JP2024076998A - Inkjet recording method, inkjet recording apparatus, and set of aqueous ink and aqueous reaction liquid - Google Patents

Abstract

[Problem] To provide an inkjet recording method and the like that can record images with excellent color development while suppressing image bleeding and suppressing dissolution of the recording head. [Solution] An inkjet recording method in which an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink is ejected from a recording head to record an image on a recording medium. The aqueous reaction liquid contains at least one selected from the group consisting of a specific polyvalent metal salt and a specific acid-type organic acid. A liquid flow path having an ejection port for ejecting the aqueous reaction liquid and a liquid supply port communicating with the liquid flow path are formed inside the recording head, and at least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is coated with a protective film containing a specific metal oxide. [Selected Figure] None

Description

The present invention relates to an inkjet recording method, an inkjet recording device, and a set of an aqueous ink and an aqueous reaction liquid.

In recent years, inkjet recording methods have been increasingly used in the field of sign and display, such as printing posters and large-format advertisements. In this field, inkjet recording devices are characterized by a larger recording area than domestic inkjet recording devices. In addition, because images need to be eye-catching, inks that can record images with high color development are required. Furthermore, there is a demand for long-lasting recording heads that can withstand repeated ink ejection. In order to prevent the dissolution of the ink flow path components in the recording head, a technology is known in which a protective film is provided on the surface of the flow path components by atomic layer deposition (ALD) (see Patent Document 1).

In the sign and display field, productivity is also important, and there is a demand for increasing the recording speed. In this case, when recording an image in which a large amount of ink is applied, the interval between ink droplets is shortened, and thickening due to drying of the ink is less likely to occur. As a result, the ink may spread laterally across the surface of the recording medium before it is fixed on the recording medium. Hereinafter, this phenomenon will be referred to as image bleeding. In response to this phenomenon, a method has been proposed in which a treatment liquid that aggregates the ink components is used to rapidly thicken the ink that has landed on the recording medium, thereby suppressing image bleeding (see Patent Document 2). In addition, a method has been proposed in which an anion component in the ink is adsorbed into the ALD pinholes in a head that has a protective film on the ink flow path by ALD, thereby suppressing dissolution of the flow path member by the ink (see Patent Document 3).

JP 2017-213860 A JP 2019-157064 A JP 2017-217907 A

As a result of the inventors' investigations, when the inks described in Patent Documents 2 and 3 were applied to the recording head described in Patent Document 1 to record an image, it was found that there was room for improvement in the color development of the resulting image.

Therefore, an object of the present invention is to provide an inkjet recording method that can record images with excellent color development while suppressing image bleeding and preventing dissolution of the recording head. Another object of the present invention is to provide an inkjet recording device for use in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid.

That is, according to the present invention, there is provided an inkjet recording method for ejecting an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink from a recording head to record an image on a recording medium, the method comprising: a reaction liquid application step of applying the aqueous reaction liquid to the recording medium; and an ink application step of applying the aqueous ink so as to overlap at least a portion of the area of the recording medium to which the aqueous reaction liquid is applied, the aqueous reaction liquid being selected from the group consisting of (i) a polyvalent metal salt having a solubility in water (g/100 mL) of 3.0 g/100 mL or more and 108.0 g/100 mL or less at 20° C., and (ii) a polyvalent metal salt having a solubility in water (g/100 mL) of 3.0 g/100 mL or more and 108.0 g/100 mL or less at 20° C. and an acid-type organic acid having a pKa of 3.2 or more and 4.6 or less in an aqueous solution, a liquid flow path having an ejection port for ejecting the aqueous reaction liquid and a liquid supply port communicating with the liquid flow path are formed inside the recording head, and at least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is coated with a protective film containing a metal oxide, and the metal oxide is at least one selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and tantalum oxide.

According to the present invention, it is possible to provide an inkjet recording method that can record images with excellent color development while suppressing image bleeding and suppressing dissolution of the recording head. In addition, according to the present invention, it is possible to provide an inkjet recording device for use in this inkjet recording method, and a set of an aqueous ink and an aqueous reaction liquid.

1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. 1 is a side view diagrammatically illustrating an embodiment of an inkjet recording apparatus of the present invention. 4 is a schematic diagram showing an example of a supply mechanism that supplies a reaction liquid to a recording head. FIG. FIG. 2 is a perspective view showing a cross section of an ejection element substrate of a reaction liquid recording head. FIG. 2 is a cross-sectional view showing an example of a reaction liquid recording head. FIG. 2 is a partial perspective view showing an example of the configuration of a reaction liquid recording head. 1A and 1B are diagrams showing an example of the configuration of a reaction liquid recording head, in which (a) is a front view and (b) is a cross-sectional view taken along the line AA of (a).

The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing a salt". In addition, the aqueous ink for inkjet and the reaction liquid may be simply referred to as "ink" and "reaction liquid". In addition, since the reaction liquid does not need to contain a coloring material and is colorless and transparent, "recording" on the recording medium is not performed only by the reaction liquid, but for convenience, the head for ejecting the reaction liquid is referred to as "recording head". Physical property values are values at room temperature (25°C) unless otherwise specified. When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively.

In the sign and display field, non-absorbent recording media are often used, the surface of which is made of polyvinyl chloride (PVC) or polyethylene terephthalate (PET), which has almost no ink absorption. Since ink does not easily penetrate non-absorbent recording media, image bleeding is likely to occur. Therefore, it is important to prevent ink dots from being repelled on non-absorbent recording media to suppress bleeding. In order to suppress image bleeding while achieving high productivity, it is useful to use a reaction liquid containing a reactant that aggregates the components in the ink, as in Patent Document 2. In order to suppress image bleeding in a recording method using a reaction liquid, it is necessary that the components of the ink (pigment, resin, etc.) quickly aggregate and are fixed on the recording medium when the reaction liquid and the ink come into contact with each other on the recording medium. Here, the pigment and resin of the ink are dispersed or dissolved mainly due to the charge repulsion of the anionic groups. The charge repulsion due to this anionic group is eliminated by the reactant in the reaction liquid, causing the pigment and resin to aggregate. In order to suppress image bleeding, a sufficient amount of reactant is required to eliminate the charge repulsion of the anionic groups of the ink. In other words, to fix the amount of anionic groups in the ink, it is necessary to increase the amount of reactant in the reaction liquid or to increase the amount of reaction liquid applied.

On the other hand, from the viewpoint of color development of an image, when the ink and the reaction liquid contact each other on a recording medium, increasing the amount of reactant in the reaction liquid described above or increasing the amount of the reaction liquid applied increases the cohesion. Therefore, the ink dots rapidly cohere, and the ink is fixed in a bulky state without spreading wet on the recording medium. It is considered that an image formed with bulky ink dots has an uneven surface, and light scattering occurs on the image surface, resulting in a decrease in color development. In order to suppress the decrease in color development of an image, for example, a method of suppressing the bulkiness of the ink dots by reducing the amount of reaction liquid applied and reducing the cohesion with the ink components is conceivable. However, if the cohesion is weakened, it is not possible to suppress the bleeding of the image as described above. In other words, the trade-off relationship between the suppression of bleeding of an image and the color development cannot be overcome by simply adjusting the amount of ink and reaction liquid applied.

In light of the above, the inventors conducted research and found that by using a specific polyvalent metal salt or an acid-type organic acid as a reactant with a certain degree of suppressed dissociation, it is possible to achieve a high level of both suppression of image bleeding and color development. However, while it is possible to achieve both suppression of image bleeding and color development, it was found that another problem arises when recording is performed for a long period of time while the above reaction liquid is ejected from the recording head. Specifically, it was found that the members in the recording head that come into contact with the reaction liquid are eroded by the influence of the reaction agent. As the erosion progresses, the members that make up the recording head are more likely to dissolve, making the electrothermal conversion elements and the like more likely to be damaged.

