Inkjet recording method and inkjet recording apparatus

Abstract

To provide an inkjet recording method which is excellent in sticking recovering properties, and enables recording of a high quality image reduced in unevenness even when an inkjet recording device having a small size and high durability is used.SOLUTION: An inkjet recording method for recording an image using an inkjet recording device which includes a plurality of aqueous ink, a first ink storage part, a second ink storage part, a plurality of tubes for supplying the aqueous ink, a recording head having a discharge port surface arrayed with a plurality of discharge port arrays for discharging the aqueous ink, and a recovery mechanism collectively covering the plurality of discharge port arrays, and having suction means for sucking the aqueous ink. A ratio (η2 / η1) of viscosity η2(mPa s) of the second ink to viscosity η1(mPa s) of the first ink is 0.7 or more and 1.5 or less, and the first ink contains a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus used therein. [Background technology]

[0002] In recent years, inkjet recording devices have been increasingly used in offices and commercial printing fields. These fields require high productivity to record large volumes of images. For example, in order to improve productivity, an inkjet recording device has been proposed that has a large-capacity ink storage section, eliminating the need to replace ink cartridges (Patent Document 1).

[0003] Furthermore, the increased capacity of the ink storage unit has led to an increase in the number of printable sheets, which has led to longer usage periods for inkjet recording devices. This has led to a strong trend toward ensuring the durability of the components constituting the device and the reliability of the ink. For example, an ink supply tube for inkjet recording devices that is flexible and resistant to bending has been proposed (Patent Document 2).

[0004] Furthermore, in order to meet the demand for miniaturization of the device, there is known an inkjet recording device equipped with a recovery mechanism that sucks multiple inks from multiple ejection port arrays together through the same suction cap. In order to maintain high reliability even when using an inkjet recording device equipped with such a simple recovery mechanism, an inkjet recording device has been proposed in which the difference in evaporation viscosity of the ink set is specified to enhance recovery (Patent Document 3).

[0005] Recently, for example, in stores and photo studios, there has been an increase in opportunities to sell products printed using inkjet recording apparatuses to customers as merchandise. Inkjet recording apparatuses used for such purposes are required to be capable of recording photographs and images with high image quality. In response to such requirements, an inkjet recording method has been proposed that reduces unevenness caused by image recording (Patent Document 4).

[0006] In addition, an inkjet recording device has been proposed that is equipped with a mechanism for sucking multiple inks from multiple nozzle rows through the same suction cap, and that specifies the relationship between the ratio of low-dielectric-constant solvent to high-dielectric-constant solvent contained in the ink and the nozzle flow path volume (Patent Document 5).This inkjet recording device is said to be able to maintain adhesion recovery. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-081150 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-080724 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-171070 [Patent Document 4] Japanese Patent Application Publication No. 2019-130898 [Patent Document 5] Japanese Patent Application Publication No. 2017-081056 Summary of the Invention [Problem to be solved by the invention]

[0008] The present inventors have investigated configurations for providing an inkjet recording apparatus that is both compact and highly durable, and as a result have found that the following three configurations (1) to (3) are suitable. (1) The length of the ink supply tube is not necessarily the same for each ink (it varies depending on the ink). (2) A recovery operation is performed in which a plurality of inks are sucked together from a plurality of ejection port arrays through the same suction cap. (3) Use a flexible ink supply tube.

[0009] When arranging each component of the device in a compact space, the lengths of the multiple tubes connecting the sub-tank and the main tank are not necessarily the same for each ink, and may differ for each ink (structure (1)). Furthermore, when multiple inks are collectively sucked from multiple nozzle arrays through the same suction cap, the recovery mechanism can be made compact (structure (2)). This is because the distance between the multiple nozzle arrays can be narrowed compared to a system in which multiple nozzles are sucked through individual suction caps. Furthermore, the sub-tank is usually located above the print head mounted on the carriage or is integrated with the print head. Therefore, an ink supply tube, one end of which is connected to the main tank and the other end of which is connected to the sub-tank, is routed within the device as the carriage scans during image printing. Therefore, to ensure durability, it is preferable to use an ink supply tube that is flexible enough to withstand the reciprocating scanning of the carriage (structure (3)). However, Patent Documents 1 to 5 do not disclose an inkjet printing device equipped with all of the above structures (1) to (3).

[0010] The present inventors recorded images using the inkjet recording device and ink set proposed in Patent Document 3. As a result, they found that even after filling the device with ink and leaving it unused for a long period of time, clogging of the ejection ports can be cleared by operating the recovery mechanism, and the ink can be restored to a state where it can be ejected normally, i.e., the ink adhesion recovery is good. However, in the case of an inkjet recording device employing the above configurations (1) to (3), it was found that repeated suction is required to properly record an image, and that the ink adhesion recovery may be insufficient. Furthermore, they found that unevenness is likely to occur in the image obtained immediately after the start of recording.

[0011] Therefore, an object of the present invention is to solve the problems that arise when using an inkjet recording apparatus having the following configurations (1) to (3). That is, an object of the present invention is to provide an inkjet recording method that is excellent in adhesion recovery and can record high-quality images with reduced unevenness even when using the above-mentioned inkjet recording apparatus. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method. (1) The length of the ink supply tube is not necessarily the same for each ink (it varies depending on the ink). (2) A recovery operation is performed in which a plurality of inks are sucked together from a plurality of ejection port arrays through the same suction cap. (3) Use a flexible ink supply tube. [Means for solving the problem]

[0012] That is, according to the present invention, there is provided a recording head including: a plurality of water-based inks each containing a colorant; a first ink containing section containing each of the plurality of water-based inks; a second ink containing section; a plurality of tubes for supplying the water-based ink from the first ink containing section to the second ink containing section; a plurality of nozzles connected to the second ink containing section and through which the plurality of water-based inks supplied from the second ink containing section flow; a plurality of ejection ports communicating with the plurality of nozzles and ejecting the plurality of water-based inks respectively; and a recording head having an ejection port surface on which a plurality of ejection port arrays constituted by the plurality of ejection ports are arranged corresponding to the plurality of water-based inks; a suction cap abutting against an area including the ejection port surface of the recording head and covering the plurality of ejection port arrays collectively; and a recovery mechanism having suction means for collectively sucking the water-based inks in the plurality of nozzles through the suction cap, an inkjet recording apparatus that includes an ink-jet recording section, the ink-jet recording section including a first tube for supplying the first ink to the second ink holding section and a second tube for supplying the second ink to the second ink holding section; a length L1 (mm) of the first tube being 1.15 or more times the length L2 (mm) of the second tube in terms of a ratio (L1 / L2) of the first tube to the length L2 (mm) of the second tube; and a water vapor transmission rate W (mg / day) of the first tube and the second tube at 40°C of 2 mg / day or more; the ink-jet recording method comprising a step of applying the aqueous ink ejected from the ejection openings to a recording medium to record an image, wherein the ink-jet recording apparatus includes an ink-jet recording section, the tubes including a first tube for supplying the first ink to the second ink holding section and a second tube for supplying the second ink to the second ink holding section; a length L1 (mm) of the first tube being 1.15 or more times the length L1 (mm) of the second tube in terms of a ratio (L1 / L2) of the second tube to the length L2 (mm) of the second tube; and a water vapor transmission rate W (mg / day) of the first tube and the second tube at 40°C of 2 mg / day or more; [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an inkjet recording method that is excellent in adhesion recovery and is capable of recording high-quality images with reduced unevenness, even when using an inkjet recording apparatus having the following configurations (1) to (3). Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus used in this inkjet recording method. (1) The length of the ink supply tube is not necessarily the same for each ink (it varies depending on the ink). (2) A recovery operation is performed in which a plurality of inks are sucked together from a plurality of ejection port arrays through the same suction cap. (3) Use a flexible ink supply tube. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating an example of an ink supply system. [Figure 3] FIG. 2 is a schematic diagram illustrating an example of a sub-tank. [Figure 4] FIG. 10 is a schematic diagram showing a state in which the suction cap is in contact with the nozzle; DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience, it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0016] As mentioned above, when the inkjet recording apparatus proposed in Patent Document 3 employs the above configurations (1) to (3) and is filled with ink and left unused for a long period of time, adhesion recovery may become insufficient. Patent Document 3 states that in order to eliminate variations in the amount of ink suctioned in the recovery operation and maintain adhesion recovery, the difference in evaporation viscosity between inks with different evaporation rates is kept within a predetermined range.

