of (a) to (k) below were evaluated. The results are shown in Table I and Table II.

[0358] (a) Viscosity at a shear rate of 1000 [1 / s]

[0359] (b) Viscosity at a shear rate of 100 [1 / s]

[0360] (c) Viscosity at shear rate 1 [1 / s]

[0361] (d)|A1-A100|

[0362] (e)|A100-A1000|

[0363] (f) Does it conform to equation (I): A1000 < A100 < A1

[0364] (g) Does it conform to formula (II): |A100-A1000|<|A1-A100|

[0365] (h) Equation (III): 1 mPa·s < |A1-A1000|

[0366] (i) Equation (IV): |A100-A1000|<10mPa·s

[0367] (j) Equation (V): 2 mPa·s < A1000 < 20 mPa·s

[0368] (k) Surface tension: Surface tension was measured using a multifunctional automatic surface tension meter K100 (manufactured by KRUSS).

[0369] [Table 1]

[0370]

[0371] [Table 2]

[0372]

[0373] (Image Formation)

[0374] For each ink obtained above, using an inkjet image forming apparatus (inkjet printer (manufactured by TRYTEC Corporation) with a device having a mechanism that circulates ink within the head through two circulation paths (ink discharge paths), at a resolution of 720×720 dpi, the following discharge speed stability was evaluated under the conditions shown in Table III below. The results are shown in Table III below.

[0375] In addition, the conditions in Table III are as follows.

[0376] • Circulating pressure difference ΔP: The pressure difference between the INLET and OUTLET of the inkjet head (specifically, the circulating pressure difference between the first and fourth ink ports 53 and 56).

[0377] • Nozzle circulation flow rate Q: Calculated using the following formula

[0378] Circulation flow rate Q = Circulation pressure difference ΔP / Head flow path resistance R

[0379] The average flow velocity and average shear rate are calculated using the following formulas.

[0380] Average shear rate = Average flow velocity ÷ Radius of the circular pipe

[0381] The radius of a circular tube is the positive square root of (cross-sectional area ÷ π) when the flow path is not circular.

[0382] The circulating flow rate of a single nozzle = the circulating flow rate of all nozzles ("circulating flow rate Q") ÷ the number of nozzles

[0383] Average flow velocity = circulating flow rate of a single nozzle ÷ cross-sectional area of ​​the flow path connected to the nozzle

[0384] also,

[0385] • Number of nozzles: 1024

[0386] • Cross-sectional area of ​​the flow path connected to the nozzle: 2.5 × 10 -8 [m 2 ]

[0387] • Representative circular pipe radius of the flow path connected to the nozzle: 8.9 × 10 -5 [m].

[0388] (Discharge rate stability)

[0389] The discharge velocity of a single nozzle was set to 6 m / s. Subsequently, the discharge velocity was measured ten times every minute using the method described below. Then, based on the maximum and minimum discharge velocities in the ten measurements, the velocity variation of the discharge velocity was calculated using the following formula and evaluated according to the following criteria.

[0390] Average speed = (maximum speed + minimum speed) ÷ 2

[0391] Speed ​​variation = (maximum speed - minimum speed) / average speed × 100

[0392] (Benchmark)

[0393] ◎: Speed ​​variation is less than 5%

[0394] ○: Speed ​​variation greater than 5% but less than 10%

[0395] ×: Speed ​​variation greater than 10%

[0396] Furthermore, the above-mentioned discharge rate was measured as follows, referring to paragraphs

[0049] to

[0056] of Japanese Patent Application Publication No. 2007-15192.

[0397] A droplet is ejected from all nozzles at the same time by using a stroboscopic and CCD camera at each of the stroboscopic delay times (1) and (2), and the following processes are performed.

[0398] Here, for the same droplet discharged from the nozzle, the droplet captured during the first stroboscopic delay time (1) is designated as "droplet 1", and the droplet captured during the second stroboscopic delay time (2) is designated as "droplet 2".

[0399] The upper limit of the strobe delay time (1) and the delay time from the strobe delay time (1) to the strobe delay time (2) for the second shooting are set in advance through the computer's setting input section.

[0400] "Flicker delay time" refers to the delay time from the timing of the inkjet head ejecting droplets, such as the triggering of droplet ejection, to the time when the strobe light is emitted and the image is captured by the CCD camera. In addition, the flicker delay time (1) is the time when the image is initially captured, and the flicker delay time (2) is the time when the image is captured after a set delay time from the flicker delay time (1).