The inventors analyzed the phenomenon of dissolution of the recording head that occurs when a reaction liquid containing a specific reactant is ejected for a long period of time, and found that the protective layer provided on the surface of the member that constitutes the recording head is dissolved. In light of this phenomenon, they considered adjusting the characteristics of the reactant in order to solve the above problem. As a result, they discovered that by using a polyvalent metal salt with a solubility in water within a specified range or an organic acid with a pKa within a specified range as a reactant, dissolution of the recording head is suppressed while suppressing bleeding of the image and color development, and images can be recorded for a long period of time.

That is, the inkjet recording method of the present invention has the following characteristics. The reaction liquid contains at least one type selected from the group consisting of the following (i) and (ii) as a reactant. The reactant is at least one type selected from the group consisting of (i) polyvalent metal salts having a solubility in water at 20 ° C. of 3.0 g/100 mL or more and 108.0 g/100 mL or less, and (ii) acid-type organic acids having a pKa of 3.2 to 4.6 at 20 ° C. Inside the recording head, a liquid flow path having an ejection port for ejecting the reaction liquid and a liquid supply port communicating with the liquid flow path are formed. At least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is covered with a protective film containing a metal oxide. The metal oxide contained in the protective film is at least one type selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and acid value tantalum. Then, the reaction liquid and the ink are applied so as to overlap on the recording medium to record an image. The inventors speculate that the mechanism by which the above configuration prevents the recording head from dissolving while also suppressing bleeding and allowing images to be recorded with excellent color development is as follows.

The time from when the ink dots come into contact with the reaction liquid on the recording medium until the bulk of the ink dots is determined is thought to be on the order of several hundred milliseconds after the ink comes into contact with the reaction liquid. In polyvalent metal salts with a solubility in water of 108.0 g/100 mL or less at 20° C. and acid-type organic acids with a pKa of 3.2 or more at 20° C., the dissociation of cationic components in the reaction liquid is suppressed to a certain degree. Therefore, the dissociation of cationic components can be kept below a certain concentration during the above time scale. Therefore, the height of the ink dots can be suppressed compared to polyvalent metal salts and acid-type organic acids outside the above range, that is, when a large amount of cationic components are dissociated. On the other hand, from the perspective of suppressing image bleeding, it is only when the pigment of the ink dots moves on the order of several mm that bleeding is recognized to have occurred in the image. The time required for the pigment to move on the order of several mm is on the order of several seconds, during which time all the cationic components of the reaction liquid dissociate and the reaction with the anionic components of the ink proceeds sufficiently, resulting in an image with suppressed bleeding.

On the other hand, it has been found that when a reaction liquid containing the above-mentioned reactant is filled into a recording head and discharged for a long period of time, the protective film coated on the surface of the member inside the recording head may dissolve. The cause is considered to be as follows. As described above, the above-mentioned reactant is in a state in which the cationic components are difficult to dissociate sufficiently. In other words, in the reaction liquid, the above-mentioned reactant is in a state in which the dissociation proceeds only to a certain concentration, although the above-mentioned reactant dissociates into anionic components and cationic components. Therefore, it is considered that some of the anionic components neutralize with the cationic components and return to their original state. Here, when the cationic components are difficult to dissociate sufficiently, it is considered that the anionic components are also poorly dissociated, that is, the anionic components are in an unstable state in the reaction liquid. Here, most of the destabilized anionic components neutralize with the original cationic components and return to their original state, but some of the destabilized anionic components form a complex with the metal components that form the protective film. As a result, it is considered that this leads to the dissolution of the protective film. In the recording head of the present invention, examples of the metal components used as the protective film include titanium, zirconium, vanadium, and tantalum, and all of them form complexes with the above-mentioned polyvalent metal salts and organic acids. Therefore, by using a reactant that dissociates the cationic components to a certain extent, dissolution of the protective film can be suppressed.

From the above, by using at least one selected from the group consisting of (i) and (ii) below as the reactant, the dissociation of the anion component of the reactant can be suppressed within a preferred range. The reactant is at least one selected from the group consisting of (i) polyvalent metal salts having a solubility in water at 20°C of 3.0 g/100 mL or more and 108.0 g/100 mL or less, and (ii) acid-type organic acids having a pKa of 3.2 or more and 4.6 or less at 20°C. Therefore, it is possible to suppress dissolution of the recording head, while suppressing bleeding and recording images with excellent color development.

<Inkjet recording method, inkjet recording device, and set of aqueous ink and aqueous reaction liquid>
The inkjet recording method of the present invention is a method of ejecting an aqueous ink and an aqueous reaction liquid from an inkjet recording head and applying them to a recording medium to record an image. The inkjet recording method of the present invention includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium, and an aqueous ink applying step of applying an aqueous ink so as to overlap at least a part of the area to which the aqueous reaction liquid is applied. The aqueous reaction liquid contains at least one selected from the group consisting of (i) a polyvalent metal salt having a solubility in water (g/100 mL) at 20° C. of 3.0 g/100 mL to 108.0 g/100 mL, and (ii) an acid-type organic acid having a pKa at 20° C. of 3.2 to 4.6. Inside the recording head, a liquid flow path having an ejection port for ejecting the aqueous reaction liquid and a liquid supply port communicating with the liquid flow path are formed. At least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is covered with a protective film containing a metal oxide (at least one selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and tantalum oxide).

The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid are ejected from an inkjet recording head and applied to a recording medium to record an image. The inkjet recording apparatus is an apparatus suitable for use in the above-mentioned recording method. In the inkjet recording method and inkjet recording apparatus of the present invention, it is not necessary to cure the image by irradiation with active energy rays or the like.

The set of aqueous ink and aqueous reaction liquid of the present invention is a set used in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink are ejected from a recording head to record an image on a recording medium. The set is suitable for use in the above recording method. The form of the set includes a set of multiple ink cartridges each containing multiple inks (reaction liquids) independently, and an ink cartridge formed integrally by combining multiple ink storage sections each containing multiple inks (reaction liquids). The set of the present invention is not limited to the above form and may be in any form as long as it is configured so that the inks and reaction liquids can be used in combination.

The inkjet recording method and inkjet recording device of the present invention (hereinafter, simply referred to as the "recording method and recording device") will be described in detail below.

FIG. 1 is a perspective view showing an embodiment of the inkjet recording device of the present invention. FIG. 2 is a side view showing an embodiment of the inkjet recording device of the present invention. As shown in FIGS. 1 and 2, the recording device of this embodiment includes an inkjet recording head 22 that ejects ink. The recording head 22 is a recording head that ejects ink by the action of thermal energy. A recording head that ejects ink by the action of thermal energy applies thermal energy to the ink by applying an electric pulse to an electrothermal conversion element, thereby ejecting the ink from the ejection port. Here, a recording head that ejects ink by the action of thermal energy is given as an example, but a recording head that ejects ink by the action of mechanical energy may also be used. Also, the recording head 22 that ejects ink can be configured similarly to a recording head that ejects a reaction liquid.

When the temperature of the ink or reaction liquid changes due to the surrounding environment, the viscosity may change, causing the amount of ink ejected to fluctuate. As a result, bleeding of the image may not be sufficiently suppressed. For this reason, it is preferable that a thermal type recording head is equipped with a heating mechanism that heats the reaction liquid inside the recording head. In other words, it is preferable that the recording head has a temperature control mechanism. On the other hand, when a temperature control mechanism is provided, when the recording head is filled with a reaction liquid that can dissolve the protective film of the recording head, dissolution of the protective film is promoted. However, by adopting the configuration of the present invention, dissolution of the protective film can be sufficiently suppressed.