[0017] However, when configurations (1) to (3) are adopted to provide a compact, durable inkjet recording device, it has been found that variations in the amount of suction during the recovery operation occur due to factors other than differences in viscosity between the inks, resulting in insufficient ink adhesion recovery. If the tube lengths are not necessarily uniform between inks in order to miniaturize the device, the surface area of ​​the tube, i.e., the area of ​​contact with air, differs, resulting in differences in the amount of ink evaporation. The flexibility of the tube is correlated with its barrier properties. Specifically, highly flexible tubes tend to have a higher water vapor permeation rate. Therefore, when flexible tubes are used to improve durability, the water vapor permeation rate increases, making the difference in evaporation rate between inks more pronounced. As a result, the ink in a long tube, which evaporates more, is thought to be more concentrated than the ink in a short tube, which evaporates less.

[0018] Furthermore, because ink evaporates from the tube wall, the ink near the tube's inner wall is more concentrated than the ink near the center of the tube in the cross-sectional direction. Therefore, near the inner wall of a long tube, the ink is likely to become locally viscous due to evaporation of liquid components and an increase in colorant concentration, and when this ink flows to the print head, pressure loss increases, making it difficult to suck the ink. On the other hand, in the case of a short tube, the surface area of ​​the wall is relatively small, so the amount of evaporation is small, and it is therefore thought that localized high viscosity of the ink near the tube's inner wall is unlikely to occur.

[0019] The inventors further investigated inks that suppress deterioration of adhesion recovery even in inkjet recording devices having the above-described configurations (1) to (3). Specifically, the ink supplied through a relatively long tube (first tube) is referred to as the "first ink," and the ink supplied through a relatively short tube (second tube) is referred to as the "second ink." Because the first ink evaporates more than the second ink, the viscosity of the first ink was adjusted to be lower than that of the second ink. Adjusting the viscosity relationship between the first and second inks in this way improved adhesion recovery to some extent, but it was found that a new problem arose: unevenness was more likely to occur in images obtained immediately after the start of recording. It is believed that the difference in the viscosities of the first and second inks increased the difference in the molar fraction of water between the inks, making unevenness more likely to occur in images obtained immediately after the start of recording.

[0020] The molar fraction of water in ink refers to the molar fraction of water among all water-soluble compounds (including water) with a molecular weight of 300 or less contained in the ink, and theoretically takes a value greater than 0% and less than 100%. Compounds with a "molecular weight of 300 or less" are used to calculate the molar fraction of water because compounds with a molecular weight sufficiently larger than that of water do not substantially affect the molar fraction of water at the normal content in aqueous inkjet inks.

[0021] Generally, when compared at the same temperature, aqueous solutions containing non-volatile solutes have a lower vapor pressure than pure water, making it difficult for the liquid components to evaporate. The degree of vapor pressure reduction is proportional to the mole fraction of the solute, regardless of the type of solute, in the case of sufficiently dilute solutions or ideal gases (Raoult's law). Raoult's law can also be applied to inks. Water-based inkjet inks are typically composed of colorants and resins that are treated as non-volatile solutes at room temperature (25°C), and water-soluble organic solvents that have a lower vapor pressure than water, so the vapor pressure of water in the ink can be calculated using the following formula (1): "Vapor pressure of water in ink" = "Vapor pressure of pure water" x "Mole fraction of water in ink" …(1)

[0022] Next, consider the equilibrium state of water when the nozzle surface, on which multiple nozzle arrays corresponding to multiple water-based inks are arranged, is covered with a suction cap, creating an enclosed space inside the suction cap. If the molar fraction of water in the ink is higher than the relative humidity of the enclosed space inside the suction cap, the water in the ink inside the nozzles evaporates. On the other hand, if the molar fraction of water in the ink is lower than the relative humidity of the enclosed space inside the suction cap, the water inside the suction cap dissolves into the ink inside the nozzles. Evaporation and dissolution occur until the state represented by the following formula (2) is reached, eventually reaching equilibrium. "Relative humidity of the sealed space inside the suction cap" = "molar fraction of water in the ink inside the nozzle" …(2)

[0023] When a nozzle surface with multiple nozzle arrays arranged to correspond to multiple water-based inks is covered by a single suction cap, an equilibrium state is reached where the relative humidity of the sealed space inside the suction cap equals the mole fraction of water in each ink. If the mole fraction of water differs between inks, water evaporates from the ink with a higher mole fraction of water and dissolves in the ink with a lower mole fraction of water. Eventually, the mole fraction of water in all inks reaches the same relative humidity as the sealed space inside the suction cap, and equilibrium is reached. In other words, inks with a lower mole fraction of water absorb moisture and become diluted, while inks with a higher mole fraction of water evaporate and become concentrated.

[0024] To decrease the viscosity of an ink, the water content can be increased and the water-soluble organic solvent content can be reduced. On the other hand, to increase the viscosity of an ink, the water content can be reduced and the water-soluble organic solvent content can be increased. However, simply increasing or decreasing the water content increases the difference in the water molar fraction between inks, resulting in repeated concentration and dilution of the ink as described above. The ink present in the nozzles of the print head near the ejection ports becomes concentrated or diluted from its initial state, and therefore an image is printed using concentrated or diluted ink immediately after printing begins. After this ink is consumed, the image is printed using ink that is neither diluted nor concentrated, which is thought to result in unevenness in the resulting image.

[0025] Based on the above, the ratio (η2 / η1) of the viscosity of the second ink η2 (mPa s) to the viscosity η1 (mPa s) of the first ink is set to 0.7 to 1.5. If the η2 / η1 ratio is outside the above range, the difference in viscosity between the first and second inks will be large, and the difference in the molar fraction of water between the first and second inks will also likely be large. For this reason, when multiple ejection port arrays are covered with the same suction cap to form an enclosed space, the ink with a low molar fraction of water will be diluted and the ink with a high molar fraction of water will be concentrated, which can easily cause unevenness in the image immediately after printing begins.