[0401] First, the stroboscopic delay time (1) for capturing images of droplet 1 ejected from the inkjet head using a CCD camera and stroboscopic imaging is set to 100 μsec. Then, after the droplet is ejected from the nozzle, the droplet 1 is captured at a timed interval of the set stroboscopic delay time (1). Based on the captured images of droplet 1, the centroids X1 and Y1 of droplet 1 are calculated.

[0402] Next, the preset delay time is added to the strobe delay time (1), and the strobe delay time (2) is set to 100 μsec. Then, the same droplet is photographed at the set strobe delay time (2), and droplet 2 is captured. Based on the captured image of droplet 2, the centroids X2 and Y2 of droplet 2 are calculated.

[0403] Next, using the centers of gravity and stroboscopic delay times (1) and (2) of droplets 1 and 2, the apparent discharge velocity is calculated. The apparent discharge velocity is the velocity determined based on the position of the droplets as captured in the photograph. The apparent discharge velocity is calculated using the following formula.

[0404] [Formula 1]

[0405]

[0406] [Table 3]

[0407] Table III

[0408]

[0409] As shown in the above results, it can be seen that by using the thixotropic ink of the present invention and controlling the average shear rate in the flow path connected to the nozzle to be above 100 [1 / s], the stability of the discharge rate can be improved.

[0410] This invention is applicable to an image forming method that uses highly thixotropic inks and circulates the ink near the nozzle to facilitate ink discharge, thereby suppressing changes in ink viscosity during discharge and ensuring uniform discharge speed between nozzles to improve image quality.

[0411] Explanation of reference numerals: 1…head chip, 8…ink circulation device, 11…nozzle substrate, 111…nozzle, 12…flow path isolation substrate, 121…individual ink discharge path, 122…first individual ink discharge path, 123…second individual ink discharge path, 13…pressure chamber substrate, 131…pressure chamber, 132…air chamber, 133…common ink discharge path, 134…first common ink discharge path, 135…second common ink discharge path, 136…partition (pressure generating unit), 100…inkjet head, 200…inkjet recording device, 240…control unit, R…flow path communicating with the nozzle.

Claims

1. An image forming method, which is an image forming method using an inkjet recording apparatus having an inkjet head, the inkjet head comprising: a pressure chamber that supplies ink from an ink supply path and freely applies pressure to the ink stored in the inside; a nozzle that has a discharge opening for discharging the ink and is disposed in communication with the pressure chamber; and a plurality of ink discharge flow paths connected in proximity to a communication position of the nozzle with respect to the pressure chamber, wherein two or more of the plurality of ink discharge flow paths are provided for the discharge opening of the nozzle, the inkjet recording apparatus comprises an ink circulation device that circulates the ink from the ink supply path to the ink discharge flow path, when a viscosity of the ink at 25°C at a shear rate of 1 [1 / s] is set as Al, a viscosity of the ink at 25°C at a shear rate of 100 [1 / s] is set as A100, and a viscosity of the ink at 25°C at a shear rate of 1000 [1 / s] is set as A1000, the following relations of Expression (I) and Expression (II) are satisfied, the ink circulation device performs control so that an average shear rate in a flow path in the pressure chamber that communicates with the nozzle is 100 [1 / s] or more, Expression (I): A1000 < A100 < Al Expression (II): |A100 - A1000| < |Al - A100|.

2. The image forming method according to claim 1, wherein the ink satisfies the following relations of Expressions (III) to (V), Expression (III): 1 mPa-s < |Al - A1000| Expression (IV): |A100 - A1000| < 10 mPa-s Expression (V): 2 mPa-s < A1000 < 20 mPa-s.

3. The image forming method according to claim 1 or 2, wherein a speed variation of a discharge speed of the ink discharged from the nozzle is 5% or less.

4. The image forming method according to claim 1 or 2, wherein the inkjet recording apparatus comprises an actuator that gives pressure to the ink in the pressure chamber, and a swing waveform that is smaller in voltage than a drive waveform that discharges the ink from the nozzle and vibrates an interface of the ink in the pressure chamber is applied.

5. The image forming method according to claim 1 or 2, wherein the ink contains a pigment, a fixing resin, a water-soluble solvent, and water, contains the pigment in a range of 3 to 10 mass%, contains the fixing resin in a range of 8 to 20 mass%, contains the water-soluble solvent in a range of 10 to 30 mass%, and contains the water in a range of 40 to 79 mass%.

6. The image forming method according to claim 1 or 2, wherein a surface tension of the ink is in a range of 22 to 25 mN / m. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images