Examples of heating methods include a heater for temperature adjustment arranged in contact with the recording head, and a heater for liquid ejection. To heat or warm the recording head using a heater for liquid ejection, for example, a current that does not eject liquid may be repeatedly passed through the recording head. The temperature of the recording head and the liquid inside the recording head can be read, for example, by a temperature sensor provided on the recording head. The temperature of the recording head, ink, and reaction liquid is preferably adjusted to 40°C or higher and 70°C or lower.

[Heating process]
The recording method of the present invention may include a step of heating (heat treatment) the recording medium to which the ink (and reaction liquid) has been applied. Heating the recording medium to which the ink has been applied can promote drying and increase the strength of the image.

Examples of the means for heating the recording medium include known heating means such as a heater, air blowing means using air blowing such as a dryer, and combinations of these. Examples of the heating means include the above heating means, air blowing means, and combinations of these. Examples of the heat treatment method include a method of applying heat from the opposite side (back side) to the recording surface (ink application surface) of the recording medium using a heater, a method of applying warm or hot air to the recording surface of the recording medium, and a method of heating from the recording surface or back side using an infrared heater. A combination of these methods may also be used.

The heating temperature of the recording medium to which the ink has been applied is preferably 50°C or higher and 90°C or lower, in order to increase the abrasion resistance of the image. The heating temperature of the recording medium to which the ink has been applied may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined according to the type of ink and recording medium.

In the recording device shown in Figures 1 and 2, a heater 25 supported by a frame (not shown) is disposed downstream in the sub-scanning direction A from the position where the recording head 22 reciprocates in the main scanning direction B. The recording medium 1 to which ink has been applied is heated by the heater 25. Examples of the heater 25 include a sheath heater and a halogen heater. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 to the recording medium 1. Furthermore, the heater cover 26 is also a member for protecting the heater 25. The recording medium 1 to which ink has been applied ejected from the recording head 22 is wound by a winding spool 27 to form a roll-shaped wound medium 24.

The inkjet recording method preferably includes a mechanism for circulating the reaction liquid within the recording head. When water from the reaction liquid evaporates near the nozzles of the recording head, the viscosity of the liquid increases, causing a decrease in ejection properties, and it may not be possible to sufficiently suppress bleeding of the image. Therefore, by circulating the liquid within the recording head, the increase in viscosity near the nozzles can be suppressed, stable ejection can be always achieved, and bleeding of the image can be effectively suppressed.

Figure 3 is a schematic diagram showing an example of a mechanism for circulating the reaction liquid within the recording head. As shown in Figure 3, pump P2 supplies liquid from main tank T1 to sub tank T2. Next, pump P1 supplies liquid from sub tank T2 to head H1000. When circulation is required, valve V1 is opened and P1 is kept operating, so that the liquid that has passed through the flow path of recording head H1000 is returned to T2, and the liquid can be circulated through a path that sends it back to recording head H1000. The flow rate at which the reaction liquid is circulated (circulation flow rate) is preferably 1.0 mL/min or more and 10.0 mL/min or less, and more preferably 2.0 mL/min or more and 5.0 mL/min or less.

In particular, the recording head preferably includes an ejection port for ejecting the reaction liquid, an ejection element for generating energy for ejecting the reaction liquid, and a first flow path and a second flow path that communicate between the ejection port and the ejection element and through which the reaction liquid flows. In this case, a circulation process can be performed in which the reaction liquid in the first flow path is circulated to the second flow path, separate from the reaction liquid ejection process.

The recording head having the above-mentioned circulation process will be described in detail below with reference to FIG. 4. FIG. 4 is a perspective view showing a cross section of the discharge element substrate of the recording head of the reaction liquid. Here, it is described as a recording head of the reaction liquid, but the recording head of the ink can have a similar configuration. Hereinafter, the recording head of the reaction liquid will also be simply described as a recording head. As shown in FIG. 4, the discharge element substrate 10 includes a discharge port forming member 5 in which a discharge port 17 is formed, and a substrate 11 in which a discharge element (not shown) is arranged. The discharge port forming member 5 and the substrate 11 are laminated to form a first flow path 18 and a second flow path 19 through which the reaction liquid circulates. The first flow path 18 is a region from the inlet 8 through which the reaction liquid in the inflow path 6 flows in to the part between the discharge port 1 and the discharge element. The second flow path 19 is a region from the part between the discharge port 1 and the discharge element to the outlet 9 through which the reaction liquid flows out to the outflow path 7. For example, if a pressure difference is created between the inlet 8 and the outlet 9, such as a high-pressure inlet 8 and a low-pressure outlet 9, the reaction liquid can flow from the high-pressure side to the low-pressure side (in the direction of the arrow in Figure 4). The reaction liquid that passes through the inlet 6 and the inlet 8 enters the first flow path 18. Then, the reaction liquid that passes through the portion between the outlet 17 and the ejection element flows through the second flow path 19 and the outlet 9 to the ejection path 7.

The circulation process of circulating the reaction liquid in the first flow path to the second flow path can be a separate process (different process) from the ejection process of ejecting the reaction liquid from the ejection port. In addition, the circulation of the reaction liquid from the first flow path to the second flow path in the circulation process is preferably performed separately from the filling of the reaction liquid between the ejection port and the ejection element. The circulation process is preferably a process of circulating the reaction liquid in the first flow path to the second flow path without discharging the reaction liquid from the ejection port. Discharging the ink from the ejection port includes a recovery operation such as preliminary ejection or suction. During the recovery operation of the recording head, the circulation of the reaction liquid from the first flow path to the second flow path may be stopped. Furthermore, in the circulation process, it is preferable to circulate the reaction liquid from the first flow path to the second flow path by a circulation means other than the ejection element.

Next, a method of circulating the reaction liquid intermittently will be described with reference to FIG. 5. FIG. 5 is a cross-sectional view partially showing an example of a recording head. As shown in FIG. 5, the reaction liquid flowing in from the inlet 210 flows in the direction of the arrow by the action of the circulation pump 206, which is a means for circulating the reaction liquid, and flows out from the outlet 212. The circulation pump 206 is also a pump that can circulate the reaction liquid intermittently. Therefore, by driving the circulation pump 206, the reaction liquid can be circulated intermittently between the outlet 116 and the ejection element 216.

[Reaction liquid recording head]
FIG. 6 is a partial perspective view showing an example of the configuration of a reaction liquid recording head. FIG. 7 is a diagram showing an example of the configuration of a reaction liquid recording head, where (a) is a front view and (b) is a cross-sectional view taken along the line A-A of (a). As shown in FIGS. 6 and 7, the recording head includes a substrate 11 on which a heater 16, which is a heat generating resistor, is formed, and an orifice plate 12 on which a plurality of ejection ports 17, which are orifices for ejecting droplets, are formed. Furthermore, the recording head includes a liquid flow path 13, which communicates with each ejection port 17 and has a heater 16 disposed on its inner wall surface, and a liquid supply port 14 which communicates with the liquid flow path 13. The heater 16 functions as an electrothermal conversion element. Moreover, the plurality of ejection ports 17 are formed so as to be disposed at positions of the orifice plate 12 corresponding to the heater 16.

In the recording head, at least one inner wall surface selected from the group consisting of the liquid flow path 13 and the liquid supply port 14 is covered with a protective film 15 containing a metal oxide. The protective film 15 is located on the outermost surface that comes into contact with the liquid, and this protective film 15 can suppress dissolution of the inner wall surface of the substrate 11 that comes into contact with the liquid. The thickness of the protective film 15 is preferably 5 nm to 200 nm, more preferably 5 nm to 150 nm, and particularly preferably 5 nm to 100 nm. The surface treatment with the protective film 15 is preferably performed on both the liquid flow path 13 and the liquid supply port 14. The material forming the protective film 15 is at least one metal oxide selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and tantalum oxide. The metal oxide is preferably at least one selected from the group consisting of titanium oxide and tantalum oxide, and more preferably titanium oxide.