[0026] As a result of further investigation, the inventors discovered that a high level of adhesion recovery and image quality can be achieved by adding a water-soluble organic solvent (first water-soluble organic solvent) having a relative dielectric constant of 40.0 or more to the first ink supplied through the first tube, and thus arrived at the present invention. The inventors speculate as follows about the reason why the above-mentioned effect is obtained by adding a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more to the first ink.

[0027] As mentioned above, the ink inside the tube evaporates from the tube wall. Typically, water-based inks for inkjet printing are primarily composed of water, with the other components having lower vapor pressures than water. Among the ink components, water has a high vapor pressure and evaporates quickly, so it is thought that the proportion of water-soluble organic solvents near the inner wall of the tube is higher than in the center of the tube's cross section. Furthermore, the higher the relative dielectric constant of a water-soluble organic solvent, the more polar it is. Water-soluble organic solvents with a high relative dielectric constant and large polarization tend to stabilize the state of ionized colorants in the ink. Therefore, it is thought that they solvate the concentrated colorants, preventing the formation of strong aggregates or aggregates.

[0028] Here, let's consider a case where the first ink contains a first water-soluble organic solvent. In this case, as water evaporates, ink with a locally high viscosity is present near the inner wall of the tube, and the proportion of the first water-soluble organic solvent also increases. As a result, the colorant that has become concentrated and highly viscous near the inner wall of the tube is loosened by the action of the first water-soluble organic solvent to solvate the colorant, and the colorant is dispersed by the flow of the first ink inside the tube. As a result, the viscosity of the first ink present near the inner wall of the tube, which was the cause of the reduced suction volume during the recovery operation, is reduced, and it is thought that adhesion recovery is improved.

[0029] When multiple inks are suctioned from multiple nozzle arrays through the same suction cap to achieve a compact recovery mechanism, it is difficult to set the ink suction volume for each ink. In inkjet recording devices with such limitations, the conventional approach to improving adhesion recovery is to standardize the viscosity of each ink to eliminate variations in the suction volume. However, in inkjet recording devices equipped with multiple flexible tubes of different lengths and with high water vapor permeability, the difference in the degree of ink evaporation between the tubes is greater than expected for conventional inkjet recording devices. Therefore, attempting to standardize the viscosity of inks from which water has evaporated results in a larger difference in viscosity between inks from which water has not evaporated, which can easily degrade image quality. In other words, the conventional approach of simply adjusting the ink viscosity fails to achieve both adhesion recovery and high image quality. In response to this, the inventors discovered that the cause of reduced adhesion recovery when using tubes with high water vapor permeability is ink with high viscosity near the inner wall of the tube. The inventors have also found that by incorporating a water-soluble organic solvent with predetermined physical properties into the ink, it is possible to improve the adhesion recovery property without degrading the image quality, rather than simply adjusting the viscosity of the ink.

[0030] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention uses an inkjet recording device equipped with multiple aqueous inks, a first ink storage unit containing each of the multiple aqueous inks, a second ink storage unit, multiple tubes, a recording head, and a recovery mechanism. Each of the multiple aqueous inks contains a colorant. The tubes are components (ink supply tubes) that supply the aqueous ink from the first ink storage unit to the second ink storage unit. The recording head is connected to the second ink storage unit and has multiple nozzles through which the multiple aqueous inks supplied from the second ink storage unit flow. The recording head further has multiple ejection ports communicating with the multiple nozzles and ejecting each of the multiple aqueous inks, and an ejection port surface formed by the multiple ejection ports and on which multiple ejection port arrays corresponding to the multiple aqueous inks are arranged. The recovery mechanism includes a suction cap that contacts an area including the ejection port surface of the recording head and collectively covers the multiple ejection port arrays, and suction means that collectively sucks the aqueous inks from the multiple nozzles through the suction cap. The multiple aqueous inks include a first ink and a second ink. The plurality of tubes includes a first tube that supplies the first ink to the second ink holding portion and a second tube that supplies the second ink to the second ink holding portion. The inkjet recording method of the present invention includes a step of applying the aqueous ink ejected from the ejection openings of the recording head onto a recording medium to record an image.

[0031] The inkjet recording apparatus of the present invention includes a plurality of aqueous inks, a first ink storage unit that stores the plurality of aqueous inks, a second ink storage unit, a plurality of tubes, a recording head, and a recovery mechanism. Each of the plurality of aqueous inks contains a colorant. The tubes are components (ink supply tubes) that supply the aqueous ink from the first ink storage unit to the second ink storage unit. The recording head is connected to the second ink storage unit and has a plurality of nozzles through which the plurality of aqueous inks supplied from the second ink storage unit flow. The recording head further includes a plurality of ejection ports that communicate with the plurality of nozzles and eject the plurality of aqueous inks, and an ejection port surface on which a plurality of ejection port arrays are arranged, each formed of the plurality of ejection ports and corresponding to the plurality of aqueous inks. The recovery mechanism includes a suction cap that contacts an area including the ejection port surface of the recording head and collectively covers the plurality of ejection port arrays, and suction means that collectively sucks the aqueous inks from the plurality of nozzles through the suction cap. The plurality of aqueous inks include a first ink and a second ink. The plurality of tubes includes a first tube that supplies the first ink to the second ink containing section and a second tube that supplies the second ink to the second ink containing section.

[0032] (Inkjet recording device) FIG. 1 is a perspective view schematically illustrating one embodiment of an inkjet recording apparatus according to the present invention. The inkjet recording apparatus of this embodiment is a so-called serial inkjet recording apparatus that performs a recording operation by reciprocating a recording head in the X direction (main scanning direction). A recording medium 101 is intermittently transported in the Y direction (sub-scanning direction) by a transport roller 107. A recording unit 102 mounted on a carriage 103 is reciprocally scanned in the X direction (main scanning direction), which is perpendicular to the Y direction, the transport direction of the recording medium 101. A recording operation is performed by transporting the recording medium 101 in the Y direction and reciprocating scanning of the recording unit 102 in the X direction. The recording unit 102 is comprised of an inkjet recording head 203 (FIG. 2) that ejects ink from multiple nozzles and a sub-tank 202 (FIG. 2) that serves as a second ink container, and is mounted on the carriage 103. The carriage 103 is supported so as to be movable along a guide rail 105 arranged along the X direction, and is fixed to an endless belt 106 that moves parallel to the guide rail 105. The endless belt 106 moves back and forth by the driving force of a motor, thereby causing the carriage 103 to scan back and forth in the X direction.

[0033] A main tank 201 (FIG. 2) serving as a first ink storage section is stored inside the main tank storage sections 108 and 109. The main tank 201 of the main tank storage sections 108 and 109 and the sub-tank 202 of the recording unit 102 are connected via an ink supply tube 104 including a tube 111 and a tube 112. Ink is supplied from the main tank 201 to the sub-tank 202 via the ink supply tube 104, and then ejected from the ejection openings of the recording head 203. The number of main tanks 201, ink supply tubes 104, and sub-tanks 202 can all be provided in a number corresponding to the type of ink.