When a protective film is provided on the surface of the heater 16, it may be made of the same material as the inner wall surface of the liquid flow path 13 and the liquid supply port 14, or a different material. The protective film on the inner wall surface of the liquid flow path 13 and the liquid supply port 14 and the protective film on the surface of the heater 16 are preferably made of different materials, and more preferably made of materials containing different metals. Specifically, it is preferable to form a protective film on the inner wall surface of the liquid flow path 13 and the liquid supply port 14, which is made of a material containing at least one metal selected from the group consisting of titanium and vanadium. On the other hand, it is preferable to form a protective film on the surface of the heater 16, which is made of a material containing at least one metal selected from the group consisting of zirconium and tantalum. On the surface of the substrate 11 on which the heater 16 and the driving circuit of the heater 16 are formed, a passivation film is usually formed to protect the wiring and integrated circuit (IC) from, for example, oxygen, moisture, and other chemical damage sources. Examples of methods for forming a film on the surface of the heater 16 include methods that use physical or chemical action, such as plasma CVD (Chemical Vapor Deposition), catalytic CVD, vapor deposition, and sputtering.

To form a protective film on at least one inner wall surface selected from the group consisting of the liquid flow path 13 and the liquid supply port 14, for example, the following can be done. If necessary, the boundary between the substrate 11 and the orifice plate 12 is shielded. Then, in this state, a film source is introduced into the liquid supply port 14 from the back side of the substrate 11. This allows a protective film 15 containing a metal oxide to be selectively formed on the inner wall surface of the liquid supply port 14. On the other hand, if the film source is introduced from the front side of the substrate 11, a protective film can be selectively formed on the inner wall surface of the liquid flow path 13. Also, if the film source is introduced in an unshielded state, a film can be formed on both the liquid flow path 13 and the liquid supply port 14. Atomic layer deposition (ALD), which is a type of plasma CVD (Chemical Vapor Deposition) method, can be used as a method for forming a film on the inner wall surfaces of the liquid flow path 13 and the liquid supply port 14.

(recoding media)
In the recording method and recording device of the present invention, it is preferable to use a low-absorbency or non-absorbency recording medium (low to non-absorbency recording medium). A low to non-absorbency recording medium is a recording medium having a water absorption amount of 0 mL/ ^m2 or more and 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51 "Liquid Absorbency Test Method for Paper and Paperboard". In the present invention, a recording medium that satisfies the above water absorption amount condition is defined as a "low to non-absorbency recording medium". A recording medium for inkjet recording (glossy paper, matte paper, etc.) having a coating layer (ink receiving layer) formed of inorganic particles, and plain paper without a coating layer are "absorbency recording media" having the above water absorption amount of more than 10 mL/ ^m2 .

Examples of low to non-absorbent recording media that can be used include plastic films; recording media in which a plastic film is adhered to the recording surface of a substrate; and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Of these, plastic films are preferred, and recording media in which a resin coating layer is provided on the recording surface of a substrate containing cellulose pulp are also preferred. Note that the recording medium in this specification does not refer to a transfer medium, but rather refers to a recording medium on which an image is recorded as a recorded matter.

(Reaction solution)
The recording method of the present invention has a reaction liquid applying step of applying an aqueous reaction liquid containing a reactant that reacts with the aqueous ink to a recording medium. In particular, it is preferable to have a reaction liquid applying step before an ink applying step of applying the aqueous ink to the recording medium, or to perform the ink applying step and the reaction liquid applying step in parallel. Each component used in the reaction liquid will be described in detail below.

[Reactants]
The reaction liquid reacts with the ink by contacting with the ink, and aggregates the components in the ink (components having anionic groups such as resins, surfactants, and self-dispersing pigments), and contains a reactant. The presence of the reactant can destabilize the state of the components having anionic groups in the ink when the ink and the reactant come into contact with each other on the recording medium, and promote the aggregation of the ink. Examples of the reactant include cationic components such as polyvalent metal ions and cationic resins, and organic acids, but it is necessary to use at least one type selected from the group consisting of the following (i) and (ii). That is, the reactant is at least one type selected from the group consisting of (i) polyvalent metal salts having a solubility in water at 20° C. of 3.0 g/100 mL or more and 108.0 g/100 mL or less, and (ii) acid-type organic acids having a pKa of 3.2 or more and 4.6 or less at 20° C. The reactant may be used alone or in combination of two or more types.

Polyvalent metal salt is a compound that is formed by combining polyvalent metal ions and anions.Polyvalent metal salt may be a hydrate.The polyvalent metal ions that constitute polyvalent metal salt include, for example, divalent metal ions such as Ca2 ⁺ , Cu2 ⁺ , Ni2 ⁺ , Mg2 ⁺ , Sr2 ⁺ , ^Ba2+ , and Zn2 ⁺ , and trivalent metal ions such as Fe3 ⁺ , Cr3 ⁺ , ^Y3+ , and Al3 ⁺ . Examples of the anion include inorganic anions such as O ²⁻ , Cl ⁻ , Br ⁻ , I ⁻ , ClO ⁻ , ClO ₂ ⁻ , ClO ₃ ⁻ , ClO ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , SO ₄ ²⁻ , CO ₃ ²⁻ , HCO ₃ ⁻ , PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ₄ ⁻ ; HCOO ⁻ , (COO ⁻ ) ₂ , COOH(COO ⁻ ), CH ₃ COO ⁻ , C ₂ H ₅ COO ⁻ , CH ₃ CH(OH)COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₅ COO ⁻ , C ₆ H ₄ (COO ⁻ ) ₂ , and CH _3SO3- ^and other organic anions. Examples of polyvalent metal salts that satisfy the above (i) include barium oxide (3.5 g/100 mL), calcium lactate (4.4 _g /100 mL), calcium acetate (31.1 g/100 mL), magnesium sulfate (33.7 g/100 mL), magnesium acetate (53.4 g/100 mL), and beryllium nitrate (108.0 g/100 mL).

When the polyvalent metal salt is used as the reactant, the concentration (mol/g) of the polyvalent metal ions derived from the polyvalent metal salt in the aqueous reaction solution is preferably 0.003 mol/g or more and 0.020 mol/g or less. The concentration of the polyvalent metal ions is the concentration at which the polyvalent metal salt in the reaction solution is substantially completely dissociated, and assumes that the reaction with the pigment on the surface of the recording medium has progressed completely. If the concentration is less than 0.003 mol/g, the amount of polyvalent metal ions capable of reacting with the ink components is too small, and the ink components do not aggregate sufficiently, and the bleeding of the image may not be sufficiently suppressed. On the other hand, if the concentration is more than 0.020 mol/g, the amount of polyvalent metal ions capable of reacting with the ink components increases, causing the ink components to aggregate rapidly, and making it easier for unevenness to occur on the surface of the recorded image. As a result, the color development of the image may not be sufficient. In particular, the reaction liquid preferably contains a polyvalent metal salt having a solubility in water at 20° C. (g/100 mL) of 3.0 g/100 mL or more and 50.0 g/100 mL or less. If the solubility exceeds 50.0 g/100 mL, the color development of the image may not be sufficient. In addition, the content (mass %) of the polyvalent metal salt in the reaction liquid is preferably 1.0 mass % or more and 20.0 mass % or less based on the total mass of the reaction liquid. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass %) of the polyvalent metal salt in the reaction liquid means the "content (mass %) of the anhydride of the polyvalent metal salt" excluding water as the hydrate.

The reaction liquid containing an organic acid has a buffering ability in the acidic region (less than pH 7.0, preferably pH 2.0 to 5.0), and thus efficiently converts the anionic groups of the components present in the ink into an acid form and causes them to aggregate. As the reactant, an acid-form organic acid having a pKa of 3.2 or more and 4.6 or less, which represents the acid dissociation constant at 20° C., can be used. However, when the organic acid has multiple acid dissociation constants, the value of pKa ₁ , that is, the first acid dissociation constant, is used. Examples of organic acids that satisfy the above conditions include malic acid (pKa ₁ = 3.2), succinic acid (pKa ₁ = 4.0), glutaric acid (pKa ₁ = 4.1), levulinic acid (pKa ₁ = 4.4), and propionic acid (pKa = 4.6).

When an organic acid is used as a reactant, the concentration (mol/g) of hydrogen ions derived from the organic acid in the aqueous reaction solution is preferably 0.006 mol/g or more and 0.040 mol/g or less. The concentration of hydrogen ions derived from the organic acid is the concentration when substantially all of the organic acid in the reaction solution releases protons, and assumes the case where the reaction with the pigment on the surface of the recording medium has progressed completely. If the concentration is less than 0.006 mol/g, there are too few hydrogen ions that can turn the anionic groups of the ink components into an acid form, so that the ink components do not aggregate sufficiently, and the bleeding of the image may not be sufficiently suppressed. On the other hand, if the concentration is more than 0.040 mol/g, there are too many hydrogen ions that can turn the anionic groups of the ink components into an acid form, so that the ink components aggregate rapidly and unevenness is likely to occur on the surface of the recorded image. Therefore, the color development of the image may not be sufficient. In particular, it is preferable that the reaction solution contains an acid-type organic acid whose pKa at 20°C is 3.5 to 4.6. If the pKa is less than 3.5, the color development of the image may not be sufficient. In addition, the content (mass %) of the organic acid in the reaction solution is preferably 1.0 mass % or more and 50.0 mass % or less based on the total mass of the reaction solution.

The concentration of polyvalent metal ions derived from polyvalent metal salts can be measured, for example, by ICP emission spectrometry or an ion electrode. When using an ion electrode, it can be measured using an ion electrode that is appropriate for the polyvalent metal salt in the reaction solution. In addition, the concentration of hydrogen ions derived from organic acids can be measured by ion chromatography.

The reaction liquid may contain other reactants other than the specific polyvalent metal salt and the specific organic acid, as long as the effect of the present invention is not impaired. For example, a cationic resin can be used as the other reactant. Examples of the cationic resin include resins having a structure of primary to tertiary amines and resins having a structure of quaternary ammonium salts. Specific examples of the cationic resin include resins having structures such as vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, guanidine, diallyldimethylammonium chloride, and alkylamine-epichlorohydrin condensates. In order to increase the solubility in the reaction liquid, the cationic resin may be used in combination with an acidic compound, or the cationic resin may be subjected to a quaternary treatment. In addition, the content (mass%) of the cationic resin in the reaction liquid is preferably 0.1 mass% or more and 10.0 mass% or less based on the total mass of the reaction liquid.

[Aqueous medium]
The reaction liquid is an aqueous reaction liquid containing at least water as an aqueous medium. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the reaction liquid is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the reaction liquid. The content (mass%) of water-soluble organic solvent in the reaction liquid is preferably 5.0 mass% or more and 40.0 mass% or less, more preferably 15.0 mass% or more and 30.0 mass% or less based on the total mass of the reaction liquid. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used.

The reaction liquid contains a water-soluble organic solvent, and the relative dielectric constant of the water-soluble organic solvent at 20°C is preferably 15.0 or more. If the relative dielectric constant of the water-soluble organic solvent is less than 15.0, the dissociation state of the polyvalent metal salt or acid-type organic acid used as the reactant is likely to become unstable, and the protective film on the inner wall surface of the recording head may be easily dissolved. The relative dielectric constant is preferably 45.0 or less.

The dielectric constant of the 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. When the reaction solution contains a plurality of water-soluble organic solvents, the dielectric constant can be calculated as an average dielectric constant. Here, the average dielectric constant is a value calculated by multiplying the dielectric constant of each organic solvent by the proportion (mass%) of each organic solvent in the total amount of organic solvents in the reaction solution, and integrating the values. For example, the average dielectric constant of a reaction solution containing 10 mass% of 1,2-butanediol (24.8) and 5.0 mass% of propylene glycol (29.5) can be calculated as follows. Here, the numbers in parentheses are the measured values of the dielectric constant at 20°C.
(Average relative dielectric constant) = 24.8 x 10.0/15.0 + 29.5 x 5.0/15.0 = 26.4

The dielectric constant of a water-soluble organic solvent that is a solid at 20° C. is a value calculated from the dielectric constant of a 50% by mass aqueous solution by measuring the dielectric constant according to the following formula (1). Although the term "water-soluble organic solvent" usually refers to a liquid, in the present invention, water-soluble organic solvents that are solid at 20° C. are also included in the water-soluble organic solvents.
ε _sol = 2ε _50% -ε _water ... (1)
ε _sol : relative dielectric constant of a water-soluble organic solvent in a solid state at 20°C ε _50% : relative dielectric constant of a 50% by mass aqueous solution of a water-soluble organic solvent in a solid state at 20°C ε _water : relative dielectric constant of water

Examples of water-soluble organic solvents that are generally used in aqueous inks and reaction liquids and are solid at 20° 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 20° C. from the dielectric constant of a 50% by mass aqueous solution is as follows. Among water-soluble organic solvents that are solid at 20° C. and can be used as components of aqueous inks, it is difficult to prepare an aqueous solution with a high concentration of more than 50% by mass. On the other hand, in an aqueous solution with a low concentration of 10% by mass or less, the dielectric constant of water becomes dominant, and it is not possible to obtain a reliable (effective) value of the dielectric constant of the water-soluble organic solvent. As a result of the inventors' investigation, it was found that, among water-soluble organic solvents that are solid at 20° C., most of those that can be used in inks and reaction liquids can be used to prepare aqueous solutions to be measured, and the dielectric constant that is determined is consistent with the effect of the present invention. For these reasons, it was decided to use a 50% by mass aqueous solution. For a water-soluble organic solvent that is solid at 20° C. and has low solubility in water and therefore cannot be prepared into a 50% by mass aqueous solution, an aqueous solution of the solvent at a saturated concentration is used, and the value of the relative dielectric constant calculated in accordance with the above-mentioned case of calculating ε _sol is used for convenience.

[Other ingredients]
The reaction liquid may contain various other components as necessary. Examples of the other components include the same components as those that can be contained in the ink, which will be described later.

[Properties of reaction solution]
The reaction liquid is an aqueous reaction liquid applied to the inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the reaction liquid at 25°C is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the reaction liquid at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction liquid at 25°C is preferably 5.0 or more and 9.5 or less, more preferably 6.0 or more and 9.0 or less.

<Ink>
The recording method of the present invention includes an ink application step of applying a water-based ink to the recording medium so as to overlap at least a part of the region of the recording medium to which the reaction liquid is applied. The ink is preferably a water-based ink for inkjet use that contains a coloring material. Each component constituting the ink will be described in detail below.

[Colorant]
The ink preferably contains a coloring material. Pigments and dyes can be used as the coloring material. In particular, from the viewpoint of reactivity with the reaction liquid, it is preferable that the ink contains a coloring material that is dispersed by the action of an anionic group. The content (mass %) of the coloring material in the ink is preferably 0.1 mass % or more and 15.0 mass % or less, and more preferably 1.0 mass % or more and 10.0 mass % or less, based on the total mass of the ink.

Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine. One type of pigment may be used alone, or two or more types may be used in combination.

As a method for dispersing pigments, resin-dispersed pigments using resin as a dispersant, and self-dispersed pigments in which hydrophilic groups are bonded to the pigment particle surface can be used. In addition, resin-bonded pigments in which organic groups containing resin are chemically bonded to the pigment particle surface, and microencapsulated pigments in which the pigment particle surface is coated with resin can be used. It is also possible to use a combination of pigments with different dispersion methods. In particular, it is preferable to use resin-dispersed pigments in which a resin as a dispersant is physically adsorbed onto the pigment particle surface, rather than resin-bonded pigments or microencapsulated pigments. In other words, it is preferable that the pigment is dispersed by a resin (resin dispersant) having an anionic group.