[0034] Fig. 2 is a schematic diagram showing an example of an ink supply system, and Fig. 3 is a schematic diagram showing an example of a sub-tank. Ink (shown hatched) contained in a main tank 201 is supplied to a sub-tank 202 via an ink supply tube 104, and then supplied to a print head 203. The print head 203 is connected to the sub-tank 202, which is a second ink storage section, and has a plurality of nozzles (not shown) through which ink supplied from the sub-tank 202 flows. As shown in Fig. 3, the print head 203 further has a discharge port surface 215 on which a plurality of discharge port arrays 212 are arranged, each formed of a plurality of discharge ports communicating with the plurality of nozzles and discharging ink.

[0035] A gas introduction tube 204, which serves as an atmosphere communication section, is connected to the main tank 201. When printing is performed and ink is consumed, ink is supplied from the main tank 201 to the sub-tank 202, and the ink in the main tank 201 decreases. Then, air is introduced into the main tank 201 from the gas introduction tube 204, one end of which is open to the atmosphere, and the internal negative pressure for retaining ink in the ink supply system is maintained at a substantially constant level.

[0036] The housings of the main tank 201 and the subtank 202 are made of thermoplastic resins such as polyester, polycarbonate, polyethylene, polypropylene, polystyrene, polyphenylene ether, and mixtures or modifications of these materials. An ink absorber capable of generating negative pressure to retain ink may be provided inside the housing. Compressed fibers of polypropylene, polyurethane, or the like are preferred as the ink absorber. Alternatively, ink may be stored directly inside the housing without providing an ink absorber. To reduce the frequency of tank replacement and achieve high productivity by increasing the number of recordable sheets, it is preferable to increase the maximum capacity V1 (mL) of the main tank 201.

[0037] The maximum capacity V1 (mL) of the main tank 201 is preferably 30 mL or more and 200 mL or less, and more preferably 50 mL or more and 150 mL or less. The initial ink filling amount of the main tank 201 is preferably about 95% of the maximum ink capacity. The capacity V2 (mL) of the ink supply tube 104 is preferably 1 mL or more and 30 mL or less, and more preferably 2 mL or more and 20 mL or less.

[0038] The recording unit 102 is composed of a recording head 203 and a subtank 202. The subtank 202 may be attached to the recording unit 102, which is a head cartridge incorporating the recording head 203, and the recording unit 102 with the subtank 202 attached may be attached to the carriage 103. Furthermore, the recording unit 102 integrally composed of the subtank 202 and recording head 203 may be attached to the carriage 103. Among these, it is preferable to adopt a serial system in which the recording unit 102 with the subtank 202 attached is set on the carriage 103.

[0039] The ink ejection method of the recording head 203 can be a method of applying mechanical energy to the ink or a method of applying thermal energy to the ink, but it is preferable to adopt a method of ejecting ink by applying thermal energy to the ink.

[0040] FIG. 4 is a schematic diagram showing the state in which the suction cap is in contact, where (a) shows the bottom surface of the subtank and (b) shows the suction cap. During non-printing, in order to suppress evaporation of ink from the ejection ports, the suction cap 205 contacts an abutment position 214 in an area of ​​the support substrate 213 that includes an ejection port surface 215 of the print head 203, thereby covering the multiple ejection port arrays 212. As shown in FIG. 2, the suction cap 205 is connected to a tube 207 serving as an air communication unit provided with an air communication valve 206, and a waste ink tube 208 for discharging waste ink that accumulates in the suction cap 205 and is not used for printing. As shown in FIG. 2, waste ink discharged from the multiple ejection ports that communicate with the multiple nozzles provided in the print head 203 is stored in a waste ink storage unit 209. The waste ink tube 208 is provided with a suction valve 210, and ink in the nozzles is sucked using a pump 211, which is a suction means, thereby restoring the ejection state of the recording head 213 to a normal state. The location from which ink is sucked and the amount of ink to be sucked can be set appropriately depending on the purpose. In either case, the pump 211 is operated to suck ink while the atmosphere communication valve 206 is closed.

[0041] [tube] The multiple tubes (ink supply tubes) include a first tube that supplies the first ink to the second ink storage unit and a second tube that supplies the second ink to the second ink storage unit. The tubes are routed through the inkjet recording device as the carriage reciprocates, resulting in high bending rigidity. Therefore, the tubes are preferably made of a resin material to ensure flexibility sufficient to withstand the reciprocating scanning of the recording head. The resin material constituting the tubes may be a single resin material or a combination of two or more resin materials. It may also be a resin material blended with various additives. The tubes may have a single-layer structure or a multilayer structure. Thermoplastic elastomers are preferred as resin materials because of their excellent moldability, rubber elasticity, and flexibility. Examples of thermoplastic elastomers include olefin-based, urethane-based, ester-based, styrene-based, and vinyl chloride-based resins. Among these, styrene-based thermoplastic elastomers are preferred because of their particularly excellent flexibility and rubber elasticity. Examples of additives that may be blended into the resin material include softeners, lubricants, surfactants, antioxidants, antiaging agents, adhesion promoters, and pigments. The properties of the first and second tubes may be the same or different, and it is particularly preferred that the first and second tubes are made of the same material.

[0042] The inner diameter and wall thickness of the tube are appropriately set in consideration of productivity such as molding, bending rigidity when routed through a recording device, ink supply performance, gas barrier properties, etc. The inner diameter of the tube is preferably 1 mm or more and 5 mm or less, and more preferably 1 mm or more and 3 mm or less. The wall thickness of the tube is preferably 0.5 mm or more and 5 mm or less, more preferably 0.5 mm or more and 3 mm or less, and particularly preferably 1 mm or more and 3 mm or less.

[0043] The flexibility of the tube correlates with its water vapor permeability. That is, tubes with a high water vapor permeability tend to have excellent flexibility. The water vapor permeability W (mg / day) of the first and second tubes at 40°C is 2 mg / day or more, preferably 3 mg / day or more. If the water vapor permeability W is less than 2 mg / day, the tube will lack flexibility, making it difficult for it to follow the carriage scan and resulting in insufficient durability. There is no particular upper limit for the water vapor permeability W of the tube, as long as it is 10 mg / day or less. If the water vapor permeability is too high, water evaporation will proceed significantly, and the ink will tend to be excessively concentrated. However, if the water vapor permeability W is 10 mg / day or less, the water-soluble organic solvent with a relative dielectric constant of 40.0 or more will efficiently solvate with the colorant, suppressing the formation of associations and aggregates.

[0044] The water vapor permeability (W) of a tube can be measured using the following method. First, pure water is poured into a tube cut to a length of 200 mm, and both ends of the tube are sealed with pinch cocks. The tube is then left in this state in an environment at a temperature of 40°C and a relative humidity of 20%, and the change in the tube's mass is recorded at regular intervals. The amount of water vapor that permeates the tube is measured, and the water vapor permeability (W) (mg / day) can be calculated. The water vapor permeability (W) is the water vapor permeability (mg / day) per 200 mm of tube length (L). When a tube is constructed by connecting two or more tubes made of different materials, the water vapor permeability of each tube calculated as above is calculated proportionally by length. For example, the water vapor permeability (W) of a tube constructed by connecting a tube with a water vapor permeability (Wa) (mg / day) and a length (La) (mm) and a tube with a water vapor permeability (Wb) (mg / day) and a length (Lb) (mm) is calculated as follows: W=(La×Wa+Lb×Wb) / (La+Lb).