As a resin dispersant for dispersing the pigment in an aqueous medium, it is preferable to use one that can disperse the pigment in an aqueous medium by the action of anionic groups. As a resin dispersant, a resin having an anionic group can be used, and a resin such as that described below, especially a water-soluble resin, can be used. The content (mass %) of the pigment in the ink is preferably 0.3 to 10.0 times the mass ratio of the content of the resin dispersant.

As the self-dispersing pigment, an anionic group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group can be bonded to the particle surface of the pigment directly or via another atomic group (-R-). The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include an alkali metal cation, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include a linear or branched alkylene group having 1 to 12 carbon atoms; an arylene group such as a phenylene group or a naphthylene group; a carbonyl group; an imino group; an amide group; a sulfonyl group; an ester group; and an ether group. A group that is a combination of these groups may also be used.

It is preferable to use a dye having an anionic group. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes. A single type of dye may be used alone, or two or more types may be used in combination. The coloring material is preferably a pigment, and more preferably a resin-dispersed pigment or a self-dispersed pigment.

[resin]
The ink may contain a resin. By using an ink containing a resin, an image with improved abrasion resistance can be recorded. The content (mass %) of the resin in the ink is preferably 0.1 mass % or more and 20.0 mass % or less, and more preferably 0.5 mass % or more and 15.0 mass % or less, based on the total mass of the ink.

The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, (ii) to improve various properties of the recorded image. Examples of the resin form include block copolymers, random copolymers, graft copolymers, and combinations of these. Also, the resin may be a water-soluble resin that can be dissolved in an aqueous medium, or may be resin particles that are dispersed in an aqueous medium. The resin may be used alone or in combination of two or more types.

[Resin Composition]
Examples of the resin include acrylic resins, urethane resins, olefin resins, etc. Among them, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylate are more preferred.

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as constituent units is preferable. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer is preferable. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer selected from the group consisting of styrene and α-methylstyrene is preferable. These resins are easily interacted with pigments, and therefore can be suitably used as a resin dispersant for dispersing pigments.

The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring such as styrene, α-methylstyrene, and benzyl (meth)acrylate; (meth)acrylic acid ester monomers such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and the like.

Urethane-based resins can be obtained, for example, by reacting polyisocyanate with polyol. They may also be obtained by further reacting a chain extender. Examples of olefin-based resins include polyethylene and polypropylene.

[Resin properties]
In this specification, "a resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, the resin is present in an aqueous medium in a state in which no particles whose particle size can be measured by a dynamic light scattering method are formed. Whether or not a resin is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10 mass%) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. Then, when the particle size of the resin in the sample solution is measured by a dynamic light scattering method, if no particles having a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3 times, and measurement time: 180 seconds. In addition, as a particle size distribution measurement device, a particle size analyzer using a dynamic light scattering method (for example, the product name "UPA-EX150", manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions used are not limited to those described above.

The acid value of the water-soluble resin is preferably 100 mgKOH/g or more and 250 mgKOH/g or less. The weight average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less.

The acid value of the resin constituting the resin particles is preferably 5 mgKOH/g or more and 100 mgKOH/g or less. The weight average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 3,000,000 or less, more preferably 100,000 or more and 3,000,000 or less. The volume-based cumulative 50% particle diameter (D ₅₀ ) of the resin particles measured by dynamic light scattering is preferably 50 nm or more and 500 nm or less. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particles that is 50% when integrated from the small particle diameter side based on the total volume of the measured particles in the particle diameter integration curve. The volume-based cumulative 50% particle diameter of the resin particles can be measured using the particle size analyzer and measurement conditions using the dynamic light scattering method described above. The glass transition temperature of the resin particles is preferably 40°C or more and 120°C or less, more preferably 50°C or more and 100°C or less. The glass transition temperature (° C.) of the resin particles can be measured using a differential scanning calorimeter (DSC). The resin particles do not necessarily contain a coloring material.

[Wax particles]
The ink may contain particles formed of wax (wax particles). By using an ink containing wax particles, an image with further improved abrasion resistance can be recorded. In this specification, the wax may be a composition containing components other than wax, or the wax itself. The wax particles may be dispersed by a dispersant such as a surfactant or a water-soluble resin. The wax may be used alone or in combination of two or more kinds. The content (mass %) of the wax particles in the ink is preferably 0.1 mass % or more and 10.0 mass % or less, and more preferably 1.0 mass % or more and 5.0 mass % or less, based on the total mass of the ink.

In the narrow sense, wax is an ester of a water-insoluble higher monohydric or dihydric alcohol and a fatty acid, and includes animal waxes and vegetable waxes, but does not include oils and fats. In the broad sense, wax includes high-melting-point fats, mineral waxes, petroleum waxes, and blends and modified products of various waxes. In the recording method of the present invention, any wax in the broad sense can be used without particular restrictions. Wax in the broad sense can be classified into natural waxes, synthetic waxes, blends of these (blended waxes), and modified products of these (modified waxes).

Examples of natural waxes include animal waxes such as beeswax, spermaceti, and wool wax (lanolin); vegetable waxes such as wood wax, carnauba wax, sugarcane wax, palm wax, candelilla wax, and rice wax; mineral waxes such as montan wax; and petroleum waxes such as paraffin wax, microcrystalline wax, and petrolatum. Examples of synthetic waxes include hydrocarbon waxes such as Fischer-Tropsch wax and polyolefin wax (e.g., polyethylene wax and polypropylene wax). The blended wax is a mixture of the above-mentioned various waxes. The modified wax is a wax obtained by subjecting the above-mentioned various waxes to a modification treatment such as oxidation, hydrogenation, alcohol modification, acrylic modification, and urethane modification. One of the above waxes may be used alone, or two or more may be used in combination. The wax is preferably at least one selected from the group consisting of microcrystalline wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and modified or blended products thereof. Among these, a blend of multiple types of wax is more preferable, and a blend of petroleum-based wax and synthetic wax is especially preferable.

The wax is preferably solid at room temperature (25°C). The melting point (°C) of the wax is preferably 40°C or higher and 120°C or lower, and more preferably 50°C or higher and 100°C or lower. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (melting point test method) of JIS K2235:1991 (petroleum wax). In the case of microcrystalline wax, petrolatum, and a mixture of multiple types of wax, the test method described in 5.3.2 can be used to measure more accurately. The melting point of the wax is easily affected by characteristics such as molecular weight (the higher the molecular weight, the higher the melting point), molecular structure (the higher the melting point if the chain is straight, and the lower the melting point if the chain is branched), crystallinity (the higher the crystallinity, the higher the melting point), and density (the higher the crystallinity, the higher the melting point). Therefore, by controlling these characteristics, it is possible to obtain a wax having a desired melting point. The melting point of the wax in the ink can be measured in accordance with the above test method, for example, after the ink is subjected to ultracentrifugation, the wax separated is washed and dried.

[Aqueous medium]
The ink used in the recording method of the present invention is an aqueous ink containing at least water as an aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the aqueous ink is preferably 50.0 mass% or more and 95.0 mass% or less based on the total mass of the ink. In addition, the content (mass%) of the water-soluble organic solvent in the aqueous ink is preferably 3.0 mass% or more and 50.0 mass% or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, can be used. The water-soluble organic solvent may be used alone or in combination of two or more.

[Other ingredients]
The ink may contain various other components as necessary. Examples of other components include various additives such as defoamers, surfactants, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain a reactant to be contained in the reaction liquid.