[0045] "Tube length" refers to the length from one end of the tube to the other, including the connection between the main tank and the sub-tank. The ratio (L1 / L2) of the length L1 (mm) of the first tube to the length L2 (mm) of the second tube is 1.15 or more. By setting the L1 / L2 ratio to 1.15 or more, the inkjet recording device can be made more compact. There is no particular upper limit to the L1 / L2 ratio, and it is sufficient if it is 1.90 or less. The length L (mm) of each tube is preferably 200 mm or more and 1,200 mm or less, and more preferably 300 mm or more and 1,000 mm or less. The length L1 (mm) of the first tube is preferably 400 mm or more and 1,000 mm or less. Furthermore, the length L2 (mm) of the second tube is preferably 300 mm or more and 800 mm or less.

[0046] It is preferable that the first ink is a black ink and the second ink is a color ink. In this case, the ratio (La / Lb) of the length La (mm) of the tube for the black ink to the length Lb (mm) of the tube for the color ink is preferably 1.20 or more. By making the La / Lb ratio 1.20 or more, the ejection stability of the ink can be improved. If the La / Lb ratio is less than 1.20, the ejection stability may be slightly reduced when each ink is ejected over a long period of time. The La / Lb ratio is preferably 2.00 or less, more preferably 1.90 or less, and particularly preferably 1.50 or less. When multiple color inks are used, it is preferable that the tube for the black ink is longer than any of the tubes for the color inks.

[0047] (Recording process) The inkjet recording method of the present invention includes a step of recording an image using the inkjet recording apparatus (recording step). Specifically, in the recording step, ink is ejected from the ejection openings of a recording head and applied to a recording medium to record an image. Any recording medium may be used as the target for recording the image. In particular, it is preferable to use permeable paper such as recording media without a coating layer, such as plain paper or uncoated paper, or recording media with a coating layer, such as glossy paper or art paper.

[0048] Examples of recording methods include a serial method in which an image is recorded by scanning a recording head back and forth in a main scanning direction perpendicular to the recording medium transport direction (sub-scanning direction), and a line method in which an image is recorded by using a long recording head (line head) corresponding to the width of the recording medium (paper) while the recording medium is transported.

[0049] (water-based ink) The inkjet recording method of the present invention includes a step of recording an image by applying inks ejected from ejection openings of a recording head onto a recording medium. The inks are water-based inks containing coloring materials, and include a first ink and a second ink.

[0050] [Colorant] The coloring material may be a pigment or a dye. The content C1 (mass%) of the coloring material in the first ink and the content C2 (mass%) of the coloring material in the second ink are preferably from 0.1% to 15.0% by mass, based on the total mass of the inks. Of these, a content of from 1.0% to 10.0% by mass is even more preferable.

[0051] When a pigment is used as a colorant, the pigment dispersion method is not particularly limited. For example, resin-dispersed pigments dispersed with a resin dispersant, pigments dispersed with a surfactant, and microencapsulated pigments in which at least a portion of the pigment particle surface is coated with a resin or the like can be used. Self-dispersed pigments in which functional groups containing hydrophilic groups such as anionic groups are bonded to the pigment particle surface, and pigments in which organic groups containing polymers are chemically bonded to the pigment particle surface (resin-bonded self-dispersed pigments) can also be used. Pigments with different dispersion methods may also be used in combination.

[0052] Examples of pigments include inorganic pigments such as carbon black, and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, etc. These pigments can be used alone or in combination of two or more.

[0053] Examples of dyes include direct dyes, acid dyes, basic dyes, disperse dyes, and food dyes. Among these, dyes with anionic groups are preferred. Specific examples of dye skeletons include azo, triphenylmethane, phthalocyanine, azaphthalocyanine, xanthene, and anthrapyridone. It is also preferred to use dyes with CI numbers. Examples include CI Food Black 2; CI Direct Black 195; CI Direct Yellow: 86, 132, 173; CI Acid Yellow: 17, 23; CI Acid Red: 52, 249, 289; CI Acid Blue 9; and CI Direct Blue: 86, 199.

[0054] It is preferable to use a dye as the coloring material. Compared with a pigment contained in a dispersed state in an aqueous medium, a dye that dissolves in the aqueous medium at the molecular level is more easily solvated, and therefore, can further improve the fixation recovery property.

[0055] It is preferable that the maximum number of ionic groups per molecule of the colorant (dye) in the first ink, N1, and the maximum number of ionic groups per molecule of the colorant (dye) in the second ink, N2, satisfy the relationship N1 ≥ N2. Colorants with a large number of ionic groups per molecule are more likely to interact with the highly polar first water-soluble organic solvent, and are therefore more likely to solvate even when concentrated near the inner wall of the tube. Therefore, by having more ionic groups in the colorant in the first ink flowing through the long tube (first tube), which is more likely to be concentrated, the fixation recovery can be further improved. The maximum number of ionic groups per molecule of the colorant (dye) in each ink is preferably 1 or more and 10 or less, and more preferably 2 or more and 8 or less.

[0056] [Aqueous medium] The ink is an aqueous ink containing an aqueous medium, which is a mixed liquid of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The content (mass %) of the water-soluble organic solvent in the ink is preferably 3.0% to 50.0% by mass, based on the total mass of the ink. This water-soluble organic solvent content includes the first water-soluble organic solvent and a second water-soluble organic solvent that may be used as needed. If the content of the water-soluble organic solvent is too low, reliability such as ejection stability may be slightly reduced. On the other hand, if the content of the water-soluble organic solvent is too high, the viscosity of the ink increases, which may slightly reduce ink supply. Furthermore, the content (mass %) of water in the ink is preferably 40.0% to 95.0% by mass, based on the total mass of the ink.

[0057] As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, sulfur-containing compounds, and sulfur-containing compounds, can be used. Specific examples of the water-soluble organic solvent include monohydric alcohols having 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol (18.3), n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; 1,2-propanediol (28.8), 1,3-butanediol, 1,5-pentanediol (27.0), 1,2-hexanediol (14.8), and 1,6-hexanediol (7.1). ), 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol (23.9), and other dihydric alcohols; 1,2,6-hexanetriol (28.5), glycerin (42.3), trimethylolpropane (33.7), trimethylolethane, and other polyhydric alcohols; ethylene glycol (40.4), diethylene glycol (31.7), triethylene glycol (22.7), tetraethylene glycol, propylene glycol (1 Examples of suitable water-soluble organic solvents include alkylene glycols such as butylene glycol, hexylene glycol, and thiodiglycol; glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether (9.8), tetraethylene glycol monobutyl ether, and pentaethylene glycol monobutyl ether; polyalkylene glycols having a number average molecular weight of 200 to 1,000, such as polyethylene glycol (4.6) and polypropylene glycol, each having a number average molecular weight of 1,000; nitrogen-containing compounds such as 2-pyrrolidone (28.0), N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylmorpholine, urea (110.3), and ethyleneurea (49.7); and sulfur-containing compounds such as dimethyl sulfoxide and bis(2-hydroxyethyl sulfone). The parenthesized value for each water-soluble organic solvent indicates the relative dielectric constant of the water-soluble organic solvent at 25°C.It is preferable to use a water-soluble organic solvent having a relative dielectric constant of 3.0 or more and 120.0 or less, and it is also preferable to use a water-soluble organic solvent having a vapor pressure lower than that of water.