[Ink properties]
The ink is a water-based ink applied to an inkjet method. Therefore, from the viewpoint of reliability, it is preferable to appropriately control the physical property values. Specifically, the surface tension of the ink at 25° C. is preferably 20 mN/m or more and 60 mN/m or less. In addition, the viscosity of the ink at 25° C. is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25° C. is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples as long as it does not deviate from the gist of the invention. Unless otherwise specified, the terms "parts" and "%" used to describe the amounts of components are based on mass.

<Preparation of reaction solution>
Each component (unit: %) shown in Tables 1 to 3 was mixed and thoroughly stirred, and then pressure filtered with a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm to prepare each reaction solution. In Tables 1 to 3, "Capstone FS3100" is the trade name of a fluorine-based nonionic surfactant manufactured by LEHVOSS Group. "Acetylenol E100" is the trade name of a hydrocarbon-based nonionic surfactant manufactured by Kawaken Fine Chemicals. The numerical value attached to polyethylene glycol is the number average molecular weight of polyethylene glycol. The two numerical values in parentheses attached to the monovalent or polyvalent metal salt, which is the reactant, indicate the value of solubility in water at 20° C. (g/100 mL) and the molecular weight, respectively. "Sodium chloride" is a monovalent metal salt, and all of the compounds listed above "sodium chloride" in Tables 1 to 3 are divalent metal salts. The two numbers in parentheses attached to the organic acids indicate the pKa value (pKa ₁ in the case of a compound having multiple pKas) and the molecular weight at 20° C., respectively. Malonic acid, malic acid, succinic acid, propionic acid, 2,2-dimethylpropanoic acid, and formic acid are organic acids. The number in parentheses attached to the water-soluble organic solvents indicates the relative dielectric constant value at 20° C. Furthermore, when each reaction solution contains multiple water-soluble organic solvents, the average relative dielectric constant value calculated by the above method is shown in the (average) relative dielectric constant column of Tables 1 to 3.

In Tables 1 to 3, the concentrations of polyvalent metal ions derived from polyvalent metal salts were measured by ICP emission analysis. A multi-type ICP emission device (product name "5900ICP OES", manufactured by Agilent Technologies) was used as the measuring device. The concentration of hydrogen ions derived from organic acids was calculated by quantifying the anion components after dissociation of the organic acids using ion chromatography. An ion chromatograph (product name "Prominence HIC-SP", suppressor type, manufactured by Shimadzu Corporation) was used as the measuring device.

<Preparation of Pigment Dispersion>
(Pigment Dispersion 1)
A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) with an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide in an amount equimolar to the acid value, and then an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solid content) content of 20.0%. 10.0 parts of pigment (C.I. Pigment Blue 15:3), 15.0 parts of the aqueous solution of resin 1, and 75.0 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of zirconia beads with a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 5 hours while cooling with water. After centrifuging to remove coarse particles, the mixture was pressure-filtered with a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare a pigment dispersion 1 with a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0%.

(Pigment Dispersion 2)
A pigment dispersion 2 having a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0% was prepared in the same manner as in the pigment dispersion 1 described above, except that the pigment was changed to C.I. Pigment Red 122.

(Pigment Dispersion 3)
A pigment dispersion 3 having a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0% was prepared in the same manner as in the pigment dispersion 1 described above, except that the pigment was changed to C.I. Pigment Yellow 74.

(Pigment Dispersion 4)
Pigment dispersion 4 having a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0% was prepared in the same manner as in the above-mentioned pigment dispersion 1, except that the pigment was changed to carbon black.

<Preparation of Resin Particles>
(Resin Particles 1)
In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 74.0 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, 24.0 parts of ethyl methacrylate, 1.5 parts of methacrylic acid, and 0.3 parts of a reactive surfactant were mixed to prepare an emulsion. As the reactive surfactant, the product name "ADEKA REASOAP ER20" (manufactured by ADEKA, nonionic surfactant, number of moles of ethylene oxide group added: 20) was used. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and polymerization reaction was carried out for 2 hours while stirring at 80 ° C. After cooling to 25 ° C., ion-exchanged water and an aqueous solution containing potassium hydroxide equimolar to the acid value of the resin particles were added to prepare an aqueous dispersion of resin particles 1 having a resin particle (solid content) content of 25.0%.

(Resin Particles 2)
In a four-neck flask equipped with a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 81.8 parts of ion-exchanged water and 0.2 parts of potassium persulfate were mixed. In addition, 16.1 parts of ethyl methacrylate, 1.6 parts of methoxypolyethylene glycol methacrylate, and 0.3 parts of the above-mentioned reactive surfactant were mixed to prepare an emulsion. As the methoxypolyethylene glycol methacrylate, the product name "Blenmer PME1000" (manufactured by NOF Corp., number of moles of ethylene oxide group added: about 23) was used. Under a nitrogen atmosphere, the prepared emulsion was dropped into the four-neck flask over 1 hour, and polymerization reaction was carried out for 2 hours while stirring at 80 ° C. After cooling to 25 ° C., ion-exchanged water was added to prepare an aqueous dispersion of resin particles 2 with a resin particle (solid content) content of 25.0%.

<Ink Preparation>
The components (unit: %) shown in Table 4 were mixed and thoroughly stirred, and then pressure filtered through a cellulose acetate filter (manufactured by Advantec) having a pore size of 3.0 μm to prepare each ink.

<Preparing the recording medium>
The following recording media 1 to 4 were prepared.
Recording medium 1: Product name "Scotchcal Graphic Film IJ1220-10" (manufactured by 3M, substrate: polyvinyl chloride, water absorption amount from start of contact to 30 msec ^1/2 in the Bristow method is in the range of 0 mL/ ^m2 to 10 mL/ ^m2 )
Recording medium 2: Product name "LL Soft Tarpaulin LLBASF135" (manufactured by Sakurai Co., Ltd., base material: polyester and PVC, water absorption amount from start of contact to 30 msec ^1/2 in the Bristow method is in the range of 0 mL/ ^m2 to 10 mL/ ^m2 )
Recording medium 3: Product name "Printeria OW PROY400F" (manufactured by Lintec Sign Systems, substrate: polyolefin, water absorption amount from start of contact to 30 msec ^1/2 in the Bristow method is in the range of 0 mL/ ^m2 or more and 10 mL/ ^m2 or less)
Recording medium 4: Product name "Canon Photo Paper Glossy Pro [Platinum Grade] PT-201" (manufactured by Canon, the amount of water absorbed from the start of contact to 30 msec ^1/2 in the Bristow method is more than 10 mL/ ^m2 )

<Evaluation>
The prepared reaction liquid and ink were filled in a cartridge, and the cartridge was set in an inkjet recording device (product name "imagePROGRAF PRO-2000", manufactured by Canon) equipped with a recording head that ejects ink by thermal energy. A heating device for drying the recording medium to which the reaction liquid and ink were applied was incorporated in this recording device at a position downstream of the recording head in the conveying direction of the recording medium. The surface temperature of the recording medium was set to 80°C by heating with the heating device. The recording head used was a serial type recording head having the configuration shown in FIG. 5. This recording head has a first flow path and a second flow path that communicate between the ejection port and the ejection element for each ejection port, and circulates the ink in the first flow path to the second flow path using a pump. The density of the ejection ports was 1200 per inch, and the amount of ink ejected per droplet was 4.0 ng. The protective film of the recording head was prepared by the ALD method described above so as to have the configuration shown in Table 3. In the liquid flow path 13, a protective film 15 (FIG. 7(b)) having a thickness of about 100 nm was provided on the orifice plate 12 made of a silicon material. In the liquid supply port 14, a protective film 15 (FIG. 7(b)) having a thickness of about 100 nm was provided on the substrate 11 made of a silicon material. In this embodiment, an image recorded under the condition that one drop of 4.0 ng of ink is applied to a unit area of 1/1200 inch x 1/1200 inch is defined as having a recording duty of 100%. The amount of reaction liquid applied to the unit area was 0.8 ng, and the amount of ink applied to the unit area was 4.8 ng. The recording environment was a temperature of 20° C. and a relative humidity of 50%. When the liquid was circulated in the recording head, the circulation flow rate of the reaction liquid was 4.0 mL/min. In the present invention, in the evaluation criteria for each item below, "A" and "B" were defined as acceptable levels, and "C" was defined as unacceptable levels. The evaluation results are shown in Table 6. In Table 6, the "liquid heating temperature" column lists the liquid heating temperature by temperature control of the print head. In Example 35, no temperature control was performed, and "-" is listed in the "liquid heating temperature" column.