[0058] The relative permittivity of a water-soluble organic solvent can be measured using a dielectric constant meter (for example, trade name "BI-870" manufactured by BROOKHAVEN INSTRUMENTS CORPORATION) at a frequency of 10 kHz. The relative permittivity of a water-soluble organic solvent that is solid at 25°C is determined by measuring the relative permittivity of a 50% by mass aqueous solution and calculating the value from the following formula (3). Usually, the term "water-soluble organic solvent" refers to a liquid, but in the present invention, water-soluble organic solvents also include those that are solid at 25°C (room temperature). ε sol =2ε 50% -ε water ···(3) ε sol : Dielectric constant of solid water-soluble organic solvent at 25℃ ε 50% : Relative dielectric constant of a 50% by mass aqueous solution of a solid water-soluble organic solvent at 25°C ε water : relative dielectric constant of water

[0059] Examples of water-soluble organic solvents commonly used in aqueous inks that are solid at 25°C include 1,6-hexanediol, trimethylolpropane, ethylene urea, urea, and polyethylene glycol with a number-average molecular weight of 1,000. The reason for determining the dielectric constant of a water-soluble organic solvent that is solid at 25°C from the dielectric constant of a 50% by mass aqueous solution is as follows: Among water-soluble organic solvents that are solid at 25°C and can be used as components of aqueous inks, it is difficult to prepare aqueous solutions with high concentrations exceeding 50% by mass. On the other hand, in aqueous solutions with low concentrations of 10% by mass or less, the dielectric constant of water dominates, making it impossible to obtain a reliable (effective) dielectric constant value for the water-soluble organic solvent. Therefore, the inventors conducted research and found that aqueous solutions to be measured can be prepared using almost all water-soluble organic solvents that are solid at 25°C and can be used in inks, and that the dielectric constants obtained are consistent with the effects of the present invention. For these reasons, we decided to use a 50% by mass aqueous solution. For water-soluble organic solvents that are solid at 25°C and cannot be prepared as a 50% by mass aqueous solution due to their low solubility in water, use an aqueous solution of saturated concentration and use the above ε sol For convenience, the value of the relative permittivity calculated in accordance with the case of determining the relative permittivity will be used.

[0060] [First water-soluble organic solvent] The first ink contains a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more. If the relative dielectric constant of the water-soluble organic solvent contained in the first ink is less than 40.0, the polarity is low and the effect of solvating the colorant is weak, making it impossible to eliminate the localized high viscosity of the ink near the inner wall of the tube, which is a factor in reducing adhesion recovery.

[0061] Furthermore, it is preferable that the second ink also contains a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more. The content X1 (mass %) of the first water-soluble organic solvent in the first ink and the content X2 (mass %) of the first water-soluble organic solvent in the second ink preferably satisfy the relationship X1>X2. By satisfying the relationship X1>X2, the ease of suction of the first ink from the nozzle connected to the first tube and the ease of suction of the second ink from the nozzle connected to the second tube tend to be consistent, thereby further improving adhesion recovery.

[0062] Examples of the first water-soluble organic solvent include ethylene urea (49.7), bis(2-hydroxyethyl sulfone) (44.1), glycerin (42.3), and ethylene glycol (40.4). The parenthesized value following each water-soluble organic solvent indicates the relative dielectric constant of the water-soluble organic solvent at 25°C. The relative dielectric constant of the first water-soluble organic solvent is preferably 120.0 or less, and it is also preferable that the first water-soluble organic solvent has a vapor pressure lower than that of water. The first water-soluble organic solvent contained in the first ink and the first water-soluble organic solvent that can be contained in the second ink may be the same or different.

[0063] The content (% by mass) of the first water-soluble organic solvent in each ink is preferably 1.0% to 50.0% by mass, and more preferably 3.0% to 30.0% by mass, based on the total mass of the ink. The content X1 (% by mass) of the first water-soluble organic solvent in the first ink is preferably 1.0% to 20.0% by mass, based on the total mass of the ink. Furthermore, the content X2 (% by mass) of the first water-soluble organic solvent in the second ink is preferably 0.5% to 15.0% by mass, based on the total mass of the ink.

[0064] [Second water-soluble organic solvent] The second ink preferably contains a second water-soluble organic solvent having a relative dielectric constant of 25.0 or less. The second water-soluble organic solvent is more hydrophobic than water-soluble organic solvents having a relative dielectric constant of more than 25.0, and is less likely to solvate with the colorant. Therefore, by including the second water-soluble organic solvent in the second ink flowing through the second tube, where the amount of water evaporation is small and the colorant is less likely to concentrate, the following effects can be achieved: That is, the ease of suction of the first ink from the nozzle connected to the first tube and the ease of suction of the second ink from the nozzle connected to the second tube are more likely to be consistent, thereby further improving adhesion recovery.

[0065] Examples of the second water-soluble organic solvent include 3-methyl-1,5-pentanediol (23.9), triethylene glycol (22.7), isopropyl alcohol (18.3), propylene glycol (16.9), 1,2-hexanediol (14.8), triethylene glycol monobutyl ether (9.8), tetraethylene glycol monobutyl ether (9.4), 1,6-hexanediol (7.1), and polyethylene glycol (4.6) having a number-average molecular weight of 1,000. The parenthesized value for each water-soluble organic solvent indicates the relative dielectric constant of the water-soluble organic solvent at 25°C. The second water-soluble organic solvent preferably has a relative dielectric constant of 3.0 or higher and a vapor pressure lower than that of water. The content (mass %) of the second water-soluble organic solvent in the ink is preferably 1.0% to 50.0% by mass, and more preferably 3.0% to 30.0% by mass, based on the total mass of the ink. The content Y1 (mass %) of the second water-soluble organic solvent in the first ink is preferably 0.5% to 15.0% by mass, based on the total mass of the ink, and the content Y2 (mass %) of the second water-soluble organic solvent in the second ink is preferably 1.0% to 20.0% by mass, based on the total mass of the ink.

[0066] The first ink and the second ink preferably contain a first water-soluble organic solvent and a second water-soluble organic solvent, respectively. The content of the first water-soluble organic solvent in the first ink is defined as "X1" (mass %), and the content of the second water-soluble organic solvent in the first ink is defined as "Y1" (mass %). The content of the first water-soluble organic solvent in the second ink is defined as "X2" (mass %), and the content of the second water-soluble organic solvent in the second ink is defined as "Y2" (mass %). In this case, it is preferable to satisfy the relationship (X1 / Y1) ≥ (X2 / Y2). Both (X1 / Y1) and (X2 / Y2) are the ratios of the content of the water-soluble organic solvent with high affinity for the colorant to the content of the water-soluble organic solvent with low affinity for the colorant. The larger this ratio, the stronger the ink's ability to solvate the colorant. In other words, satisfying this relationship allows the first ink, whose liquid components evaporate easily and whose colorant is easily concentrated, to have a stronger ability to solvate the colorant than the second ink, thereby further improving fixation recovery. The first and second water-soluble organic solvents contained in the first ink and the first and second water-soluble organic solvents contained in the second ink may be the same or different.

[0067] The content of the first water-soluble organic solvent in the first ink is defined as "X1" (mass %), and the content of the colorant in the first ink is defined as "C1" (mass %). The content of the first water-soluble organic solvent in the second ink is defined as "X2" (mass %), and the content of the colorant in the second ink is defined as "C2" (mass %). Furthermore, the length of the first tube is defined as "L1" (mm), and the length of the second tube is defined as "L2" (mm). In this case, it is preferable to satisfy the relationship (X1 / C1) / (X2 / C2)≧(L1 / L2). The larger the ratio (L1 / L2) of the length L1 (mm) of the first tube to the length L2 (mm) of the second tube, the more easily the first ink in the relatively long first tube is concentrated, and the stronger the association and aggregation of the colorant in the first ink. Therefore, it is preferable to include a larger amount of the first water-soluble organic solvent in the first ink to loosen the strong association and aggregation of the colorant. The ratios of the first water-soluble organic solvent in the ink to the colorant content (X1 / C1 and X2 / C2) are indicators of the amount of the first water-soluble organic solvent that solvates the colorant present in the ink. If "X1," "C1," "X2," "C2," "L1," and "L2" do not satisfy the above relationship, the content of the first water-soluble organic solvent in the first ink will be somewhat low, and the effect of improving adhesion recovery may not be sufficiently achieved.

[0068] [Other ingredients] The ink may contain various additives as needed, such as surfactants, antifoaming agents, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, etc. These additives are not included in the "water-soluble organic solvent" that is the subject of calculating the relative dielectric constant.

[0069] [Ink properties] The ratio (η2 / η1) of the viscosity η2 (mPa·s) of the second ink to the viscosity η1 (mPa·s) of the first ink is 0.7 to 1.5 times. The viscosity of each ink at 25°C is preferably 1.0 to 5.0 mPa·s, and more preferably 1.0 to 3.5 mPa·s. The viscosity of the ink can be measured using a rotational viscometer. The static surface tension of the ink at 25°C is preferably 28 to 45 mN / m. The pH of the ink at 25°C is preferably 5 to 9. [Example]

[0070] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0071] <Preparing color materials> (Compound 1) According to the description of JP 2015-193792 A, a sodium salt of a compound represented by the following formula (1) in free acid form (Compound 1) was obtained.

[0072] TIFF0007746120000001.tif43170

[0073] (Compound 2) According to the description of JP-A-2006-143989, a sodium salt of a compound represented by the following formula (2) in free acid form (Compound 2) was obtained.

[0074] TIFF0007746120000002.tif72170

[0075] (Compound 3) According to the description of JP 2012-149212 A, a potassium salt of a compound represented by the following formula (3) in free acid form (Compound 3) was obtained.

[0076] TIFF0007746120000003.tif49170

[0077] <Preparing pigment dispersion> A pigment dispersion containing a self-dispersing pigment (product name "Cab-o-jet300", manufactured by Cabot) was prepared. The pigment content in the pigment dispersion was 15.0%.

[0078] <Ink Preparation> The components (unit: %) shown in the upper part of Tables 1-1 to 1-3, 2-1, and 2-2 were mixed, thoroughly stirred, and then pressure-filtered through a 0.20 μm pore-size filter to prepare each ink. When a pigment was used as the colorant, the ink was also pressure-filtered through a 3.0 μm pore-size microfilter. In Tables 1-1 to 1-3, 2-1, and 2-2, the parenthesized numbers next to the dyes indicate the maximum number of ionic groups for each dye, and the parenthesized numbers next to the water-soluble organic solvents indicate the relative dielectric constant of each water-soluble organic solvent. In Tables 1-1 to 1-3, 2-1, and 2-2, "Acetylenol E100" is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The ink viscosity was measured at 25°C using a rotary viscometer (trade name "E-type viscometer," manufactured by Toki Sangyo Co., Ltd.).

[0079] TIFF0007746120000004.tif227170

[0080] TIFF0007746120000005.tif245170

[0081] TIFF0007746120000006.tif245170

[0082] TIFF0007746120000007.tif255154

[0083] TIFF0007746120000008.tif255157

[0084] <Tube production> Tubes 1 to 13 were produced from resin compositions with an inner diameter of 2 mm and an outer diameter of 4 mm using a styrene-based thermoplastic elastomer, a lubricant, and a softener. The water vapor transmission rates (W) of the produced tubes are shown in Table 3. The water vapor transmission rate (W) of the tube is the value per tube length L = 200 mm, and is expressed in mg / day.

[0085] TIFF0007746120000009.tif112170

[0086] <Evaluation> An inkjet recording apparatus was prepared that had the main components configured as shown in Figure 1 and incorporated an ink supply system configured as shown in Figure 2. This recording apparatus was equipped with the first and second inks, and the first and second tubes, of the types shown in Table 4. Each evaluation was carried out using this recording apparatus.

[0087] (Adhesion recovery) Each ink was filled from the main tank through the ink supply tube to the subtank and the nozzles of the recording head, and then the device was placed in an environment with a temperature of 35°C and a relative humidity of 10% for three months. The ink ejection state was then confirmed after a predetermined number of recovery operations, and adhesion recovery was evaluated according to the following evaluation criteria. This recovery operation refers to "printhead cleaning" of the inkjet recording device. Specifically, a suction cap was placed on the area including the nozzle face of the recording head, and the first ink and the second ink were sucked together from the nozzle arrays for the first ink and the nozzle arrays for the second ink through the suction cap. According to the evaluation criteria below, "AA," "A," "A'," and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Table 4. Reference Examples 1 to 5 did not satisfy the aforementioned conditions (1) to (3) and did not exhibit issues such as reduced adhesion recovery, so all were rated "AA." AA: All outlets recovered to a state where they could eject normally after one recovery operation. A: All outlets recovered to a state where they could discharge normally after two or three recovery operations. A': All outlets were restored to a state where they could eject normally after 4 or 5 recovery operations. B: All outlets recovered to a state where they could discharge normally after 6 to 10 recovery operations. C: There was a discharge port that could not discharge normally even after performing the recovery operation 11 or more times.

[0088] (Image unevenness) Each ink was filled from the main tank through the ink supply tube to the sub-tank and the printhead nozzles. After performing a recovery procedure (similar to the procedure used in the evaluation of "sticking recovery"), the printhead was capped and placed in an environment at 30°C and 10% relative humidity for 120 hours. A solid image with a secondary color was then printed on A4-size plain paper (product name "High-Quality Specialty Paper HR-101S" manufactured by Canon) at a print duty of 50%. The print duties for the first and second inks were each 25%. In this example, the print duty of a solid image printed under conditions in which two ink droplets, each with a mass of 5 ng, were applied to a unit area of ​​1 / 600 inch x 1 / 600 inch, was defined as 100%. Image unevenness was evaluated according to the following evaluation criteria. "A" was an acceptable level, and "C" was an unacceptable level. The evaluation results are shown in Table 4. A: When visually comparing the images at the start and end of the writing position, there was no difference between the two. C: When visually comparing the images at the writing start and end positions, unevenness was observed.