(Prevention of dissolution of recording head)
The reaction liquid shown in Table 6 was discharged 8×10 ¹⁰ times per discharge port of the recording head. The recording head was then disassembled, cleaned, and dried, and the inner wall surface of the recording head was observed with a SEM-EDS (product name "S-3400N", manufactured by Hitachi High-Technologies Corporation) and an elemental analysis of the inner wall surface was performed. The dissolution inhibition of the recording head was evaluated according to the following evaluation criteria.
A: Metal elements forming a protective film on the inner wall surface were confirmed, but silicon elements originating from the member on which the protective film was provided were not confirmed.
B: Metal elements forming a protective film on the inner wall surface were confirmed, and silicon elements derived from the material on which the protective film was formed were confirmed in some places.
C: No metal element forming a protective film on the inner wall surface was found, and silicon element originating from the member on which the protective film was provided was found throughout.

(Image bleeding suppression)
Using the above recording device, the reaction liquid and ink shown in Table 6 were applied in the same recording pass to record a thin line having a line width of 4 pixels (input line width: 1/600 inch x 4 = 169 μm) on the recording medium so that the recording duty was 200%. The line width of the recorded line image was measured (actual line width) using a personal image quality evaluation system Personal IAS (product name, manufactured by Quality Engineering Associates). The difference from the input line width was calculated based on the formula (difference from input line width) = (actual line width (μm)) - 169 (μm), and the bleeding suppression of the image was evaluated according to the evaluation criteria shown below.
A: The difference from the input line width was 120 nm or less.
B: The difference from the input line width was more than 120 nm and 140 nm or less.
C: The difference from the input line width exceeded 140 nm.

(Color development of image)
Using the inkjet recording device described above, ten types of solid images were recorded with the recording duty changed in 10% increments between 10% and 200% by applying the reaction liquid and ink shown in Table 6. In this case, the reaction liquid application process and the ink application process were performed in parallel to record the solid images. The lightness (L ^* ) and chroma (C ^* ) of each solid image were measured using a fluorescence spectrodensitometer (product name "FD-7", manufactured by Konica Minolta). L ^* and C ^* are based on the color difference display method specified by the CIE. The color development of the image was evaluated according to the evaluation criteria shown in Table 5. In this example, black ink was used when the color material was carbon black, cyan ink was used when the color material was C.I. Pigment Blue 15:3, magenta ink was used when the color material was C.I. Pigment Red 122, and yellow ink was used when the color material was C.I. Pigment Yellow 74. In the case of black ink, the lower the lightness, the darker the image and the better the color development, while in the case of color inks (cyan, magenta, and yellow), the higher the saturation, the more vivid the image and the better the color development.

Claims (11)

An inkjet recording method for recording an image on a recording medium by ejecting an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink from a recording head, comprising the steps of:
a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
the aqueous reaction liquid contains at least one selected from the group consisting of: (i) a polyvalent metal salt having a solubility in water (g/100 mL) at 20° C. of 3.0 g/100 mL or more and 108.0 g/100 mL or less; and (ii) an acid-type organic acid having a pKa at 20° C. of 3.2 or more and 4.6 or less;
a liquid flow path having an ejection port for ejecting the aqueous reaction liquid, and a liquid supply port communicating with the liquid flow path are formed inside the recording head, and at least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is coated with a protective film containing a metal oxide,
The ink-jet recording method according to claim 1, wherein the metal oxide is at least one selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and tantalum oxide. The inkjet recording method according to claim 1, wherein the aqueous reaction liquid contains a water-soluble organic solvent, and the relative dielectric constant of the water-soluble organic solvent at 20°C is 15.0 or more. The inkjet recording method according to claim 1, wherein the concentration (mol/g) of the polyvalent metal ions derived from the polyvalent metal salt in the aqueous reaction liquid is 0.003 mol/g or more and 0.020 mol/g or less. The inkjet recording method according to claim 1, wherein the aqueous reaction liquid contains a polyvalent metal salt whose solubility in water (g/100 mL) is 3.0 g/100 mL or more and 50.0 g/100 mL or less. The inkjet recording method according to claim 1, wherein the concentration (mol/g) of hydrogen ions derived from the organic acid in the aqueous reaction liquid is 0.006 mol/g or more and 0.040 mol/g or less. The inkjet recording method according to claim 1, wherein the aqueous reaction liquid contains an acid-type organic acid having a pKa of 3.5 or more and 4.6 or less. 2. The ink jet recording method according to claim 1, wherein the recording medium has an amount of water absorption of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. The inkjet recording method according to claim 1, further comprising a mechanism for circulating the aqueous reaction liquid within the recording head. The inkjet recording method according to claim 1, wherein the recording head is provided with a heating mechanism for heating the aqueous reaction liquid in the recording head. An inkjet recording apparatus used for recording an image on a recording medium by ejecting from a recording head an aqueous reaction liquid containing an aqueous ink and a reactant that reacts with the aqueous ink, the ink comprising:
a reaction liquid applying means for applying the aqueous reaction liquid to the recording medium;
an ink applying means for applying the water-based ink so as to overlap at least a portion of an area of the recording medium to which the water-based reaction liquid is applied,
the aqueous reaction liquid contains at least one selected from the group consisting of: (i) a polyvalent metal salt having a solubility in water (g/100 mL) at 20° C. of 3.0 g/100 mL or more and 108.0 g/100 mL or less; and (ii) an acid-type organic acid having a pKa at 20° C. of 3.2 or more and 4.6 or less;
a liquid flow path having an ejection port for ejecting the aqueous reaction liquid, and a liquid supply port communicating with the liquid flow path are formed inside the recording head, and at least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is coated with a protective film containing a metal oxide,
The ink-jet recording apparatus is characterized in that the metal oxide is at least one selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and tantalum oxide. A set of an aqueous ink and an aqueous reaction liquid for use in an inkjet recording method in which an aqueous ink and an aqueous reaction liquid containing a reactant that reacts with the aqueous ink are ejected from a recording head to record an image on a recording medium, comprising:
the inkjet recording method includes a reaction liquid applying step of applying the aqueous reaction liquid to the recording medium;
an ink applying step of applying the aqueous ink so as to overlap at least a portion of an area of the recording medium to which the aqueous reaction liquid is applied,
the aqueous reaction liquid contains at least one selected from the group consisting of: (i) a polyvalent metal salt having a solubility in water (g/100 mL) at 20° C. of 3.0 g/100 mL or more and 108.0 g/100 mL or less; and (ii) an acid-type organic acid having a pKa at 20° C. of 3.2 or more and 4.6 or less;
a liquid flow path having an ejection port for ejecting the aqueous reaction liquid, and a liquid supply port communicating with the liquid flow path are formed inside the recording head, and at least one inner wall surface selected from the group consisting of the liquid flow path and the liquid supply port is coated with a protective film containing a metal oxide,
A set of an aqueous ink and an aqueous reaction liquid, wherein the metal oxide is at least one selected from the group consisting of titanium oxide, zirconium oxide, vanadium oxide, and tantalum oxide.

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