[0089] TIFF0007746120000010.tif184170

Claims

1. a plurality of water-based inks containing colorants; a first ink storage section for storing each of the plurality of water-based inks; a second ink storage section; a plurality of tubes for supplying the water-based ink from the first ink containing section to the second ink containing section; a recording head connected to the second ink storage section, the recording head having a plurality of nozzles through which the plurality of water-based inks supplied from the second ink storage section flow, a plurality of ejection ports communicating with the plurality of nozzles and ejecting the plurality of water-based inks, and an ejection port surface on which a plurality of ejection port arrays are arranged, the ejection ports being configured by the plurality of ejection ports and corresponding to the plurality of water-based inks; a recovery mechanism including a suction cap that contacts an area of ​​the recording head including the ejection port surface and covers the plurality of ejection port arrays collectively, and a suction unit that collectively sucks the water-based ink from the plurality of nozzles through the suction cap, the plurality of water-based inks include a first ink and a second ink, and the plurality of tubes include a first tube that supplies the first ink to the second ink containing section and a second tube that supplies the second ink to the second ink containing section; The length L of the first tube １ (mm) is the length L of the second tube ２ (mm) to the ratio (L １ / L ２ ) is 1.15 times or more, and the water vapor permeation amount W (mg / day) of the first tube and the second tube at 40°C is 2 mg / day or more, an inkjet recording method comprising a step of applying the water-based ink ejected from the ejection orifices to a recording medium to record an image, The viscosity η of the second ink ２ (mPa·s) is the viscosity η of the first ink １ Ratio (η ２ / η １ ) is 0.7 times or more and 1.5 times or less, An ink jet recording method, wherein the first ink contains a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more.

2. the second ink contains a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more; the content X of the first water-soluble organic solvent in the first ink １ (mass %), and the content X of the first water-soluble organic solvent in the second ink ２ (mass%) and X １ >X ２ The ink jet recording method according to claim 1, wherein the following relationship is satisfied:

3. the content X of the first water-soluble organic solvent in the first ink １ (mass %), the content C of the coloring material in the first ink １ (mass %), the content X of the first water-soluble organic solvent in the second ink ２ (mass %), the content C of the coloring material in the second ink ２ (mass %), the length L of the first tube １ (mm), and the length L of the second tube ２ (mm) is (X １ / C １ ) / (X ２ / C ２ ) ≧ (L １ / L ２ 3. The ink jet recording method according to claim 2, wherein the relationship:

4. 4. The ink jet recording method according to claim 1, wherein the first water-soluble organic solvent has a relative dielectric constant of 120.0 or less.

5. 5. The inkjet recording method according to claim 1, wherein the content (mass %) of the first water-soluble organic solvent in the first ink is 1.0 mass % or more and 20.0 mass % or less, based on the total mass of the first ink.

6. 6. The inkjet recording method according to claim 1, wherein the second ink contains a second water-soluble organic solvent having a relative dielectric constant of 25.0 or less.

7. 7. The ink jet recording method according to claim 6, wherein the second water-soluble organic solvent has a relative dielectric constant of 3.0 or more.

8. the first ink and the second ink contain the first water-soluble organic solvent and the second water-soluble organic solvent, respectively; the content X of the first water-soluble organic solvent in the first ink １ (mass %), the content Y of the second water-soluble organic solvent in the first ink １ (mass %), the content X of the first water-soluble organic solvent in the second ink ２ (mass %), and the content Y of the second water-soluble organic solvent in the second ink ２ (mass%) is (X １ / Y １ ) ≧ (X ２ / Y ２ 8. The ink jet recording method according to claim 6, wherein the relationship:

9. 9. The inkjet recording method according to claim 8, wherein the content (mass %) of the second water-soluble organic solvent in the first ink is 0.5 mass % or more and 15.0 mass % or less based on the total mass of the first ink.

10. 10. The inkjet recording method according to claim 8, wherein the content (mass %) of the first water-soluble organic solvent in the second ink is 0.5 mass % or more and 15.0 mass % or less, based on the total mass of the second ink.

11. 11. The inkjet recording method according to claim 8, wherein the content (mass %) of the second water-soluble organic solvent in the second ink is 1.0 mass % or more and 20.0 mass % or less, based on the total mass of the second ink.

12. 12. The ink jet recording method according to claim 1, wherein the coloring material is a dye.

13. the maximum number N of ionic groups per molecule of the colorant in the first ink; １ and the maximum number N of ionic groups per molecule of the colorant in the second ink. ２ But, N １ ≧N ２ The ink jet recording method according to claim 12, wherein the following relationship is satisfied:

14. The length L of the first tube １ (mm) is the length L of the second tube ２ (mm) to the ratio (L １ / L ２ 14. The ink jet recording method according to claim 1, wherein the ratio of the ink jet density to the ink jetting amount is 1.90 or less.

15. 15. The inkjet recording method according to claim 1, wherein the water vapor permeation amount W (mg / day) of the first tube and the second tube at 40[deg.] C. is 10 mg / day or less.

16. The length L of the first tube １ (mm) and the length L of the second tube ２ 16. The ink jet recording method according to claim 1, wherein each of (mm) is 200 mm or more and 1,200 mm or less.

17. The length L of the first tube １ 17. The ink jet recording method according to claim 1, wherein (mm) is 400 mm or more and 1,000 mm or less.

18. The length L of the second tube ２ 18. The ink jet recording method according to claim 1, wherein (mm) is 300 mm or more and 800 mm or less.

19. 19. The inkjet recording method according to claim 1, wherein the viscosity of the first ink and the viscosity of the second ink at 25[deg.] C. are each 1.0 mPa.s or more and 5.0 mPa.s or less.

20. a content (mass %) of the coloring material in the first ink is 0.1 mass % or more and 15.0 mass % or less based on the total mass of the first ink; 20. The inkjet recording method according to claim 1, wherein the content (mass %) of the colorant in the second ink is 0.1 mass % or more and 15.0 mass % or less, based on the total mass of the second ink.

21. a plurality of water-based inks containing colorants; a first ink storage section for storing each of the plurality of water-based inks; a second ink storage section; a plurality of tubes for supplying the water-based ink from the first ink containing section to the second ink containing section; a recording head connected to the second ink storage section, the recording head having a plurality of nozzles through which the plurality of water-based inks supplied from the second ink storage section flow, a plurality of ejection ports communicating with the plurality of nozzles and ejecting the plurality of water-based inks, and an ejection port surface on which a plurality of ejection port arrays are arranged, the ejection ports being configured by the plurality of ejection ports and corresponding to the plurality of water-based inks; a suction cap that contacts an area of ​​the recording head that includes the ejection port surface and covers the plurality of ejection port arrays collectively; and a recovery mechanism having suction means for collectively sucking the water-based ink from the plurality of nozzles through the suction cap, the plurality of water-based inks include a first ink and a second ink, and the plurality of tubes include a first tube that supplies the first ink to the second ink containing section and a second tube that supplies the second ink to the second ink containing section; The length L of the first tube １ (mm) is the length L of the second tube ２ (mm) to the ratio (L １ / L ２ ) is 1.15 times or more, and the water vapor permeation amount W (mg / day) of the first tube and the second tube at 40°C is 2 mg / day or more, The viscosity η of the second ink ２ (mPa·s) is the viscosity η of the first ink １ Ratio (η ２ / η １ ) is 0.7 times or more and 1.5 times or less, An ink jet recording apparatus, wherein the first ink contains a first water-soluble organic solvent having a relative dielectric constant of 40.0 or more.

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